Fatigue behavior and deformation of thermally sprayed materials

This research investigates the fatigue behavior and deformation of thermally sprayed materials. Various materials science aspects were examined; including (i) the effect of surface preparation (grit blasting, shot peening) on the fatigue strength of the substrate materials and (ii) studying the effects of the coating on the fatigue strength and fracture mechanism of the substrate materials.; The specimens were made from three different materials Al 2024-T4, SAE 12L14 steel and superalloy (Inconel 600) in accordance to ASTM E466-82. These materials were selected on the basis of establishing how E influenced the fatigue life of a substrate/coating system. The HCF tests were performed at room temperature and 370°C (700°F) on specimens in the polished, grit blasted, and peened conditions to establish the base-level for the coated specimens.; The aluminum based alloy, steel and superalloy were coated with WC-based and YSZ materials using plasma and HVOF processes. The HCF tests were performed at room temperature and 370°C on the coated specimen and the results were statically analyzed. The fracture surfaces of the specimens were characterized using optical microscope (OM) and scanning electron microscope (SEM). Strain gauges were glued to the surface of the specimen to measure the strain, ϵ, and the stress-strain curve was determined.; The effect of grit blasting on the substrate materials was accomplished by carrying out HCF tests on specimens in the as-received and grit-blasted conditions. The specimens were of aluminum and steel so that the interaction of grit blasting with respect to the substrate elastic modulus could be investigated. The results, in common with the literature, indicate that grit blasting improves the fatigue strength of the substrate material. It was also concluded that grit blasting is more effective in increasing the relative fatigue strength of softer materials (aluminum) than harder materials (steel). The data collected from the fatigue tests were analyzed according to normal distributions and constitute the base-level results for the subsequent coatings work.; The effect of thermally sprayed coatings on the substrate material was examined by carrying out HCF tests on coated specimens. Results indicate that the zirconia coating only slightly influences the fatigue strength of the aluminum. However, the fatigue strength of aluminum and steel is significantly improved by the WC-Co (HVOF) coating. Furthermore, the WC-Co (HVOF) coating was much more effective in increasing the fatigue strength of the specimen compared to the plasma sprayed WC-Co. The results of superalloy (Inconel 600) material with a TBC indicate that the coating has a slight effect on the fatigue strength of the substrate. However, elevated temperature pre-exposure of TBCs in air causes an increase in the fatigue strength of the component.