Experimental Research On The Surface Residual Stresses After Grinding For Nanostructured WC/12Co Coatings

Nanostructured ceramic coatings is a novel class of engineering material in recent years, its fine properties make it have very extensive application perspective in industry.Grinding with diamond wheel is the main machining method of nanostructured ceramic coatings (WC/12Co). Surface residual stresses emerges during the grinding process. It is the surface residual stresses that cause the cracks.Based on the literature reviews, the thesis firstly gives preliminary analysis for the formation of residual stresses in the ground surface of nanostructured ceramic coatings after precision grinding. It discusses the effects of surface residual stresses on the parts's ground strength, surface hardness, fatigue strength, broken strength, corrosion strength as well as wear resistance, it also sets forth grinding mechanism for ceramic work pieces based on "indentation fracture mechanics model" and "cutting machining model". It points out that the formating mechanism of surface residual stresses is the synthetic actions on machining stresses including squeezing stresses and cutting stresses and thermally stresses. Compared with all kinds of measurement methods, X-ray diffraction method is decided to measure the residual stresses in this experiment.The paper specifically focuses on grinding surface residual stresses in the thermally sprayed nanostructed WC/12Co coatings on low carbon steel substrates. The influence of grinding parameters, such as depth of cut (DOC), workpiece feedrate, abrasive grit size and wheel bond type, on surface residual stresses after precision grinding is studied. The limitations of X-ray diffractometry for residual stresses measurements are discussed. It turns out that the surface residual stresses σ₀ caused by thermal sprayed are strenth stresses, while the whole residual stresses σ caused by precision grinding process are compress stresses. Surface residual compress stresses are raised with increasing of both grinding depth and feedrate and with decreasing of grits size despite of the direction of parallel or vertical grinding line. The surface residual stresses are larger led by resinoid bond wheels than those led by vitrified bond wheels under the condition of the same grits size.