Effects of nano-ZrO2 content on microstructure and mechanical properties of GNPs/nano-ZrO2 reinforced Al2O3/Ti(C, N) composite ceramics

Abstract

Dense Al2O3/Ti(C,N) composite ceramics reinforced with GNPs/nano-ZrO2 were fabricated by hot-press sintering. The effects of nano-ZrO2 content on the microstructure and mechanical properties of the prepared Al2O3/Ti(C,N)/GNPs/ZrO2 composites were investigated. Results showed that nano-ZrO2 inclusions refined the matrix grains significantly and resulted in the formation of intra-granular structure. Excellent comprehensive mechanical properties were achieved via addition of combined GNPs and nano-ZrO2. In particular, the fracture toughness of composites incorporating GNPs (0.4 wt%)/ZrO2 (1 wt%) exceeded 11 MPa m1/2, which was increased by more than 86 % compared with that of Al2O3/Ti(C,N) ceramic composites without GNPs/ZrO2. The main toughening mechanisms have been identified as stress-induced phase transformation, crack bridging, deflection and pull-out of GNPs. The toughening effects originated from GNPs were enhanced with the introduction of nano-ZrO2 because of not only the residual stress resulted from phase transformation but also the formation of intra-granular structure with uneven surface around GNPs.