Fabrication of Ni–Al composite coating on stainless steel using hybrid gas-phase coating technique and its corrosion study

Abstract

Working in high-concentration acidic environments is required in some important applications. One of the most important determinants of using stainless steel is the breakage when working at high acidic concentrations, where failure can occur by a mechanism similar to chloride attack that leads to stress corrosion cracking. On the other hand, superalloys containing nickel are chosen to be used in certain applications because of their good surface stability, corrosion resistance, and oxidation resistance. In this work, a composite coating based on Ni–Al phases was performed by using a hybrid gas-phase coating technique on the surface of 316 austenitic stainless steels. The deposition temperatures were ranging from Td = 650–950 °C, where the Ni–Al-based vapors was obtained in an evacuated chamber by using pure metal powders in such system. The structural characterization for the deposited Ni–Al coating was performed by using XRD technique and the scanning electron microscopy. The scratch test was performed to determine the thin-film adhesion with the substrate by a diamond indenter that was drawn across the coated surface under a specific load. Electrochemical corrosion tests have been performed to obtain the anodic polarization curves for the base metal and the coated surfaces. From the electrochemical test, the Ni–Al coating surfaces show a great future in reducing the current density of the steel surface in the anodic region, which indicating improved pitting resistance for all Ni–Al coating samples. No pitting corrosion was observed after the test in all the coated surfaces were deposited at 750, 850, and 950 °C with Inters. Pot.: − 495.1 (mV) Inters. Cur.: 18.35 µA, Inters. Pot.: − 661.5 (mV) Inters. Cur.: 11.94 µA, and Inters. Pot.: − 344.4 (mV) Inters. Cur.: 7.19 µA, respectively, at potential test that reaches up to 2000 mV (i.e., no breakdown potential).