High velocity oxy-fuel spraying of a NiCoCrAlY and an intermetallic NiAlTaCr alloy

The high velocity oxy-fuel (HVOF) spray systems of the third generation can be used to process some oxidation sensitive materials such as MCrAlYs, due to possible lower melting degrees and higher kinetic energies of the powder particles. In the study presented here, a NiCoCrAlY and an intermetallic NiAlTaCr were sprayed using the HVOF process. The influence of the spray parameters on the oxidation during spraying was investigated. Both the O/H ratio and the spray distance could significantly influence the oxygen content of the coatings. Coatings containing low oxygen contents were developed. The microstructures of the coatings were studied in as-sprayed as well as heat-treated states. The NiCoCrAlY coating showed a homogeneous two-phase structure after the heat-treatment. The NiAlTaCr coating consisted of the intermetallic NiAl phase and an intermetallic phase of Ta, Ni, Al and Cr. The high temperature oxidation behaviour of the coatings was also tested. The oxide scales on the NiCoCrAlY and NiAlTaCr coatings formed at 1100°C consisted mainly of Al2O3. Traces of some intermetallic phase components could be detected in the oxide scale on the NiAlTaCr coating after 100 h oxidation.