Influence of heat treatment on microstructure of laser solid forming Ti-6.5Al-3.5Mo-1.5Zr-0.25Si alloys

The as-deposited microstructure and heat-treated microstructure of Ti-6.5Al-3.5Mo-1.5Zr-0.25Si alloys (TC11) by Laser Solid Forming (LSF) were compared, and approaches to improve LSF microstructure and high-temperature combination properties of TC11 alloys were researched. Results show the as-deposited microstructure of TC11 alloy consists of coarse columnar grains and equiaxed grains throughout cladding layers, and the prior columnar β-Ti grains are composed of lathlike α and residual β. The microstructure of as-deposited samples after 950°C heat treatment is a similar triplex mixture of equiaxed α, basketweave α lath and transformed β. The majority of continuous prior α boundary is broken, and become spheroidized and illegible; α laths grow up to bunch on some unbroken boundary; the equiaxed α in coarse β grains is related with subgrains. The microstructure after heat treated at 970°C is a certain basketweave structure consisting of a few equiaxed-α and α laths which have coarsening tendency; the microstructure after recrystallization at 1030°C followed by 950°C heat treatment is typical Widmanstätten structure consisting of coarse α laths, and lots of β-Ti is found to separate out inside α and on α boundaries without breaking basically.