| Stainless steel exhibits attractive properties as high tensile strength, good corrosion resistance, low yield point and excellent plastic and toughness. So, it was wide applications in the fields of auto parts, food industry, medical, chemical and ocean engineering etc. However, it has some disadvantages, such as low surface hardness, poor wear resistance and the cause of producing adhesive wear on the friction pair. That blocks its way to further application. Surface engineering technology is the most direct and effective way to improve the wear resistance. Nowadays, there are a variety of methods to improve the wear resistance of stainless steel, and double glow plasma surface alloying (DG-PSA) technology is widely used in surface modification of stainless steel for the advantages of wide choice of alloying elements, process simple and can be easily controlled, high diffusion speed, energy conservation and environmental safety etc.In this paper,304stainless steel were treated with Mo alloying and nitriding after Mo alloying using DG-PSA technology. Some well-performance alloying layers were prepared on the surface of stainless steel. Through the analyses of cross-section morphology, phase structure, composition distribution, micro-hardness, friction and wear properties and the diffusion process of Mo atom, we can draw the following conclusions:1. Mo alloying layer(1) Under different treatment conditions, the Mo alloying layers mainly consist of Mo phase and the maximum thickness of the layer is9.6μm. The maximum micro-hardness of the alloying layer is806HV0.05, which is3.6times higher than that of substrate. The micro-hardness gradually increase with the prolonging of processing time and processing temperature. The increase of surface micro-hardness can be attributed to solid solution strengthening mechanism.(2) The maximum diffusion coefficient of each treatment time is not in the substrate surface where the concentration of Mo element is highest. The mean diffusion coefficient is negatively correlated with treatment time. With the increase of treatment time, the ion bombardment effect on the diffusion of Mo atoms decrease gradually. The diffusion mechanism of Mo atoms in304substrate is vacancy diffusion.(3) Under dry friction conditions, the friction coefficients of different processing time and processing temperature were increase than that of substrate, but the change range of friction coefficients were decreased. The sample that treated at1000℃for60min show the best wear resistance, and the specific wear rate is only1/61of the substrate. The wear mechanism of304substrate is mainly adhesive wear and abrasive wear. The wear mechanism of alloying sample is abrasive wear, accompanying with adhesive wear.(4) Scratch test show that the flake phenomenon did not occur in the internal and edge of scratch, which indicate that the alloying layers have relative high bonding strength with substrate.2. Nitriding after Mo alloying layer(1) The layer of nitriding after Mo alloying is homogeneous and compact. The thickness of alloying layer is about9.5μm and doesn’t increase than the Mo alloying layer. The modified layer show two-layer structure. The outermost layer is the nitride layer and the thickness of nitride layer is0.5μm, and the sub-surface layer is Mo alloying layer. Mo alloy layer and the substrate present an excellent metallurgical bond with high bonding strength. The layer mainly consist of Mo, MoN and Mo2N, and the diffraction peaks of MoN and Mo2N are weaken than that of Mo. The micro-hardness of the layer is921HV0.05, which is higher than the Mo alloying sample.(2) Compared with the Mo alloying sample, nitriding after Mo alloying sample not only has a relative low friction coefficient, but show a relative low specific wear rate. And the specific wear rate is only1/85of substrate. The wear mechanism of nitriding after Mo alloying sample is abrasive wear, accompanying with micro-cutting wear. |
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