Effect of TaC particles on the microstructure and oxidation behavior of NiCoCrAlYTa coating prepared by electrospark deposition on single crystal superalloy

Abstract

NiCoCrAlYTa/TaC metal matrix composite coatings were prepared on single crystal superalloy (SX) using electrospark deposition (ESD) to improve its high temperature performance. The effect of TaC addition on the coating microstructure, oxidation behavior, wear resistance and physical properties of electrode were investigated. The results showed that, with the addition of TaC particles, the density of electrode increased, while the thermal conductivity and thermal diffusivity decreased. In the electrode, TaC particles were distributed around or embedded into the NiCoCrAlYTa powders, while in ESD coatings, they were distributed homogeneously in both dendrite cores and interdendritic regions. The generation of β-NiAl phase in ESD coating was prevented by adding TaC particles. During 1000 °C/100 h oxidation, the mass gain of coating with TaC addition was lower than that without TaC addition during the first 40 h, and then became higher. The oxidative products were similar, except that θ-Al2O3 was relatively more in coating without TaC, while Y3Al5O12 was more in coating with TaC addition. The microhardness and wear resistance in both coatings decreased after oxidation, however, it was on the same level for NiCoCrAlYTa coating before oxidation and NiCoCrAlYTa/TaC coating after oxidation. Thus, the overall high temperature performance of the coatings was improved due to the addition of TaC particles.