Process Optimization and Microstructural Evolution of TC4 Alloy with YH2 Addition Fabricated by PBF-LB

A three-factor, four-level orthogonal design was employed to optimize the overall forming quality of powder bed fusion with a laser beam (PBF-LB)-fabricated TC4 alloy containing 0.3 wt.% YH2. Sixteen process-parameter combinations were established, and two specimens were fabricated for each combination. Laser power, scanning speed, and hatch spacing were selected as the investigated variables. Relative density, surface roughness, and Vickers hardness were evaluated using the entropy weight method combined with the weighted-sum method. On this basis, the microstructure of the specimens produced under the optimal process parameters was systematically characterized. The results showed that the influence of the investigated factors on overall forming quality followed the order: hatch spacing > laser power > scanning speed. The optimal process parameters were a laser power of 200 W, a scanning speed of 1100 mm/s, and a hatch spacing of 0.10 mm, under which the specimens exhibited superior overall forming quality. The addition of 0.3 wt.% YH2 did not significantly alter the dominant phase constitution of the alloy, but promoted α′ martensite refinement and weakened the texture through the in situ formation of Y2O3 nano-oxide particles.