Effect of thermal spraying of different ceramic coatings on rotational fatigue life of AISI 1020 alloy

The effect of thermal coating of AISI 1020 alloy substrate on the fatigue life during rotation was studied in comparison with the fatigue strength of the substrate. A rotating fatigue tester (HSM 19) was used to test the specimens at room temperature. Fatigue tests were carried out at various stress levels to obtain S-N curves. Two coatings were applied to the AISI 1020 steel alloy using thermal spraying method: a NiAlCrSi bonding coating and a thermal barrier coating based on an alloy (Al2O3+MgO). The microstructure and phase composition of the coatings were investigated using SEM and XRD methods. Compositional analysis revealed the presence of numerous precipitates and primary phases, including Al2O3, Cr2O3, and CrNiO4, nickel or chromium secondary phases, as well as different oxides like CrMgO4. The morphological results also show that the coating was quite heterogeneous, with a significant concentration of oxide inclusions, pores and microcracks. The fatigue strength results show that all coated alloys have reduced strength compared with the uncoated base alloy, which gradually decreases with increasing loads applied to them. It was also discovered that the alloy A4, which contains a high weight fraction of Al2O3, was closest to the base alloy and showed the greatest improvement in fatigue compared to the other alloys.