Microstructure of first-stage aluminized coating on a Ni–Cr alloy

First-stage aluminized coating on pure Ni–Cr alloy are prepared by pack cementation aluminizing method at 750 °C. The microstructures were analyzed with scanning electron microscope, transmission electron microscopy and electron probe micro-analyzer. The coating consists of several layers which, in sequence from substrate to coating surface, are substrate γ, polygonized γ, γ′-Ni3Al, β-NiAl+α-Cr, δ-Ni2Al3, and δ-Ni2Al3+Cr5Al8 layers. A high compositional gradient is present across these interfaces together with a high density of dislocations. No crystallographic relationship was found at the γ/γ′, γ′/β and β/δ interfaces. The γ′ and β+α layers consist of very fine grains with some scattered amorphous regions.