Enhancing high-temperature strength and ductility of γ-TiAl matrix composites with controllable dual alloy structure

Abstract

Gamma-TiAl matrix composites can function as promising high-temperature structural materials. In this study, to improve the poor ductility and insufficient strength of composites at high temperatures, they were successfully prepared via powder metallurgy by adding the Ti–6Al–4V alloy. The experimental results indicate that the soft phases of Ti–6Al–4V were surrounded by the hard phase of Ti–48Al–2Cr–2Nb, and the special structure exhibited a unique strain hardening mechanism, which resulted in the high strength and ductility of the composites at high temperature. The 8 wt% Ti–6Al–4V composites were fractured with an elongation approximately 90.65% and tensile strength of 427.75 MPa at 800 °C and 5 × 10−5 s−1; the elongation and tensile strength were both higher than those of single unreinforced Ti–48Al–2Cr–2Nb alloy. Moreover, with an increase in the deformation strain, the deformation behavior started from the Ti–6Al–4V area, which had good ductility. The dislocation movement was hindered by the Ti–48Al–2Cr–2Nb area, and dislocation accumulation and grain deformation occurred, leading to strength increase. The stress concentration and high-density dislocations were stored in the soft phases, which delayed the initiation and propagation of pores and cracks. Moreover, besides grain sliding, evident dislocation activities occurred; therefore, the high ductility of the composites was obtained.