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

Abstract

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 (αGB, αWGB, and αWM) 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.