High temperature mechanical properties of Ta-10W alloy

Ta-10W alloy is a kind of high density, high melting point, high strength rare metal alloy material, with high temperature strength, good ductility, weldability and excellent corrosion resistance, suitable for high temperature, high pressure, corrosion resistance and other working environment, is widely used engineering and functional materials. In tantalum, tungsten forms an alternative continuous solid solution with tantalum. Tungsten plays a major role in strengthening the solid solution of tantalum and significantly improves the mechanical properties of tantalum metal. Because Ta-10W alloy is often used in high temperature environment, its high temperature performance is of great concern.

In the process of high temperature stretching, there are two opposite processes of work hardening and dynamic recovery or refinish. The effect of dynamic recovery is to offset the work hardening effect, but if it is carried out slowly, the energy storage will increase continuously during the deformation process, and dynamic recrystallization can occur when a certain critical condition is reached. The changes of microstructure produced by these two softening processes are different, but both belong to thermal activation process, and the flow stress is closely related to temperature and strain rate. When the strain rate is fixed, the deformation temperature plays a decisive role. The higher the temperature is, the more dynamic recrystallization is. Work hardening occurs at the same time of dynamic recrystallization. The cause of work hardening is the result of dynamic strain aging. Dynamic strain aging is the aging process of metal and alloy when plastic deformation occurs. In essence, dynamic strain aging is the result of the interaction between solute atoms and dislocations. When dynamic strain aging occurs, reinforcement and plastic deformation occur simultaneously. Solute atoms catch the movement of the dislocation by diffusion, and interact with the dislocation to cause the dislocation to be pinned. The diffusion capacity of solute atoms increases with increasing temperature. The plasticity and strength of the material change with the increase of temperature depends on the result of dynamic recrystallization and dynamic strain aging.

At 1000 ℃ drawing, material of dynamic recrystallization and work hardening caused by the dislocation multiplication interaction, with the increase of temperature, on the one hand, dislocation of the pay slip into dislocation climbing, on the other hand, the rise of temperature is further reduced the strength of the grain boundary, so in the 1200 ℃ and 1400 ℃ in the grain boundary sliding and the intergranular fracture, temperatures have also launched a new slip system, increase the plasticity of materials. At 1600℃, the appearance of double dimples in the tensile fracture further increases the plastic deformation of the material and further improves the plasticity of the material. The higher the temperature, the greater the effect of dynamic recrystallization and the better the plasticity of the material. The shrinkage of the section increases with the increase of temperature, indicating that the plastic deformation area of Ta-10W alloy increases with the increase of temperature, so that the plasticity of the alloy can be improved. The new dimple appears at 1600℃ and 2000℃. This new dimple has excellent plasticity, which makes the alloy reach the maximum elongation at 1600℃, the maximum shrinkage of the section at 1800℃, and maintain high plasticity all the way to 2000℃.The main reason for the formation of the dimple is that there are high melting point inclusions at the bottom of the dimple, and the impurities become the crack source. This was confirmed by SEM observation at 1800℃ and 2000℃.

The elastic modulus is the resistance index of metal and alloy to elastic deformation, while the yield strength is the resistance index of metal and alloy to plastic deformation. Both of them are the embodiment of material deformation resistance, so with the increase of temperature, they show a similar downward trend. The deformation resistance of Ta-10W alloy decreases slowly with the increase of temperature, which is related to the high solute atomic content of the alloy. The higher solute atomic content leads to the further enhancement of the dynamic strain aging effect, thus increasing the working hardening rate of the alloy. On the other hand, the higher the temperature is, the greater the dynamic recrystallization effect is. With the increase of temperature, the closer the tensile strength is to the yield strength, the increment of work hardening of the material decreases gradually and basically shows a linear change, which is an obvious evidence that the dynamic recrystallization increases with the increase of temperature. As a result of the combination of dynamic strain aging and dynamic recrystallization, the yield strength and elastic modulus of Ta-10W alloy decreased slowly with the increase of temperature.

1) With the increase of temperature, the tensile strength, yield strength and elastic modulus of Ta-10W alloy all decrease, but the rate of decline in tensile strength is faster, while the rate of decline in yield strength and elastic modulus is obviously slower.

2) With the increase of temperature, the elongation and section shrinkage of Ta-10W alloy increase slightly;

3) The variation of Ta-10W alloy strength and plasticity with the increase of temperature is the result of the comprehensive action between dynamic recrystallization and work hardening caused by dynamic strain aging, and dynamic recrystallization plays a leading role at high temperature.

4) Through the analysis of the fracture mechanism of Ta-10W alloy, it can be concluded that with the increase of the test temperature, the presence of high-melting point substances has more and more influence on the alloy, and the dynamic recrystallization effect is also more and more obvious.