Nano-SiC whisker-reinforced Ti6Al4V matrix composites manufactured by selective laser melting: Fine equiaxed grain formation mechanism and mechanical properties

We elucidate the effect of nano-SiC whisker (SiCw) on the microstructure and mechanical properties of Ti6Al4V alloy manufactured by selective laser melting (SLM). The transformation of cross-sectional plate-like α grains and longitudinal-sectional β columnar grains to equiaxed grains could be achieved by adding a trace amount of SiCw, and the weak texture strength microstructure with fine equiaxed grains was obtained. The in situ formed nanosized TiC particles promoted grain refinement through three mechanisms: (i) The diffusion distribution of nanosized TiC particles provided a favorable nucleation position for the α phase, it also limited the growth of the α phase. (ii) Nanosized TiC particles were dispersed to fix dislocations and grain boundaries, inhibit the grain growth. (iii) Nanosized TiC was embedded in the matrix and bound well to the matrix. The Ti matrix was easy to nucleate on some specific crystal planes of primary TiC, which increased the nucleation rate. In addition, the addition of SiCw significantly improved the mechanical properties of Ti6Al4V alloy, compared with that of the Ti6Al4V alloy (360.2 HV), the microhardness of the sample with 1.0-wt% SiCw (522.7 HV) increased by 45.1%. The addition of 0.5-wt% SiCw (1445.34 MPa) increased the ultimate tensile strength by 19.4% compared with that of the Ti6Al4V alloy (1210.13 MPa), and good ductility was maintained. The results show that the microstructure of Ti6Al4V alloy can be significantly improved by adding a trace amount of SiCw, which provided an effective way for the grain refinement of titanium matrix composites manufactured by SLM.