Characterization, growth kinetics and formation mechanism of aluminide coating by plasma paste aluminizing on IN738

Abstract In this research, with the single-step plasma paste aluminizing technique which has been considered in recent years, aluminizing of a Ni-base superalloy (IN738) was performed at 600, 700 and 800 °C for 0.5, 1, 2 and 4 h. The paste was composed of pure Al powder and ethanol. FE-SEM analysis showed that a multi-layer aluminide coating was formed on the IN738 samples. The outer layer of the coatings consisted of Al3Ni2, ζ-phase in Al–Ni–Cr system and Ni0.35Al0.3Ti0.35 in the sample aluminized at 600 and 700 °C for 2 h, and Al0.96Ni1.04, Al3Ni2, Al8Cr5 and Ni0.35Al0.3Ti0.35 in the sample aluminized at 800 °C for 2 h. Moreover, in the outer layer in addition to enriching each of the aluminide phases, morphological evolution from an interconnected structure to an island-like structure and eventually to an equiaxed grain structure happened with the increase of aluminizing temperature. The growth kinetic of aluminide coating in plasma paste aluminizing obeyed a parabolic law and the growth activation energy was calculated as low as about 83 kJ/mol. Enhanced diffusion in this aluminizing process can be related to the presence of liquid-state diffusion in early stages and the effect of plasma radiation on solid-state diffusion in later stages.