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The tribologically transformed structure of the white etching layer (WEL) always appears with some cracks accompanying microstructural evolution under friction. This work investigated crack behavior with the existence of WEL on pearlitic steel after rolling-sliding friction tests. The WEL microstructure was characterized using scanning electron microscopy, nano-indentation, focused ion beam, and transmission electron microscopy. According optical images, the WEL zone could be divided into white and yellowish zones; cracks existed at the boundary separating these two zones. The deformation degree of the cementite structure caused color differences in optical images and inhomogeneous chemical composition distributions in the same WEL zone. For cracks initiated and propagated at the WEL colony boundary, crack holes remained unconnected along the plastic deformation line. • Crack initiation and propagation in white etching layer (WEL) are investigated. • Under rolling–sliding friction, WEL of cementite appears on pearlitic steel. • WEL contains two "phases" of dissolved versus nanoscale cementite. • Cementite form determines color of WEL under optical microscopy. [ABSTRACT FROM AUTHOR]

• The effects of fretting parameter, environmental conditions, irradiation, fretting wear mode, and spacer grid on GTRF are reviewed, and the key influence factor of wear rate is discussed. • The accident tolerant fuel coating and its tribological behavior are investigated. • The highlighted points and research directions of GTRF are prospected. Fuel rods are the most important safety barrier in pressurized water reactors (PWR) and operates at high temperature, high pressure, high speed, and strong irradiation water condition. The grid-to-rod fretting (GTRF) induced by flow-induced vibration (FIV) is the main factor that causes failures in fuel rods. The effects of fretting parameter, environmental conditions, irradiation, fretting wear mode, and spacer grid on the GTRF are systematically reviewed, and the key influencing factor on GTRF is analyzed. The accident tolerant fuel (ATF) coating and its tribological behavior are investigated. Finally, key research guidance and popular topics consideration GTRF are proposed. [ABSTRACT FROM AUTHOR]

The plasma electrolytic oxidation (PEO) coating on Zirconium (Zr) alloy was employed and immersed under 400 °C/10.3 MPa steam conditions. The surface morphology, phase composition, microstructure, and element distribution of the PEO coating after corrosion were analyzed. The results indicate that the PEO coating presents lower corrosion weight gain because the compact oxide layer on the PEO coating presents few cracks and prevents the corrosion media from entering the substrate. The compact oxide layer is caused by the high compressive stress in PEO coating, which is helpful for the nucleation of t-ZrO 2 grain and restricting the phase transformation from t-ZrO 2 to m-ZrO 2 , thus reducing the volume expansion and defects. Based on the XRD, SEM, XPS, Raman mapping, and TEM results, the corrosion mechanism and phase transformation processes of the PEO coating under 400 °C/10.3 MPa conditions were summarized. • The microstructure and corrosion mechanism of PEO coating under 400 °C/10.3 MPa condition are investigated. • The phase transformation process of zirconia under 400 °C/10.3 MPa condition is studied. • The corrosion weight gain of PEO coating are reduced by the compact inner layer. [ABSTRACT FROM AUTHOR]

Abstract CoMoCrSi superalloy coatings were prepared on Mar-M247 Ni-based superalloy by high velocity oxygen fuel (HVOF) under various spraying parameters. Dense coatings with porosity < 0.8% were prepared, and the fretting wear properties of the coatings was investigated. The coatings showed good adaptability to the spraying parameters. As the temperature increased from R.T. to 400 °C, the friction coefficient of the coating decreased from 0.8 to 0.6, and the wear morphology gradually changed from pits to bulges. A large amount of material transfer occurred, and the main wear mechanisms at R.T. were abrasive wear and delamination; adhesive wear appeared slowly at elevated temperatures. The coating exhibited better wear resistance than the substrate during the experiments. Highlights • How the spraying parameters effect the fretting wear behavior of high velocity oxygen fuel (HVOF) coating was concerned. • The effect of temperature on the friction and wear properties of coatings has been studied. The friction coefficient decreases with increasing temperature, but the materials loss had the similar rule • The wear mechanism was abrasive wear and delamination in RT, and adhesive wear appeared slowly at elevated temperature. [ABSTRACT FROM AUTHOR]

Cladding fuel rods supported in grids are important core components in pressurized water nuclear reactors. Small rod-to-grid misalignments can occur during the core manufacturing process. The presence of tilted contacts may promote fretting wear damage between claddings and grids by flow-induced vibrations (FIV). In this study, the influence of tilted contacts on the fretting wear between fuel rod cladding and a Zr-4 alloy grid, caused by deviations during assembly, was analyzed and discussed. A 3D finite element model was set up to obtain the stress state on the contact interface between the cladding and grid under different included angles. Results show that the wear morphology and profile presented evident dependence on the included angle. The change of the included angle between the cladding and grid changes the contact form of the two, leading to changes in the local stress and contact area in the interface. This process ultimately changes the thickness of the wear debris accumulation layer (WDL). [ABSTRACT FROM AUTHOR]

A multiple-layer graphene was prepared on steel surface to reduce friction and wear. A graphene-containing ethanol solution was dripped on the steel surface, and several layers of graphene flakes were deposited on the surface after ethanol evaporated. Tribological performance of graphene-contained surface (GCS) was induced by reciprocating ball against plate contact in different RH (0% (dry nitrogen), 30%, 60%, and 90%). Morphology and wear scar were analyzed by OM, 2D profile, SEM, Raman spectroscopy, and XPS. Results show that GCS can substantially reduce the wear and coefficient of friction (COF) in 60% relative humidity (RH). Low COF occurs due to graphene layer providing a small shear stress on the friction interface. Meanwhile, conditions of high RH and textured surface could make the low COF persist for a longer time. High moisture content can stabilize and protect the graphene C-network from damage due to water dissociative chemisorption with carbon dangling bonds, and the textured surface was attributed to release graphene layer stored in the dimple. [ABSTRACT FROM AUTHOR]

The Ti/TiN multi-layer film was prepared on the depleted uranium (DU) substrate by cathodic arc ion plating equipment. The character of multi-layer film was studied by SEM, XRD and AES, revealed that the surface was composed of small compact particle and the cross-section had a multi-layer structure. The fretting wear performance under different frequencies was performed by a MFT-6000 machine with a ball-on-plate configuration. The wear morphology was analyzed by white light interferometer, OM and SEM with an EDX. The result shows the Ti/TiN multi-layer film could greatly improve the fretting wear performance compared to the DU substrate. The fretting wear running and damaged behavior are strongly dependent on the film and test frequency. The fretting region of DU substrate and Ti/TiN multi-layer under low test frequency is gross slip. With the increase of test frequency, the fretting region of Ti/TiN multi-layer change from gross slip to mixed fretting, then to partial slip. [ABSTRACT FROM AUTHOR]

[Display omitted] • The friction performance of 2.25Cr-1Mo steel in liquid sodium were improved by salt bath nitriding. • The microstructure and corrosion behavior of the nitrided samples were characterized and discussed. • The fretting wear mechanism of matrix and nitrided samples in liquid sodium at different temperatures was revealed. In this study, nuclear grade 2.25Cr–1Mo steel was surface strengthened by quench–polish–quench (QPQ) at two salt bath nitriding temperatures (550 °C and 590 °C). At 250 °C and 450 °C liquid sodium, the fretting wear test was carried out, and the possible effects of salt bath temperature on friction performance and microstructure of different samples were investigated. The results show that the surface of 2.25Cr-1Mo steel after QPQ treatment forms a multilayer structure with a hardness 3.7–5.8 times higher than that of the substrate, while the excessively high nitriding temperature also causes premature failure of the nitride layer of QPQ 590. Compared to the substrate, QPQ 550 and QPQ 590 experienced 40% and 16% reductions in the material loss at 450 °C, and 86% and 57% at 250 °C, respectively. The substrate showed different wear mechanisms in liquid sodium at varying temperatures. At 250 °C, the abrasive wear is dominant, while at 450 °C, the adhesive wear is dominant, accompanied by abrasive wear. The nitrided samples are dominated by abrasive wear in liquid sodium at varying temperatures, accompanied by the corrosion effect of the liquid sodium. [ABSTRACT FROM AUTHOR]

• Quench–polish–quench (QPQ) salt bath nitriding of different time was used on TP316H steel. • The surface structure and cross-sectional hardness of the nitrided samples were characterized. • The microstructural characteristics of nitrided samples in liquid sodium at varying temperatures were characterized. • The fretting wear mechanism of nitrided samples in liquid sodium at varying temperatures was discussed. In this study, TP316H steel was subjected to quench-polish-quench (QPQ) salt bath nitriding at different times. The effects of QPQ on the fretting wear behavior of TP316H steel at varying temperatures in liquid sodium were investigated. The results show that QPQ treatment significantly improves the wear resistance of TP316H due to the high hardness nitride layer. The main fretting wear mechanism of nitrided samples in liquid sodium is diffusion-tribo-oxidation-rediffusion. QPQ 90 with a thicker nitride layer has the best wear resistance, although the nitride layer cracks in high-temperature liquid sodium. As a result, QPQ treatment may be a viable option for combating the wear of TP316H steel in liquid metals. [ABSTRACT FROM AUTHOR]

The impact wear test of 2.25Cr–1Mo steel against Gr5C12 alloy was performed at a controlled kinetic energy impact wear rig. The effect of temperatures (from 25 °C to 450 °C) on the impact wear damage mechanism was investigated. The contact force, energy absorption, and interface deformation during the impact process were recorded and analyzed in real time. Wear volume, morphology, and elemental distribution of the wear scars were used to characterize wear and tribo-chemistry behavior. Results demonstrate that at varied temperatures, the interface behavior of 2.25Cr–1Mo steel is different. With the rise in temperature, both the contact force, absorption energy, and wear volume first increase and then decrease. The explanation is that higher temperatures can modify the material's surface properties. Delamination, plastic deformation, and oxidative wear are the major mechanisms of impact wear, but the proportions of the three wear mechanisms differ at varied temperature. • The impact wear behavior of 2.25Cr–1Mo steel at elevated temperature was investigated. • The interface behavior of impact wear was analyzed. • The impact wear mechanism of 2.25Cr–1Mo steel at elevated temperature was discussed. [ABSTRACT FROM AUTHOR]

Heat transfer tubes are subjected to cyclic and direct contact under high temperature liquid conditions due to flow-induced vibration. The influence of water temperatures (25, 60, and 95 °C) and loads (10, 20, and 30 N) on the fretting wear behavior of 2.25Cr–1Mo tube against Gr5C12 rod was investigated. Results indicate that the fretting regime changes from gross slip to partial slip as the load increases from 10 N to 30 N. The fretting regime remains unchanged as the water temperature increases from 25 °C to 95 °C. The fretting regime is more related to load than water temperature, implying that the water temperature and load play different roles in the fretting wear process. The coefficient of friction (COF), wear morphology, wear volume, and wear rate show an evident dependence on load and water temperature, while the COF has a significant relationship with the load. The effect of micro-pitting may be ignored due to the material removal from the original surface and formation of wear debris layer (WDL) in the gross slip regime. • The influence of water temperatures and loads on the fretting wear behavior of 2.25Cr–1Mo tube is investigated. • The fretting regime is more related to load than water temperature. • The micro-pitting may be ignored in the gross slip regime. [ABSTRACT FROM AUTHOR]

In the heat exchangers of sodium-cooled fast reactors, sodium flow can cause the tubes to vibrate, resulting in fretting wear damage due to the contact between the tubes (2.25Cr-1Mo steel) and their support plate (Gr5C12 alloy). In this work, the effects of temperature on the fretting wear behavior of a 2.25Cr-1Mo heat transfer tube on a Gr5C12 alloy rod were studied. The results showed that the coefficient of friction (COF) and wear volume increased first and then decreased with the increase in temperature. Moreover, 2.25Cr-1Mo showed great wear performance at high temperatures than at room temperature and 80 °C, because of the antifriction nature of the oxidative layer and the high hardness of the tribological transformed structure layer. As the temperature increased, material transfer and plastic deformation became increasingly obvious, but average wear depth decreased. This provides data support for the practical engineering application of 2.25Cr-1Mo steel at elevated temperatures. Wear mechanisms were found to depend modestly on temperature and largely on normal load. As temperature increases, the wear mechanism gradually changes from abrasive wear to adhesive wear. [ABSTRACT FROM AUTHOR]

The fretting capabilities of 690 alloy against 405 stainless steel were evaluated through a series of tube-plate tests in different experimental conditions. The results indicated that as the temperature increased in air, the wear volume and wear depth increased first until reaching a maximum value at 90 °C and then decreased. This was attributed to spinel oxides formed above 200 °C in combination with adhesive wear, which contributed to oxidation resistance and a reduction of interfacial wear, resulting in the decrease of wear volume and wear depth. Metallic nickel, iron and chromium were observed in water, which indicated low oxidation, associated with lower wear damage. • Compared to air, unoxidized metal elements were observed in water, associated with lower oxidation and wear damage. • The testing environmental condition has a huge effect on the chemical state of chromium. • The spinel oxides and adhesive layer seemed to protect the surfaces and led to lower wear volume at 200 °Cand 285 °C. [ABSTRACT FROM AUTHOR]