Behaviour of NiAl APS-coatings in chlorine-containing atmospheres

摘要

Due to their thermal expansion coefficient being close to those of ferritic steels, NiAl atmospheric plasma spraying (APS)-coatings have been chosen to be tested in chloridizing atmosphere. A new type of quasi-stability diagram which couples thermodynamic and kinetic approaches was developed to define the stability domains of the pure metals aluminium and nickel in dynamic chlorine- and oxygen-containing atmospheres. NiAl APS-coatings (300 mm) with low porosity on steels were applied and tested in an atmosphere containing 0.2 v/o chlorine and 3 ppm oxygen. After 280 h of exposure one quarter of the outer coating was transformed into a protective alumina layer. Much nickel depletion, due to the evaporation of nickel chlorides, was observed.