Preparation and properties of Mo₂NiB₂ based cermets

Mo₂NiB₂ based cermets were prepared using element powders of boride, nickel and molybdenum. The phase transformation and dimensional change in the sintering stage as well as the effects of sintering temperature and holding time on the mechanical properties and microstructure of Mo₂NiB₂ based cermets were studied. The results show that with the increasing of sintering temperature, the phase gradually transfers from elemental phase to diboride and then to ternary boride phase, the dimension of the cermets also firstly slightly decreases, then obviously increases in the boronizing sintering process, and finally significantly reduces in the subsequent liquid sintering process. The bending strength and hardness of the cermets firstly increase and then decrease when the sintering temperature rises. The cermets sintered 1290℃ for 60 min show the best mechanical properties with the bending strength of 1346.5 MPa and the hardness of 83.7 HRA. Holding time has a similar effect on the mechanical properties of the cermets. When the holding time is 30 min at 1290℃, the bending strength reaches the maximum of 1453.3 MPa.