CN110524082A - A Method for Rapid Wetting of Carbon Fibers in Ceramic Matrix Composites Using Fe as Active Element - Google Patents

Abstract

The invention discloses a method for quickly wetting carbon fibers in ceramic matrix composite materials with Fe as an active element, that is, using Fe-based or alloy-type solders containing sufficient Fe as high-temperature active solders, through the generation of active element Fe and carbon fibers The way of eutectic reaction realizes fast and dense wetting of carbon fibers. Its advantages are: the use of eutectic reaction to achieve rapid wetting of carbon fibers, and the densification of the original pores in the base metal of the composite material near the seam and the densification of the brazing seam, avoiding the formation of a continuous interface reaction phase from the interface reaction; The carbon is fully graphitized, which can reduce thermal stress; the brazing temperature is above 1154°C, which can increase the service temperature of the brazed joint; there is no need for long-term heat preservation, and no need to modify the surface of the composite material before welding; it does not contain or contain a small amount precious metals. The invention solves the problems of low joint heat resistance temperature and long heat preservation time of traditional Ag-based active solder and Ni-based solder respectively when they are used for brazing ceramic matrix composite materials.

Description

A Method for Rapid Wetting of Carbon Fibers in Ceramic Matrix Composites Using Fe as Active Element

technical field

The invention relates to the active brazing material design and brazing method for carbon fiber reinforced ceramic matrix composite materials such as C _f /C (namely C/C) and C _f /SiC (namely C/SiC).

Background technique

Compared with metal materials, ceramic matrix composites (such as C _f /C, C _f/ SiC) reinforced with continuous fibers have two advantages: (1) high temperature strength (C _f /C is in the oxidation resistance It starts to oxidize above 450°C in the atmosphere, reference [1]); (2) light density (only 1/4 of nickel-based superalloy, 1/2 of ceramic material, reference [2, 3]); so It has a wide range of uses as a high-temperature structural material. Among them, C _f /C composite materials are currently mainly used in aircraft brake systems and spacecraft heat-resistant and ablation-resistant structural materials.

The welding method of carbon fiber reinforced ceramic matrix composites mainly adopts brazing (References [4, 5]). Similar to ordinary ceramic materials, there are two reasons for its poor brazeability: one is the poor wettability of commonly used metal solders; the other is that there is a large gap in thermal expansion coefficient with metal solders, which will cause large gaps during joint cooling. of thermal stress. In addition, when C _f /C composite materials are used as high-temperature structural materials, the heat resistance of brazed joints is also required to be high. In order to solve the wettability problem, most reports use Ti as the active element, using Ti-containing Ag-based solder, Ti-containing Cu-based solder or Ti-based solder, or C _f /C composite materials before welding. The surface is pre-treated to improve wettability.

In 1997, Italy's Milena Salvo (reference [6]) reported the use of Si sheet (silicon sheet), Al foil, Ti powder three kinds of active interlayer pairs (C _f /C) / (C _f /C) the same mother Welding of the material combination: for the middle layer of the Si sheet, under the condition of 1420 ° C × 90 min and flowing Ar protection (which has exceeded the melting point of Si of 1414 ° C), the SiC with a thickness of 20 μm is formed by the reaction, and a joint with a shear strength of 22 MPa is obtained. The interlaminar shear strength (interlaminar shearstrength) close to C _f /C is 20-25MPa; however, the structure observation shows that the unreacted Si layer in the center of the interlayer is still obvious (thickness ~120μm), and the interlayer is in the cooling process Vertical cracks are formed (through the SiC reaction layer and the remaining Si sheet). For the Al foil interlayer, under the condition of 1000℃×45min and flowing Ar protection, a 15 μm thick Al ₄ C ₃ reaction layer was formed at the interface of Al and C _f /C composites, and a joint with a shear strength of 10 MPa was obtained. Joint failure occurs at the (C _f /C)/Al ₄ C ₃ interface. For the Ti powder intermediate layer, under the condition of 1420℃×45min (solid-phase welding), only a few parts of Ti adhere to the C _f /C composite base material. It can be seen that (C _f /C)/(C _f /C) solid phase welding of the same base metal is more difficult, even if the "active interlayer (Si, Al, Ti are all active interlayers that can react with SiC) ", Due to the limitation of reaction degree, reaction product and original contact degree, it is also difficult to achieve high-strength and large-area welding.

In 2005, M.Singh of NASA (reference [7]) used three kinds of Ti-containing solders (Cu base: 92.8Cu-3Si-2Al-2.25Ti; Ti base: 70Ti-15Cu-15Ni; Ag base: 68.8 Ag-26.7Cu-4.5Ti) was vacuum brazed to the combination of pure Ti and C _f /C according to the tube on plate structure at (920～1050)℃×5min. All Ti-containing solders wet the C _f /C composites well, without interfacial voids, and react to form Ti-rich carbides (TiC _1-x ), which connect C and solder well ; Among them, the joint performance of Cu-based solder is better. From the perspective of thermodynamics, M.Singh analyzed the Gibb's free energy change for TiC formation from the reaction of Ti and C to form TiC (The Gibb's free energy change for TiC formation), indicating that the Gibb's free energy change in the range of 920 ° C to 1050 ° C is -174 ~-169 kJ; thermodynamic calculations show that TiC _0.48~0.95 can be formed from Cu. At the same time, the free energy change of Si in Cu-based solder to form SiC through the reaction of Si and C is -62.4～-61.1k in the range of 920～1050℃. Ti and Si in the Cu-based solder can react with C to form TiC and SiC respectively, so the joint performance is better.

In 2007, Qin Youqiong and Feng Jicai of Harbin Institute of Technology (reference [8]) used a 50-micron thick Ag-26.7Cu-4.6Ti (wt.%) foil strip at (860-1000) ℃ × (3-30) min conditions Under vacuum brazing C _f /C and TC4, the shear strength obtained under the condition of 910℃×10min is the highest, which is 25MPa; the microstructure analysis of the interface structure shows that the reaction layer on the C _f /C side is two layers: (C _f /C)/[(TiC+C)/TiCu]; the reaction layer on the TC4 side is four layers: Ti ₃ Cu ₄ /TiCu/Ti ₂ Cu/Ti ₂ Cu+Ti(ss)/TC4. Qin Youqiong et al. (Reference [9]) also used Ag-28Cu solder to braze C _f /C composite materials and TC4, and the test specification was 10min×(820～900)℃; at the brazing temperature of 850℃, heat preservation Under the condition of brazing for 10 minutes, the highest shear strength was obtained, reaching 38MPa. The active element Ti that wets C _f /C actually comes from the dissolution of the Ti base material on the other side. Xiujie Cao of Beihang University (reference [10]) used 50μm thick Ag68.83-Cu26.77-Ti4.4 foil to C _f /C composite material and TC17 under the condition of (840～920)℃×15min Vacuum brazing is carried out, and the shear strength obtained under the condition of 860°C×15min is the largest, which is 24±1MPa.

In recent years, Feng Jicai's research group at Harbin Institute of Technology has begun to try the compounding of solder. Zhou YH (Reference [11]) brazed _Cf /C composites with TC4 with AgCuTi filler metal reinforced with nano-alumina particles by adding nano-alumina particles to the AgCuTi filler metal. The interface structure on the TC4 side is TC4/diffusion layer/Ti-Cu intermetallic compound, and the interface structure on the C _f /C side is TiCu/TiC/(C _f /C); when the brazing temperature reaches 920°C , the TiCu phase in the brazing joint is very developed, replacing Ag(s,s) and Cu(s,s). The addition of nano-alumina particles improves the joint performance by inhibiting the growth of the Ti-Cu layer adjacent to TC4 and providing dispersed TiCu nucleation sites in the braze joint. Under the condition of 880℃×10min, the joint can obtain the highest strength of 27.8MPa. Zhou Y et al. from Harbin Institute of Technology (reference [12]) also added graphene nanosheets (GNSs: graphene nanosheets) to the AgCuTi solder. When the welding condition was 900℃×10min, the shear strength of the obtained joint reached a maximum of 30.2MPa ; The main beneficial effect of GNSs is to reduce the thickness of the brittle reaction layer, promote the formation of TiC and TiCu in the brazing joint, thereby reducing the thermal expansion coefficient.

KX Zhang from Shenyang Institute of Metal Research, Chinese Academy of Sciences (reference [13]) focused on the application background of nuclear reactor thermal management and aviation industry, and used copper-based Ti-containing active solder (Ag-68.8Cu-4.5Ti) for Cu/CC combination Vacuum brazing under the condition of 910℃×10min proved the interface shape effect (interfacial shape effect), that is, the conical interface structure design (conical interface) can greatly improve the four-point bending performance of the joint than the straight interface (straight interface). At the same time, it was observed that there is another layer of pyrolytic carbon coating (PyC: pyrolytic carbon coating) on the surface of the carbon fiber. On the surface of the pyrolytic carbon, a TiC reactant with a thickness of about 1 μm is formed, which promotes wetting and bonding. It was also observed that the brazing filler metal can enter the inherent pores in the C _f /C base metal.

In addition to the above-mentioned Ag-based and Cu-based active solders with Ti as the active element, another widely studied solder is the traditional Ni-based commercial solder.

In 2008, M.Singh of NASA (reference [14]) carried out Ti/CC, Ti/C-SiC, Hastealloy/C– Brazing of SiC (the first two are brazing of industrial pure Ti and ceramic matrix composite materials). Microscopic analysis of the interface structure of Ti/CC joints shows that both commercial Ni-based amorphous solders can wet the _Cf /C composites well without cracks and void defects. Among them, the interface layer of CC/MBF-20 is extremely thin (less than 1 μm), which is rich in Ti and contains a small amount of Cr and Fe; the interface on the side of CC/MBF-30 "precipitates" scallop-like Ti-rich on the surface of C _f /C Layer and thicker Ni-rich layer (5 ~ 10μm thick). The Ti content as high as 87-98 at.% near the surface of C _f /C indicates that the Ti base material has actually been dissolved in the two Ni-based solders and segregated on the surface of C _f /C. The formation of a segregated Ti-rich layer on the surface of C _f /C promotes the wetting and bonding of C _f /C. Thermodynamic analysis shows that the free energy changes (values of the Gibbs free energy change, ΔG, for TiC formation) of TiC formed by the reaction of Ti and C are -172kJ and -168kJ at 1045°C and 1085°C, respectively. Although at 1045°C and 1085°C, the SiC formation free energy is also negative, but because the Gibbs free energy change of TiC is larger than that of SiC formation free energy, the interface is correspondingly preferential to form TiC.

Tian Xiaoyu et al. (reference [15]) brazed C _f /C composites and superalloy GH99 with nickel-based solder BNi-2 at 1170 °C × 60 min, and obtained a shear strength of 35 MPa; when BNi-2 powder When 1-8% TiH ₂ powder is added to the steel, the addition amount of 3-5% makes the shear strength of the joint higher than that of BNi2. When the TiH ₂ powder content is 3%, the shear strength can reach up to 40MPa. Microscopic analysis of the interface structure shows that strips of Cr ₃ C ₂ are formed on the surface of C _f /C.

Toshitaka Ikejo of Tokyo Institute of Technology (reference [16]) combined C _f /C base metal with Inconel 600 (Ni-based alloy), using Fe-Cr-Ni-(Si,B) solder, and pre-prepared Mo The wire and Nb foil (in order to reduce thermal stress) are vacuum brazed under the condition of 1080℃×300s, and the joint strength obtained is 2-16MPa (varies with the thickness of Nb layer).

Compared with the commercial Ni-based solder, the Ti-containing Ag-based active solder (Ag-Cu-Ti) with good plasticity can balance wettability and low thermal stress, and the joint strength is slightly higher, about 20-40MPa. Both commercial Ni-based solder and commercial Ag solder have a common problem, that is, the melting point is too low, respectively around 1000°C and 800°C, which affects the high-temperature performance of the joint. In addition, although Ag solder has good plasticity, it contains precious metals. However, Ni-based solder contains a large amount of brittle phases, and it takes a long holding time to achieve isothermal solidification, so as to eliminate the brittle phases in the solder.

Ni-based commercial solder (such as BNi-2 with Ni-Cr-Fe-Si-B system) in high-temperature brazing of heat-resistant metal materials not only has excellent wettability, but also can use isothermal solidification to improve the remelting of the brazing seam Temperature and heat resistance, so it is widely used in high temperature brazing of heat-resistant metal materials. However, when Ni-based commercial solder is used for brazing of carbon fiber-reinforced ceramic matrix composites (such as C _f /C, C _f /SiC), although the wettability of the interface is acceptable, short-term heat preservation of several minutes cannot be achieved. Isothermal solidification leads to low remelting temperature of the brazing seam, poor heat resistance, and brittle brazing seam, so the room temperature and high temperature performance of the joint are poor.

Recently, there are more and more literatures on "modification or coating pretreatment" of C _f /C surface before welding to improve wettability and inhibit excessive reaction, and the effect is also more significant, as follows.

In 2004, Pietro Appendino in Italy (reference [17]) directly _{poured Cu on the surface of C f /} C (via On the basis of the welding method of laser processing (surface treated with Ti activation treatment), the following improved method is proposed: first, the powder alcohol suspension (slurry technique: metal of transition metal of the VI B group: Cr, Mo) powdersuspension in ethanol) is pre-placed on the _Cf /C surface, and the _Cf /C surface is modified by the high-temperature solid-state reaction (above 1000°C, in flowing Ar or vacuum environment) of VIB group transition metal powder and _Cf /C Pretreatment, and then pouring the Cu solution on the modified _Cf /C surface (modified CFC) at 1100°C. The 5-10μm thick carbide formed on the surface of C _f /C improves the wettability of liquid Cu on the surface of C _f /C. This method can also be used to connect Si-doped _Cf /C (silicon doped CFC) to Cu.

In 2011, Guo Lingjun and others from Northwestern Polytechnical University (reference [18]) used the technology of pack cementation coating technique in the welding of C _f /C and _GH3128 . (1700～2400)℃×(1～3)h under the condition of using C powder + Si powder to prepare SiC modified coating in flowing argon atmosphere, and then using Ti+Ni powder at (1050～1250)℃×(15～ 60) min × (8 ~ 20) MPa conditions for hot-press welding. After modifying the C _f /C surface with a SiC layer, the shear strength of the joint obtained at 1170 °C is 22.5 MPa, while the joint strength without modification with the SiC layer is 0. The SiC coating is closely combined with C _f /C, and the wettability of Ni-Ti alloy liquid to C _f /C is improved, and the thermal mismatch stress is reduced.

In 2018, Xinrui Song et al. from Northwestern Polytechnical University (reference [19]) placed high-purity Cr powder on the surface of C _f /C composites, and under the protection of Ar, heat-treated at 1300 °C for 1 h to obtain CrC-modified C _f /C surface, and then vacuum brazing with Ti-23Cu-11Zr-9Ni solder at 960°C×20min. The 20 μm thick chromium carbide layer on the surface of C _f /C before brazing is thinned to 5 μm after brazing, which is considered to be part of the chromium carbide dissolved into the brazing filler metal, which becomes the TiC layer and TiC particles, which avoids thick and continuous The TiC layer reduces the thermal stress, and the joint shear strength increases to 52±6MPa, which is much higher than the joint shear strength (15±2MPa) without chromium carbide pretreatment.

In 2019, Yang ZW from Tianjin University (reference [20]) proposed to pre-oxidize and modify C _f /C composites (which can form a ring-shaped artificial channel around the carbon fiber), combined with the introduction of carbon nanotubes, to greatly improve the efficiency. Joint Strength of 0.1mm Thick Ag-27.6Cu-1.5Ti Active Solder Brazing (C _f /C)/Nb. Through pre-oxidation at 800℃×5min, the room temperature shear strength of the brazed joint of C _f /C and Nb can be increased from 29MPa to 57MPa; further adding Ti, through the formation of TiC, the shear strength of the joint can be increased to 62MPa; at 500℃, it can maintain At 48MPa. It is also believed that the improved joint strength is attributed to the small residual stress, large welded area and pinning effect.

In terms of welding methods, in addition to C _f /C surface pretreatment and direct melting and casting of the metal base material, there is also a combustion synthesis method (Combustion synthesis, reference 21).

references

[1] Fu Qiangang, Li Hejun, Shen Xuetao, Li Kezhi. Research progress on matrix modification of C/C composite materials in China. Progress in Materials in China, 2011,30(11):6-12.

[2] Li Hejun, Zeng Xierong, Li Kezhi. Research and application status and thinking of carbon/carbon composite materials. Carbon Technology, 2001, (5): 24-27.

[3] Guo Chen, Guo Lingjun, Li Hejun, Li Kezhi. Thermal compression bonding of C/C composite materials and metal materials. Carbon Technology, 2009, 28(5):27-30.

[4] Chen Junhua, Geng Haoran, Chen Guangli, Chen Maoai, Li Hui. Research progress in carbon/carbon composite welding technology. Thermal Processing Technology, 2006,35(11):75-78.

[5] Qiu Dong, Bi Jianxun, Mao Jianying. Research Status of C/C Composite Welding. Welding, 2017, (4): 39-44.

[6] Milena Salvo, Patrick Lemoine, Monica Ferraris, Margherita Montorsi. Joining of carbon-carbon composites for thermonuclear fusion applications [J]. Journal of the American Ceramic Society, 1997, 80(1): 206-212.

[7]M.Singh,T.P.Shpargel,G.N.Morscher,R.Asthana.Active metal brazing and characterization of brazed joints in titanium to carbon–carboncomposites.Materials Science and Engineering A, 2005,412:123–128.

[8] Qin Y Q, Feng J C. Microstructure and mechanical properties of C/Ccomposite/TC4 joint using AgCuTi filler metal [J]. Materials Science and Engineering: A, 2007(454/455): 322-327.

[9] Qin Youqiong, Feng Jicai, Zhang Li. Microstructure and Fracture Analysis of C/C Composite Materials and TC4 Brazed Joints, Journal of Welding Society, 2007,28(3):13-16.

[10]Xiujie Cao, Ying Zhu, Wei Guo, Peng Peng and KaituoMa. Microstructure and mechanical properties of C/C composite/TC17 joints with Ag-Cu-Ti brazing alloy. IOP Conference Series: Materials Science and Engineering 275(2017) 012040 doi :10.1088/1757-899X/275/1/012040

[11] Zhou Y.H., Liu D., Niu H.W., Song X.G., Yang, X.D., Feng J.C. Vacuumbrazing of C/C composite to TC4 alloy using nano-Al2O3 strengthened AgCuTicomposite filler. Materials and Design, 2016, 93:347-356 .

[12] Zhou Y., Liu D., Song X., Liu J., Song Y., Wang Z., Feng J. Characterization of carbon/carbon composite/Ti6Al4V joints brazed with graphene nanosheets strengthened AgCuTi filler. Ceramics International, 2017, 43(18):16600-16610

[13] Kexiang Zhang, Lihong Xia, Fuqin Zhang, Lianlong He. Active Brazing of C/C Composite to Copper by AgCuTi Filler Metal. Metallurgical and Materials Transactions A, 2016, 47(5): 2162-2176.

[14] M.Singh, R.Asthana, T.P.Shpargel. Brazing of ceramic-matrixcomposites to Ti and Hastealloy using Ni-base metallic glass interlayers. Materials Science and Engineering A, 2008, 498:19–30.

[15] Tian Xiaoyu, Qi Junlei, Zhang Lixia, Liang Yingchun, Li Hongwei, Feng Jicai. BNi2+TiH2 composite solder brazing C/C composite materials and GH99 nickel-based superalloy. Journal of Welding, 2014,35(5):35-38.

[16] Toshi-Taka Ikeshoji, Tatsuya Tokunaga, Akio Suzumura, Takahisa Yamazaki. Brazing of C/C composite and Ni-based alloy using interlayer. Proceeding of International Symposium on interfacial joining and surface technology, 49-50.2013, Nov. 27-29, Osaka ,Japan

[17] Pietro Appendino, Monica Ferraris, Valentina Casalegno, Milena Salvo, Mario Merola, Marco Grattarola. Direct joining of CFC to copper. Journal of Nuclear Materials, 2004, 329–333: 1563–1566.

[18]Guo L J, Li H J, Guo C, et al.Joining of C/C composites and GH3128Ni-based superalloy with Ni-Ti mixed powder as an interlayer[J].Rare MetalMaterials and Engineering.2011, 40(12) :2088-2091.

[19] Xinrui Song, Hejun Li, Valentina Casalegno, Milena Salvo, Monica Ferraris. In situ TiC particle reinforced TiCuZrNi brazing alloy for joining C/C composites to Ti6Al4V. International Journal of Applied Ceramic Technology, 2018, 15(3): 611-618.

[20] Yang Z.W., Wang C.L., Han Y., Zhao Y.T., Wang Y. Design of reinforced interfacial structure in brazed joints of C/C composites and Nb by pre-oxidation surface treatment combined with in situ growth of CNTs. Carbon, 2019 , 143:494-506.

[21] J.Cao, H.Q.Wang, J.L.Qi, X.C.Lin and J.C.Feng. Combustion synthesis of TiAl intermetallics and their simultaneous joining to carbon/carboncomposites. Scripta Materialia, 2011,65:261–264.

Contents of the invention

For (1) the existing Ag-based active solder (Ag-Cu-Ti) has a low melting point (780°C) and a large noble metal content (~70%); (2) traditional commercially available Ni-based solder (such as BNi-2, BNi-3, etc.) have high brittleness, low melting point (~1000°C), and need a long time of heat preservation to achieve wetting and isothermal solidification; Inherent problems (difficult wetting; thermal stress; poor high temperature resistance), the present invention proposes a method for quickly wetting carbon fibers in ceramic matrix composites using Fe as an active element.

In order to achieve the above object, the present invention proposes following solder design method and corresponding brazing method:

A kind of filler metal for carbon fiber (C _f ) reinforced ceramic matrix composite (CMC), in terms of composition design, the filler metal is designed for carbon fiber reinforced phase in ceramic matrix composite materials (such as C _f /C, C _f /SiC, etc. ) in large content (>40% ~ 50%), high melting point (3827 ℃), it is proposed to use weak carbide-forming elements, non-carbide-forming elements or medium-strength carbide-forming elements that can undergo eutectic reactions with carbon fibers As the main active elements for wetting carbon fibers (for C _f /C ceramic matrix composites, C matrix can be wetted at the same time, for C _f /SiC ceramic matrix composites, only carbon fibers can be wetted), to replace all or part of the traditional solder Strong carbide-forming elements (for example, Ti, Nb, V, Si, B), and follow this idea to design and form a series of high-temperature active solders for the ceramic matrix composite material. The high-temperature active solder has the following unique advantages in terms of interface wettability improvement and brazing seam structure improvement: in terms of interface wettability, since the eutectic reaction product is a liquid phase, its reaction and formation speed (controlled by dissolution rate) ) is much faster than the growth rate of solid-phase carbide products generated by the reaction of strong carbide-forming elements in traditional solder and carbon fibers (controlled by solid-phase diffusion rate), so it can quickly wet carbon fibers and carbon matrix; In terms of improvement, while using the eutectic reaction product (i.e. eutectic liquid phase) to improve the compactness of the brazing seam, it also automatically introduces the graphite phase formed by the "dissolution-crystallization" of carbon fibers into the brazing seam, reducing the brazing seam. The coefficient of thermal expansion is beneficial to reduce the harm of thermal stress.

Preferably, the "high temperature" means that the brazing temperature is higher than 1000° C., reaching the temperature range of high temperature brazing (HTB: High Temperature Brazing).

Preferably, the "active solder" means that the solder can have an obvious eutectic reaction with the carbon fiber, that is, the liquefaction of the solder itself and its wetting to the carbon fiber and the carbon matrix are all by means of the active element and the carbon fiber. The eutectic reaction of carbon fibers (for example, Fe/C _f , Ni/C, Cr/C eutectic reaction products) is achieved (not a chemical mechanism to form a new interface phase).

Preferably, the active element is selected from cheap weak carbide-forming element Fe or non-carbide-forming element Ni or medium-strength carbide-forming element Cr, rather than other expensive and resource-poor elements (such as Ti, Pd, etc.) .

Preferably, the present invention proposes a solder design idea that uses Fe as the active element (ie eutectic active element, using eutectic reaction to achieve wetting). The Fe-containing high-temperature active solder used can be Fe-based active solder, or other metal bases containing sufficient Fe (as alloying elements) (the metal does not undergo eutectic reaction with carbon, or although eutectic reaction with carbon can occur Reaction, but the eutectic reaction temperature is higher than the Fe-C _f eutectic reaction temperature) alloy type solder. Following this idea, the corresponding high-temperature active solder can also be Ni-based active solder, Cr-based active solder, or other metal-based alloy-type solder containing active elements Ni or Cr.

Preferably, the high-temperature active solder has Fe as the active element, and the high-temperature active solder contains a sufficient amount of Fe, which is sufficient to react with the carbon fiber (C _f ) of the ceramic matrix composite at the Fe-C _f eutectic reaction temperature of 1154 Above 1154°C (greater than 1154°C) the eutectic reaction occurs and a liquid phase reaction product is formed, thereby wetting the carbon fibers.

Preferably, the high-temperature active solder uses Ni as the active element, and the high-temperature active solder contains enough Ni to react with the carbon fiber (C _f ) of the ceramic matrix composite material at a Ni-C _f eutectic reaction temperature of 1327 Above 1327°C (greater than 1327°C) the eutectic reaction occurs and a liquid phase reaction product is formed, thereby wetting the carbon fibers.

Preferably, in the above-mentioned high-temperature active solder with Fe or Ni as the active element, ceramic phases with low thermal expansion coefficients, refractory metal powders or short fibers (1 to 10 microns) with low thermal expansion coefficients can be added, thereby reducing the high-temperature activity The thermal expansion coefficient of the brazing filler metal is used to further reduce the thermal stress between the high-temperature active brazing filler metal and the base material of the ceramic matrix composite material.

A brazing method for carbon fiber (C _f ) reinforced ceramic matrix composites (CMC), comprising the following steps:

(1) Brazing material design and preparation: design and prepare alloys containing sufficient amounts of the above-mentioned weak carbide-forming elements (Fe), non-carbide-forming elements (Ni) or medium-strength carbide-forming elements (Cr) or corresponding eutectic activities The simple substance of elements (Fe, Ni, Cr) is used as a high-temperature active solder ("eutectic element" specifically refers to the eutectic element for "carbon fiber";"sufficientamount" refers to the liquid formed after the eutectic reaction with carbon fiber phase enough to fill the interfacial gap). That is to use the weak carbide, non-carbide or medium-strength carbide-forming elements in the above-mentioned high-temperature active solder as the wet carbon fiber through the eutectic reaction (for C _f /C ceramic matrix composites, it can wet the C matrix at the same time, and for C The _f /SiC ceramic matrix composite only wets the active elements (such as Fe, Ni, Cr) of carbon fibers, and replaces the traditional strong carbide-forming elements (such as Ti, Nb, V, Si, B) in whole or in part.

(2) Brazing process: through the eutectic reaction of the active elements (such as Fe, Ni, Cr) and carbon fibers to generate liquid phase products, it can realize the rapid and dense wetting of carbon fibers and carbon matrix in carbon fiber reinforced ceramic matrix composites. Wet, and full fill the interfacial gap, forming a brazing seam. On the one hand, this process takes advantage of the relatively high eutectic reaction temperature of the active elements and carbon fibers (300°C and 150°C higher than the melting points of traditional Ag-based solder and Ni-based solder, respectively) (Fe-C _f eutectic reaction temperature is 1154°C; Ni- _Cf eutectic reaction temperature is 1327°C; Cr- _Cf eutectic reaction temperature is 1534°C), which can improve the heat-resistant temperature of brazed joints, which is the "specific optimization" proposed by the present invention Combining eutectic reaction brazing methods (such as Fe-C _f , Ni-C _f , Cr-C _f )" is one of the advantages. On the other hand, since the eutectic reaction temperature is lower than the active element itself, and more graphite phases can be introduced into the brazing seam (introduced into the brazing seam after the carbon fiber is dissolved by the eutectic reaction), "low eutectic reaction temperature" and "Graphite phase generated in situ in the brazing seam" is conducive to reducing the thermal stress between the brazing filler metal and the base metal, which is based on a specific optimized combination (such as Fe-C _f , Ni-C _f , Cr-C _f ) The second advantage of the eutectic reaction brazing method.

Preferably, in terms of specific brazing methods, pure Fe or Fe-containing alloys are used as an intermediate layer to be pre-placed between carbon fiber (C _f ) reinforced ceramic matrix composite (CMC) base materials, and Fe-C _f eutectic reaction is used to obtain The eutectic liquid phase can achieve reaction-wetting carbon fibers and form brazing seams without long-term heat preservation; and use the eutectic liquid phase formed by the reaction to deeply fill the original remaining pores between the carbon fibers and the ceramic matrix of the ceramic matrix composite (ceramic The ceramic matrix composite material often contains about 15% of the original pores due to the difficulty in densification during the preparation process), which can further strengthen the ceramic matrix composite material near the seam. It is the third advantage of the eutectic reaction brazing method based on a specific optimized combination (such as Fe-C _f ) proposed by the present invention to deeply fill and strengthen the base material of the ceramic matrix composite material near the seam by using the surplus eutectic reaction liquid phase.

In addition, the "eutectic reaction brazing method" proposed by the present invention has the advantages of the above three aspects in terms of eutectic reaction products, and in terms of reaction participants, a specific part (active element) in the solder and A specific part (carbon fiber) in the solder participates in the eutectic reaction, which provides a broader idea for the design of the solder. This is the fourth advantage of the eutectic reaction brazing method proposed by the present invention.

Preferably, for joints whose heat resistance temperature of brazing joints is required to reach 1000°C to 1154°C, the brazing uses active solder with Fe as the active element, and the brazing temperature (insulation temperature) is the Fe-C _f eutectic reaction temperature Above 1154°C (eg, >1154°C, and ≤1400°C).

Preferably, for joints whose heat resistance temperature of brazing joints is required to reach 1200°C to 1300°C, the brazing uses active solder with Ni as the active element, and the brazing temperature is above the Ni- _Cf eutectic reaction temperature of 1327°C .

Preferably, for joints whose heat resistance temperature is required to reach 1400°C to 1500°C, the active solder with Cr as the active element is used for brazing, and the brazing temperature is above 1534°C.

Preferably, in the above brazing, the holding time is 1-10 minutes, and the pressure is 0.1-10 MPa.

The beneficial effects of the present invention are reflected in:

1. Features of the present invention

(1) The present invention focuses on solving the wettability of the carbon fiber reinforced phase, which is different from the traditional brazing thinking that focuses on the matrix as the research object.

(2) The present invention proposes a eutectic active element represented by Fe (replacing the traditional active element Ti) for the carbon fiber reinforced phase. The reaction product of these active elements is a eutectic liquid phase, which brings two major advantages: First, it can react quickly and quickly wet the carbon fiber reinforced phase; second, the brazing joint is actually a composite material composed of carbon (graphite) and Fe, and the carbon (graphite) in it can reduce the thermal expansion coefficient of the brazing joint, thereby reducing the internal temperature of the joint. The thermal stress is beneficial to improve the room temperature performance in the joint preparation process.

(3) The active elements in the present invention include Fe, Ni, Cr, etc., which are not noble metals or rare metals, and have the advantages of economical price and easy availability.

(4) The wetting reaction speed of the present invention is fast, the production efficiency is high, and no long-term heat preservation is required.

(5) The present invention does not need a vacuum system in brazing, and the requirements for production conditions are low and the cost is low.

(6) The present invention does not require any modification treatment on the surface of the carbon fiber reinforced ceramic matrix composite material before welding.

(7) The present invention is particularly remarkable in improving the high-temperature performance of the brazing joint: increasing the service temperature of the joint, for example, even in the range of 700 to 900°C (the solidus line of the Ag-Cu-Ti solder is 780°C; the Ni-based solder The solidus line is close to 970～1080℃), and the brazing joint can also maintain the strength of common austenite.

2. Advantages of the present invention

(1) Compared with the active metal brazing method of traditional Ag-based solder

(a) In terms of interfacial wettability and wetting products: use the eutectic reaction (for example, Fe-C _f ) to obtain a liquid phase, and quickly realize the wetting of the carbon fiber reinforced phase; and no brittle phase is formed on the surface of the carbon fiber . (b) In terms of improving the brazing seam structure and reducing thermal stress: Although the obtained brazing seam cast iron structure, the cast iron can actually be regarded as a composite material of graphite and active elements (such as Fe), so that the brazing seam can be used The graphite phase reduces the thermal expansion coefficient of the brazing joint and reduces thermal stress. (c) In terms of joint heat resistance: because the eutectic reaction temperature of Fe-C _f , Ni-C _f , and Cr-C _f (above 1154°C) is higher than the solidus line of Ag-Cu-Ti solder (780°C) 374 ℃, so the remelting temperature of the joint can be greatly increased; it can be inferred that since the brazing seam is cast iron or alloy cast iron structure, even at a high temperature of 700-900 ℃ (which is close to or exceeds that of Ag-Cu-Ti solder) The strength of the brazing seam at the solidus line (780°C) can reach the strength of high-temperature austenite.

(2) Compared with the eutectic reaction brazing of traditional metals (such as Al/Cu/Al), long-term isothermal solidification is not required.

(3) Compared with traditional Ni-based solder high-temperature brazing, it has three advantages: (a) Fe-C _f , Ni-C _f , Cr-C _f eutectic reaction temperature is much higher than the melting point of Ni-based solder by 100 ~150°C, the remelting temperature of the brazing joint and the heat-resistant temperature of the joint can be improved; (b) the brittleness of the brazing joint is less than that of traditional Ni-based solders (such as BNi-2, etc.), and does not require long-term isothermal solidification; (c ) The cost of solder is low (Ni resources are limited).

Further, Fe-based or alloy-type solder containing sufficient Fe is used as the high-temperature active solder to achieve rapid and dense wetting of the carbon fiber through the eutectic reaction between the active element Fe and the carbon fiber. Its advantages are: the use of eutectic reaction to achieve rapid wetting of carbon fibers, and the densification of the original pores in the base metal of the composite material near the seam and the densification of the brazing seam, avoiding the formation of a continuous interface reaction phase from the interface reaction; The carbon is fully graphitized, which can reduce thermal stress; the brazing temperature is above 1154°C, which can increase the service temperature of the brazed joint; there is no need for long-term heat preservation, and the surface of the composite material should be modified before welding; it does not contain or contain a small amount precious metals. The invention solves the problems of low joint heat-resistant temperature and long heat preservation time respectively existing when the traditional Ag-based active solder and Ni-based solder are used for brazing ceramic matrix composite materials.

Description of drawings

Figure 1 is the backscattered BSE photo of the (C _f /C)/pure Fe/(C _f /C) brazed joint as a whole and different selected regions (welding specification: 1250℃×5min), among which, Figure 1(a) It shows the overall low magnification structure uniformity of the brazed joint and extruded liquid solder beads: it shows that both pure Fe and C are dissolved smoothly; Fig. 1(b) is a magnified 2000 times of the brazing seam at b in Fig. 1(a) Microstructure: Composed of coarse primary graphite phase, retained austenite, and secondary graphite phase; Figure 1(c) is a 500-fold magnified microstructure of the diffusion zone in the brazing seam area at c in Figure 1(a): dense brazing slit and its internal thick primary graphite rod; Figure 1(d) is a high-magnification photo (3000 times) of the interface and diffusion area in Figure 1(c): the interface is dense and wetted well, Fe is easier to diffuse in the carbon matrix, and the diffusion depth Reach ~ 25μm; Figure 1(e) is a super high magnification (10000 times) magnified photo of the interface in Figure 1(d): the interface is still dense, no voids and cracks are observed; Figure 1(f) is the f in Figure 1(a) Solidification structure of extruded liquid beads: composed of primary spherical graphite, secondary short strip graphite and retained austenite.

Fig. 2 is the BSE photo of (C _f /C)/4J36/(C _f /C) brazing joint as a whole and different selected regions (1250℃×5min). Double structure uniformity and extruded liquid solder beads: It shows that 4J36 (low expansion alloy) and C are dissolved smoothly; Figure 2(b) is an enlarged view of b in Figure 2(a): solder melting (but due to Fe content is low and there is no primary graphite), C matrix and solder interface are wet and dense; Figure 2(c) is an enlarged view of point c in Figure 2(a): the solder melts (but there is no primary graphite due to low Fe content) , the interface between C fiber and solder is wet and dense; Figure 2(d) is an enlarged view of point d in Figure 2(a): the solder melts (but there is no primary graphite due to low Fe content), and the interface between C fiber and solder is dense ; Fig. 2(e) is an enlarged view of e in Fig. 2(d): even at 15,000 times magnification, the interface between C fiber and solder is still dense.

Fig. 3 is the BSE photo of (C _f /C)/630SS/(C _f /C) brazing joint overall and different selected regions (1250℃×5min), in which, Fig. 3(a) is the brazing joint overall low Double structure uniformity and extruded liquid solder beads: pure Fe and C were dissolved smoothly; the contact angle between the extruded beads and the C/C base material was an acute angle, indicating that the wettability of the liquid to the carbon matrix was also good; Figure 3 (b) is the microstructure at b (extruded solder beads) in Figure 3(a): the appearance of a large amount of carbon indicates that the carbon eutectic reaction occurs, and the carbon fails to precipitate in the graphite phase but in the form of Fe-Cr- C ternary compound (Fe, Cr) ₇ C ₃ exists in the form; Figure 3(c) is the microstructure of the brazing joint at point c in Figure 3(a): the carbon matrix/brazing material interface is dense, and the brazing joint is ternary carbonization Figure 3(d) is the microstructure of the brazing seam at d in Fig. 3(a): the fiber/solder interface is dense, and the brazing seam is ternary carbide; Fig. 3(e) is the microstructure in Fig. 3(d) Enlarged picture of the fiber/solder interface at e: the fiber/solder interface is dense at 10,000 times.

Fig. 4 is the displacement-load curve of (C _f /C)/630SS/(C _f /C) brazed joint (1250℃×5min) compression shear test.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments.

Aiming at the problem of low joint heat resistance temperature when traditional Ti-containing silver-based and copper-based active solders are used for brazing C _f /C and C _f /SiC and other ceramic matrix composite materials, and Ni-based commercial solders are used for brazing The brittleness of existing ceramic matrix composites such as welding C _f /C and C _f /SiC is big and needs the problem of keeping warm for a long time, the present invention is in the brazing of the ceramic matrix composite (CMC) that carbon fiber (C _f ) reinforces, It is proposed that through the eutectic reaction of weak carbide-forming element Fe, non-carbide-forming element Ni, or medium-strength carbide-forming element Cr with carbon fibers, carbon fiber-reinforced ceramic matrix composites can be quickly realized at higher temperatures (above 1154°C). Wetting of carbon fibers (for C _f/ C ceramic matrix composites, C matrix can be wetted at the same time).

The "active element for carbon fiber" proposed by the present invention should meet the following requirements: first, it can undergo eutectic reaction with carbon fiber; second, when eutectic reaction occurs, it has a higher solubility for carbon, which is conducive to obtaining a clean carbon interface and wet it; the third is that the eutectic reaction temperature should be lower than its high melting point stable carbide formation temperature, that is, before the reaction forms a high melting point stable carbide, it can first react with the carbon fiber in a eutectic reaction to obtain a liquid phase and wet the carbon fibers. Otherwise, the high-melting-point stable carbide will cover the surface of the carbon fiber and become a barrier layer, which prevents the carbon fiber from contacting with the eutectic element and causing a eutectic reaction, so that wetting cannot be achieved.

Although carbon (C) itself has a very high melting point (3827°C), carbon, as an interstitial atom, can undergo eutectic reactions with various elements to form a eutectic liquid phase, so it is possible to use eutectic reactions in places with a lower melting point than carbon. The temperature dissolves C _f and thus wets C _f . The common elements that can undergo eutectic reaction with C are summarized in Table 1. Among them, there are not many elements that can meet the above three requirements at the same time, mainly weak carbide-forming element Fe, non-carbide-forming element Ni and medium-strength carbide-forming element Cri. Although the common strong carbide forming elements Ti and Si can undergo eutectic reaction with C from the phase diagram, the solubility of the eutectic liquid relative to C is extremely low, and the solubility of Ti-C eutectic liquid relative to C is only 1.8C %; especially the solubility of Si-C eutectic liquid relative to C is close to 0. Therefore, Ti and Si are excluded, and their eutectic reaction with C cannot be used to wet C fibers. In fact, when Milena Salvo et al. used Si as the intermediate layer, even though the welding temperature (1420°C) had slightly exceeded the melting point of Si (1414°C), the center of the weld was still Si, and the base material of the C/C composite material did not dissolve in. This result also proves that the Si- _Cf eutectic reaction cannot be used for the purpose of wetting.

See Table 1. Below 1300°C (slightly higher than the high-temperature brazing temperature of traditional Ni-based solder), among the common alloying elements, only Fe and C can undergo eutectic reaction, thereby rapidly wetting C. Since other elements cannot undergo eutectic reaction with C at 1300°C, when these elements are used as the intermediate layer, because they cannot undergo eutectic reaction with C, they can only form solid compounds on the surface of C with a high melting point through solid-state diffusion reaction. Forming a bond with C, and forming a solid compound through a solid-state diffusion reaction requires a long holding time, which reduces production efficiency, and the formed compound reaction layer is continuously distributed in layers on the interface, and it is difficult to enter the brazing seam. The cracks are dispersed, disordered, and uniformly distributed. This continuous layered reaction product that only exists at the interface is not conducive to reducing the harm of thermal stress.

When the service temperature is required to gradually increase, the candidate eutectic active elements can be selected in sequence Ni, Cr, V, and Nb. This is because the remelting temperatures of the obtained eutectic solder joints are 1327°C, 1543°C, 1690°C, and 2340°C in sequence.

Table 1. Eutectic point composition and eutectic reaction temperature of carbon and main alloying elements

The idea of quickly wetting the carbon fiber in the ceramic matrix composite material proposed by the present invention is: adopt low-cost "high-temperature active solder with Fe as the active element", and perform high-temperature brazing in the form of Fe- _Cf eutectic reaction, In this way, the purpose of quickly wetting the carbon fiber can be achieved. In this high-temperature active brazing method, the active element is not the classic Ti element, but a low-cost Fe element, that is, the design feature of the solder composition is to design and prepare a high-temperature active solder with Fe as the active element. Following this idea, a series of low-cost, practical high-temperature active solders for carbon fiber-reinforced ceramic matrix composites can be developed. The advantages of this idea are reflected in the following aspects: (1) Use the eutectic reaction to achieve rapid wetting and densification (including the densification of the interface and the brazing seam), avoiding the formation of a continuous reaction phase from the interface reaction (traditional active metal brazing In the welding method, the interface product grows on the C surface according to the solid phase diffusion reaction rate, and cannot enter the liquid brazing seam and be dispersed, which is not conducive to reducing the harm of thermal stress); (2) the brazing temperature is relatively high (Fe-C The eutectic temperature of 1154°C is much higher than the Ag-Cu eutectic temperature of 780°C), which can increase the service temperature; (3) fully graphitize the dissolved carbon in the brazing seam, which can reduce the thermal expansion coefficient of the brazing seam, Thereby it is beneficial to reduce the thermal stress; (3) the degree of brittleness of the solder joint is less than that of the traditional Ni-based solder, and there is no need for long-term heat preservation; (4) there is no need to modify the surface of the ceramic matrix composite material before welding; (5) it does not contain or Contains only a small amount of precious metals; (6) Using the abundant eutectic liquid phase in the brazing seam can fill the original pores in the base material of the ceramic matrix composite material located in the near seam area (referring to the remaining pores in the preparation process of the ceramic matrix composite material), improving the near-slit area. The compactness of the base material in the fracture area strengthens the base material near the fracture area.

(1) High temperature active solder with Fe as active element

The brazing tests of pure Fe and Fe-based alloys are respectively carried out below to reveal the characteristics of the "method for rapid wetting of C _f /C composite materials by high-temperature active solder with Fe as the active element" proposed by the present invention.

(1) Pure Fe middle layer

In order to verify the correctness of the technical route of "rapid reaction wetting with Fe as the active element for carbon fibers" proposed by the present invention, a rapid eutectic reaction wetting experiment was first performed with pure Fe flakes.

The actual welding method is: select the commercially available (C _f /C)/(C _f /C) composite material combination as the base material, select the commercially available pure Fe sheet as the solder (thickness: 0.3mm); sandpaper grinding, ultrasonic cleaning After the surface of the base metal to be welded and the surface of the pure Fe solder sheet, pre-set the pure Fe sheet at the welding interface between the (C _f /C)/(C _f /C) composite material; apply appropriate pressure (0.5MPa); Enter Ar gas protection; heat to 1250°C and keep warm for a short time (5min). The interface wettability and microstructure are shown in Fig. 1.

The welding temperature is 1250°C, which is higher than the Fe-C eutectic reaction temperature (1154°C) and cementite melting point (1227°C), but far lower than the pure Fe solder melting point (1538°C) and C base metal melting point (3827°C). ℃). At this temperature, there is liquid phase extrusion at the edge (see Figure 1(a)), indicating that the expected Fe-C eutectic reaction can be successfully realized; and the backscattered photo of the brazing seam is mixed with white (the atomic number of Fe is 26 , much higher than the atomic number 6 of C, so Fe is white) indicating that liquid Fe has not been completely extruded, which is beneficial to ensure wettability and compactness; even under high magnification (Fig. 1(c) is 500×, (b) is 2000×, Figure 1(d) is 3000×, Figure 1(e) is ×10000), the interface is still dense and without defects, the brazed joint is well wetted, and the brazing seam is also dense and defect-free (see Figure 1( c)).

Energy spectrum point analysis (see Figure 1(b) and Figure 1(f)) shows that there are only two elements, Fe and C, in the brazing joint, which fully proves that the Fe-C eutectic reaction occurs smoothly, and the tight wettability is excellent, and the brazing The seams are dense. After welding, the brazing seam changes from pure Fe to Fe-20C (at.%), the composition of the extruded solder beads changes from pure Fe to Fe-36C (at.%) and the brazing seam/base metal interface is basically straight, indicating that Both the carbon fiber and the carbon matrix are uniformly dissolved, and both participate in the Fe-C eutectic reaction; after the reaction, the excess dissolved C exists in the form of: or crystallized from graphite in various forms (coarse rod-shaped, spherical, worm-shaped) , or solid solution in the retained austenite.

Although the thickness of the brazing joint is as high as 50 μm (caused by the excessive thickness of the original _Fe sheet), there is no elemental Fe; It is composed of the primary graphite phase directly crystallized from the hypereutectic liquid phase), vermicular graphite (average size 10 μm), and retained austenite with a carbon content of up to 20 at.% (back scattering shows that the white brazing seam matrix components are evenly distributed , it can be seen that this high-carbon austenite is very stable and has not yet decomposed). On both sides of the brazing seam, there is a white (because of Fe) diffusion layer. It can be seen from Figure 1(d) that it is mainly formed by the diffusion of Fe into the loose C matrix (not dense carbon fiber), with a thickness of about 25 μm on each side. Since the primary coarse graphite phase in the brazing seam is obvious, it is speculated that the white matrix in the brazing seam is obtained by direct cooling of the eutectic high-carbon austenite after the hypereutectic liquid phase solidifies, even in the backscattered photos up to 10000 times ( Figure 1(e)) also did not observe signs of carbon precipitation, probably because the extremely high carbon content increased the stability of the high-carbon austenite and inhibited its phase transformation and decomposition during cooling, so The matrix is correspondingly retained austenite. The extruded liquid beads have primary spherical graphite (average size d=10μm) and flake graphite (average size: 5μm) remaining in the solder beads, but no structure between nodular cast iron and vermicular graphite cast iron has been formed. The matrix is still high carbon retained austenite.

The observation of the microstructure above shows that the interface between the C _f /C composite material and the brazing joint is dense without voids and microcracks, which confirms that Fe can act as an active element to react with carbon fiber and carbon matrix and wet the carbon fiber and carbon matrix. Ability to obtain excellent interfacial wetting effect. Moreover, the diffusion of Fe in the carbon matrix is easier, and the depth can reach 25 μm. However, due to the thicker pure Fe, the amount of carbon dissolved is too large, resulting in coarse (even across the entire weld thickness) primary graphite in the brazing seam structure; in addition, a large amount of carbon dissolves in Fe, making the brazing seam matrix become brittle. As a result, although the wettability of the joint is ideal, the performance of the joint is very low (below 5MPa) due to the high brittleness of the brazing seam.

(2) 4J36 (Fe-36Ni) Invar alloy middle layer:

In order to simultaneously reduce the thermal stress caused by the mismatch between the dissolved amount of carbon and the thermal expansion coefficient, the low-expansion alloy 4J36 (Fe-36Ni-0.2C, Invar alloy) with low Fe content and extremely low thermal expansion coefficient is used as the intermediate layer. The melting point of 4J36 is about 1430°C.

The actual welding method is: after sandpaper grinding, ultrasonic cleaning (C _f /C)/(C _f /C) composite material welding surface and 4J36 solder sheet (thickness: 0.3mm), preset 4J36 sheet in (C _f / C)/(C _f /C) Welding interface between composite materials; Appropriate pressure (0.5MPa); Ar gas protection; Heating to 1250°C and holding it for a short time (5min). The interface wettability and microstructure are shown in Fig. 2.

The appearance of the extruded liquid solder in Figure 2(a) proves that the Fe-C eutectic reaction has been successfully realized, but the contact angle between the extruded solder beads and the surface of the C _f /C base metal is about 90 degrees; On the one hand, the liquid phase is not completely squeezed out of the solder joint. The high-magnification observation shows that the brazed joint with 4J36 as the solder has good wetting and no graphite precipitation. The interfaces of C _f /C composite brazed joints can be classified into: C matrix/solder interface (as shown in Figure 2(b)) and C _f /solder interface (as shown in Figure 2(c)). Wet well. When C _f / solder is magnified to 15000 times (as shown in Figure 2(d) and Figure 2(e)), it can be found that the C _{f /} solder interface is still tightly bonded. Comprehensively extruded solder beads, dense interface and brazing seam, and EDS data show that wetting can only rely on Fe-C eutectic reaction, but the amount of 4J36 to dissolve C is less than that of pure Fe (than the solubility of pure Fe Weak), so graphite is not precipitated in the brazing seam, and the brazing seam is Cr-free and highly stable Fe-Ni-C ternary retained austenite and compounds. Although the interface is dense, the failure of dissolved carbon to precipitate will lead to the embrittlement of the brazing joint. In addition, the contact angle is slightly larger, and the joint strength is still low (less than 5MPa).

(3) 630 stainless steel middle layer (630SS)

The middle layer is precipitation hardening martensitic stainless steel, whose thermal expansion coefficient (10×10 ^-6 /℃) is smaller than that of common austenitic stainless steel (17×10 ^-6 /℃), which is beneficial to suppress thermal stress; Its composition is 0Cr17Ni4Cu4Nb, its Fe content is 75% (higher than low expansion alloy 4J36, lower than pure Fe), and it also contains other carbide forming elements (such as Cr and Nb); melting point is about 1450 ° C.

The actual welding method is: after sandpaper grinding, ultrasonic cleaning (C _f /C)/(C _f /C) composite material welding surface and 630SS solder sheet (thickness: 0.3mm), preset 630SS sheet on (C _f / C)/(C _f /C) Welding interface between composite materials; Appropriate pressure (0.5MPa); Ar gas protection; Heating to 1250°C and holding it for a short time (5min). The interface wettability and microstructure are shown in Fig. 3.

The extruded liquid phase beads are also observed in Fig. 3(a), indicating that the eutectic reaction is successfully realized; the contact angle between the edge of the extruded liquid phase beads and the surface of the _Cf /C composite parent material is acute, indicating that wetting Sex has been improved to a certain extent. The liquid metal in the brazing seam is not completely squeezed out, and the interface is dense without cracks, but there are two long strips of graphite phases in the central area that penetrate the brazing seam, which should be the primary graphite phase directly crystallized from the hypereutectic liquid phase. It can be seen from Figure 3(b) that the extruded liquid phase contains a large amount of C and Cr, and the appearance of Cr is beneficial to further improve the wettability of the C _f /C interface. From Figure 3(c)~(e), it can be seen that the C _f / solder interface is still dense even if it is enlarged (10000×). From the energy spectrum analysis data in Figure 3(b) and Figure 3(c), it can be seen that the content of C in the solder bead and the brazing seam increased significantly, and it can be seen that the wetting (C _f /C) composite of 630SS mainly depends on Fe- C eutectic reaction, combined with Cr element to further strengthen the combination after wetting. Although the measured carbon content is relatively large, there is no elemental graphite precipitation in the brazing joints in most areas, indicating that Cr has a tendency to inhibit the precipitation of carbon as elemental graphite.

Joint strength: According to the fracture load (see Figure 4) and the cross-sectional area of the brazed joint (7.5×7.5mm), the (C _f /C)/630SS/(C _f /C) brazed joint (1250°C×5min) can be obtained ) The shear strength can reach 18.4MPa. The shear strengths of the three parallel samples are 18.1MPa, 17.2MPa, and 18.4MPa respectively, indicating that the brazing results of the present invention have little dispersion and good repeatability. The shear strength is close to that of Italy's Milena Salvo (reference [6]) reported that using a silicon sheet (silicon sheet), under the conditions of 1420 ° C × 90 min and flowing Ar protection (it has exceeded the melting point of Si 1414 ° C), through the reaction to generate With 20μm thick SiC, a joint with a shear strength of 22MPa is obtained, which is close to the interlaminar shear strength (interlaminar shear strength) of C _f /C of 20-25MPa. But the present invention has the obvious advantage of short holding time (5min<<90min).

In the high-temperature brazing of carbon fiber reinforced ceramic matrix composites (such as C _f /C), from the perspective of production and application, the present invention has the advantages relative to the widely used Ag-Cu-Ti solder: (1) overcomes The brazing filler metal cost that classic Ag-Cu-Ti active brazing filler metal exists is high (contains more Ag, about 72%); (2) the present invention is active element with cheap Fe etc., and welding temperature is at Fe-C eutectic Above the reaction temperature (1154°C), the eutectic reaction can be used to greatly improve the production efficiency, which can be described as fast and good; especially in the range of 700-900°C, the brazing joint can maintain the strength of common austenite; and the Ag-based The low melting point of active solder leads to low service temperature (generally below 600°C).

(2) High temperature active solder with Ni as active element

The invention proposes a low-cost Ni-containing high-temperature active solder to quickly wet the carbon fiber in the carbon fiber-reinforced ceramic matrix composite material through Ni-C eutectic reaction. In this method, the active element is not the classic Ti element, but Ni element, that is, the design feature of its solder composition is to design and prepare a high-temperature active solder with Ni as the active element, for example, Ni-based active solder.

Described Ni-based active solder is different from traditional Ni-based solder (such as BNi-2), and its difference is: (1) melting point is high——traditional Ni-based solder has a low melting point, and self-melting in heating, and the present invention says Only when the heating temperature exceeds the C-Ni eutectic temperature (1327 ° C) can the Ni solder be melted through the eutectic reaction between the two; (2) the active elements and the wetting mechanism are different - the present invention wets the carbon fiber Ni is used as the active element, and the C fiber is wetted through the eutectic reaction of Ni and C, while the traditional Ni-based solder wets the carbon fiber through the alloy elements Cr, B, Si and other active elements, not Ni itself. .

In the high-temperature brazing of carbon fiber reinforced ceramic matrix composites (such as C _f /C), the present invention has the advantages relative to the traditional commercial Ni-based solder: compared with the Ni-based commercial solder, it does not need to realize isothermal solidification, and the brazing The holding time can be greatly shortened. Traditional commercial nickel-based brazing filler metals cannot achieve isothermal solidification when used for brazing ceramic matrix composites, resulting in low remelting temperature of the brazing seam, poor heat resistance, and very brittle brazing seam, so there are problems with poor room temperature and high temperature performance of the joint .

Claims (10)

1. a kind of solder for carbon fiber-reinforced ceramic matric composite, it is characterised in that: the solder is in ingredient design Using weak carbide formation element, non-carbide forming element or the moderate strength carbide shape that eutectic reaction can occur with carbon At element as wetting carbon fiber or as wetting carbon fiber and the active element of carbon base body, formed compound towards the ceramic base The high temperature active solder of material.

2. a kind of solder for carbon fiber-reinforced ceramic matric composite according to claim 1, it is characterised in that: institute It states active element and is selected from Fe, Ni or Cr.

3. a kind of solder for carbon fiber-reinforced ceramic matric composite according to claim 1, it is characterised in that: institute State the alloy-type solder that high temperature active solder is selected from Fe base solder or other Metal Substrates containing Fe.

4. a kind of solder for carbon fiber-reinforced ceramic matric composite according to claim 1, it is characterised in that: institute High temperature active solder is stated using Fe as active element, which contains enough Fe, with the ceramic base composite wood Eutectic reaction occurs on eutectic reaction temperature and forms liquid-phase reaction product for the carbon of material, to soak carbon fiber, carbon base body； Alternatively, the high temperature active solder, using Ni as active element, which contains enough Ni, with the ceramic base Eutectic reaction occurs on eutectic reaction temperature and forms liquid-phase reaction product for the carbon of composite material, thus soak carbon fiber, Carbon base body.

5. a kind of solder for carbon fiber-reinforced ceramic matric composite according to claim 1, it is characterised in that: institute State the refractory metal powder or low-heat of ceramic phase, low thermal coefficient of expansion that low thermal coefficient of expansion is also added in high temperature active solder The staple fiber of the coefficient of expansion.

6. a kind of method for welding for carbon fiber-reinforced ceramic matric composite, it is characterised in that: the following steps are included:

1) prepare high temperature active solder, the high temperature active solder is formed using the weak carbide that eutectic reaction can occurs with carbon Element, non-carbide forming element or moderate strength carbide former as wetting carbon fiber or as wetting carbon fiber and The active element of carbon base body；

2) soldering processes: generating liquid product by the eutectic reaction of the active element and carbon, utilizes liquid product realization pair The quick and fine and close wetting of carbon fiber, carbon base body in the ceramic matric composite, and full filling weld interface gap, with shape At brazed seam.

7. a kind of method for welding for carbon fiber-reinforced ceramic matric composite, feature exist according to claim 6 In: the soldering processes are specifically includes the following steps: be preset in the ceramic base using the high temperature active solder as middle layer Between composite material base material, the then held for some time on eutectic reaction temperature.

8. a kind of method for welding for carbon fiber-reinforced ceramic matric composite, feature exist according to claim 6 In: reach 1000 DEG C~1154 DEG C of connector for the requirement of soldered fitting heat resisting temperature, uses the activity using Fe as active element Solder, brazing filler metal melts temperature is on 1154 DEG C of Fe-C eutectic reaction temperature in soldering, and≤1400 DEG C.

9. a kind of method for welding for carbon fiber-reinforced ceramic matric composite, feature exist according to claim 6 In: reach 1200 DEG C~1300 DEG C of connector for the requirement of soldered fitting heat resisting temperature, uses the activity using Ni as active element Solder, brazing filler metal melts temperature is on 1327 DEG C of Ni-C eutectic reaction temperature in soldering；For the requirement of soldered fitting heat resisting temperature The connector for reaching 1400 DEG C~1500 DEG C uses the active solder using Cr as active element, and brazing filler metal melts temperature is Cr- in soldering On 1534 DEG C of C eutectic reaction temperature.

10. a kind of method for welding for carbon fiber-reinforced ceramic matric composite, feature exist according to claim 6 In: the condition of the soldering processes are as follows: soaking time is 1~10min, and pressure is 0.1~10MPa.