Fengyuan Yan

Tribocorrosion Behaviors of Inconel 625 Alloy Sliding against 316 Steel in Seawater

Passive alloys require not only high resistance to corrosion but also excellent tribological properties for seawater equipment applications. In this research, the tribocorrosion behaviors of Inconel 625 alloy sliding against 316 stainless steel were investigated using a ring-on-block test rig in artificial seawater and distilled water. The results showed that the friction coefficients were larger for sliding in distilled water as compared to seawater. However, the wear loss of Inconel 625 and 316 steel alloys was lower for sliding in distilled water than that in seawater. Interestingly, the corrosion of seawater obviously accelerated the wear. Moreover, with the increase of normal load, the wear loss increased but the average friction coefficient decreased in both aqueous media. The synergistic effect between wear and corrosion was significant, due to the mechanical removal of passive film. Seawater salinity does significantly influence the friction coefficient and wear loss. The Inconel 625 alloy has a maximum corrosion rate in 3% seawater, which is due to the synergism of salt concentration and dissolved oxygen in seawater. The high corrosion rate accelerated the wear loss but decreased the friction coefficients.

Influence of potentials on the tribocorrosion behavior of 304SS in artificial seawater

Corrosive wear involves chemical and mechanical mechanisms and the combination of these mechanisms often results in accelerated materials degradation. In this work, pin-on-disk friction experiments were carried out in artificial seawater to investigate the influence of applied potential on the tribocorrosion behavior of 304SS. The obtained results demonstrate that when the applied potential was below the pitting potential of passive film, corrosion and wear interacted to make the total material loss increase obviously; however, when it exceeded this pitting potential, corrosion was inhibited by the rubbing process. Study of the worn surfaces and the cross-sections indicate that depending on varying applied potential, different features of wear tracks were involved, and it was the form of mechanical and corrosion-accelerated delamination wear that determined the total mass loss of 304SS during tribocorrosion.

The buildup of the electric field during positron annihilation lifetime spectroscopy measurement

Positron annihilation lifetime spectra were measured on pure polystyrene (PS) and PS samples whose film surfaces were coated with gold, graphite (GR-PS), or MoS2. The results showed the longest lifetime remained constant with measured time in all experimental samples, whereas the corresponding intensity decreased with time at different rates. The experimental phenomena were associated with the buildup of an electric field inside the polymer during extended positron annihilation lifetime spectroscopy (PALS) measurement. The decrease in the rate was attributed to the presence of conductive film causing the neutrality between positive charges and negative charges, thereby reducing the buildup of the electric field. Additionally, we also performed PALS measurement on GR-PS under different experimental conditions, such as the conductive film being grounded or not grounded or the presence of an external electric field. These results further indicated that the buildup of the electric field was responsible for the decrease in the intensity with time.

Tribocorrosion behaviors of 304SS: Effect of solution pH

The tribocorrosion behavior of 304SS in chloride-containing solutions with different pH (pH 7.2–9.2) was investigated under rubbing conditions of 50 N and 100 R min−1 using a pin-on-disc tribometer with an Al2O3 pin mounted on a vertical rotating axis. When combined with rubbing, the corrosion of 304SS was accelerated due to the formation of galvanic couples between the mechanical depassivated areas and the surrounding passivated areas. In addition, the continuous sliding-over processes also make the pitting corrosion to occur more easily due to the affinity of Cl− to metal cations near the active surface. However, OH− has better affinity than Cl−; therefore, a high pH solution mitigates the local corrosion with a wear track. It was found that high pH solution exhibits good lubricity, and both the friction coefficient and total material loss reduce evidently with increasing pH. From the calculation results and wear morphologies, we can confirm that pure mechanical and corrosion-accelerated wear, including abrasion and delamination, are among the chief reasons for material loss.

Graphite-Controlled Fabrication of Ultrathin WSe2 Nanosheets with Tower-Like Structure and Their Tribological Properties

Uniform hexagonal tungsten diselenide (WSe2) nanosheets, with thicknesses as small as 10 nm and diameters as small as 100 nm, self-assembled into tower-like arrays, were successfully synthesized by the solid-state reaction of the elements W and Se in the presence of graphite in a sealed stainless steel reactor at 800°C. However, scattered submicrometer WSe2 sheets, 250 nm thick and 1–3 μm in diameter, were obtained in the absence of graphite. Subsequently, the formation mechanism of this assembled structure was proposed. Furthermore, the lubricity of as-fabricated arrays added into paraffin in steel–steel interaction was investigated by a ball-on-disc tribometer, as compared to that of commercial graphite and as-obtained submicrometer WSe2 sheets, respectively. The results showed that the addition of small amounts (0.5 wt%) of as-fabricated arrays greatly improved the friction reduction and antiwear properties of paraffin and did well then the same amount of commercial graphite and submicrometer WSe2 sheets, suggesting that as-fabricated arrays are an excellent lubricating material. Therefore, this process provides a strategy for the large-scale, cost-effective, and environmental friendly preparation and tribological application of small-sized laminar transition-metal dichalcogenide with good lubricity.

Time Dependence of Tribocorrosion Behavior for Stainless Steel and Alumina Tribocouples in Seawater

ABSTRACT Tribocorrosion is an important phenomenon encountered in many practical engineering situations, resulting in accelerated materials degradation and serious economic losses. In this work, pin-on-disk friction experiments were carried out in seawater to investigate the dependence of tribocorrosion on time. As rubbing proceeded, the mass loss rate of 304SS decreased, and the dominant wear mechanism changed from abrasion to delamination. In addition, during tribocorrosion, friction-induced α′-martensite would be transformed at room temperature. The volume fraction of transformed martensite was determined by test time, which played a dual role in accelerating corrosion and reducing wear. Additionally, the synergistic effect between corrosion and wear was analyzed; the main causes of 304SS degradation during tribocorrosion were pure mechanical wear and corrosion accelerated wear.