Synthesis, microstructure and mechanical properties of (Ti1−x,Nbx)2AlC/Al2O3 solid solution composites

(Ti,Nb)2AlC/Al2O3 in-situ solid solution composites were successfully synthesized from the elemental powder mixtures of Nb2O5, Ti, Al and carbon black using hot-press-aided reaction synthesis. The reaction path was investigated by differential scanning calorimetry (DSC) and X-ray diffractometry (XRD), and a possible reaction mechanism was proposed to explain the formation of (Ti,Nb)2AlC/Al2O3 composites in which the thermite reaction between Al and Nb2O5 formed Al2O3 and Nb, and the latter together with TiAl and TiC reacted to form (Ti,Nb)2AlC. The synthesized composites show plate-like grains packed in a laminated structure typical of Ti2AlC, and the fine Al2O3 particles formed in-situ tend to disperse on the matrix grain boundaries. Compared with the monolithic Ti2AlC synthesized using an identical process, the Vickers hardness, maximum compressive stress, flexural strength and fracture toughness of (Ti0.96,Nb0.04)2AlC/5 wt% Al2O3 were enhanced by 33.8%, 12.1%, 118.4% and 111.8%, respectively. The mechanisms by which Al2O3 increases the strength and toughness of the material were also discussed.