In this work, a Fe-rich nonequiatomic Fe₄₀Cr₁₅Co₁₅Mn₁₀Ni₂₀ high-entropy alloy was successfully prepared based on phase analysis and cost reduction. Fe₄₀Cr₁₅Co₁₅Mn₁₀Ni₂₀ high-entropy alloy with a single-phase face-centered cubic (FCC) structure was strengthened by the addition of 11 at.% Al or 10 at.% Mo, and the variations of phase and mechanical properties of the strengthened alloys were subsequently investigated. It has been found that the addition of 11 at.% Al led to the formation of FCC and body-centered cubic (BCC) dual-phase structure in the Fe₄₀Cr₁₅Co₁₀Mn₄Ni₂₀Al₁₁ alloy, while its yield strength (σ_0.2) and tensile strength increased from 158 ± 4 MPa and 420 ± 20 MPa to 218 ± 7 MPa and 507 ± 16 MPa, respectively, as compared to the single-phase FCC structure Fe₄₀Cr₁₅Co₁₅Mn₁₀Ni₂₀ alloy. The addition of 10 at.% Mo introduced intermetallic compounds of μ and σ phases, which resulted in improved yield strength of 246 ± 15 MPa for the Fe₄₀Cr₁₅Co₁₀Mn₅Ni₂₀Mo₁₀ alloy. However, the alloy exhibited premature brittle fracture due to the existence of a large number of intermetallic compounds, which led to deteriorated tensile strength of 346 ± 15 MPa. The findings of this work suggest that the introduced secondary phases by the addition of Al and Mo can effectively strengthen the high-entropy alloy; however, the number of intermetallic compounds should be controlled to achieve a combination of high strength and good ductility, which provides a reference for the follow-up study of nonequiatomic high-entropy alloys.

In this study, we investigated the impact of K₂ZrF₆/Al₂O₃ composite additives on the microstructure evolution and corrosion behavior of ceramic coatings formed through micro-arc oxidation (MAO) treatment on hot-dip aluminum-coated 316L stainless steel surfaces. Our findings revealed the successful preparation of micro-arc oxidation ceramic coatings, presenting a dual-layer structure consisting of a porous micro-arc oxidation ceramic outer layer and a relatively dense/thick hot-dip aluminum inner layer. The incorporation of K₂ZrF₆/Al₂O₃ composite additives induced a self-sealing effect on the ceramic coating surface. Optimal coating performance was achieved with a composite additive concentration of 7.5 g/L, resulting in remarkable improvements not only in thickness, hardness, and surface smoothness but also in corrosion resistance. This research introduces a pioneering investigation of K₂ZrF₆/Al₂O₃ composite additives in the context of micro-arc oxidation technology, offering fresh perspectives and methodologies for the development of highly corrosion-resistant materials.

This study investigates the corrosion state of the floating bead low-density cement stone/P110 steel system in simulated CO₂-saturated formation water under high and atmospheric CO₂ pressure. Results show that the resistance of the cement stone reaches a maximum value at 28 days and then decreases. The corrosion rate of P110 steel under high pressure is greater than that under atmospheric pressure. There is a certain gap and accumulation of corrosion products between the cement stone and the steel. Additionally, the maximum gap size and corrosion product thickness reach 27.5 and 67.69 μm, respectively. The composition of the corrosion products on the steel surface is mainly FeCO₃, and the presence of the iron oxides are caused by oxidation. The corrosion products of the cement are also confirmed to be CaCO₃ and a small amount of SiO₂.

In the extraction of shale gas, Cl⁻ and S₂O₃²⁻ are one of the important factors causing severe corrosion and failure of equipment and pipelines. Addressing the Cl⁻/S₂O₃²⁻ corrosion challenge in shale gas exploitation pipeline steels, this study evaluates the corrosion rates of L245 steels under diverse conditions, including S₂O₃²⁻ concentration and exposure time, utilizing the weight loss method. The microstructural, elemental, and phase compositions of the corrosion products were examined, and the electrochemical behavior of L245 steel was scrutinized under various conditions. Findings indicate that S₂O₃²⁻ addition intensifies localized corrosion on L245 steel, with the corrosion nature being contingent upon S₂O₃²⁻ concentration in the Cl⁻-containing solution. Concurrently, an escalation in S₂O₃²⁻ concentration correlates with a reduction in capacitive arc diameter and a significant decrease in film resistance, culminating in an accelerated corrosion rate.