Effects of heat treatment on the microstructure and mechanical properties of in situ inhomogeneous TiBw/Ti6Al4V composite fabricated by pre–sintering and canned powder extrusion

Abstract

Heat treatments with different parameters were performed on the as–extruded 4.5 vol% TiBw/Ti6Al4V composite rods with TiBw columnar reinforced structure fabricated by pre–sintering and canned powder extrusion to pursue further performance optimization for high temperature applications. Microstructure observations reflected that the fraction of martensite α′ phase, which was transformed from high–temperature β phase after water quenching, increased with the rising solution temperature and then stabilized above 1000 °C, resulting in a significant enhancement in hardness/strength of the composite; both the fraction and size of the dispersed (α + β) phases, which were decomposed from martensite α′ phase during aging, increased monotonously with the rising aging temperature, leading to an effective improvement of the toughness with sacrificing strength moderately. Under the treatment of water quenching at 1000 °C and aging at 600 °C for 6 h, a plus 11% increase in ultimate strength could be achieved in the heat–treated TiBw/Ti6Al4V than that in the as–extruded below 600 °C on the premise of good interface bonding between TiBw and Ti matrix, resulting in 1520 MPa at ambient temperature, 1173 MPa at 400 °C and 947 MPa at 500 °C. Optimizing matrix alloys/composition is suggested to retard interface debonding arising from the softening of Ti matrix for further strengthening above 600 °C.