Preparation of ceramic coating on Ti substrate by Plasma electrolytic oxidation in different electrolytes and evaluation of its corrosion resistance

Niobium addition enhancing the corrosion resistance of nanocrystalline Ti5Si3 coating in H2SO4 solution

“…Moreover, highly covalent-dominated atomic bonds endow Ti 5 Si 3 with good chemical inertness and high hardness, which has generated vigorous pursuit of Ti 5 Si 3 as a wear-and corrosion-resistant coating material. Unfortunately, since Ti 5 Si 3 has a hexagonal crystal structure, the thermal expansion anisotropy, originating from a large difference between the coefficients of thermal expansion (CTE) in the crystallographic c and a directions (CTE(c)/ CTE(a) ratios of $3), results in appreciable residual stresses in the material during heating and cooling that can give rise to microcracking [15,16].…”

“…To alleviate or eliminate this problem, alloying by substitutional elements, which acts to change the chemical bond nature and/or refine the crystal size, has been performed to control the degree of strain or microcracking. For example, Thom et al [17] suggested that a critical grain size of pure Ti 5 Si 3 and carbon-containing Ti 5 Si 3 is 2-3 lm and 5-6 lm, respectively, needed to completely avoid microcracking. Experimental observations also indicated that the thermal-expansion anisotropy of Ti 5 Si 3 exhibits a substantial reduction by replacing some of the titanium by zirconium, niobium or chromium [18,19].…”

“…For example, Thom et al [17] suggested that a critical grain size of pure Ti 5 Si 3 and carbon-containing Ti 5 Si 3 is 2-3 lm and 5-6 lm, respectively, needed to completely avoid microcracking. Experimental observations also indicated that the thermal-expansion anisotropy of Ti 5 Si 3 exhibits a substantial reduction by replacing some of the titanium by zirconium, niobium or chromium [18,19]. It is worth noting that previous studies focused mainly on physical and mechanical properties, with little attention devoted to understanding the electrochemical behavior of Ti 5 Si 3 in aqueous corrosive environments.…”

“…Furthermore, under the application of static or dynamic contact loads, the thin passive film would be easily destroyed. Because bare titanium alloys have a strongly negative standard electrode potential (À1.63 V), they often suffer galvanic and crevice corrosion as well as corrosion embrittlement caused by intensive interactions with the interface material and/or the surrounding environment [5]. In the past decade, various surface modification techniques, including micro-plasma oxidation [6], laser treatment [7], chemical vapor deposition [8], physical vapor deposition [9] and ion implantation [10], have been developed to improve the resistance of titanium alloys against abrasion and corrosion damage.…”

“…As a promising high-temperature engineering material, Ti 5 Si 3 has recently attracted much interest because of its high melting temperature (2130°C), low density (4.32 g cm À3 ), excellent creep strength and high oxidation resistance [13,14]. Moreover, highly covalent-dominated atomic bonds endow Ti 5 Si 3 with good chemical inertness and high hardness, which has generated vigorous pursuit of Ti 5 Si 3 as a wear-and corrosion-resistant coating material.…”