Characterization Studies of Slurry-Sprayed Mullite–Nickel Coatings on ASTM 1018 Steel

Abstract

Slurry spray technique (SST) is a simplistic deposition technique which could easily be contrived to the choice of material for appropriate functionality. With the continual technological progress and manufacturing efficiency, the appropriacy of SST needs to be expanded to meet the growing demand for surface engineering. Functionally graded mullite–nickel $$(\hbox {3Al}_{2}\hbox {O}_{3}\cdot \hbox {2SiO}_{2}\hbox {-Ni})$$ -based environmental barrier coatings were slurry sprayed on ASTM 1018 steel. This study reports the findings pertaining to the fundamental mechanical, thermal, corrosion and microstructural investigations performed to evaluate and ascertain the utility of the coatings produced by SST. Sound and resilient coatings with density in the range 1238– $$5320\hbox { kg/m}^{3}$$ and coating thickness in the range of 99– $$380\,\upmu \hbox {m}$$ were attained at distinct processing parameters. Within the experimental design space, a maximum adhesion strength value of 18.15 MPa was measured during tensile adhesion test. The developed coatings with microhardness up to $$204.2\hbox { HV}_{0.1}$$ , exhibit the surface roughness value ranged from 3.27 to $$7.98\,\upmu \hbox {m}$$ (Ra) and the porosity with an overall mean value of 9.9% by volume. During the thermal cycling testing, the majority of the specimens did survive up to 30 thermal cycles, which encapsulate acceptable thermal shock resistance of the coatings. The corrosion studies of the mullite–nickel coatings performed by immersion test in $$0.5\hbox {M Na}_{2}\hbox {SO}_{4}$$ proclaimed a decent corrosion rate of 5.217 mpy. The microstructural studies supported by SEM/EDS and XRD demonstrate as-sprayed splat morphology and the continuous interface and suggest a good adherence of the coatings fabricated wielding SST.