Study Of The Microstructure And Properties Of HVOF Spraying Fe-Based Coating Based On Orthogonal Test

In this paper Fe based alloy coating was prepared by HVOF. There are many factors that affect the properties of the coating, among which kerosene oil flow rate, oxygen flow rate and standoff were the main factors. Orthogonal test was carried out based on the three main factors with three levels. Orthogonal analysis was applied in which microhardness, porosity, metallurgical structure and combination property were taken as the objects .Then the optimized parameters were got. When oxygen flow rate was 944L/min, kerosene oil flow rate was 28 L/h and standoff was 330mm the coating had the best properties.Morphology and phase composition of the coating were attentively studied by means of metallographic microscopy, scanning electron microscopy(SEM), transmission electron microscope(TEM) and X-ray diffraction(XRD).The study showed that the coating was composed of deformed strip shaped particles, un-melted particles and some pores. Also, SEM was used to study the atom diffusion along interface. It was found that the substrate and the coating were well bonded. It was mainly mechanical bonding and partly metallurgical bonding. Amorphous was formed in the coating because of high cooling rate of spraying particles. Part of amorphous transformed into nano-crystalline because of the heat of the following layer. The coating was composed of amorphous, nano-crystalline and boride. The mechanics of formation of amorphous and nano-crystalline was analyzed as well as the reason leading to the pores. For optimized parameter coating, micro-hardness of the coating was four times that of the substrate and the micro-hardness parallel to the binding site was nearly the same as that vertical to the bingding site. Micro-hardness of the substrate near the coating was a little higher than that far from coating layer. It was due to the work-hardening and the formation of the twin crystals as well as part of metallurgical bonding. The corrosion resistance of coating and substrate was checked by salt spray test. The corrosion type for the coating was pitting corrosion. The corrosion resistance of the coating with optimized parameters was better than both substrate and coating with higher porosity. All these analysis indicated that by HVOF technique the coating with high micro-hardness, density and goodcorrosion resistance with the optimized parameters can be got.