CN107630152A - A kind of nickel-based isometric crystal alloy and its Technology for Heating Processing and application containing yttrium and hafnium - Google Patents

Abstract

The invention discloses a nickel-based equiaxed crystal alloy containing yttrium and hafnium, a heat treatment process and application thereof, and belongs to the technical field of nickel-based equiaxed crystal alloys. The alloy composition is: C 0.03-0.15%, Cr 8.0-10.0%, Al 5.5-6.2%, Co 3-8%, W 6.0-9.0%, Mo 2.5-3.5%, Nb 1.8-2.4%, B 0.001-0.04 %, Hf 1.0-2.0%, Y 0.005-0.05%, Ni balance. The alloy has a durable life of ≥50 hours at 1100°C and 55MPa, and can be cast directly. The alloy can be used to prepare hot-end components such as aero-engines and gas turbine blades that work at 1100°C for a long time. Using the heat-resistant alloy to manufacture gas turbine turbine blades for power generation can significantly increase the working temperature and efficiency of the gas turbine, thereby greatly improving power generation efficiency.

Description

A nickel-based equiaxed crystal alloy containing yttrium and hafnium and its heat treatment process and application

technical field

The invention relates to the technical field of nickel-based equiaxed crystal alloys, in particular to a nickel-based equiaxed crystal alloy containing yttrium and hafnium and its heat treatment process and application.

Background technique

With the increase of gas inlet temperature, the temperature bearing capacity of the deformed superalloy guide vane can no longer meet the requirements. Cast superalloys have a higher temperature bearing capacity, which can reach 1000-1100 °C, so the development of cast superalloys has received extensive attention. Since the advent of cast high-temperature alloys in the 1940s, the development speed has been very fast. By the end of the 1950s, many alloys with excellent performance such as IN100, ЖС6К, B1900 and Mar-M200 have been developed, and domestically developed and produced one after another. A series of cast superalloys such as K403 and K417G.

Whether it is Britain, the United States or Russia, the guide vane material of aero-engine is nickel-based superalloy. The famous Russian ЖС6У and ЖС6К nickel-based superalloys are mainly used to prepare guide vanes. The АЛ-31Ф engine equipped with the third-generation fighter Su-27 is high, The four blades of the low-pressure turbine and the guide vane are all made of ЖС6У alloy, while a large number of nickel-based single crystal guide vanes are used in developed countries in Europe and the United States. American PWA1480 single crystal is the first guide vane material used in the JT9D-7R4 aero-engine, and the F100-PV-229 aero-engine primary and secondary guide vanes equipped with the famous F15 and F16 fighter jets in the United States are also made of this alloy. .

The development of aero-engines depends to a large extent on the development of materials and manufacturing technologies. In order to improve the rigidity and airtightness of the guide, reduce the forward warpage caused by the load acting on a single blade, and reduce the risk of blade cracks caused by vibration, the third-generation aero-engine adopts conjoined combined guide blades. At present, there are guide vanes such as doublets, triplets, and quadruples. For example, the high-pressure and low-pressure guide vanes of the АЛ-31Ф engine are triple-unit hollow air-film cooling blades; the high-pressure guide vanes of aeroengines produced in my country with a thrust-to-weight ratio of 8 are double-unit hollow air-film cooling blades.

While improving the structure, the foreign aero-engine industry is also looking for superalloys with high initial melting temperature, low cost, good process performance and comprehensive mechanical properties. For example, Allison Corporation in the United States has developed CMSX-4 single crystal alloy and other matching advanced blade materials while developing Castcool and Lamilloy cooling blades.

Although many nickel-based superalloys for aero-engines have been developed in China, such as K403, K405, K441 and K417G alloys, the biggest disadvantage of these alloys is that the initial melting temperature and plasticity are quite different from those of cobalt-based superalloys. application of these alloys. In addition, due to the complex shape of the overall guide, it is not easy to prepare a single crystal or adopt a directional solidification process. Although intermetallic compounds have the characteristics of low specific gravity and high strength, their use is limited due to their poor plasticity and oxidation resistance. Therefore, it is necessary to develop an alloy that requires high initial melting temperature, low density, good casting performance, good thermal fatigue performance, high high temperature oxidation resistance and comprehensive mechanical properties.

Contents of the invention

The object of the present invention is to provide a nickel-based equiaxed crystal alloy containing yttrium and hafnium and its heat treatment process and application. The alloy has better durability and can be used to prepare aeroengines and gas turbine blades for long-term operation at 1100 ° C. Hot end parts.

Technical scheme of the present invention is:

A nickel-based equiaxed crystal alloy containing yttrium and hafnium, by weight percentage, the chemical composition of the alloy is as follows:

C 0.03～0.15%, Cr 8.0～10.0%, Al 5.5～6.2%, Co 3～8%, W 6.0～9.0%, Mo2.5～3.5%, Nb 1.8～2.4%, B 0.001～0.04%, Hf 1.0-2.0%, Y 0.005-0.05%, Ni balance.

In the alloy, the total content range of aluminum and yttrium elements is: 5.5wt.%<Al+Y<6.6wt.%.

In the alloy, the total content range of tungsten, molybdenum, niobium and hafnium is: 13.9wt.%<W+Mo+Nb+Hf<16.9wt.%.

The alloy has an equiaxed crystal structure.

The alloy has a durable life of ≥50 hours under the conditions of 1100°C and 55MPa.

The heat treatment system of alloy of the present invention is:

(1) At 1200℃～1220℃, keep warm for 3h～5h, and air cool to room temperature;

(2) At 1040°C ~ 1060°C, keep warm for 3h ~ 5h, and air cool to room temperature;

(3) Keep warm at 850℃～890℃ for 20h～28h, then air cool to room temperature.

The alloy of the invention is used to prepare hot end components of aeroengines and gas turbine turbine blades that work at 1100°C for a long time.

Design principle of the present invention is as follows:

More aluminum and aluminum-yttrium master alloy (the sum of Al+Y up to 6.5wt.%) is added in the alloy composition of the present invention. Aluminum is the most basic alloying element in nickel-based superalloys. The reason why nickel-based alloys can become irreplaceable superalloys is because of the presence of γ′ strengthening phase, and aluminum is the main forming element of γ′ phase. Adding more aluminum elements forms a high volume fraction of γ′ phase to increase its strength; keeping the chromium content above 8.0wt.% can make the alloy reach a complete anti-oxidation level at high temperature; chromium and yttrium can improve the oxidation resistance; yttrium can also It can improve the morphology of carbides, improve their stability and crack resistance.

The alloy composition of the present invention contains about 1.5 wt.% hafnium. Hf is a strong positive segregating element, which significantly promotes the formation of γ+γ′ eutectic. When the Hf and Zr contents are the same, the Hf content of γ′ in the eutectic is twice as high as that of Zr, which indicates that Zr is not as effective as Hf in strengthening γ′. Moreover, one of the important functions of hafnium is to inhibit the massive precipitation of M ₂₃ C ₆ or M ₆ C carbides along the grain boundaries, and to form secondary stable fine, dispersed and irregular MCs (mainly HfC) with the carbon released by MC decomposition. ) particles.

Niobium can replace part of the aluminum and enter the γ' phase. The distribution ratio of niobium in γ/γ′ is about 1:<0.05, that is, most niobium almost enters the γ′ phase except for combining with carbon. Niobium has a great affinity with carbon and can form stable NbC, thereby effectively refining the grains. Niobium dissolves into the γ′ phase and enters the carbide, thereby improving the thermal stability of these phases, delaying the aggregation and growth process of the γ′ phase, and improving the strength index of the alloy. By adding niobium to further increase the number of γ′ phases, the lattice mismatch degree of γ-γ′ is increased, the strengthening effect of γ′ phase is enhanced, and stable MC is formed with carbon.

By adding niobium and hafnium, etc., the present invention can further increase the number of γ′ phases, improve the lattice mismatch degree of γ-γ′, enhance the strengthening effect of γ′ phase, and form γ″ phase at the same time to enhance its room temperature and medium temperature mechanical properties. Performance; add a certain amount of carbon, on the one hand to strengthen the grain boundary, on the other hand, form more carbides with hafnium, niobium, chromium, etc. to strengthen the alloy; alloy elements such as tungsten and cobalt mainly play an important role in solid solution strengthening alloys , the content of W+Hf+Nb is an important parameter to increase the creep life, and the creep life increases with the increase of their content. Co has little effect on the thermal strength of the alloy, but it can significantly improve the plasticity of the alloy, and Co can improve the creep life under high stress, and can be substituted with Ni to improve the performance of the alloy casting process.

The alloy of the present invention contains about 8.0 wt.% of W. After tungsten is added to the alloy, it can increase the bonding force between atoms, increase the activation energy of diffusion, slow down the diffusion process, and increase the recrystallization temperature, thereby improving the high-temperature mechanical properties of the alloy. The distribution ratio of tungsten in the γ and γ′ phases is approximately equal to 1. Therefore, a high tungsten content can significantly increase the number of γ′ phases and improve the thermal stability of the alloy. In nickel-based casting alloys, tungsten is preferentially distributed on dendrite axes, while hafnium is preferentially distributed on grain boundaries and dendrite boundaries. Therefore, adding tungsten, molybdenum, niobium and hafnium at the same time has a comprehensive strengthening effect on the properties of the alloy. However, excessive tungsten will precipitate intermetallic compound Ni ₄ W and increase the tendency to precipitate harmful phases of TCP phase (mainly μ phase). In addition, tungsten is a carbide-forming element and promotes the formation of M ₆ C carbides. Carbide is one of the important strengthening phases in superalloys, and its size, shape and distribution have an important impact on the mechanical properties of the alloy.

A small amount of carbon and boron is added to strengthen the grain boundary on the one hand, and form carbides and borides with chromium, tungsten, molybdenum, niobium and hafnium on the other hand to strengthen the alloy. The content of alloy carbon and boron is low, and it does not contain titanium, which ensures that the alloy has a high initial melting temperature and good cold and heat fatigue performance.

The present invention has the following advantages:

1. The nickel-based equiaxed crystal alloy of the present invention has excellent high temperature strength and temperature bearing capacity and good casting process performance. The alloy not only has high aluminum and yttrium content (Al+Y>6.0wt%), but also has high melting point alloy elements. The content (W+Nb+Mo+Hf) is also relatively high (>15wt%); the upper limit of W content reaches 9.0wt%, and the upper limit of Hf content reaches 2.0wt%. Because the alloy has the above-mentioned compositional characteristics, it has outstanding high-temperature strength and high-temperature thermal stability, and is suitable for preparing hot-end parts such as engine turbine blades that work at 1100°C for a long time.

2. The alloy of the present invention has better durability performance, and the durability life is ≥ 50 hours under the conditions of 1100°C and 55MPa.

3. The alloy of the present invention can be directly cast and used, with low cost and high production efficiency.

4. The alloy of the present invention has good high-temperature oxidation resistance and thermal corrosion resistance, that is, good thermal stability.

Description of drawings

Fig. 1 is the Larson-Miller comparison curve of the alloy of the present invention and the K417 alloy.

Figure 2 is the total strain-life curve of 900°C cycle.

Figure 3 is the cyclic total strain-life curve at 1000°C.

Fig. 4 is the microstructure of the alloy in Example 1; wherein: (a) microstructure of equiaxed grains; (b) carbides on grain boundaries.

detailed description

The present invention is described in detail below in conjunction with accompanying drawing and embodiment.

Example 1

ALD 500Kg vacuum induction furnace made in Germany is used to smelt the experimental master alloy. The smelting crucible is alumina crucible. Coated with ZrO ₂ (CeO stable) and BN Mo-Al ₂ O ₃ cermet tube, the vacuum degree should be maintained in the order of ≤10 ^-1 Pa. The operation process is as follows: put carbon, nickel-boron intermediate alloy, chromium, tungsten, niobium, hafnium, cobalt, zirconium and other alloy elements into the crucible; vacuumize the crucible to remove the adhesion Gas, when the vacuum degree reaches ^10-3 Pa, increase the power to melt the alloy; ensure that the carbon and oxygen reaction is sufficient at the initial stage of the material, and then refine at high temperature after clearing to ensure uniform composition of the alloy. Add Al and AlY intermediate alloys during power failure, conjunctiva, and membrane rupture, and then stir with high power. After stirring, power off and cool down; strictly control the temperature and amount of Al addition to ensure that the impurities melted into the alloy can be effectively removed. Large current (200kw ~ 240kw) impacts and ruptures the membrane, and casts it into a master alloy ingot at 1450°C.

Through the above process steps, the composition of the master alloy of this embodiment was smelted, as shown in Table 1. Cast into a master alloy ingot, then cut about 5.0Kg of alloy material on the master alloy ingot, and use a 10Kg vacuum induction melting furnace for remelting. The temperature is 900°C, and it is cast into the alloy sample of the embodiment. And adopt the following heat treatment system:

(1) Keep warm for 3 hours at 1200°C, then air cool to room temperature;

(2) Keep warm for 5 hours at 1060°C, then air cool to room temperature;

(3) Keep warm for 20 hours at 850°C, then air cool to room temperature.

The microstructure of the alloy obtained in this embodiment is shown in FIG. 4 , and it can be seen that it is an equiaxed crystal structure.

The relationship between Young's modulus and temperature of the alloy obtained in this embodiment is shown in Table 2.

Table 1 Alloy element composition (wt.%)

C Cr co Nb al W Mo f B Y Ni 0.03 9.0 5.0 2.4 6.2 6.0 3.5 2.0 0.001 0.005 margin

Table 2 Alloy Young's modulus and temperature relationship of the present invention

The Young's modulus variation law of the K417G alloy in the second edition of the Aeronautical Materials Handbook, Volume 2 (P640～609) is the same as that of the alloy of the present invention, and the Young's modulus decreases with the increase of temperature. However, at the same temperature, the Young's modulus of the alloy in Example 1 is significantly lower than that of the K417G alloy, which indicates that the elastic deformation of the alloy of the present invention is larger under the same stress conditions. That is to say, the alloy has a relatively large tolerance for elastic deformation. Engineering materials generally wish to have a small modulus of elasticity.

Example 2

The difference from Example 1 is that the alloy composition is different. The composition of the master alloy melted in Example 2 is shown in Table 3, and cast into a master alloy ingot. Then cut about 5.0Kg of alloy material block from the master alloy ingot, and remelt it in a 10Kg vacuum induction melting furnace. EXAMPLES Alloy samples. And adopt the following heat treatment system:

(1) Keep warm for 5 hours at 1220°C, then air cool to room temperature;

(2) Keep warm for 3 hours at 1040°C, then air cool to room temperature;

(3) Keep warm for 28 hours at 890°C, then air cool to room temperature.

The relationship between the shear modulus and temperature of the alloy obtained in this embodiment is shown in Table 4.

Table 3 Example 2 Alloy element composition (wt.%)

C Cr co Nb al W Mo f B Y Ni 0.15 10.0 8.0 2.4 5.5 9.0 2.5 2.0 0.001 0.005 margin

Table 4 Alloy shear modulus (GPa) and temperature relationship of the present invention

The shear modulus change law of the K417G alloy in the second edition of the Aeronautical Materials Handbook, the second volume (P640～609) is the same as that of the alloy of the present invention, and the shear modulus decreases with the increase of temperature. However, at the same temperature, the shear modulus of the alloy in this example is significantly higher than that of the K417G alloy, which indicates that the shear deformation of the alloy of the present invention is relatively small under the same stress conditions. This is very advantageous for the engineering application of the alloy of the present invention.

Example 3

Table 5 Example 3 Alloy element composition (wt.%)

C Cr co Nb al W Mo f B Y Ni 0.09 8.0 3.0 1.8 6.0 9.0 3.0 1.0 0.024 0.03 margin

Table 6 Example 3 Alloy Tensile Properties

The difference from Example 2 is that the composition of the smelted master alloy is different, as shown in Table 5, and cast into a master alloy ingot. Then cut about 5.0Kg of alloy material block from the master alloy ingot, and remelt it in a 10Kg vacuum induction melting furnace. EXAMPLES Alloy samples. And adopt the following heat treatment system:

(1) 1210 ° C, heat preservation for 4 hours, air cooling to room temperature;

(2) Keep warm for 4 hours at 1050°C, then air cool to room temperature;

(3) Keep warm at 870°C for 24 hours, then air cool to room temperature.

The relationship between the tensile properties of the alloy obtained in this example and the temperature is shown in Table 6.

From the tensile properties of the alloy shown in Table 6, it can be seen that the variation range of the tensile strength of the alloy of the present invention is less than 900 MPa from room temperature to 800 ° C, and the tensile strength gradually decreases after exceeding 800 ° C, but the tensile strength at 1100 ° C It can also reach more than 265MPa, which is higher than the tensile strength of most equiaxed superalloys, such as K417G and K418. It can be seen that the alloy has excellent high temperature tensile properties.

Example 4:

The difference from Example 3 is that the composition of the smelted master alloy of this embodiment is shown in Table 7 and cast into a master alloy ingot. Then cut about 5.0Kg of alloy material block from the master alloy ingot, and remelt it in a 10Kg vacuum induction melting furnace. EXAMPLES Alloy samples. And adopt the following heat treatment system:

(1) 1210 ° C, heat preservation for 4 hours, air cooling to room temperature;

(2) Keep warm for 4 hours at 1050°C, then air cool to room temperature;

(3) Keep warm at 870°C for 24 hours, then air cool to room temperature.

The Larson-Miller curve of the comparison between the alloy obtained in this embodiment and the K417G alloy in terms of durability is shown in FIG. 1 .

Table 7 Example 4 Alloy element composition (wt.%)

C Cr co Nb al W Mo f B Y Ni 0.10 9.0 5.0 2.4 5.8 6.5 3.4 2.0 0.04 0.03 margin

From the composite curves of the thermal strength parameters of the inventive alloy and the comparison alloy in Fig. 1, it can be seen that the alloy of the present invention gradually reduces the durable stress of the alloy along with the increase of the thermal strength parameter, and the comparison alloy also has a similar rule. The parameter (P) is less than 26, and the durability performance of the two alloys is not much different. However, when the thermal strength parameter (P) is greater than 26, the decrease in the enduring stress is relatively small. Compared with the comparison alloy K417G (same as above), the enduring performance of the alloy of the present invention has obvious advantages.

Example 5

The difference from Example 4 is that the composition of the master alloy smelted in this embodiment is shown in Table 8, and cast into a master alloy ingot. Then cut about 5.0Kg of alloy material block from the master alloy ingot, and remelt it in a 10Kg vacuum induction melting furnace. EXAMPLES Alloy samples. And adopt the following heat treatment system:

(1) 1210 ° C, heat preservation for 4 hours, air cooling to room temperature;

(2) Keep warm for 4 hours at 1050°C, then air cool to room temperature;

(3) Keep warm at 870°C for 24 hours, then air cool to room temperature.

The high-temperature cycle total strain-life curves of the alloy obtained in this embodiment are shown in Fig. 2 and Fig. 3 .

Table 8 Alloy element composition (wt.%)

C Cr co Nb al W Mo f B Y Ni 0.06 9.5 8.0 2.2 6.2 7.5 2.8 1.5 0.02 0.05 margin

The high-temperature low-cycle fatigue strain-life curves of the alloy in Example 5 are shown in Figures 2 and 3; the strain-life expression at 900°C is: Δε _t /2=0.0145(2N _f ) ^-0.2028 +0.0098(2N _f ) ^-0.4220 ; The strain-life expression at 1000°C is: Δε _t /2＝0.0075(2N _f ) ^-0.1785 +0.0313(2N _f ) ^-0.5294 ; Generally speaking, with the increase of the total strain amplitude, the low cycle fatigue life And reduce. Under the same total strain amplitude, the low-cycle fatigue life at 900°C is significantly higher than that at 1000°C, which shows that temperature has an important impact on low-cycle fatigue performance. In addition, in the total strain of low cycle fatigue at 900°C or 1000°C, the elastic strain amplitude occupies a dominant position, and the plastic strain amplitude is very small, which shows that the lower elastic modulus of the alloy of the present invention has a great influence on the low cycle fatigue performance. Beneficial influence.

Claims (7)

1. a nickel-based equiaxed crystal alloy containing yttrium and hafnium, characterized in that: by weight percentage, the alloy chemical composition is as follows: C 0.03-0.15%, Cr 8.0-10.0%, Al 5.5-6.2%, Co 3-8%, W 6.0-9.0%, Mo 2.5-3.5%, Nb 1.8-2.4%, B 0.001-0.04%, Hf 1.0 ～2.0%, Y 0.005～0.05%, the balance of Ni. 2. The nickel-based equiaxed crystal alloy containing yttrium and hafnium according to claim 1, characterized in that: in the alloy, the total content range of aluminum and yttrium elements is: 5.5wt.%<Al+Y<6.6wt .%.%. 3. The nickel-based equiaxed crystal alloy containing yttrium and hafnium according to claim 1, characterized in that: in the alloy, the total content range of tungsten, molybdenum, niobium and hafnium is: 13.9wt.%<W +Mo+Nb+Hf<16.9 wt.%. 4. The nickel-based equiaxed crystal alloy containing yttrium and hafnium according to any one of claims 1-3, characterized in that the alloy has an equiaxed crystal structure. 5. The nickel-based equiaxed crystal alloy containing yttrium and hafnium according to any one of claims 1-3, characterized in that: the alloy has a durable life of ≥50 hours under the conditions of 1100°C and 55MPa. 6. According to the heat treatment process of the nickel-based equiaxed crystal alloy containing yttrium and hafnium according to claim 1, it is characterized in that: the heat treatment system of the alloy is: (1) At 1200℃～1220℃, keep warm for 3h～5h, and air cool to room temperature; (2) At 1040°C ~ 1060°C, keep warm for 3h ~ 5h, and air cool to room temperature; (3) Keep warm at 850℃～890℃ for 20h～28h, then air cool to room temperature. 7. The application of the equiaxed crystal alloy containing yttrium and hafnium according to claim 1, characterized in that: the alloy is used to prepare hot end parts of aero-engines and gas turbine blades that work at 1100°C for a long time.