MECHANICAL-PROPERTIES AND OXIDATION BEHAVIOR OF HIPED HAFNIUM NITRIDE CERAMICS

The compaction at 1600-degrees-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) congruent-to 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-degrees-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)10N of 1450, a modulus of rupture rather low (350 MPa) and a SENB fracture toughness of 4-5 MPa square-root m. The oxidation behaviour, in dry oxygen, suggested that the reaction, between 755 and 950-degrees-C, was governed by an interfacial process occurring at the nitride-oxide interface, similarly to the behaviours of dense HIPed TaN and ZrN materials.