Mechanical properties and oxidation behaviour of HIPed hafnium nitride ceramics

Abstract The compaction at 1600°C, under an isostatic argon pressure of 195 MPa, of a coarse hafnium nitride powder, previously encapsulated in a vacuumed titanium can, has led to the formation of a porous material ( d r ≅ 85%). In order to produce a high-performance material, the same HfN powder has been encapsulated into a silica container and hot isostatically pressed at 1950°C, under a pressure of 195 MPa. In both cases, the dwell time lasted 1 h. Under these conditions, the dense material ( d r > 95%) had a Vickers microhardness H v 10 N of 1450, a modulus of rupture rather low (350 MPa) and a SENB fracture toughness of 4·5 MPa m The oxidation behaviour, in dry oxygen, suggested that the reaction, between 755 and 950°C, was governed by an interfacial process occurring at the nitride-oxide interface, similarly to the behaviours of dense HIPed TaN and ZrN materials.