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 TiB 2 /Al composites is fabricated by K 2 TiF 6 and KBF 4
systems. The effects of process parameters on the size, distribution and morphology
of in-situ TiB 2 particles, as well as the microstructure and mechanical properties of the
composite is analyzed. When the mixed salts is added at 750 °C, TiB 2 particles are
short rods. When the temperature is higher than 825 °C, TiB 2 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, TiB 2
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,
TiB 2 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 TiB 2
particles, large size hard brittle phase TiAl 3 appear in the microstructure. When the
Ti/B molar ratio is 1/2.2, the formation of hard brittle phase TiAl 3 can be inhibited,
TiB 2 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
TiB 2 particles and the matrix, so reduce the mechanical properties of the composite.