Microstructural evolution and final properties of a cold-swaged multifunctional Ti-Nb-Ta-Zr-O alloy produced by a powder metallurgy route

Body centred cubic (BCC) beta-phase multifunctional titanium alloys have been developed with a very unique combination of thermal and mechanical properties. In this investigation, a very low porosity Ti-36.8-Nb-2.7Zr-2.0Ta-0.44O (wt%) alloy was produced by powder sintering, hot forging, solution treatment and cold swaging. X-ray diffraction and transmission electron microscopy (TEM) of the solution treated alloy revealed the presence of a small amount of omega-phase in a predominantly BCC beta-phase matrix. Electron backscatter diffraction (EBSD) of the swaged alloy revealed a highly elongated and fragmented microstructure, and a strong < 110 > fibre texture. TEM also revealed the existence of stress-induced twin lamella, dislocations and omega-phase. Consistent with previous studies on these types of alloys, the swaged alloy exhibited non-linear elasticity during tensile straining, low elastic modulus (45.4 GPa), high elastic limit (2.3%), high elongation to failure (8.1%), and a high yield strength (880 MPa) and tensile strength (940 MPa). The coefficient of thermal expansion was also low (similar to 5 x 10(-6) K-1 between 50 and 300 degrees C) in this alloy. (C) 2013 Elsevier B.V. All rights reserved.