Rotational fatigue behavior of AISI 416 stainless steel coated with different ceramic powders using flame thermal spraying technology

This research aims to study rotating fatigue behavior of stainless-steel alloy (AISI 416) thermally coated with ceramic powders and compare it with uncoated base alloy. To evaluate fatigue life of these alloys, a rotating fatigue device of type (HSM 19) was used to evaluate all tests. Rotational fatigue test was conducted under normal conditions, where generated stresses by applying weights (15, 20, 25, 30 N) were calculated, then number of cycles until failure of each sample was recorded to obtain (S - N) curves. Microstructure and phases of coating were studied using scanning electron microscope (SEM) and X-ray diffraction (XRD) techniques. Microstructure showed that surface layer of coating many strong precipitates and phases such as (Al2O3) and (CoSiO3) in addition to some secondary precipitates such as (Cr2O3) and (Cr2NiO4) resultants of interaction between coating components and base alloy at high temperatures during coating and heat treatment. Microscopic examination also showed that most thermal coatings were heterogeneous , free of defects and microscopic cracks with some pores in few parts of coating layer. Results of cyclic fatigue test also showed that number of cycles to failure gradually decreased with increasing stress applied to most samples, as all tested coatings reduced fatigue life of coated alloys except for coated alloy (A2) which consists of (COCrAlSi 25% w.t + Ni2O3 56.25% w.t + Al2O3 18.75% w.t), as this alloy showed a significant improvement in fatigue resistance .