چكيده به لاتين
In the present research, the effect of behavior of carbide-forming elements of chromium and vanadium in the bath on the formation of dual-carbide coating, H13 sample was investigated. Regarding the limited research on the event inside the molten salt bath and its relationship with the growth of carbide coatings due to the high temperature, there are many ambiguities and lack of evidence in this field. This method can be widely used for other diffusion process if the exact mechanism in the bath is understood. Field emission scanning electron microscopy (FE-SEM), electron probe micro analyzer (EPMA) and X-ray diffraction analysis (XRD) were applied to study the coatings and the rapidly quenched baths.
After 8 hours of coating at 1000 ˚C, the thickness of the carbide coating layer was 6.5 ± 0.5, 5.2 ± 0.5, or 5.7 ± 0.5 μm depending on whether it was deposited in a metal, oxide, or metal/oxide bath, respectively. The phase distribution of vanadium-rich regions was 63%, 57%, and 74% of the total coating deposited in metal, oxide, and metal/oxide baths, respectively. Results showed that suspended metalic particles distributed all over the metal and oxide baths (resulted from reduction in oxide powders), had a significant role in the formation of carbide coatings on the substrate.
In the study of H13 samples in both metal and oxide baths, before 1 h and between 1 h to 12 h of the coating process, the interface and the diffusion controlled the growth, respectively. Regarding this mechanism of growth, before 1 h, the relationship between coating thickness and time was fitted to a linear function (d=at+b) and from 1 h to 12 h, it was fitted to a parabolic function (d=ct0.5+e). The growth type of carbide layers with carbon diffusion had a high concordance with experimental results. In all three ratios, the thickness of produced carbide coating was higher in the metal bath than in the oxide bath. In chromium and vanadium dual coatings, chromium carbide-rich regions and vanadium carbide-rich regions grew as columnar and equiaxed grains, respectively. In metal and oxide baths with equal chromium to vanadium molar ratios, vanadium carbide-rich regions were produced more than chromium carbide-rich regions in the coating. Thermal Reactive Diffusion method can be used to produce composite coatings by molten salt bath.
