Environmentally friendly high temperature high-activity (HTHA) and high
temperature low-activity (HTLA) CVD aluminizing processes were realized on
the Mar-M247 heat resistant superalloy substrate, that is widely used in the
hot part of aircraft engines. Additionally, commercially aluminide coatings
deposited in the above-the-pack aluminiznig process were analyzed.
Aluminizing of the Mar-M247 superalloy by the HTHA, HTLA and above-the-pack
processes led to formation of two layers of the coatings. The outer layer of
coatings formed by the above-the-pack process consisted of the ?-NiAl phase
with precipitates, while the outer layer of coatings formed by the HTHA and
HTLA processes consisted of the pure ?-NiAl phase. Aluminizing successfully
improved lifetime of Mar-M247 superalloy. Despite the fact that coatings
formed by the above-the-pack process is thicker and more aluminium
concentration was found than those formed by the HTLA aluminizing and
process, the lifetime of coated superalloy was lower. Moreover the oxidation
resistance of the coated superalloy in the HTLA aluminizing process was
better than those coated by the HTHA aluminizing process. The removal of
impurities in the HTLA aluminizing process ensured a ?pure? outer layer of
coatings. Clean aluminide coatings may create a purer alumina oxide and may
prolong its lifetime.