Experimental study on the tribocorrosion behavior of additively manufactured TC4 alloy in simulated seawater

Three-dimensional (3D) printing, widely referred to as additive manufacturing (AM) in industrial and academic communities, has emerged as a revolutionary manufacturing approach for fabricating complex, high-performance metallic components. Among various metallic materials suitable for AM, the Ti6Al4V (TC4) alloy stands out owing to its high specific strength, excellent corrosion resistance, and favorable biocompatibility. These properties collectively make it an indispensable structural material in the aerospace, biomedical, and marine engineering sectors. The marine environment constitutes a particularly demanding service condition in which structural materials are subjected to the combined effects of mechanical wear and aggressive electrochemical corrosion; this synergistic degradation process is defined as tribocorrosion. For potential marine applications (e.g., propulsion system components, underwater connectors, valve parts, and offshore platform fittings), elucidating the tribocorrosion behavior of AM-fabricated TC4 alloy is critical for predicting its service life and ensuring structural integrity in practical engineering.

A simulated seawater solution was formulated in accordance with the ASTM G1148-98 standard for experimental tests, and its pH was adjusted to 8.2 with 0.1 mol/L HCl and NaOH aqueous solutions; ultrapure water was employed as the control medium. The chemical composition of the as-received AM-fabricated TC4 alloy was determined by inductively coupled plasma optical emission spectrometry, while the contents of oxygen, nitrogen, and hydrogen were quantified by mass spectrometry. Tribocorrosion tests of the AM-fabricated TC4 alloy in simulated seawater and ultrapure water were performed on an MFT-5000 multifunctional tribo-tester using a 5 mm diameter silicon nitride ceramic ball as the tribological counterbody. TC4 alloy was wire-electrode cut into cuboid specimens with dimensions of 10 mm × 10 mm × 10 mm for the tests. Open-circuit potential (OCP) and polarization curves during the tribological wear process were monitored using in situ electrochemical methods. After the tribocorrosion tests, the surface topographies of the tested TC4 specimens were characterized by white-light interferometry for 3D surface profiling and wear volume analysis. Morphological characterization of the worn surfaces was carried out using scanning electron microscopy, and the elemental composition and chemical states of the worn surface films were analyzed by X-ray photoelectron spectroscopy.

This study investigated the tribocorrosion behavior of AM-fabricated TC4 alloy in simulated seawater and systematically examined the correlations among applied load, sliding frequency, friction coefficient, and wear loss of the alloy. In situ electrochemical tests were simultaneously conducted to monitor the OCP evolution and polarization curves during the tribocorrosion process. The results showed that under the same applied load in aqueous media, the friction coefficient of TC4 decreased as the sliding frequency increased. At constant load and sliding frequency, the friction coefficient of the alloy in simulated seawater was considerably lower than in ultrapure water. Wear volume loss decreased gradually with increasing sliding frequency, while the wear volume loss in simulated seawater was markedly higher than in ultrapure water under identical test parameters. During tribocorrosion, the OCP of the alloy exhibited a trend of rapid decline, followed by stabilization. The OCP values and polarization curves of the alloy in simulated seawater shifted toward more negative potentials than those in ultrapure water. The dominant wear mechanism of AM-fabricated TC4 alloy in simulated seawater was identified as a synergistic interaction between oxidative wear and adhesive wear.

The tribocorrosion performance of AM-fabricated TC4 alloy depends strongly on the mechanical parameters (load and sliding frequency) and the chemical nature of the service environment. Although the simulated seawater environment paradoxically reduces the friction coefficient of the alloy, it markedly exacerbates overall material degradation arising from the pronounced synergistic effect of electrochemical corrosion and mechanical wear. This comprehensive insight into the tribocorrosion behavior and degradation mechanisms of AM-fabricated TC4 alloy is critical for the reliable and safe application of AM-fabricated titanium alloys in next-generation marine and offshore engineering systems. Furthermore, the findings provide a fundamental experimental basis for subsequent performance optimization and surface modification of AM-fabricated titanium alloys for marine service.