Surface formation and crack damage in grinding of alumina ceramic insulation coating

Abstract

The surface morphology and subsurface crack damage of alumina ceramic coatings were observed under different grinding process parameters. Micro–macro simulations were used to analyze the mechanisms underlying surface formation and crack damage. The results showed that the surface morphology after grinding consisted of fragmented pits, brittle fractures, lamellar spalling, pores, ductile surfaces, and plowing marks. Both ductile and brittle removal processes occurred during grinding, with the ductile removal reaching a maximum rate of 59.22 % during the experiment. Brittle removal primarily occurred at the pores and end of the cutting arc of abrasive grains. In addition, alternating tensile and compressive stresses caused by squeezing and friction of the rounded cutting edge led to the formation of powdery chips on the machined surface. The transformations between tensile and compressive stresses as well as the rebound effects in the grinding contact arc zone resulted in transverse propagation cracks in the alumina coating. The greater the grinding force, the more severe the transverse crack damage. Three types of transverse cracks were observed in the cross-section of the alumina coating. The first type originated from surface pit defects, initially propagating downward and then extending along the grinding direction to form transverse cracks. The second type started at the interface between the bond coat and alumina coat, particularly at the convex peak of the bond coat. The third type initiated at the pores near the middle of the alumina coating and then propagated to both sides, forming transverse cracks.