Autogenous electrospark deposition of NiCoCrAlY

Abstract

Electrospark deposition is a microarc welding process that has been successfully used to deposit an autogenous ultrafine NiCoCrAlY coating. Primary solidification of the β phase shows epitaxial growth where orientation and heat flux coincide. Electron channelling contrast imaging of the deposits shows a homogeneous distribution of non-stoichiometric phases from the rapid solidification of the electrospark deposition process. Electron backscatter diffraction mapping of the deposit indicates that an ultrafine β structure can grow epitaxially where favourable conditions prevail. The equiaxed structure associated with the γ to β solidification shift was not observed and is believed to result from the homogeneous electrode and substrate compositions. Oxidation of the deposit shows advantageous alumina growth stemming from the ultrafine aluminium rich β phase. The transition from θ- to α-alumina was nearly complete in only 6 h at 1000°C in air.