Effect of heat treatment on microstructure and mechanical properties of a new β high strength titanium alloy

Microstructure and mechanical properties of a new β high strength Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe titanium alloy were investigated in this paper. Both the α/β and β solution treatment and subsequent aging at temperatures ranging from 440. °C to 560. °C for 8. h were introduced to investigate the relationship between microstructures and properties. Microstructure observation of α/β solution treatment plus aging condition shows that the grain size is only few microns due to the pinning effect of primary α phase. The β solution treatment leads to coarser β grain size and the least stable matrix. The size and volume fraction of secondary α are very sensitive to temperature and strongly affected the strength of the alloy. When solution treated at 775. °C plus aged at 440. °C, the smallest size (0.028. μm in width) of secondary α and greatest volume fraction (61%) of α resulted in the highest yield strength (1624. MPa). And the yield strength decreased by an average of 103. MPa with every increase of 40. °C due to the increase of volume fraction and decrease of the size of secondary α. In β solution treatment plus aging condition, tensile results shows that the strength if the alloy dramatically decreased by an average of 143. MPa for every increase of 40. °C because of larger size of secondary α phase than α/β solution treated plus aged condition.