Effect of holding time and Ti/B molar ratio on microstructure and mechanical properties of in-situ TiB₂/Al composites fabricated by mixed salt reaction

Abstract In this study, in situ TiB₂/Al composites is fabricated by K₂TiF₆ and KBF₄ systems. The effects of process parameters on the size, distribution and morphology of in situ TiB₂ particles, as well as the microstructure and mechanical properties of the composite is analyzed. When the mixed salts is added at 750 °C, TiB₂ particles are short rods. When the temperature is higher than 825 °C, TiB₂ particles are cubic columns and hexagonal columns. When the reaction temperature is 825 °C, the grain refinement of the composite is most obviously. When the holding time is 80 min, TiB₂ particles are uniformly distributed in the matrix and the size is less than 2 μm. The ultimate tensile strength, yield strength and elongation of the composite reach the maximum values of 230 MPa, 125 MPa and 9.5%. When the holding time is 110 min, TiB₂ particles agglomerate at the grain boundary, and the mechanical properties of the composites decrease. When the Ti/B molar ratio is 1/1, in addition to forming TiB₂ particles, large size hard brittle phase TiAl₃ appear in the microstructure. When the Ti/B molar ratio is 1/2.2, the formation of hard brittle phase TiAl₃ can be inhibited, TiB₂ particles are uniformly distributed in the matrix and the grain refinement is most obviously. The ultimate tensile strength, yield strength and elongation of the composite reach the maximum values of 225 MPa, 110 MPa and 8.5%. When the Ti/B molar ratio is 1/3, the unreacted residual mixed salts appear in the microstructure of the composite, and the residual mixed salts impurities exist at the interface between TiB₂ particles and the matrix, so reduce the mechanical properties of the composite.