Effect of Nb2O5 on the microstructure and mechanical properties of TiAl based composites produced by hot pressing

In situ composites of TiAl reinforced with Al2O3 particles are successfully synthesized from an elemental powder mixture of Ti, Al and Nb2O5 by the hot-press-assisted reaction synthesis (HPRS) method. The as-prepared composites are mainly composed of TiAl, Al2O3, NbAl3, as well as small amounts of the Ti3Al phase. The in situ formed fine Al2O3 particles tend to disperse on the matrix grain boundaries of TiAl resulting in an excellent combination of matrix grain refinement and uniform Al2O3 distribution in the composites. The Rockwell hardness and densities of TiAl based composites increase gradually with increasing Nb2O5 content, and the flexural strength and fracture toughness of the composites have the maximum values of 634 MPa and 9.78 MPa m1/2, respectively, when the Nb2O5 content reaches 6.62 wt.%. The strengthening mechanism was also discussed.