Search

The objective of this study is to explore the influence of grinding stone granularity on the grinding force and rail material removal behaviors using a rail grinding friction machine. The results indicate that with the increase in granularity, the grinding force, and friction coefficient in the grinding interface obviously increase, which brings about a rise in the hardness and grinding temperature-rise of rail specimens. The increase in the grinding stone granularity causes a fall in the grinding volume and surface roughness of rail materials and brings about stronger vibration in the grinding interface owing to different material removal mechanisms. In view of the experimental results, the optimization of grinding stone granularity is significant for improving the rail grinding efficiency and surface quality. [ABSTRACT FROM AUTHOR]

Bonded MoS2solid lubricant coatings are widely used in tribology for their friction-reducing and antiwear properties. However, such coatings have been rarely investigated in complex fretting conditions, such as dual-rotary fretting (DRF). DRF is a complex fretting wear mode that combines torsional fretting with rotational fretting. In this work, the antiwear properties of bonded MoS2solid lubricant coating under dual-rotary fretting conditions were studied. Results indicated that the MoS2coating had better friction-reducing and antiwear properties than the substrate for alleviating DRF wear. The coating can greatly influence the fretting regimes and reduce the coefficient of friction. Furthermore, the service life of the coating was strongly dependent on the competition of the two fretting components and was reduced as the rotational fretting component increased. [ABSTRACT FROM PUBLISHER]

ABSTRACT The aim of this study is to investigate the lubrication of hyaluronic acid (HA) and chondroitin sulfate (CS) on the condylar cartilage of the temporomandibular joint. The wear behaviour of bovine condyle cartilage was explored against a zirconia ball with different lubrications under torsional fretting mode. The worn cartilage morphologies were observed using scanning electron microscopy and hemotoxylin and eosin staining. The results indicated that HA or CS could significantly lower the friction torque and dissipated energy of fretting interface and reduce the damage of the articular cartilage surface compared to the control (phosphate-buffered saline). The mixture (HA and CS) could provide better protection for the cartilage layer. Absence of good lubrication in overloading torsional fretting process caused excessive cartilage wear. High concentration and high molecular weight HA or CS acted as good boundary lubricants, and the lubrication effect of their mixture was better due to their synergistic function. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The fretting corrosion behavior of quench–polish–quench (QPQ)-treated TP316H steel was investigated in liquid sodium at 450 °C. The surface of the sample after QPQ is a multi-layer structure, consisting of the outermost oxide layer, the middle nitriding layer, and an underneath diffusion layer. The fretting wear and corrosion increased the material damage. With increasing thickness of the nitriding layer, the cross-sectional hardness and wear resistance remarkably increased, the fretting corrosion volume decreased. The effect of multilayer structure anti-wear and anti-corrosion were examined. Possible fretting corrosion mechanisms of the multilayer structure prepared by QPQ on TP316H in liquid sodium are discussed. • Time of QPQ treatments influence the multilayer structure of modified surface. • The high-hardness nitriding layer exerts the main anti-wear effect. • The diffusion layer exerts better anti-corrosion effect, and decomposes into the harder CrN and α-Fe phases. • QPQ treatments are promising for combating fretting corrosion of TP316H in liquid sodium. [ABSTRACT FROM AUTHOR]

The high‐temperature fretting fatigue damage characteristics of dovetail specimens strengthened by nanosecond laser (NL) and nanosecond combined femtosecond laser (F‐NL) were investigated. The results show that the fretting fatigue life of the NL strengthened sample (NL sample) is improved by 211.2% compared to the base metal samples (BM sample). The lifetime of the nanosecond combined femtosecond strengthened sample (F‐NL sample) was increased by 319.6%. It was attributed to the strengthening introducing hardened layers, residual compressive stress field, and high density of dislocations. The combined strengthening process reduces the surface roughness of the NL strengthened surfaces, while the strengthening influence layer is further increased. The fracture morphology shows that the crack source of the strengthened specimen has changed from multi‐source sprouting to single‐source sprouting, and the crack source sprouted on the subsurface. The fatigue strip morphology similarly confirms that a reduction in the crack propagation rate occurs. [ABSTRACT FROM AUTHOR]

The micro-arc oxidation (MAO) coating with different nanoparticles (Al 2 O 3 , MoS 2 , CeO 2 , and graphene oxide (GO)) was prepared on zirconium (Zr) alloy. The surface morphology, cross-section morphology, element composition, and phase structure of different composite MAO coating were investigated. Results show the composite MAO coating consists of ZrO 2 and nanoparticle, along with all the coating present a typical porous structure. The composite MAO coating is comprised of an outer porous layer and inner dense layer, and most of the nanoparticle is gathered to the outer layer. The electrochemical results demonstrate that composite MAO coating presents better corrosion protection to Zr alloy, and the MAO coating with Al 2 O 3 shows the best corrosion resistance. Because the Al 2 O 3 nanoparticle can stabilize the t-ZrO 2 during MAO process and has a denser inner layer. Meanwhile, the nanoparticles in the coating can play the part of a barrier to the diffusion pathway of corrosion medium and restrain aggressive corrosion medium entering the Zr alloy. The fretting corrosion test shows that the MAO coating with GO has the lowest wear volume, and it has the highest material loss volume ratio of corrosion induced by wear. Because GO in MAO coating can reduce the friction by small shear force between the layers. • The formation mechanism of MAO coating with different nanoparticles was proposed. • Role of nanoparticles on the corrosion behavior of MAO coating was inveatigeted. • MAO coating with GO shows the highest material loss ratio of corrosion induced by wear. [ABSTRACT FROM AUTHOR]

• Annealing at different temperatures was used on cold rolling fe-13cr-4al-2mo thin-walled tubes. • The microstructure and axial tensile properties of the samples before and after annealing were measured. • The annealed samples were embrittled by aging, and the enhanced particles and hardness were characterized. • The strengthening mechanism of FeCrAl alloy at room temperature and failure mechanism at high temperature were investigated. FeCrAl alloy has great application potential to replace traditional zirconium alloy as an accident-tolerant fuel (ATF) candidate material. In this study, Fe-13Cr-4Al-2Mo-0.65Nb-0.4Ta alloy was prepared into a thin-walled tube with a diameter of 9.5 mm and a wall thickness of 0.35 mm by cold rolling. The effects of different annealing temperatures on the microstructure morphology, texture growth direction, and mechanical properties of FeCrAl alloy were studied., alloy underwent recovery and recrystallization with increasing annealing temperature, and the grain size increased. The theoretical calculation showed that the pinning action of Fe2Mo4C and Fe2Nb increased the dislocation density, and the interaction with the dislocation increased the room temperature strength. The addition of Ta led to the formation of more second-phase precipitates at the grain boundary, which hindered the growth and refined grains. The high-temperature stable second phase provided sufficient temperature strength for the alloy. [ABSTRACT FROM AUTHOR]

Salt layer preparation on the contact surface of Ti6Al4V dovetail joint specimens using solid NaCl and Na 2 SO 4 deposition, the effect of hot salt layer on fretting fatigue properties of Ti6Al4V alloy at high temperature was studied. The maximum stress load and temperature are 10 kN and 500 °C, respectively. The results show that the average fatigue life of the base metal dovetail joint sample (BM sample) is 9.93×104, and the average fatigue life of the hot salt dovetail joint sample (HS sample) is increased to 69.9×104. The increase in fatigue life stems from the fact that the hot salt layer promotes the generation of thicker loose oxides on the surface of the Ti6Al4V alloy, besides, the lubricating effect of the oxide with higher hardness and the wear debris alleviates the fretting damage between the dovetail joint sample and the contact surface of the fretting pad. Fracture analysis shows that the hot salt layer does not change the crack initiation mechanism, and all of them show single crack source propagation and ductile fracture mechanism. Analysis of crack formation zone by electron back-scattered diffraction (EBSD), it is found that the presence of less dislocation distribution in the HS sample relative to the BM sample. The dislocations are more concentrated on the crack propagation paths and the fretting fatigue contact surfaces. This indicates that the BM sample produced more significant plastic deformation in the crack formation zone, accelerating crack initiation. The contact surface plastic deformation of the HS sample is small and the fretting fatigue life is enhanced. • The salt-coated dovetail specimens designed for high-temperature fretting fatigue testing. • The salt-coated specimens had longer life under high temperature fretting fatigue test compared to the matrix specimens. • The mechanism of improved fretting fatigue life of salt-coated specimens relative to matrix specimens. [ABSTRACT FROM AUTHOR]

• Microstructure and fretting wear properties of Zr alloys treated by LSP were studied. • The plastic deformation was caused by grain refinement and dislocation entanglement. • Zr alloys treated by LSP exhibit abrasive wear and oxidation wear. In this study, the microstructure and fretting wear properties of zirconium (Zr) alloy treated by laser shock peening (LSP) were studied. The Zr alloy treated by LSP presents grain refinement and dislocation entanglement, resulting in the increase of hardness. The friction coefficient, wear area, wear loss, and wear depth of Zr alloy treated by LSP are significantly reduced, indicating that LSP treatment can enhance the wear resistance. The primary wear mechanism of substrate is adhesive wear, and Zr alloy treated by LSP exhibits abrasive wear and oxidation wear. [ABSTRACT FROM AUTHOR]

Ultrasonic surface rolling processing (USRP) was carried out at zirconium (Zr) alloy with different rolling speeds to prepare gradient nanostructured layers, and the corrosion behavior of USRP treated Zr alloy was studied under 360 °C/18.6 MPa water condition. The surface morphology, microstructure, phase composition, and element distribution of USRP treated Zr alloy after corrosion was investigated. Results show that the oxide layer on Zr alloy comprises of t-ZrO 2 , m-ZrO 2 , and metal Zr. The thickness of oxide layer Zr alloy is reduced after USRP treatment, indicating that the gradient nanostructure can effectively improve corrosion resistance. This process is attributed to that the gradient nanostructure layer is helpful for the nucleation of equiaxed t-ZrO 2 at the oxide/metal (O/M) interface with small grain size. The high compressive stress induced by USRP treatment is beneficial for the maintenance of t-ZrO 2 phase and inhabiting the phase transformation from t-ZrO 2 to m-ZrO 2 , which reduces the micro-cracks and defects due to volume expansion. The oxide layer on USRP treated Zr alloy with high content of t-ZrO 2 phase presents a dense structure and prevents oxygen anions from diffusing to Zr alloy. • The characterization of oxide layer on USRP treated Zr alloy is investigated. • The gradient nanostructured layer is beneficial for improving the corrosion behavior of Zr alloy. • The corrosion mechanism of USRP treated Zr alloy is analyzed. [ABSTRACT FROM AUTHOR]

Low energy laser shock peening (LE-LSP) with different energies was carried out at zirconium (Zr) alloy. Characterization and electrochemical corrosion behavior of Zr alloy after LE-LSP treatment were investigated. Results show that the surface profile of Zr alloy after LE-LSP treatment is rough due to the regular undulations on the surfaces. The hardness of Zr alloy increases after LE-LSP treatment because the grain size of Zr alloy is refined, and the plastic deformation generated on the surface induces the working hardening. A melting layer, plastic deformation layer, and transition layer are formed on Zr alloy after LE-LSP treatment. The dislocation entanglement is observed at the plastic deformation layer, which indicates that the dislocation slip is the main deformation mechanism of Zr alloy. The electrochemical corrosion resistance of Zr alloy after LE-LSP treatment is improved because of an increase in the grain boundary, which improves the activity of Zr alloy and is beneficial for forming passive films. • A melting layer, plastic deformation layer, and transition layer were formed on Zr alloy after LE-LSP treatment. • The dislocation slip is the main deformation mechanism of Zr alloy during LE-LSP process. • The increase in the grain boundary of Zr alloy after LE-LSP treatment is beneficial for forming passive films. [ABSTRACT FROM AUTHOR]

Grid-to-rod fretting (GTRF) is the main factor leading to the failures of fuel rods in reactor. The oxide layer formed on pre-wear stage has a significant impact on the wear resistance of zirconium (Zr) alloys fuel cladding. In this research, Zr alloy was immersed in high-temperature water conditions for 30 days,110 days,145 days, and 195 days. The characterization and fretting wear behavior of oxide layer on Zr alloy were investigated. Results show that the oxide layer consists of t-ZrO 2 , m-ZrO 2 , and metal Zr. The thickness and hardness of oxide layer increases with the corrosion time increase. The fretting running region and F-D curve are dependent on the oxide layer. Compared with Zr alloy, the wear volume of oxide layer on Zr alloy is significantly reduced because the structure of oxide layer is dense with a high hardness, leading to that the oxide layer is not easy to be destroyed during the fretting. The wear mechanism of Zr alloy is adhesive wear, and the wear mechanism of oxide layer is abrasive wear. • The fretting wear behavior of pre-oxidized Zr alloy cladding was investigated. • The wear volume of oxide layer on Zr alloy decreases with the corrosion time increase. • The fretting running region and F-D curve are significantly dependent on the oxide layer. [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]

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]

[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]