NiCoCrAlYTa coatings on nickel-base superalloy substrate: Deposition by high velocity oxy-fuel spraying as well as investigation of mechanical properties and wear resistance in relation to heat-treatment duration

Abstract

NiCoCrAlYTa coating, a metal-based coating, was prepared on Inconel 718 Ni-base superalloy substrate by high velocity oxy-fuel (HVOF) spraying. The as-polished NiCoCrAlYTa coating was heated at 1000 °C for different durations to afford coatings C1, C2, C3, and C4. The microstructure, element distribution, phase composition and crystalline structure of the as-deposited coating and heat-treated ones were analyzed by transmission electron microscopy, scanning electron microscopy-energy dispersive spectrometry, X-ray diffraction and electron back-scattered diffraction. Moreover, the oxidation behavior of the NiCoCrAlYTa coatings was evaluated based on isothermal oxidation kinetics as well as weight loss measurements; and the effects of surface oxide layers on the microstructure, mechanical properties as well as friction and wear behavior of the NiCoCrAlYTa coatings were investigated. Results show that the as-sprayed coating exhibits dense and uniform microstructure as well as excellent oxidation resistance. Oxide layers, mainly composed of Al2O3, Cr2O3, NiO, Y2O3, Ta2O5, NiCr2O4, and CoCr2O4, are formed on the surface of the coating upon heat-treatment in air; and the microstructure and mechanical properties of the NiCoCrAlYTa coatings as well as oxide layers are governed by heat-treatment time. Particularly, coating C3, obtained after heat-treatment of the as-polished NiCoCrAlYTa coating at 1000 °C for 50 h, exhibits greatly increased indentation hardness, elastic modulus, and wear resistance. This is because the joint functions of a compact and continuous surface oxide layer with gradient nanostructure formed after heat-treatment, and the amorphous protective layer generated on the rubbed surface of coating C3.