Titanium alloy and stainless steel dissimilar metal vacuum brazing

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Titanium alloys have low density, high specific strength, excellent corrosion resistance, good high temperature strength and low temperature toughness, and biological phase.It is widely used in aerospace, shipbuilding, nuclear industry, petrochemical and other fields. With the gradual development of modern industry and manufacturing, various industries have put forward higher requirements for the materials they use, how to make them lightweight, corrosion-resistant and economical under the condition of ensuring the performance of the materials. characteristics became an important issue. The poor welding performance and processing performance of titanium alloys, coupled with the high price, make them exert their respective advantages in performance and economy. The research of dissimilar metal welding between titanium alloy and stainless steel has become more and more important in advanced manufacturing, and it has far-reaching significance and broad prospects in practical engineering applications.

Vacuum brazing is a kind of Ti-Fe intermetallic compound caused by melting the brazing filler metal in a vacuum environment where the base metal remains solid. At the vacuum brazing temperature of 1050 ℃, the holding time was extended from 10 min to 60 min, and the tensile strength was increased from 32 MPa to 60 MPa. The fracture is a river-like pattern with the characteristics of cleavage fracture, which is a typical brittle fracture.

Craft System

The vacuum brazing of TC4 titanium alloy and 304 stainless steel was carried out using Ag -26.7Cu- 4.6Ti solder at 920~980℃, and the effect of vacuum welding temperature on the microstructure and properties of the brazed seam was studied. The results show that after welding at 920℃, the microstructure of the joint is obviously stratified, and the microstructure is 1Cr18N9T/CrTi/Ag-rich +CuT/Cu4Ti/B -T/TC4 from left to right. After the shear test, the brazed joint was fractured in the Ag-rich phase IP9 with a shear strength of 188 MPa. With the increase of brazing temperature, the joint structure changed. At 980 C, the microstructure of the joint was 1Cr18Ni9Ti/Ag-rich/CuTi/Ti-Cu-rich/B-T/TC4, and the shear strength decreased to 123 MPa. It can be seen that with the increase of welding temperature, the Ag-rich phase in the joint decreases, and the brittle phases CuTi2, Ti-Cu-rich and β-Ti increase and are dendritic, resulting in a significant decrease in the mechanical properties of the joint.

TASHIRS et al. P9 vacuum brazed TC4 titanium alloy and 304 stainless steel without using active elements, and studied the effect of wettability and temperature on the joint structure. The research results found that the wettability of AgCuZn solder was poor in a short time, but with the increase of time, the wettability became better when it was more than 300 s. Fe-Cu-Ti compounds, brittle phases CuzTi and FeTi were found in the joints, and with the increase of welding temperature and time, the number of brittle phases would gradually increase, resulting in poor joint performance. When the vacuum welding temperature was 800 °C and the holding time was 5 min, the shear strength of the joint was 85 MPa; when the temperature was increased to 860 °C and the holding time was extended to 10 min, the shear strength of the joint was 45 MPa. It can be seen that intermetallic compounds have a serious impact on the mechanical properties of joints, so how to control the content and distribution of intermetallic compounds has become the key to vacuum brazing titanium alloys.

In general, the connection between titanium alloy and stainless steel is easy to use conventional welding methods due to the difference in physical and chemical properties between dissimilar metals.

A large number of brittle intermetallic compounds are formed at the interface, and large residual stress is generated, which seriously affects the quality of welded joints. The use of vacuum brazing can improve the precision, quality and welding efficiency of titanium alloy and stainless steel brazed joints, but even under suitable brazing process conditions, there are still low joint strength, unstable joint performance under high temperature and large load conditions, etc. For many problems, the main reason for analysis is the generation of intermetallic compounds. Therefore, the main solution should be to start from the design of the solder, assist the improvement of the brazing process and equipment, and design the solder with the corresponding composition according to different application conditions.

Equipment recommendation

The RHVB-H high temperature vacuum brazing furnace produced by SIMUWU is a high-quality product for this kind of brazing process. It adopts PLC automatic control, and the good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum brazing process. SIMUWU has more than ten years of experience in vacuum furnace sales and manufacturing, and is exported to developed regions in Europe, America and Asia. It is a well-received vacuum furnace manufacturer.