Preparation and toughness mechanism of in-situ Ti3AlC2 enhanced and toughened TiAl3 matrix composites

Abstract

In this paper, dense MAX phase Ti3AlC2 enhanced and toughened TiAl3 matrix composites with mass fractions of 10∼40% were prepared by in-situ reaction via powder metallurgy route which using TiH2, Al and TiC powder as the starting materials. Then, the microstructure and phase structure of the composites were characterized, and the relationship between microstructure, mechanical properties and fracture mechanism was systematically investigated. The results show that the lath-like (micron level) and fine-needle-like (submicron level) reinforcements Ti3AlC2 are uniformly distributed in TiAl3 matrix. With the increases of mass fraction of reinforcements, the average grain size of the TiAl3 matrix decreases remarkably from 7.6 μm to 4.8 μm, indicating that the reinforcements Ti3AlC2 can effectively refine the matrix grains and plays a good pinning effect on the TiAl3 matrix. The prepared Ti3AlC2/TiAl3 composite with 30% mass fraction exhibits excellent comprehensive mechanical properties: the Vickers hardness, flexural strength, fracture toughness is 575 ± 5 HV, 470 ± 18 MPa, and 3.83 ± 0.05 MPa m1/2, 14.1%, 174.9% and 117.6% higher than that of the pure TiAl3 matrix, respectively. Both the strengthening and toughening effects are significant. The strengthening mechanism are fine grain strengthening and deformation strengthening, while the toughening mechanism is a synthetic effect in terms of crack deflection, crack bifurcation, grain refinement and stress-induced microcrack. Fracture analysis shows that the fracture mechanism is transgranular (cleavage) fracture.