Response surface analysis, tensile properties, and microstructure of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si fabricated by laser powder bed fusion

In this work, Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy samples under different laser process parameters were successfully fabricated by laser powder bed fusion technology. The influence of three processing parameters (laser power P, scanning speed V, and hatch spacing H) on the forming quality and tensile properties of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si samples was investigated by response surface analysis. The Non-Dominated Sorting Genetic Algorithm-II was employed to optimize and attain laser process parameters with optimal forming quality and tensile properties. Specifically, the response surface was established to reveal the optimization method of two response values (forming densification and ultimate tensile strength). The results demonstrated that hatch spacing (H) and its secondary influencing factor (H2) exerted significant effects on densification. In addition, the secondary influencing factors of laser power and hatch spacing (P2 and H2) exerted significant effects on the ultimate tensile strength of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si samples. The influence mechanism of laser process parameters on the densification and tensile properties of samples was further illuminated from the perspective of melting instability and the grain growth process. The maximum tensile strength of the Ti–6.5Al–3.5Mo–1.5Zr–0.3Si sample obtained after optimization reached above 1300 MPa. The maximum strain of the Ti–6.5Al–3.5Mo–1.5Zr–0.3Si sample with the optimal plastic performance reached 16.6%. The strength and toughness of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si samples were analyzed from the aspects of the microstructure and phase composition.