Electron probe microanalysis of ball-bearing steel powder obtained using the method of electroerosion dispersion in kerosene
The results of electron probe microanalysis of powder obtained using the method of electroerosion dispersion of ball-bearing steel scrap have been provided. It has been determined that the main elements of powder obtained using the method of electroerosion dispersion of ball-bearing steel scrap in water are ferrum, oxygen, carbon, silicon, molybdenum, and chrome.
The influence of bearing geometry on the residual stress state in cold drawn wire, analysed by the FEM
Abstract Finite element simulations have been performed in order to study the influence of bearing geometry on the residual stress-state in cold drawn wires. Experiments in full industrial scale have been performed in order to verify the FEM results. The residual stresses were measured with X-ray diffraction in both the axial and tangential direction. The material used was a high carbon steel for roller bearings, 100Cr6. It was found that the geometry of the bearing has a large influence of the residual stress-state. When the bearing is somewhat tapered, a gap in the beginning of the bearing is formed. This “double contact” reduces the axial and tangential residual stress to minimum or even to a compressive state. A cylindrical bearing gave no contact in the bearing at all due to elastic deformation. This resulted in a large axial and tangential residual stress. It was shown that even a small divergence from the desired bearing geometry due to the grinding of the die could affect the residual stress immensely.
Influence of residual stresses on fracture and delamination of thin hard coatings
The risk of fracture and delamination of residually stressed coating systems is examined. Stress concentrations are generated at the interface of coated systems where the substrate deviates from being perfectly smooth, flat and infinitely large. Using finite element calculations, such stresses induced at pores, edges or scratches are analysed for a number of representative coating/substrate systems. The effect of the interface topography, coating thickness and elastic mismatch on the interfacial stresses are investigated. Generally, thin coatings compared to the interface topography are less sensitive to residual stress induced failure. At a critical coating thickness, normal stress across the interface of a magnitude comparable to that of the residual stress level is induced, which may initiate coating delamination. The interface stress state becomes independent of the coating thickness if the coating is thicker than about three times the amplitude of the interface roughness. The interface stress scales approximately linearly with the maximum inclination of the surface profile. It is demonstrated experimentally that the high residual stress in ceramic coatings may cause local coating fracture and delamination at, e.g., the tip of an edge or at rough substrate surfaces when the coating is thick relative to the edge radius or the surface topography, respectively.