Abstract
Fatigue behavior and Young’s modulus of plasma sprayed gray alumina on low-carbon steel substrates were investigated. The investigation of the properties of composite material “coating-substrate” included the measurements of microhardness profile, residual stress on the top of the coating and residual stress profile in substrate. Fatigue samples were periodically loaded as a cantilever beam on a special testing machine. Failed samples were observed in SEM to determine failure processes in the coating. The Young’s modulus of the coating was measured by the four-point bending method. Samples were tested both in tension and compression at low (300 N) and high (800 N) loads. Our experiments revealed that the average fatigue lives of coated specimens were nearly 2 times longer than those of the uncoated specimens. The Young’s modulus of the coating varied between 27 and 53 GPa with an average value of 43 GPa. Loading in tension caused decrease in Young’s modulus of the coating while loading in compression lead to increase in Young’s modulus. Increase in the lifetime of coated samples was likely due to compressive residual stresses in the substrate, originating from the spray process. Failure of the coating consisted of several processes, among which the most important are splat cracking, splat debonding and coalescence of cracks through the voids in the coating.
