Optimization of processing parameters and microstructure evolution of (TiB+La2O3)/Ti6Al4V manufactured by laser melting deposition

Abstract

Due to the intrinsically ultrahigh cooling rate and thermal gradient during laser melting deposition (LMD), columnar-to-equiaxed transition (CET) of grains has been a significant challenge in titanium-based alloys. In this study, two strategies, including the optimization of processing parameters and the addition of ceramics particles, were utilized to promote the CET of Ti6Al4V. The optimal processing parameters of Ti6Al4V were confirmed by response surface methodology (RSM). The width of prior β grains effectively decreases under the minimum dilution of single track. Besides, different contents of TiB2 and La2O3 were added to Ti6Al4V powder and the in situ (TiB + La2O3)/Ti6Al4V composites were manufactured using the identified optimal processing parameters. In situ TiB whiskers segregating at the grain boundaries tailor the coarse columnar to equiaxed grains with La2O3 particles dispersed in the composites. With increasing formation of the reinforcements, equiaxed grain size decreases from 23.3 to 11.9 μm. The ultimate tensile strength of the components was improved by 19.6% and 26.4% compared to that of Ti6Al4V. This work provides systematic solutions to suppress the coarse columnar grains and refine the microstructure for titanium-based alloys.