Formation mechanisms of Ti₂AlC and Ti₃AlC during solid-state sintering between multilayer graphene and TiAl alloy composite

Abstract

Ti₂AlC and Ti₃AlC formed by the reaction between C and TiAl alloy can improve the plasticity and strength of TiAl alloy respectively. Generally, the peritectic reaction of L + TiC→Ti₂AlC (Ti₃AlC) occurs in the process of liquid-phase sintering, but different formation mechanisms of Ti₂AlC and Ti₃AlC may exist in the solid-state sintering. In this work, multilayer graphene is employed to fabricate the reaction interface with TiAl alloy under 1100–1350 ℃, which is the common solid-state sintering temperature of TiAl alloy. According to the microstructure characterization and analysis, Ti₂AlC and Ti₃AlC are verified to contain no TiC. The interface energy values of TiC/TiAl, Ti₂AlC/TiAl and Ti₃AlC/TiAl are calculated to be about 1.2, 0.87 and 0.39 J·m², respectively, indicating that Ti₂AlC and Ti₃AlC can be formed directly without TiC mesophase. Besides, only Ti₂AlC is observed to be formed at 1150–1250 ℃, while the interface products at 1250–1350 ℃ change into Ti₃AlC with a small amount of Ti₂AlC. The mechanism that the sintering temperature affects the formation tendency of Ti₂AlC and Ti₃AlC can be ascribed to the content of α phase. The TiAl alloy matrix is composed of γ and a few α phases at 1150–1250℃, but almost completely transforms into α phase at 1250–1350 ℃, and the increase in the α content can promote the formation of Ti₃AlC. The above results demonstrate the possibility of regulating the relative content of Ti₂AlC and Ti₃AlC through controlling the sintering temperature, which provides a promising method to improve the plasticity and strength of TiAl alloy.