Research On Microstructures And Tribological Properties Of Composite Sulfurizing Layers

Wear is caused by friction, which is a common phenomenon in various fields. The tremendous economic losses have been resulted in by the wear, therefore it is a world wide difficult problem that applying tribological theories reduces the losses caused by wear. Kinds of methods have been studied to improve the wear resistance of the frictional pairs, including surface modification, microstructure improvement, antifriction materials and wear resistant materials application, liquid and solid lubrication. The solid lubrication materials have been utilized extensively due to its suitability for many harsh conditions, such as high temperature, high load, ultra-low temperature, ultra-high vacuum, and intense radiation.In this dissertation, the technology of low temperature ion sulfurizing was developed. Several kinds of advanced and practical composite solid lubrication layers were prepared. For example, high velocity electric arc spraying + low temperature ion sulfuration, supersonic velocity plasma spraying + low temperature ion sulfuration, metal inert-gas arc welding + low temperature ion sulfuration were utilized to prepare four kinds of solid lubrication coatings containing composite 3Cr13/FeS layer, composite FeCrBSi/FeS layer, composite Zn/ZnS layer and composite sulfurized surfacing layer. Scanning electron telescope(SEM) was used to observe the morphologies of surface, cross-section and wear scars of the coatings, X-ray Diffraction(XRD) was employed to analyze the phase structures, X-ray stress determinator was used to measure the residual stress within the coatings, the nano-hardness and nano elastic modulus were surveyed by the nano-indentation tester. The tribological properties of the coatings were investigated on T-11 ball-on-disk friction and wear tester under dry friction and oil lubrication respectively.The experimental results show that the bonding strength between the five kinds of solid lubrication coatings and the substrates are very well, the mechanical performance of the coatings are excellent. The composite 3Cr13/FeS layer, composite FeCrBSi/FeS layer, and composite sulfurized surfacing layer all have better tribological properties under dry friction and oil lubrication conditions, the composite Zn/ZnS layer has great antifriction and wear resistance properties only under dry friction condition.FeS and ZnS all possess the close-packed hexagonal lattice structure, with low shearing force, slippage happens easily along the close-packed plane, so the frictional coefficient is very low. They are excellent solid lubricants. With the coactions of the sulfide solid lubrication layer as well as the spraying coatings or surfacing layer which possess antifriction and wear-resisting properties, the composite sulfurzing layers show eminent tribological properties superior to those of single spraying coating, surfacing layer and sulfurizing layer.The theoretical research of the composite sulfide solid lubrication coating demonstrated that they can play an important role in energy-saving and environment-protecting, so they have a brilliant prospect.