CN108772622A - A kind of diffusion welding connection method for making middle layer using Ti foils - Google Patents

Abstract

The present invention adopts a diffusion welding connection method using Ti foil as an intermediate layer. Said connection in the method refers to the connection between TiAl alloy and Ti ₂ AlNb alloy or Ti ₃ Al-based alloy. The method is to combine TiAl alloy and Ti ₂ AlNb alloy or Ti ₃ Al-based alloy to the required size; grind and polish the base metal to be welded; put the base metal and Ti foil into acetone for ultrasonic cleaning; place the Ti foil on the base metal to be welded Put it into a vacuum heating furnace, apply pressure, and complete the welding after heating, heat preservation, and cooling thermal cycles. The invention can avoid the introduction of impurity elements in the welding process, and can obtain a connection interface without continuous brittle phase. The tensile strength of the joint at room temperature can reach 380-410MPa, and the high-temperature tensile strength at 650°C can reach 350MPa-370MPa.

Description

A kind of diffusion welding connection method adopting Ti foil as intermediate layer

technical field

The invention relates to a diffusion welding connection method using Ti foil as an intermediate layer, belonging to the technical field of welding.

Background technique

Titanium-aluminum intermetallic compounds have the advantages of low density, high specific strength, specific stiffness, good oxidation resistance, good creep resistance and fatigue resistance, and are the most promising light-weight high-temperature structural materials for aerospace in the future. one. Among titanium-aluminum intermetallic compounds, research on TiAl alloys, Ti _{2 AlNb} alloys or Ti ₃ Al _- based alloys has been paid attention to. The working temperature of TiAl alloys can reach 760 ° C ~ 850 ° C. The working temperature can reach 700°C. Compared with ordinary titanium alloys, TiAl alloys, Ti ₂ AlNb alloys or Ti ₃ Al-based alloys can serve at higher temperatures; compared with superalloys, they have lower densities, which are about half of superalloys. In the aerospace field, a substantial weight reduction effect can be obtained, and in the automotive industry, it can realize the lightweight design and manufacture of parts. However, in terms of cost and process reliability, it is very difficult to prepare some parts with TiAl alloy as a whole. The current TiAl alloy has low room temperature plasticity and poor deformation ability. Relatively speaking, Ti ₂ AlNb alloy or Ti ₃ Al-based alloys have better machinability. If a good connection between TiAl alloy and Ti ₂ AlNb alloy or Ti ₃ Al-based alloy can be achieved, TiAl alloy is used in the part with higher working temperature, and Ti ₂ AlNb alloy or Ti ₃ Al-based alloy is used in the part with lower service temperature. The respective performance advantages of the two materials can be brought into play. For example, for the overall blisk in an aero-engine, TiAl alloy can be used to make the blade, and Ti ₂ AlNb alloy or Ti ₃ Al-based alloy can be used to make the disc, but the problem of heterogeneous connection of the two materials must first be solved.

At present, there are few research reports on the heterogeneous bonding of TiAl alloys with Ti ₂ AlNb alloys or Ti ₃ Al-based alloys. Some researchers have conducted a study on the interlayer-free diffusion welding of TiAl alloy and Ti ₂ AlNb alloy. Compounds such as Al(Nb,Ti) ₂ and α ₂ -Ti ₃ Al are formed in the joint area, and the shear strength of the joint at room temperature is 260MPa. Improve (JYZou, et al. Diffusion bonding of dissimilar intermetallic alloys based on Ti ₂ AlNb and TiAl [J]. Journal of Materials Science and Technology, 2009, 25:819–824.). When TiAl alloy and Ti ₃ Al base alloy are joined by titanium-based solder brazing or pressurized liquid phase diffusion, impurity elements are introduced, which may affect the thermal stability of the joint performance. The high-temperature performance of these joints is generally low, and The cost of preparing titanium-based solder is relatively high (HSRen, et al. Vacuum brazing of Ti ₃ Al-based alloy to TiAl using TiZrCuNi(Co) fillers. Journal of Materials Processing Technology, 2015 224:26–32; HSRen, et al. Transient liquid phase diffusion bonding of Ti–24Al–15Nb–1Mo alloy to TiAlintermetallics. Materials Science & Engineering A, 2016, 651:45–54.). In addition, the patent (CN101073850A) introduced a method for composite control of electron beam welding thermal cycle of TiAl alloy and Ti ₃ Al-based alloy dissimilar materials, but this method only solved the problem that cracks were easily generated on the TiAl alloy side during electron beam welding. Joint performance is unknown. Patent (CN106808079A) invented a method of diffusion bonding TiAl alloy and Ti ₂ AlNb alloy. This method does not use an intermediate layer, but directly performs diffusion welding of the two materials. This method requires a large (30MPa) axial pressure, which increases the difficulty of welding, and there is no indication of the joint strength value obtained by this method. To sum up, there are very limited research reports on heterogeneous bonding of TiAl alloys and Ti ₂ AlNb alloys or Ti ₃ Al-based alloys at home and abroad.

Contents of the invention

Aiming at the above _- mentioned technical problems, the present invention provides a kind _of diffusion welding connection method using Ti foil as the intermediate layer. The connection interface of the two layers realizes the high-strength connection of the two base materials.

Technical solution of the present invention is:

The diffusion welding connection method using Ti foil as the intermediate layer is aimed at the connection of TiAl alloy and Ti ₂ AlNb alloy or Ti ₃ Al-based alloy, and is characterized in that: the steps of the method are:

Step 1, using wire cutting to process the TiAl alloy and Ti ₂ AlNb alloy or Ti ₃ Al-based alloy into the required size to obtain the base metal to be welded;

Step 2. Polish the surface to be welded of the base material to be welded with sandpaper, and then perform polishing treatment. Put the polished base material to be welded and Ti foil with a thickness of 10-30 μm into acetone and ultrasonically clean it for 3-10 minutes;

Step 3. Place the Ti foil between the TiAl alloy and the Ti ₂ AlNb alloy or Ti ₃ Al-based alloy to be welded, and then place it in a vacuum heating furnace, and apply a pressure of 5 to 30 MPa. When the vacuum heating furnace After the vacuum degree reaches 9×10 ^-2 ~1×10 ^-3 Pa, start heating with electricity at a heating rate of 5~15°C/min. Cool at a rate of ~10°C/min to 400°C to 500°C, and then cool to room temperature with the furnace to complete the connection of the TiAl alloy with the Ti ₂ AlNb alloy or Ti ₃ Al-based alloy.

Further, the thickness of the Ti foil is 15-20 μm.

Further, the pressure applied in step 3 is 10-20 MPa.

Further, after the vacuum degree in the vacuum heating furnace mentioned in the third step reaches 1×10 ⁻³ Pa, electric heating is started.

Further, the heating rate in Step 3 is 10°C/min.

Further, the heating temperature described in Step 3 is 950° C. and kept at this temperature for 1 hour.

Further, the cooling rate described in step three is 10° C./min.

Further, the starting temperature of furnace cooling described in step 3 is 500°C.

The technical solution of the present invention has the following advantages:

(1) Ti is the main constituent element of two kinds of base materials to be welded. The present invention adopts Ti foil as the intermediate layer to avoid introducing other impurity elements in the connection process of TiAl alloy and Ti ₂ AlNb alloy or Ti ₃ Al-based alloy, ensuring In addition, the welding between TiAl alloy and Ti ₂ AlNb alloy or Ti ₃ Al-based alloy belongs to the diffusion welding of dissimilar materials. The difference is that internal stress is easily generated during the welding thermal cycle, which in turn affects the welding effect. The intermediate layer Ti foil used in the present invention has good toughness, which can relieve the internal stress in the joint and is beneficial to ensure the performance of the joint;

(2) The solution treatment temperature of the Ti ₂ AlNb alloy or Ti ₃ Al-based alloy described in the present invention is generally 980°C to 1050°C. When the welding temperature is higher than the solution treatment temperature and the holding time exceeds 1h, it will damage the mother body. material structure and properties. However, when the welding temperature is too low or the holding time is too short, the Ti foil intermediate layer may remain in the joint, and the residual Ti foil intermediate layer is not conducive to ensuring the high temperature mechanical properties of the joint. Therefore, the Ti foil intermediate layer used in the present invention is relatively thin (10-30 μm), which can ensure that the Ti foil fully reacts with the base metal under certain welding conditions, and there is no residual Ti foil in the joint to ensure the uniformity of the joint structure, and then realize The joint has good high temperature mechanical properties;

(3) There is a difference in the thermal expansion coefficients of the two base materials. If the heating is stopped after the heat preservation is over, the fast cooling rate will cause a large difference in the deformation of the two base materials, which will easily lead to crack initiation in the joint. Therefore, in the present invention, after the heat preservation is over, the cooling rate of the joint is controlled by the program, and when the temperature of the joint drops to 400°C to 500°C, the cooling with the furnace is started, and the cooling rate with the furnace has been reduced to a relatively slow rate at this time. degree, thereby ensuring a defect-free joint.

(4) The tensile strength of the dissimilar joints of TiAl alloy and Ti ₂ AlNb alloy or Ti ₃ Al-based alloy obtained in the present invention can reach 380MPa-410MPa at room temperature, and 350MPa-370MPa at high temperature at 650°C.

Description of drawings

Fig. 1 is a photo of the microstructure of a Ti ₂ AlNb/TiAl diffusion welded joint obtained with a Ti foil with a thickness of 10 μm as the intermediate layer.

Fig. 2 is a photo of the microstructure of a Ti ₂ AlNb/TiAl diffusion welded joint obtained with a 30 μm thick Ti foil as an intermediate layer.

Detailed ways

The technical scheme of the present invention will be described in further detail below in conjunction with accompanying drawing and embodiment:

Embodiment one

In this embodiment, TiAl alloy and _Ti2AlNb alloy are connected by diffusion welding using Ti foil as the intermediate layer. The steps of this method are:

Step 1, using wire cutting to process the TiAl alloy and _Ti2AlNb alloy into the required size to obtain the base material to be welded;

Step 2. Polish the surface to be welded of the base material to be welded with sandpaper, and then perform polishing treatment. Put the polished base material to be welded and Ti foil with a thickness of 10-30 μm into acetone and ultrasonically clean it for 3-10 minutes;

Step 3. Place the Ti foil between the TiAl alloy and the Ti ₂ AlNb alloy surface to be welded, then place it in a vacuum heating furnace, and apply a pressure of 5-30 MPa. When the vacuum degree in the vacuum heating furnace reaches 9×10 ^-2 to 1×10 ^-3 Pa and start heating with electricity at a heating rate of 5 to 15°C/min. When heated to 850°C to 1050°C, keep at this temperature for 0.5 to 2 hours, and then at a rate of 5 to 10°C/min Speed cooling to 400°C-500°C, and then cooling to room temperature with the furnace, that is, the connection of TiAl alloy and Ti ₂ AlNb alloy or Ti ₃ Al-based alloy is completed.

Embodiment two

The difference between this embodiment and the first embodiment is that the TiAl alloy and the Ti ₃ Al-based alloy are processed into the required size by wire cutting in the first step, and the Ti foil is placed on the TiAl alloy in the third step. between the alloy and the Ti ₃ Al-based alloy to be welded. Others are the same as in Embodiment 1.

Embodiment three

The difference between this embodiment and the first embodiment is that in the third step, the polished base metal to be welded and the Ti foil with a thickness of 20-30 μm are placed in acetone and ultrasonically cleaned for 3-10 minutes. Others are the same as in Embodiment 1.

Embodiment Four

The difference between the present embodiment and the first embodiment is that in step four, a pressure of 10-20 MPa is applied. Others are the same as in Embodiment 1.

Embodiment five

The difference between this embodiment and the first embodiment is that in step four, the electric heating is started after the vacuum degree in the vacuum heating furnace reaches 1×10 ⁻³ Pa. Others are the same as in Embodiment 1.

Embodiment six

The difference between this embodiment and the first embodiment is that the heating rate described in step four is 10° C./min. Others are the same as in Embodiment 1.

Embodiment seven

The difference between this embodiment and the first embodiment is that the heating temperature described in the fourth step is 980°C and the temperature is kept at this temperature for 0.5h. Others are the same as in Embodiment 1.

Embodiment Eight

The difference between this embodiment and the first embodiment is that the cooling rate in step four is 10°C/min, and the initial temperature of cooling with the furnace is 400°C. Others are the same as in Embodiment 1.

The structures of the diffusion welded joints obtained through the above examples are shown in Figures 1 and 2. No defects such as cracks and voids were found in the joints, and no continuous brittle reaction layer was formed. Compositional analysis showed that there was no residual Ti foil intermediate layer in the joints. , a high-quality connection of the two base metals was obtained.

Claims (8)

1. a kind of diffusion welding connection method that adopts Ti foil as intermediate layer, connection described in the method refers to the connection of TiAl alloy and Ti ₂ AlNb alloy or Ti ₃ Al base alloy, it is characterized in that: the step of this method is: Step 1, using wire cutting to process the TiAl alloy and Ti ₂ AlNb alloy or Ti ₃ Al-based alloy into the required size to obtain the base metal to be welded; Step 2. Polish the surface to be welded of the base material to be welded with sandpaper, and then perform polishing treatment. Put the polished base material to be welded and Ti foil with a thickness of 10-30 μm into acetone and ultrasonically clean it for 3-10 minutes; Step 3. Place the Ti foil between the TiAl alloy and the Ti ₂ AlNb alloy or Ti ₃ Al-based alloy to be welded, and then place it in a vacuum heating furnace, and apply a pressure of 5 to 30 MPa. When the vacuum heating furnace After the vacuum degree reaches 9×10 ^-2 ~1×10 ^-3 Pa, start heating with electricity at a heating rate of 5~15°C/min. Cool at a rate of ~10°C/min to 400°C to 500°C, and then cool to room temperature with the furnace to complete the connection of the TiAl alloy with the Ti ₂ AlNb alloy or Ti ₃ Al-based alloy. 2. The diffusion welding connection method using Ti foil as an intermediate layer according to claim 1, characterized in that: the thickness of the Ti foil is 15-20 μm. 3. The diffusion welding connection method using Ti foil as an intermediate layer according to claim 1, characterized in that: the pressure applied in step 3 is 10-20 MPa. 4. The diffusion welding connection method using Ti foil as the intermediate layer according to claim 1, characterized in that: the vacuum degree in the vacuum heating furnace mentioned in step 3 reaches 1×10 ^-3 Pa and then the electric heating starts. 5 . The diffusion welding connection method using Ti foil as an intermediate layer according to claim 1 , wherein the heating rate in step 3 is 10° C./min. 6 . The diffusion welding connection method using Ti foil as an intermediate layer according to claim 1 , characterized in that: the heating temperature in step 3 is 950° C. and the temperature is kept at this temperature for 1 hour. 7 . The diffusion welding connection method using Ti foil as an intermediate layer according to claim 1 , wherein the cooling rate in step 3 is 10° C./min. 8. The diffusion welding connection method using Ti foil as an intermediate layer according to claim 1, characterized in that: the initial temperature of the furnace cooling described in step 3 is 500°C.