文摘
Vickers indentation testing was applied to examine an additive-free monolithic sample of tantalum sesquinitride having orthorhombic U2S3 type structure, η-Ta2N3, synthesised at high pressures and temperatures. Crystallisation of η-Ta2N3 in form of elongated crystals and a high bulk to shear modulus ratio of 2.3–2.6, considered as a qualitative criterion of malleability, suggest elevated fracture toughness for this ceramic material. Here we measured Vickers hardness, HV, indentation size effect, and fracture toughness, KIc-if, as well as their dependences on the surface self-healing (densification) due to mechanical polishing for a sample with the residual porosity of p=0.14. HV of η-Ta2N3 was found to exhibit a moderate indentation size effect and approach, for the porous sample, HV(1)=16(1) GPa at the maximal load. KIc-if was measured to be 4.6(2) MPa m1/2, comparable with the values reported for hexagonal Si3N4 and SiC.