Mechanical Properties of Overaluminized MCrAlY Coatings at Room Temperature

Abstract

The objective of this study is to compare the mechanical properties of overaluminized MCrAlY coatings sprayed by a vacuum plasma spraying process for the protection against high-temperature corrosion and oxidation in the field of gas turbine components. Recently, the overaluminized MCrAlY coatings are used for improving further the high-temperature oxidation resistance. However, the mechanical properties of aluminized MCrAlY coatings, which have an important effect on coating lives, have not been clarified. Five kind of freestanding MCrAlY specimens (CoCrAlY, CoNiCrAlY, CoNiCrAlY+Ta, NiCrAlY, NiCoCrAlY) were machined from the thick vacuum plasma sprayed (VPS) coatings. And, the heat-treated MCrAlY specimens (1393 K, 2 h, argon cooled and 1116 K, 24 h, argon cooled) and the overaluminized specimens (Al-Cr-Al2O3-NH4Cl pack, 1173–1273 K, 10 h) after the heat-treatment were used. The experimental results suggested that the volume fraction of precipitated aluminum compounds in the VPS MCrAlY coatings and the residual stress induced by the overaluminizing treatment had important effects on the mechanical properties. The Vickers hardness and Young’s modulus of the overaluminized MCrAlY coatings showed higher values in comparison with the VPS MCrAlY coatings. There was a tendency that the bend strength of overaluminized VPS MCrAlY coatings decreased by the aluminizing treatment and also with increasing volume fraction of precipitated aluminum compounds in the VPS MCrAlY coatings. It was also confirmed that the bend strength of aluminized layers themselves was reduced with increasing volume fraction of precipitated aluminum compounds in the VPS MCrAlY coatings. These tendencies were caused by the enrichment of brittle precipitates, such as NiAl and/or CoAl intermetallic compounds.