A study on the microstructures and mechanical properties of Ti-B20-0.1B alloys of direct rolling in the α + β phase region

The effect of direct rolling on the microstructure and properties of Ti-B20-0.1B is studied. The alloy was double melted by vacuum arc melting and subsequently subjected to thermomechanical processing that included combinations of direct rolling and heat treatment in the α + β phase fields. The microstructural characteristics and microstructure-property relationships were investigated by solution treatment at 740 °C and subsequent aging at 550 °C for 2 h/4 h. It shows that the grain size of Ti-B20 alloy was reduced by trace boron, and TiB whiskers produced by reaction of boron and titanium distribute at the grain boundary. Primary α phase and TiB whiskers aligned along the rolling direction after the direct rolling. The large reduction ratio caused dramatic recrystallization of primary α phase which was thus transformed to equiaxed. After aging treatment, the secondary α phase whose volume fraction is 50% were precipitated, and alloy strength level was significantly increased. The strengthening effect that aligned TiB whisker has on matrix alloy is assessed. According to the calculation, it is attributable to the load-sharing mechanism by the TiB whisker that the yield strength (YS) and the ultimate tensile strength (UTS) of Ti-B20-0.1B alloy are higher than those of Ti-B20 alloy.