Abstract: The fast and deep case plasma nitriding technique is applied to gear of centrifugal compressor. The nitriding layer is investigated by using optical microscope, X-ray diffractometer, electron probe micro analyzer, knoop micro-hardness tester, micro-friction wear tester and scanning electron microscopy. The thicknesses of the nitriding layers of samples plasma nitrided at 510 ℃ for 15 h and 20 h are 341.25 μm and 502.33 μm respectively. The nitriding layer is composed of the compound layer and the diffusion layer, and the compound layer transforms from ε-Fe2-3N+γ′-Fe4N duplex-phase layer to γ′-Fe4N single-phase layer with the increase of nitriding time. Because of the strengthening effect of nitrides in the nitriding layer, the plasma nitrided sample exhibits a higher surface hardness, a lower coefficient of friction and a significant reduction in worn volume. The major wear mechanism of the nitriding layer is adhesive wear. The fast and deep case plasma nitriding technique evidently increases the surface hardness of gear while the interior remains ductile, and enhances its wear resistance too.

Key words: Centrifugal compressor, Gear, Plasma nitriding, Wear resistance