1983 Volume 69 Issue 8 Pages 1014-1021
Pack cementation process has been applied for aluminide and platinum-aluminide coating on a nickel-base superalloy IN-738LC. Burner rig test using light oil containing 0.33%S was carried out for the evaluation of hot corrosion resistance.
Aluminide coatings have two coating layers. The outer layer is high-Al NiAl and the inner layer consists mainly of low-Al NiAl. Hot corrosion resistance of the aluminide coatings can be improved by increasing the thickness of the outer layer.
In the burner rig tests at 850°C or below, the aluminide coatings whose outer layer thicknesses are about 80μ are more hot corrosion resistant than the platinum-aluminide coatings made by electroplating of platinum of 7μ thickness and aluminizing at 1120°C. This difference is attributed to the preferential attack of the PtAl2 dispersed in the outer layer of the platinum-aluminide coatings.
In the burner rig test at about 1000°C, the platinum-aluminide coatings are more hot corrosion resistant than the aluminide coatings, because of dissolution of the undesirable PtAl2 particles into the matrix and the increased Pt concentration in the coating layer, both due to the rapid diffusion of atoms at the high temperature.