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The general corrosion behavior and mechanism of low-temperature plasma nitrided 17–4PH stainless steel with and without a work-hardened layer in high temperature water were investigated. The general corrosion test was conducted under high temperature (280 °C) and high pressure (13.3 MPa) circulating water conditions. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were employed to reveal the underlying mechanism. The results showed that, for the non-nitrided specimens, high density of grain boundaries and dislocations in the work-hardened layer accelerated the formation of the inner oxide and the deposition of the outer oxide, which reduced the corrosion resistance. Besides, the increased surface roughness also enhanced the deposition of the outer oxide layer. For the nitrided specimen without a work-hardened layer, the nitrided layer was composed of expanded martensite. The compressive residual stress in the expanded martensite could inhibit element diffusion, thus reducing the thickness of the inner oxide layer and mitigating corrosion. While for the nitrided specimen with a work-hardened layer, the nitrided layer was mainly composed of γ'-Fe 4 N twins, which induced intergranular corrosion and reduced the corrosion resistance. Besides, the diffusion of nitrogen from the nitrided layer into the solution during the corrosion process influenced the local H+ content in the solution, subsequently impacting the deposition of the outer oxide particles. In conclusion, the presence of a work-hardened layer is undesirable for plasma nitriding in improving corrosion resistance in high temperature water. These findings can provide valuable insights for the extension of the material's service life. [Display omitted] • The corrosion mechanism of α' N in high temperature water is obtained. • α' N contains residual compressive stresses and lamellar-like structures. • Residual compressive stress in α' N mitigates corrosion. • γ'-Fe 4 N twins induce intergranular corrosion and reduce the corrosion resistance. [ABSTRACT FROM AUTHOR]

Space irradiation-induced damage to onefold lubricants including four multialkylated cyclopentanes (MACs) space greases, Chromium doped diamond-like carbon (Cr-DLC) and molybdenum disulfide (MoS 2 ) films was first investigated under simulated space environment (atomic oxygen (AO) and proton (PR)). Then solid-grease synergistic lubrication systems were prepared via spinning four space greases on Cr-DLC and MoS 2 film, and their tribological behaviors were evaluated under simulated space environment including ultra-vacuum, AO and PR irradiation, low temperature (−100 °C). The irradiated damage mechanism and friction mechanism were explored by surface/interface analysis techniques. The results demonstrates that Cr-DLC film have better space adaptability than MoS 2 film because irradiation induced partial transition of Cr-DLC’s micro-structure with the decrease in I D /I G ratio from 1.50 to 1.26 and the increase of sp 3 content from 0.24 to 0.59, while the surface morphology and micro-structure of MoS 2 film have dramatically changed. Solid-grease synergistic lubrication systems provide excellent friction-reducing and anti-wear behaviors (friction coefficient can be reduced up to below 0.05 under the special working conditions). Such excellent tribological performance of Cr-DLC-grease lubrication coatings is attributed to the friction-induced graphitization at the sliding interface, while that of MoS 2 film mainly depends on its original structure/merits under greases lubrication. [ABSTRACT FROM AUTHOR]

Fretting corrosion of as received and shot peened zirconium alloys exposed to high temperature high pressure water is tested. High resolution characterization techniques are applied to study the microstructure and composition of the worn surface. The results show that shot peening increases the wear resistance of the material, changing the wear mode from abrasive wear plus delamination to abrasive wear. Mechanical wear promotes corrosion of zirconium alloy by forming a thick dual-layer structure oxide scale in the debris buildup area. While the effects of corrosion on the fretting wear depend on the integrity of the oxide scale. • Fretting corrosion of as received and shot peened zirconium alloy is investigated. • Shot peening increases the corrosion and fretting corrosion resistance of zirconium alloy. • Fretting wear accelerates material corrosion by oxide film peeling off and cracking. • The integrity of the oxide scale determines the effects of corrosion on the fretting wear. [ABSTRACT FROM AUTHOR]