Effect of Mo Content on Microstructures and Mechanical Properties of Mn and V Containing MO_2NiB_2 Base Hard Alloys

摘要

Mo_2NiB_2 base hard alloy consists of a Mo_2NiB_2 type complex boride as a hard phase and a Ni base alloy as a binder phase. According to previous investigation, additions of Cr and V to the alloy changed the boride phase crystal structure from orthorhombic to tetragonal and resulted in a remarkable improvement of mechanical properties associated with microstructural refinement. Moreover, an addition of Mn turned out to be effective for further improvement of the mechanical properties in the V containing alloy. In this investigation, Ni-5B-xMo-12.5V-2.5Mn (mass percent) model alloys with four levels of Mo contents corresponding to Mo/B atomic ratio ranging from 1.0 to 1.3 were prepared to study the effect of the Mo/B atomic ratio on the mechanical properties and microstructure. The results indicated that transverses rupture strength (TRS) increased with increasing Mo/B atomic ratio and showed a maximum value of 3.2 GPa at Mo/B = 1.2 and then decreased with increasing the atomic ratio. Hardness increased linearly from 86.8 HRA to 90.8 HRA with increasing Mo/B atomic ratio.