The effect of heat treatment on α/ β phases evolution of TC4 titanium alloy fabricated by spark plasma sintering

Abstract

The spark plasma sintered (SPS) TC4 titanium alloy was deformed at deformation temperature of 900℃ and 1000℃ on Gleeble-1500D thermal simulator, and then the microstructure and α/ β phases evolution at different heat treatment parameters were investigated. The results showed that the effect of heat treatment on the microstructure of TC4 titanium alloy was not obvious when the deformation temperature lower than β-transus temperature. On the contrary, when the heat deformation temperature was above the β-transus temperature, the content of equiaxed α-phase increased and the lamellar α-phase coarsened with the decrease of solution temperature. When the solution temperature was lower than β-transus temperature 10℃-30℃ and the aging time was up to 20h, a tri-modal structure( equiaxed α-phase+lamellar α-phase+β-transformed matrix) was formed. Controlling the increase of the primary α-phase and the coarsening of the lamellar α-phase is the key to the formation of the tri-modal structure. Subsequent microhardness tests showed that the microhardness of TC4 titanium alloy with the basket-weavestructure and widmanstatten structuren was the highest, which reached 438HV. In addition, the microhardness of the equiaxed structure and tri-modal structure were 348HV and 373HV,respectively.