Effect of coating microstructure on the fatigue properties of steel thermally sprayed with Ni-based self-fluxing alloy

In order to investigate the factors that most strongly influence fatigue properties of steel thermally sprayed with Ni-based self-fluxing alloy, we prepared three types of thermally sprayed specimens which differed in heating time in the fusing process. Rotational bending fatigue tests were carried out, and coating microstructures were observed. The results show that fatigue properties of steel thermally sprayed with Ni-based self-fluxing alloy were affected by two factors. The first factor is the size and population of porosities in the coating. This factor was changed by fusing time with longer fusing times producing larger and more porosities. Because the fatigue crack initiates at the porosities, specimens fused for longer time exhibit lower fatigue strength. The second factor is lowered hardness of Ni matrix accompanying chromium segregation. The sprayed specimens fused for longer time exhibit lower fatigue strength, because the longer fusing process induces segregation of the chromium compound in the coated microstructures. Therefore, performing the fusion for a shorter time is effective for producing sprayed materials of enhanced fatigue properties.