Nitriding of Co-Cr-Mo alloy in nitrogen

Using the results of a thermodynamic analysis, a Co-Cr-Mo alloy was successfully nitrided in nitrogen at temperatures of 1073-1473 K. The near-surface microstructure of the treated Co-Cr-Mo alloy was characterized using X-ray diffraction, field-emission scanning electron microscopy, electron probe micro-analyzer, and transmission electron microscopy equipped with energy-dispersive X-ray spectroscopy. The results indicated that the highest nitriding efficiency was achieved at the treatment temperature of 1273 K, with the size and coverage of the nitride particles on sample's surface increasing with an increase in the treatment duration. After nitriding at 1273 K for 2 h, numerous nitride particles, consisting of an outer Cr₂N layer and an inner π phase layer, were formed on top of the nitrogen-containing γ phase, and some π phase also precipitated in the alloy matrix at the sub-surface level.