Microstructure and mechanical properties of submicron-grained NiAl-Al ₂O ₃ composite prepared by pulse current auxiliary sintering

Dense and submicron-grained NiAl-Al ₂O ₃ composite was fabricated by pulse current auxiliary sintering (PCAS). Its microstructure was analyzed by XRD, SEM and TEM, and its mechanical behavior was evaluated through compression test and fracture toughness test. The average grain sizes of NiAl and Al ₂O ₃ are about 200 nm and 100 nm respectively. The Al ₂O ₃ particles dispersed in NiAl matrix, forming intergranular structure and intragranular structure. During sintering, Al ₂O ₃ particles were remarkably spherized due to the unique sintering mechanism of PCAS, which is beneficial to the improvement of toughness. The NiAl-Al ₂O ₃ composite exhibits high compressive yield strength, whether at room temperature or elevated temperature. Its room-temperature (23 °C) and elevated-temperature (1 200 °C) compressive yield strength are up to 2 050 MPa and 140 MPa, respectively. Meanwhile, its fracture toughness is significantly enhanced, which is up to 8.2 MPa/m ^1/2. It is suggested that the main strengthening-toughening mechanisms are grain refinement strengthening and Al ₂O ₃ dispersion strengthening. The fracture of larger NiAl grain is the transgranular cleavage and this is induced by crack tip deflection and grain boundary weakening which are caused by intergranular and intragranular Al ₂O ₃ particles, respectively.