The improved corrosion and wear properties of Ti-Zr based alloys with oxide coating in simulated seawater environment

Abstract

A dense and adhesive oxide coating was in-situ formed on the surface of Ti56Zr44 and (Ti56Zr44)95Cr5 alloys by thermal oxidation treatment in air. The structures and compositions of the oxide coatings were analyzed by XRD and SEM with EDX. The electrochemical corrosion behavior of the oxide coatings was studied in the artificial seawater (0.05%Na2S + 3.5%NaCl solution) with the matrix alloys as the control samples. The compositions of the corrosion products were analyzed by XPS. The friction and wear testing were performed by reciprocating ball-on-disc wear test under 2 N load. The results show that the oxide coating is composed of ZrTiO4 phase with an orthogonal structure. The micro-hardness of the coatings on Ti56Zr44 and (Ti56Zr44)95Cr5 alloys reaches 860 HV and 1250 HV, and the binding forces are 25.6 N and 38.2 N, respectively. Ti56Zr44 and (Ti56Zr44)95Cr5 alloys exhibit pitting corrosion in sulfide-containing solution although Cr element reduces the degree of pitting corrosion by promoting passivation process. And the oxide coatings behave high chemical stability. Compared with the alloys, the annual corrosion rates of the oxide coatings reduce by 3–6 times. The pitting corrosion is almost completely eliminated. This is attributed to that the ZrTiO4 phase in the oxide coatings has stronger resistance to the erosion of S2− and Cl− ions than the low-valence state TiO and Ti2O3 phase in natural passive film. The volume wear rates of the oxide coatings are only 10−6 mm3/Nm, which are two orders of magnitude lower than matrix alloys. Mechanical wear is the main wear mechanism of the oxide coatings. The contribution of the corrosion-wear interaction to the total wear loss is as low as 14.2%.