Microstructure and Corrosion Resistance of Ti6Al4V Manufactured by Laser Powder Bed Fusion

Abstract

Laser powder bed fusion (LPBF) technology has a dominant position in the preparation of titanium implants with a complex structure and precise size. However, the processing characteristics of rapid melting and solidification lead to the low density and poor corrosion resistance of the alloy. Hereby, the effects of the laser power and scanning rate on the density, hardness, compressive strength, and corrosion resistance of the Ti6Al4V alloy prepared by LPBF technology have been investigated by metallographic microscopy, a mechanical analysis, and electrochemical tests. The results show that increasing the scanning rate and decreasing the laser power decreases the transformation power from the β phase to α′ phase and changes the morphology of the α′ phase from lath shaped to acicular. The hardness of the Ti6Al4V alloy reaches the maximum (480.53 HV) for a scanning rate of 1000 mm/s and laser power of 280 W, owing to the sufficient precipitation of the α′ phase. Unfused holes occur in the titanium alloy when the laser energy density is too low to melt the power. Pores occur when the laser energy density is too high to vaporize the powder. Both defects reduce the compressive strength of the alloy. The maximum relative density of the Ti6Al4V alloy is 99.96% for a scanning rate of 1200 mm/s and laser power of 240 W, and the compressive strength (1964 MPa) and corrosion resistance (3.16 MΩ·cm2) both reached the maximum.