Effects of deposition temperature on the kinetics growth and protective properties of aluminide coatings

Abstract

Chemical vapor aluminizing is a major production technique used for producing aluminide coatings on gas turbine blades to form dense and adhesive alumina surface layers and further prolong their service lives at high temperature. A chemical vapor deposited aluminizing process had been employed to deposit nickel aluminide coatings under the different deposition temperature. The phase structure, morphology, chemical composition, kinetics growth mechanism and oxidation/corrosion behavior of the aluminide coatings were studied in detail. The results show that the phase structure, microstructure and composition of the aluminide coatings are strongly influenced by the deposition temperature during chemical vapor deposition (CVD). The higher is the deposition temperature, the easier is the formation of pure β-NiAl phase. Along with the increment of the deposition temperature, the coatings’ surface will become smooth and dense, while the ridges along grain boundaries can be simultaneously approach to flat in a certain extend. Large numbers of elements of Cr, Mo and W within diffusion zone that could probably form a thin film layer, which is usually so-called as diffusion barrier. The key step of growth of coating grain is the formation of a volatile aluminium subhalide by controlling of the suitable deposition temperature during CVD. Based on the results of isothermal oxidation and hot corrosion kinetics curves, the best deposition parameter can be gained among the four coatings when the deposition temperature is adopted to be 1323K.