CN102581467B - Connection method for dissimilar metal constant strength joint of titanium-aluminum base alloy and titanium alloy - Google Patents

Abstract

The invention discloses a diffusion welding method for dissimilar metal equal-strength joints of a titanium-aluminum base alloy and a titanium alloy, which belongs to the field of welding technology. It includes the following steps: (1) performing pre-weld heat treatment on the titanium-aluminum-based alloy to be welded, the heat treatment temperature is 1330-1360 ° C, and keeping it warm for 10-40 minutes; (2) placing the titanium-aluminum-based alloy and titanium alloy to be welded in a protective cover , to prevent the plastic deformation of the titanium alloy non-welding contact surface at high temperature. (3) Under the conditions of 850-930°C and 70-80MPa, the titanium alloy and the titanium-aluminum base alloy are subjected to diffusion welding. The tensile strength of the joint obtained by the present invention is 460-490MPa at room temperature, reaching 100%-110% of the titanium-aluminum-based alloy base material; the tensile strength at 400°C is 480-510MPa, reaching 100%-110% of the titanium-aluminum-based alloy base material 95% to 105%, is a joint of equal strength.

Description

A kind of dissimilar metal equal-strength joint connection method of titanium-aluminum base alloy and titanium alloy

technical field

The invention belongs to the field of welding technology, and relates to a diffusion welding method for dissimilar metal equal-strength joints of a titanium-aluminum base alloy and a titanium alloy (TC4).

Background technique

With the rapid development of the aerospace industry, the requirements for structural materials, especially for high temperature strength and thermal stability, are getting higher and higher. TiAl alloy has excellent specific strength, specific stiffness and high-temperature oxidation resistance, and its specific gravity is only 3.8g/cm ³ , which is far lower than the Ni-based superalloy with a specific gravity of 8.3g/cm ³ used today. Therefore, titanium-aluminum alloys are used in Aircraft turbines, automobile engines, and rocket propulsion systems have become one of the candidate materials that can replace Ti alloys and Ni-based superalloys. With the rapid development of the aerospace industry, TiAl-based alloys have gradually shown the advantages of low density, high melting point, good high-temperature strength, and excellent oxidation resistance, creep resistance and fatigue resistance, which can greatly reduce the cost of aerospace engines and aircraft. increase the thrust-to-weight ratio of the engine. This kind of material has attracted the attention of scientific research units and experts, and may become a promising aerospace material. But at the same time, TiAl alloy has low room temperature ductility and poor room temperature processability, which have always limited its application in actual production. In recent years, a lot of research has been done on TiAl alloys. Through alloying and microstructure control, the room temperature plasticity and toughness of TiAl alloys have been greatly improved, making them gradually practical. At present, TiAl alloys have been used in low-pressure turbines of jet engines. Vanes and exhaust valves of internal combustion engines.

In the practical process of the alloy, connection problems will inevitably be encountered, including connection with dissimilar alloys (such as superalloys, Ti alloys). Exploring the connection method between the alloy and other metals is of great significance for promoting the practical application of the alloy, expanding its application range and exerting its performance advantages. The diffusion connection technology can quickly realize the connection of complex and large-area parts without the need to develop special flux, which will play an important role in promoting the rapid application of this material.

The connection technology between dissimilar alloys has always been a hot frontier topic of common concern in domestic and foreign academia and industry, especially the solid-state connection technology between new materials and other materials is the focus of researchers. Different from the solid-state connection of the same alloy, due to the difference in performance between dissimilar alloys, especially the difference in high temperature performance, it increases the difficulty in the selection of connection process parameters and process implementation. Especially for materials with large differences in microstructure and properties at high temperature, there is often a contradiction between the choice of joining temperature and ensuring the microstructure and properties of different materials. For example, if hot isostatic pressing is used to join TiAl-based alloys and stainless steel, choosing a lower joining temperature will greatly prolong the joining time, and increasing the joining temperature will lead to structural transformation in the steel. However, in the solid state connection of the same alloy, the diffusion bonding technology can reduce the connection temperature and shorten the connection time, but it cannot be applied due to the difference in high temperature properties of dissimilar alloys.

In recent years, in the research on the connection of TiAl-based alloys and other alloys, there have been reports on the hot isostatic diffusion bonding of TiAl-based alloys and titanium alloys, and the diffusion bonding of TiAl-based alloys and structural steels. In the document "Difusion bonding of titanium-titanium alumi-nide-alumina sandwich" (HAWickman, ESC Chin. Nevada, USA: Proceedings of the TMS. Annual Meeting on Gamma Titanium Aluminides, 2005: 499-505), HAWickman et al. studied titanium alloy/ Vacuum Diffusion Bonding Behavior of TiAl-Based Composite/Al ₂ O ₃ Ceramic Trilayer Structure. The temperature and time combinations for the three-layer structure to obtain good connections are 1573K/3.6ks, 1523K/36ks and 1473K/360ks. However, due to the high joining temperature, the Ti alloy undergoes β-phase transformation, which seriously affects the plasticity index of the titanium alloy base material. Under the connection condition of 1373K/360ks, at the interface of titanium alloy/TiAl-based composite material, a γ+α2 full-lamellar structure region, an Al-rich α phase region and a Ti-B compound region are formed, and the titanium alloy base material The crystal grains are obviously coarsened due to recrystallization. Document "Tensile and creep properties of diffusionbonded titanium alloy IMI 834to gamma titanium aluminum IHI alloy 01A" (M.Holmquist, V.Recina, B.Pettersson. Acta mater., 2005, 47(6): 1791-1799) reported that M. Holmquist et al. conducted hot isostatic diffusion bonding of TiAl-based alloys and titanium alloys under the conditions of bonding temperatures of 1173K, 1213K, and 1253K, bonding time of 1h, and bonding pressure of 200MPa. The joint performance tests showed that 1253K has the highest connection performance, and the joint room temperature is the highest. The tensile strength and elongation are similar to those of the TiAl-based alloy base metal, and most of the fractures occur at the connection interface. Due to the formation of brittle intermetallic compound Ti ₃ Al phase at the joint, the fracture is very flat, showing the characteristics of brittle fracture. It is necessary to point out that the Ti alloy base metal undergoes grain coarsening and partial β-transformation under the joining condition of 1213K, but completely undergoes β-transformation at 1253K, which brings about a decline in the overall performance of the base metal. At present, the diffusion bonding technology of TiAl-based alloys and other materials has the following characteristics: the bonding temperature is too high and the bonding time is long, which not only has the disadvantages of high process cost and high requirements for equipment, but also brings changes in the structure and performance of the base metal. , which limits the practical application of this technology.

Contents of the invention

The present invention proposes a method for diffusion welding of equal-strength joints of titanium-aluminum-based alloys and titanium alloys (TC4) that are practical and capable of welding titanium-aluminum-based alloys and broaden the application range of titanium-aluminum-based alloys. .

A method for diffusion welding of dissimilar metal joints between a titanium-aluminum base alloy and a titanium alloy, the method is as follows:

(1) Perform pre-weld heat treatment on titanium-aluminum-based alloys. The heat treatment conditions are vacuum environment, at a temperature of 1330-1360 ° C for 10-40 minutes, and cooling with the furnace;

(2) cleaning the surface of the titanium alloy to be welded and the heat-treated titanium-aluminum-based alloy;

(3) placing the titanium-aluminum base alloy and the titanium alloy to be welded in a protective cover, the protective cover is used to prevent the non-welding surface of the test piece to be welded from being deformed during diffusion welding;

(4) Diffusion welding is carried out on titanium alloys and titanium-aluminum-based alloys at a temperature of 850-930°C and a welding pressure of 70-80 MPa. The time is determined according to the size of the weldment, and the penetration of the weldment is used as the benchmark.

The preferred temperature of the pre-weld heat treatment described in step (1) is 1355° C., and the preferred holding time of the heat treatment is 30 minutes.

The preferred conditions for the diffusion welding in step (4) are: the temperature is 900° C., and the welding pressure is 80 MPa.

The titanium alloy is TC4 titanium alloy.

The protective sleeve is usually made of stainless steel material. The protective cover is made according to the size of the test piece to be welded. When the titanium-aluminum-based alloy and the titanium alloy to be welded are both in the shape of a round rod, the protective cover can be made of stainless steel tube, whose inner diameter is the same as that of the test piece to be welded, and the length is longer than that of the TiAl alloy to be welded. The sum of the lengths of the base alloy rod and the titanium alloy rod.

In step (2), the surface of the base metal is cleaned by physical cleaning, chemical cleaning, or physical cleaning followed by chemical cleaning.

The physical cleaning is to use 200#, 400#, 600#, 800#, 1000# metallographic sandpaper to polish step by step, and then put the base material into acetone solution and clean it with ultrasonic waves.

The chemical cleaning is to configure the corresponding corrosive solution according to the difference of the base material to remove the adsorption layer, impurities or oxide film on the surface of the base material.

After diffusion welding is completed, post-weld annealing can be performed on it to remove residual stress. The annealing temperature is preferably 860°C, and the time depends on the size of the weldment.

The beneficial effects of the present invention are:

In the present invention, by adding a protective sleeve on the outside of the pre-connected TiAl-based alloy and TC4 alloy, it can largely reduce the plastic deformation of the non-connected surface that is prone to occur when the TC4 alloy is in a superplastic state at 900 ° C for diffusion welding, ensuring the diffusion connection experiment. The smooth progress, and get a good connection effect.

The elements on both sides of the joint obtained by using the present invention have been sufficiently diffused to achieve the effect of metallurgical bonding; the TiAl lamellar structure torn from the TiAl-based alloy matrix appears on the fracture of the TC4 side joint of some weldments, indicating that the local joint The strength of the joint is higher than that of the TiAl-based alloy matrix; the tensile strength of some joint samples exceeds that of the TiAl-based alloy matrix.

Description of drawings:

Fig. 1 is the model of diffusion welding of TiAl-based alloy and TC4 alloy;

Figure 2 is a scanning electron micrograph of element diffusion in the joint.

Detailed ways

Example 1

Diffusion welding method of dissimilar metal equal strength joints of titanium aluminum base alloy and titanium alloy (TC4) is:

(1) The titanium-aluminum-based alloy to be welded is subjected to pre-weld heat treatment, and the heat treatment condition is a vacuum environment, at a temperature of 1355°C for 30 minutes, and then cooled with the furnace.

(2) Clean the surface of the base metal to be welded: first use 200#, 400#, 600#, 800#, 1000# metallographic sandpaper to polish step by step, then put the base metal into acetone solution and use ultrasonic cleaning.

(3) Both titanium-aluminum-based alloy and titanium alloy to be welded A small rod with a length of 30mm, the outer diameter is made according to the size of the test piece to be welded the inside diameter of A 70mm-long stainless steel tube is used as a protective sleeve, and the titanium-aluminum-based alloy and titanium alloy (TC4) to be welded are placed in it to prevent plastic deformation of the non-welded contact surface at high temperature.

(4) Under the welding parameters of temperature 900°C and welding pressure 80MPa, argon is used as shielding gas to perform diffusion welding on titanium alloy (TC4) and titanium-aluminum-based alloy for one hour.

(5) After welding, take out the welded test piece, and then perform post-weld annealing treatment on it, the annealing temperature is 860°C, and the time is half an hour.

Figure 1 is a model of diffusion welding of TiAl-based alloy and TC4 alloy. The TiAl-based alloy rod and TC4 alloy rod to be welded are located in the center of the stainless steel protective sleeve, and there is one at each end of the protective sleeve. A stainless steel rod with a length of 40 mm is inserted into the protective sleeve, and the outer end of the stainless steel rod is clamped by a chuck, and the stainless steel rod is applied to the middle to squeeze the test piece to be welded. During diffusion welding, electricity is applied to both sides of the test piece to be welded. The smaller the metal cross-sectional area, the greater the resistance. Under the same current, the higher the temperature is, there is a uniform heating zone in the middle of the test piece. As shown in Figure 1, the stainless steel protective sleeve is used to ensure that the TC4 alloy does not undergo obvious deformation on the non-welding surface when it reaches a superplastic state at 900 °C.

Figure 2 shows the diffusion of joint elements. It can be seen that TiAl on the left and TC4 on the right have achieved good metallurgical bonding, and the weld structure is relatively dense. The figure shows the diffusion of Al, Nb, Ti, V, Cr and other elements between the two alloys. The upper horizontal line in the middle is the track of line scanning, and the intensity waveforms from top to bottom represent the results of line scanning of Al, Nb, Ti, V, and Cr, respectively. It can be seen that Al, Cr, and Nb on the TiAl side are diffusing toward the TC4 side, and Ti and V on the TC4 side are also diffusing toward the TiAl side. Interdiffusion between elements facilitates the bonding of two dissimilar materials.

The tensile strength of the titanium-aluminum base alloy/titanium alloy (TC4) joint obtained by the above steps embodiment is 460-490MPa at normal temperature, reaching 100%-110% of the titanium-aluminum base alloy parent material; 400 ℃ tensile strength is 480-510MPa, reaching 95%-105% of the titanium-aluminum-based alloy base material, is a kind of equal-strength joint.

Claims (8)

1. a dissimilar metal equal strength joint diffusion welding method for titanium aluminium base alloy and titanium alloy, is characterized in that: the method step is as follows:

(1) weld front heat treatment to titanium aluminium base alloy, heat treated condition is under vacuum conditions, at temperature 1355 DEG C insulation 30min, cools with stove;

(2) clear up to titanium alloy with through heat treated titanium aluminium base alloy surface to be welded;

(3) titanium aluminium base alloy to be welded and titanium alloy are placed in protective sleeve, described protective sleeve is used for test specimen to be welded non-solder face when Diffusion Welding is not deformed;

(4) be 850 ~ 930 DEG C in temperature, pressure is under the condition of 70 ~ 80MPa, carries out Diffusion Welding to titanium alloy and titanium aluminium base alloy.

2. method according to claim 1, is characterized in that: the condition of step (4) Diffusion Welding is: temperature is 900 DEG C, and pressure is 80MPa.

3. method according to claim 1, is characterized in that: described titanium alloy is TC4 titanium alloy.

4. method according to claim 1, is characterized in that: described protective sleeve is made up of stainless steel material.

5. method according to claim 1, is characterized in that: after Diffusion Welding, takes out welding piece, carries out annealing after welding to it.

6. method according to claim 5, is characterized in that: the temperature of described annealing in process is 860 DEG C.

7. according to the method described in claim 1, it is characterized in that: in step (2), physics cleaning, soak cleaning or the rear soak cleaning of first physics cleaning are adopted to the cleaning of titanium aluminium base alloy and titanium alloy surface.

8. according to the method described in claim 7, it is characterized in that: described physics cleaning is polished step by step with 200#, 400#, 600#, 800#, 1000# abrasive paper for metallograph, then puts into acetone soln Ultrasonic Cleaning.