Search

For obtaining a thick ceramic coating with good film-forming and wear resistance, a new type of composite electrolyte was composed of sodium phosphate and sodium hexametaphosphate as the basic electrolytes, while sodium tungstate and sodium tetraborate were added as additives. In this composite electrolyte system, micro-arc oxidation treatment was performed on 1060 aluminum alloy. Using the coating thickness and surface porosity as optimization indicators, the electrolyte formula was optimized using the L9(34) orthogonal test. Meanwhile, the microstructure, surface porosity, phase composition, thickness, microhardness and wear resistance of ceramic coatings prepared under this electrolyte formula were studied systematically. Results showed that the ceramic coating prepared with a formula of Na3PO4 concentration of 32.0 g/L, Na2B4O7 concentration of 16.0 g/L, Na2WO4 concentration of 4.5 g/L and(NaPO3)6 concentration of 30.0 g/L had the structure with uniform micropores and dense film layer, the thickness of 22.8 μm, the porosity of 3.86%, and the microhardness of 475 HV. Furthermore, the wear resistance of the coating was significantly improved compared to the substrate, and the ceramic coating were mainly composed of γ-Al2O3 and a small amount of α-Al2O3 composition.

The mechanisms of ductile–brittle transition and surface/subsurface crack damage during the grinding of plasma–sprayed alumina ceramic coatings were investigated in an experiment and simulation on single diamond abrasive grain cutting. We observed that the brittle damage modes of alumina ceramic include boundary cracks, median cracks and lateral fractures. The normal force of the abrasive grain results in the initiation of median cracks, whereas the tangential force of the abrasive grain results in the propagation of median cracks in the direction of the abrasive grain cutting. Some cracks propagate downward to form machined surface cracks, whereas others propagate to the unmachined surface of the workpiece to produce brittle removal. Owing to the alternating tensile and compressive stresses, the material in contact with the top of the abrasive grain fractures continuously, forming the main morphology of the machined surface. The geometry and cutting depth of the abrasive grain have a significant influence on the ductile–brittle transition, whereas the cutting speed of the abrasive grain have no significant influence. On one hand, the stress concentration at the pore defects result in crack propagation to the deep layer; on the other hand, it reduces the local strength of the surface material, produces brittle fracturing, and interrupts crack propagation. The pores exposed on the machined surface and the broken morphology around them are important factors for reducing the surface roughness. Experimental observations show that the machined surface morphology of the alumina ceramic coating is composed of brittle fracturing, ductile cutting and plowing, cracks, original pores, and unmelted particles. [ABSTRACT FROM AUTHOR]