Microstructural characterization and dry sliding wear resistance of MoO₂-strengthened γ/NiMo alloys with different primary phases

Two γ/NiMo alloys strengthened by a refractory metal oxide MoO₂ phase were fabricated by a laser melting deposition process. Microstructural transformation of the alloys with different primary phases was identified and the crystal structure of the primary phases was confirmed by both X-ray diffraction and transmission electron microscopy. Meanwhile, room-temperature dry sliding wear behavior and mechanism difference of the alloys were also investigated mainly by scanning electron microscopy. Microstructures of the alloys varied from hypoeutectic to hypereutectic, as the molybdenum content increases. The hypoeutectic alloy was solidified on the basis of a Ni-base solid solution γ primary phase, whereas the hypereutectic alloy was grown based on an intermetallic compound with NiMo primary phase. The γ, NiMo primary phases and MoO₂ strengthening phase were confirmed to have face-centered cubic, orthorhombic and monoclinic structures, respectively. Compared with the hypoeutectic alloy, the hypereutectic alloy exhibited higher wear resistance under the same condition. The predominant wear mechanism of the γ/NiMo alloys transformed from micro-cutting to microcracking.