Effect of heat treatments on mechanical properties and wear resistance of laser-powder bed-fused Ti6Al4V alloy

The effects of heat treatment on the microstructure, mechanical properties and wear resistance of Selective Laser Melting Ti6Al4V alloy were systematically studied. The results show that the as-built part has an acicular alpha ' martensite structure. The increase in heat treatment temperature causes the decomposition of acicular alpha ' martensite, which leads to the decrease of the hardness of Ti6Al4V alloy. When the heat treatment temperature is 800 degrees C, the alloy forms an alpha '/alpha structure, which increases the tensile strength and elongation of the alloy by 12% and 23%, respectively. When the heat treatment reaches above 900 degrees C, the mechanical properties of the alloy decrease sharply due to the disappearance of the alpha '/alpha structure, the coarse grains of the alpha phase, and the increase of the content of the beta phase. The tensile strength decreased from 935 MPa to 815 MPa, and the elongation decreased from 8.7% to 3.1%. With the increase of heat treatment temperature, the friction coefficient and wear rate increase linearly, which is opposite to the changing trend of hardness, and the wear mechanism is changed from single abrasive wear to abrasive wear and oxidative wear. This is attributed to the increase in the grain size of the alloy and the increase in the content of the beta phase, resulting in a decrease in the overall hardness of the alloy.