Influence of the thermal-spray procedure on the properties of a CoNiCrAlY coating

A CoNiCrAlY coating was thermal-spray projected using different procedures (plasma, HVOF and HFPD) onto stainless steel specimens. Thermal fatigue tests were conducted in an experimental combustion chamber under a similar atmosphere to power plant service conditions.The microstructure of the coatings depend on the projection method. The oxide content depends on both the maximum temperature attained and the interaction time between powders and air that occurs during the spraying. Porosity is also related to the spraying procedure by way of the particle size, average temperature and velocity attained by the particles when they impact with the cold substrate.The substrate-coating adherence of plasma and HVOF procedures are very high and are not significantly affected by thermal fatigue. On the contrary, the adherence of HFPD spraying is significantly lower, as well as being reduced by thermal fatigue.