Structure stability of Ti3AlC2 in Cu and microstructure evolution of Cu-Ti3AlC2 composites

The structural stability of Ti3AlC2 in Cu and the microstructure evolution of Cu-Ti3AlC2 composites prepared at different temperatures were investigated by high-resolution transmission electron microscopy and X-ray diffraction. A mild reaction between Ti3AlC2 and Cu occurred at 850-950 °C, and strong reactions occurred above 950 °C. The reaction was identified as diffusion of Al from Ti3AlC2 into Cu to form Cu(Al) solid solution. Ti3AlC2 retained its structure under the partial loss of Al. Further depletion of Al resulted in highly defective Ti3AlC2 accompanied by the inner diffusion of Cu into Ti3AlC2 along the passway left by the Al vacancies. When Al was removed, Ti3AlC2 decomposed and transformed into cubic TiCx. In addition, TiC twins formed by the aggregation of C vacancies at twin boundaries. With the help of first-principles calculation and image simulation, an ordered hexagonal TiCx was identified as a transition phase linking Ti3AlC2 and c-TiCx. The effect of the reaction and phase transformation on the microstructure and properties of Cu-Ti3AlC2 composites was also discussed.