Effect of Phase Transformation Conditions on the Microstructure and Tensile Properties of Ti-3Al-15Mo-3Nb-0.2Si Alloy

The influence of phase transformation conditions (α/β solution treatment plus aging, β solution treatment plus aging, and β solution treatment plus duplex aging) on the microstructure and tensile properties of Ti-3Al-15Mo-3Nb-0.2Si alloy was studied. Microstructure observation indicates that the primary α phase, which formed during α/β solution treatment, can effectively limit the growth of the β grains. The alloy was heat treated in the α/β solution, which together with aging, formed smaller grains and finer precipitates in the sample and showed good tensile ductility with a 15% elongation. Aging temperatures from 450 to 600 °C were used to study the effects of aging treatment on the alloy’s microstructure and tensile properties. Precipitation phases appeared in particular positions (α_GB, α_WGB, and α_WM) during the aging process which depended on phase transformation conditions and caused variations in the alloy’s tensile properties. The alloy treated by duplex aging after β solution had a higher ultimate tensile strength at 1370 MPa than that of other samples, resulting from the finer α precipitates transformed from the ω phases. The relationship of tensile properties and phase transformation was investigated by observing the material fracture, and small and dense dimples were seen in the tensile specimen treated by α/β solution plus aging treatment which led to excellent ductility. Deep dimples in the duplex aging specimen resulted in beneficial high strength.