Microstructure and mechanical behavior of NixAly–Al2O3 in situ composites by pre-oxidation followed by hot-pressed reactive sintering

An in situ composite NixAly–Al2O3, with a near fully dense microstructure, is fabricated from Ni and Al elemental powders using the pre-oxidation and subsequent hot-press reactive synthesis (PORS) technique. The exact formula of the formed NixAly phase in the excessive Al-containing PORS1 and PORS2 samples deviates from the nominal stoichiometric one, dependent on the initial ratio of Ni to Al in the starting powder mixtures. Only NiAl compound is formed in the Ni50–Al50 (at.%) and Ni50–Al50 (at.%)–20 wt.% Al2O3 reaction systems during the hot-press reactive sintering process. The composites exhibit superiority to the NiAl monolithic compound in both flexural strength and fracture toughness at room temperature. Specifically, the in situ PORS1 composite has the highest room temperature flexural strength and fracture toughness with values of 453 MPa and 10.2 MPam, respectively. The toughening effect might be attributed to the interaction between the crack tip and components in the microstructure.