Abstract
A compositionally complex alloy (CCA) was developed in powder form and applied as a coating onto a carbon steels substrate by using thermal spray. The purpose of this study was to investigate the effect of microstructural modification induced by using two different powder production methods, mechanical alloying and gas atomisation, onto the corrosion resistance of the coatings for a CoCrFeMo0.85Ni composition. The evolution of microstructure from powders to coatings was analysed using scanning electron microscopy coupled with energy-dispersive spectroscopy and X-ray diffraction. In order to evaluate the corrosion performance of the coatings, electrochemical corrosion tests were performed in a 3.5 wt % NaCl solution at pH = 4. The study demonstrates that the powder production method has a significant influence on the phase composition and, in turn, corrosion behaviour of the resulting coating, with the gas atomising route imparting better corrosion resistance properties. Nevertheless, the appearance of the face-centered cubic (FCC) phase characteristic of the CoCrFeMo0.85Ni alloy within the coating produced from the mechanically alloyed powder, opens the possibility for this powder manufacturing technique to effectively produce compositionally complex alloys.
Highlights
Complex alloys (CCAs, referred to as high entropy alloys in literature) are multicomponent equi- or near-equiatomic alloys which form mostly solid solutions including random solid solutions and partially ordered ones
The powder-to-coating phase evolution and its influence on the corrosion properties of a compositionally complex alloy (CCA) of the composition CoCrFeMo0.85 Ni has been assessed by means of scanning electron microscopy-electron dispersive X-ray spectroscopy (SEM-energy-dispersive X-ray spectroscopy (EDX)), X-ray diffraction (XRD) and linear polarisation resistance (LPR)
For the same CCA composition, the powder manufacturing process has a significant influence on the microstructure of the final coating, even when manufactured using the same deposition conditions
Summary
Complex alloys (CCAs, referred to as high entropy alloys in literature) are multicomponent equi- or near-equiatomic alloys which form mostly solid solutions including random solid solutions and partially ordered ones. Depending on the property required, e.g. hardness, corrosion resistance, etc., a particular phase in the multiphase alloy is targeted for a specific application [1,2,3]. Solid state processing via mechanical alloying of powder and subsequent consolidation may present a more viable manufacturing route. The requirement for near-equiatomic mixtures can lead to potentially high cost, if more exotic or costly elements are required. Deposition of CCAs as a coating onto an inexpensive substrate may provide a low-cost means of exploiting advantageous materials properties
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