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

•A new β high strength titanium alloy is designed.•A high yield strength of 1614MPa is obtained with elongation of 6.2%.•The size and volume fraction of secondary α are sensitive to aging temperature.•The strength is relative to volume fraction and size of secondary α.

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.