Microstructure, mechanical properties and shape memory effect of a new metastable Ti-W alloy

The effect of tungsten content on the microstructure, mechanical properties and shape memory effect of Ti-W alloys were investigated in detail. The results showed that the microstructures and phase constitutions of Ti-W alloys were sensitive to tungsten contents. Only hexagonal alpha ' phase was found in Ti-10W alloy, while orthorhombic alpha '' martensite formed in Ti-15W alloy. When the content of W increased to 20 wt.%, metastable beta phase was found. The content of alpha '' phase decreased with further increasing W content. Transmission electron microscope results confirmed the presence of omega phase in Ti-20W and Ti-25W. The density of Ti-25W alloy was 5.65 g/ cm3. The elastic modulus, yield strength and hardness of Ti-W alloys decreased firstly and then increased with the additions of W. Ti-15W alloy exhibited the lowest elastic modulus of 68.4 GPa and yield strength of 309 MPa among all studied alloys, while the tensile elongation monotonically increased with increasing W additions. The Ti-10W alloy showed the highest yield strength of 516 MPa and the lowest elongation of 7.4%. The X-ray diffraction and transmission electron microscope results also confirmed the occurrence of the stress induced martensitic transformation of beta to alpha '' during tensile tests for Ti-25W alloy. Shape memory effect was also observed in Ti-W alloys. The Ti-25W alloy showed the maximal shape memory recovery ratio of 22%.