Investigating the microstructural effect of chromium addition by two methods of electroplating and powder chromizing to silicon-aluminide infiltrating coating

In this article, the microstructural characteristics of silicon-aluminide coatings with and without chromium applied on the Rene-80 nickel base superalloy substrate are presented and analyzed. To add chromium to the aluminide coating, enriching the surface layer of the alloy with chromium was carried out in two ways: (1) chrome plating and (2) pack cementation chromizing. Besides, the diffusion annealing of the plated chromium layer was also carried out with the aim of increasing the depth of the chromium-rich layer. SEM, EDS and XRD methods were used to characterize the coatings, including the quantity and quality of the coating layers, microstructural characteristics and elemental and phase composition. Investigations showed that the addition of chromium to the silicon-aluminide coating causes the presence of chromium in the upper part in the form of chromium silicide precipitates. The silicon precipitates in the upper part of the aluminide coatings is in the form of deposits of refractory elements, and the silicide chrome precipitates is formed more than other precipitates. In order to provide resistance to hot corrosion, at least 8% by weight of chromium and 10-13% by weight of silicon are required in the upper layer of the coating. The amount of chromium and silicon elements in the upper part of both CrSiAl-P and CrSiAl-E coatings was relatively similar and in the range of 12-14 and 13-14% by weight, respectively. Of course, the observations indicated that added chromium in both types of coating contributes to the formation of chromium-rich deposits, but more in the lower areas of the coating.