Mechanical Properties of Aluminized MCrAlY Alloy Coatings

Abstract

A low-pressure-plasma spray (LPPS) process is used to overlay coatings of MCrAlY alloy for protection against high temperature corrosion and oxidation. This coating process has been found to be very effective for gas turbine components. On the other hand, diffusion coating processes have been applied for many years to improve similarly the environmental resistance by enriching the surface of a substrate with Cr, Al, or Si. Recently, aluminizing on the MCrAlY coatings is used for improving further the high temperature oxidation resistance. However, the mechanical properties of aluminized MCrAlY coating, which have an important effect on coating life, have not always been clarified. In this study, five kinds of free-standing MCrAlY specimens (CoCrAlY, CoNiCrAlY, CoNiCrAlY+Ta, NiCrAlY, NiCoCrAlY) were machined from the thick LPPS coatings. And, the heat treated MCrAlY specimens (1393K, 2h, Ar atmosphere) and the aluminized specimens (Al-Cr-Al₂O₃-NH₄Cl pack, 1173K-1273K, 10h) after heat treatment were used in the experiments. The Vicker's hardness, Young's modulus, Poisson's ratio and four point bending strength of the aluminized MCrAlY coatings were measured at room temperature in comparison with the MCrAlY substrates. The experimental results suggest that the volume percentage of precipitated aluminum compound in the MCrAlY coatings and the residual stress induced by the aluminizing have an important effect on the bending strength. Namely, there is a tendency that the bending strength decreases by the aluminizing and also with increasing the volume percentage of aluminum compound. The Vickers hardness and Young's modulus of the aluminized layers show higher values in comparison with the MCrAlY coatings.