Interface microstructure evolution of functionally graded SiC/TiC/Ti6Al4V composites manufactured with selective laser melting

This study fabricated functionally graded SiC/TiC/Ti6Al4V composites via selective laser melting (SLM) using Ti6Al4V powder and SiC whiskers. The influence of processing parameters on interfacial microstructure was systematically investigated using an orthogonal experimental design. Results indicate that as the SiC content increased from 0.25 to 1.25 wt.%, the grain size gradually decreased from approximately 1.15 μm to 1.05 μm. The most significant grain refinement occurred at 0.75 wt.% SiC, where about 62.2% of grains were smaller than 1 μm. This refinement is primarily attributed to in-situ formed TiC particles during SLM, which effectively inhibit grain boundary migration through a pinning effect. Microhardness testing revealed that hardness increased with SiC content, peaking at 426 HV in the 1.25 wt.% region, while dropping to 296 HV at the 0.25/0.75 wt.% interface due to metallurgical defects from compositional discontinuity. The strengthening in high-SiC regions results from the combined effect of intrinsic SiC hardness and in-situ TiC formation. Mechanical tests showed the composite's tensile strength decreased by 22.37% to 1032.36 MPa with a 6.6% reduction in elongation, primarily due to weakened interfacial bonding and stress concentration caused by agglomerated unreacted SiC particles. This study provides a theoretical basis for preparing high-performance titanium-based graded composites.