Toughness mechanism and plastic insensitivity of submicron second phase Ta in a novel Ta–Hf6Ta2O17 composite ceramic

Abstract

The introduction of metal-second phase can improve the fracture toughness of metal-ceramic composite (MCC) material, but usually degrades the strength and hardness. The pace of exploring the process and materials to both improve the toughness and hardness has never stopped. In this study, a novel Ta–Hf6Ta2O17 composite ceramic is successfully prepared by spark plasma sintering. The effects of Ta content on microstructure and mechanical properties of the as-sintered ceramic are investigated. The fracture toughness of Ta–Hf6Ta2O17 composite ceramic first increases and then decreased slightly with the increase in Ta content, reaching the maximum value of 4.21 ± 0.09 MPa m1/2 at 20 vol% Ta. The improvement of the fracture toughness does not affect the hardness, whose value is stable between 16.74 GPa and 18.43 GPa. Based on the results of Selsing’s model, Raman spectra and TEM, it is confirmed that the toughness mechanism of Ta–Hf6Ta2O17 composite ceramics originates from good inherent interface strength and crack deflection caused by the second phase. The maintenance of hardness comes from the plastic insensitivity of submicron Ta caused by the interfacial tensile stress, which provides a potential mechanism for the design of metal-ceramic composite with excellent strength and toughness.