Synthesis of Al₂O₃/Mo₂N Composite Materials Using Capsule-free Nitrogen HIPing and their Evaluation

Abstract

Synthesis of dense composite materials with the compositions of Al₂O₃/Mo₂N=100/0∼40/60 vol% has been attempted directly from Al₂O₃/Mo mixed raw powder compacts using capsule-free N₂ hot isostatic pressing (HIP). During HIPing [1500°C/(16∼20-200MPa)/1h], solid/gas reaction between Mo and N₂ was introduced to form Mo₂N. The most of sintered composites consisting of only Al₂O₃ and Mo₂N phases reached to a higher relative density than 98.0 % with closed pores nevertheless capsule-free HIPing. Dispersion of Mo₂N particles just formed suppressed the grain growth of Al₂O₃ during sintering. Mechanical properties, such as bending strength (σ_b), Vickers hardness (H_V), fracture toughness (K_1C), and other properties have been evaluated as a function of their compositions. The best mechanical values of σ_b (∼573 MPa), H_V (∼20.3 GPa) and K_1C (∼5.00 MPa·m^1/2) were attained at the composition of Al₂O₃/Mo₂N=90/10 vol%, due to a high density (98.6 %) and small grain size of Al₂O₃ matrix (G_s∼4.70 μm). Further addition of Mo₂N reduced the sinterability of matrix grains, resulting in low densities of around 90 % at the 40/60 vol% composition.