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The complex lithology, frequent interbedding and strong heterogeneity of the shale oil reservoir in Lucaogou Formation of the Middle Permian in Jimsar Sag lead to the complexity of litho‐electric parameters and the low accuracy of conventional reservoir saturation evaluation methods. Therefore, in this paper, automatic lithologic identification was firstly performed with the optimization inversion method of mineral components and K‐means clustering algorithm, and then, litho‐electric experiments were carried out to determine the litho‐electric parameters of different lithologies. Furthermore, the shale oil reservoir saturation calculation models of different lithologies were optimized and determined. Then, a composite water saturation model (Composite‐SW) based on complex lithology identification was constructed. Finally, the model was verified and analysed with the experimental results of water saturation. The coefficient of correlation between the calculation results of the Composite‐SW model and the core experiment results reached.88, indicating that the model was much better than conventional models. The model can be widely applied in logging evaluation of the continental mixed shale oil reservoir in the study area. The study provides a new idea for oil saturation evaluation of continental shale oil reservoirs and is significant for evaluating other types of shale oil reservoirs. [ABSTRACT FROM AUTHOR]

Brittleness is important in the evaluation of the fracturing ability of shale reservoir and has a significant impact on shale gas exploration and development. This paper discusses the characteristics and controlling factors of brittleness of continental shale in the Da'anzhai Member of the Ziliujing Formation of Lower Jurassic age in the northeast Sichuan Basin. Continental shale lithofacies and their associations were grouped into four main rock types: clayey shale, silty shale, shell calcareous clayey shale, and silty clayey shale, characterized by the high clay content and local enrichment of carbonate minerals as a whole. Compared with the marine shale, the continental shale contained a low content of siliceous minerals, a high content of carbonate minerals, and a large number of shell limestone interlayers. Carbonate minerals play an important role in controlling the brittleness of continental shale. The shale interlayers were mainly shell limestone interlayers with a thickness of several centimeters and a large number of shell laminates with thicknesses of several millimeters were also observed. The shell laminates were mainly filled with calcite. Due to the dissolution process, a large number of bedding joints and corrosion joints were formed in the calcite shell layers. In the interlayers with a high shell content, a large number of microfractures developed. The energy consumption required for maintaining fracture expansion was lower after fracturing; the fractures greatly improved the reservoir's brittleness. [ABSTRACT FROM AUTHOR]

In this study, the creep properties of cylindrical metal rubber (MR) specimen under static compression at elevated temperatures were investigated by a series of creep experiments. The cylindrical MR specimen has a good symmetrical property, and the mechanical properties are consistent in its different axial section. The failure determination parameters of MR under the coupling of thermal and mechanical static load of the forming direction were proposed in four aspects: the overall height, the average stiffness, the energy dissipation, and the variation of the loss factor. The variation patterns of the properties of the MR specimens were investigated with a static load at different temperatures for 324 h. The analytical equipment, including the simultaneous thermal analyzer (TGA/DSC), X-ray diffractometer (XRD), and scanning electron microscope (SEM), were used for material characterization and failure analysis. Based on the results, it is found that there are significant differences in the MR property variations subjected to creep tests at different elevated temperatures. The results indicated that an appropriate heat treatment for MR specimens would improve the creep resistance at elevated temperatures. In addition, the overall height and energy dissipation of the MR specimens were increased, and the average stiffness and the loss factor were decreased under the creep tests at 200 °C and 250 °C. However, under the creep tests at 25 °C, 300 °C, 350 °C, and 400 °C, the overall height, the energy dissipation and the loss factor were decreased, but the average stiffness was increased. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to investigate the fatigue properties of C17200 alloy under the condition of quenching aging heat treatment at high temperatures, and to provide a design reference for its application in a certain temperature range. For this purpose, the tensile and rotary bending fatigue (RBF) tests were carried out at different temperatures (25 °C, 150 °C, 350 °C, and 450 °C). The tensile strength was obtained, and relationships between the applied bending stress levels and the number of fatigue fracture cycles were fitted to the stress-life (S-N) curves, and the related equations were determined. The fractured surfaces were observed and analyzed by a scanning electron microscopy (SEM). The results show that the RBF fatigue performance of C17200 alloy specimens is decreased with the increase in test temperature. When the temperature is below 350 °C, the performance degradation amplitudes of mechanical properties and RBF fatigue resistance are at a low level. However, compared to the RBF fatigue strength of 1 × 107 cycles at 25 °C, it is decreased by 38.4% when the temperature reaches 450 °C. It is found that the fatigue failure type of C17200 alloy belongs to surface defect initiation. Below 350 °C, the surface roughness of the fatigue fracture is higher, which is similar to the brittle fracture, so the boundary of the fracture regions is not obvious. At 450 °C, due to the further increase in temperature, oxidation occurs on the fracture surface, and the boundary of typical fatigue zone is obvious. [ABSTRACT FROM AUTHOR]

After the array acoustic full wave train is decomposed by the mode decomposition method based on time domain, there is serious mode aliasing between each Intrinsic Mode Function(IMF), which leads to the reservoir fluid response of time–frequency characteristics of each Intrinsic Mode Function that is not obvious. To solve this problem, this paper explores and compares the effects of Empirical Mode Decomposition, Ensemble Empirical Mode Decomposition, Complementary Ensemble Empirical Mode Decomposition, and Variational Mode Decomposition (VMD) in array acoustic full wave train decomposition, proves that using VMD method to decompose array acoustic full wave train has better effect, extracts the time–frequency distribution characteristics (including time edge, frequency edge and cumulative energy) of the first four full wave train Intrinsic Mode Functions, and analyzes response of time–frequency characteristics of Intrinsic Mode Functions on gas and water layers. The results show that the VMD decomposition can suppress the phenomenon of mode aliasing better, and each component represents different mode waves information in the full wave train. On features of time–frequency distribution, the peak arrival time and dominant frequency energy of IMF2, IMF3, and IMF4 show obvious response on the gas and water layer, and the cumulative energy of IMF2 and IMF3 components shows obvious response on the gas and water layer. Compared with the other three mode decomposition methods, the time–frequency characteristics of the Intrinsic Mode Function decomposed by VMD have an obvious response on the tight sandstone gas and water layer. [ABSTRACT FROM AUTHOR]

Tight sandstone reservoirs are affected by various factors such as pore structure, formation water salinity, and siliceous cementation, which lead to the abnormal phenomenon of high-resistivity water layers and increase the difficulty in identifying gas and water layers by conventional logging. In this study, the pore types and pore size distribution characteristics of tight sandstone reservoirs were firstly determined by NMR and high-pressure mercury injection experiments, and then the iterative least-square method was used to automatically optimize the inversion method of pseudo-capillary pressure curve and search for the optimal conversion coefficient. Finally, the apparent free water porosity was inversed and the fluid identification standard was obtained and applied. The results showed that the reservoirs mainly developed intergranular pores, cutting solution pores, and intergranular pores. The pore throats were poorly sorted, and the displacement pressure was high. The median radius ranged from 0.01 to 0.48 μm, and the main peak range was from 0.02 to 0.06 μm. Pores were of mainly small-hole fine throat type. In the inversion results of the optimal conversion coefficient, the correlation coefficient between the aperture parameters and the results of high-pressure mercury injection experiments was greater than 0.93. According to the fluid property identification standard based on nuclear magnetic apparent free water porosity, the high-resistivity water layers were effectively identified and its coincidence rate with the final field test was 10.7% higher than that of the conventional method. This identification method can be used to identify complex fluids in tight sandstone reservoirs. [ABSTRACT FROM AUTHOR]

• 23-8N engine valve steel was treated by ultrasonic surface rolling technique. • The microstructures of the modified layer were nano-scale lamellar grains. • The treatment led to a reduction in surface roughness and coefficient of friction. • The fatigue strength and wear resistance were increased after treatment. • The cracks initiation mechanism was influenced by the residual stress in specimens. An ultrasonic surface rolling (USR) technique was employed for the first time as a method to enhance the fatigue and wear resistance of 33Cr23Ni8Mn3N (23-8N) austenitic engine valve steel. The microstructure of the modified layer on the material surface was characterised by scanning electron microscopy (SEM) coupled with electron back scatter diffraction (EBSD) and transmission electron microscope (TEM) methods. Nanoscale lamellar grains were discovered on the top surface of the treated material, and an increase of compressive residual stress and microhardness of the surface material observed. A comparative fretting wear test and a rotating bending fatigue test were performed out to verify the surface enhancement effect. Fractured and worn faces of specimens were evaluated through utilizing SEM and energy–dispersive spectroscopy (EDS). Compared to the untreated material, the coefficient of friction of USR treated material was significantly reduced, and the wear resistance was improved. The fatigue strength of a specimen treated at 25 °C was increased from 528 MPa to 730 MPa (38.3%). At 650 °C, the fatigue strength increased from 345 MPa to 400 MPa (15.9%). The fatigue resistance extension and wear resistance improvement of treated specimen can be attributed to a combination of beneficial compressive residual stress, work hardening, and the modified microstructure with fine-grains in the surface layer, and thus demonstrates the validity of this novel technique. [ABSTRACT FROM AUTHOR]

Increasing performance of IC engines often leads to higher combustion temperatures causing premature failure of exhaust valves. This paper presents for the first time a tribological assessment of hollow head & sodium filled valves (HHSVs) produced using a new and novel manufacturing process. Tests were conducted on HHSVs using bespoke bench-top wear and fatigue apparatus and they survived defined durability tests. Compared to traditional solid valves; the highest temperature of the hollow stem & sodium filled valves decreased from 745 °C to 590 °C, the new design and manufacturing process did not adversely affect the classical wear mechanisms (e.g. oxidation accelerated adhesion) or the material loss magnitude, and the design of HHSVs gives a 16.1% reduction in mass. [ABSTRACT FROM AUTHOR]

The shale oil reservoir of the Lucaogou Formation in the Jimsar Sag has undergone tectonic movement, regional deposition and complex diagenesis processes. Therefore, various reservoir space types and complex combination patterns of pores have developed, resulting in an intricate pore throat structure. The complex pore throat structure brings great challenges to the classification and evaluation of reservoirs and the efficient development of shale oil. The methods of scanning electron microscopy, high-pressure mercury injection, low-temperature adsorption experiments and thin-slice analysis were used in this study. Mineral, petrology, pore throat structure and evolution process characteristics of the shale oil reservoir were analyzed and discussed qualitatively and quantitatively. Based on these studies, the evolution characteristics and formation mechanisms of different pore throat structures were revealed, and four progressions were made. The reservoir space of the Lucaogou Formation is mainly composed of residual intergranular pores, dissolved pores, intercrystalline pores and fractures. Four types of pore throat structures in the shale oil reservoir of the Lucaogou Formation were quantitatively characterized. Furthermore, the primary pore throat structure was controlled by a sedimentary environment. The pores and throats were reduced and blocked by compaction and cementation, which deteriorates the physical properties of the reservoirs. However, the dissolution of early carbonate, feldspar and tuffaceous minerals and a small amount of carbonate cements by organic acids are the key factors to improve the pore throat structure of the reservoirs. The genetic evolution model of pore throat structures in the shale oil reservoir of the Lucaogou Formation are divided into two types. The large-pore medium-fine throat and medium-pore medium-throat reservoirs are mainly located in the delta front-shallow lake facies and are characterized by the diagenetic assemblage types of weak compaction–weak carbonate cementation–strong dissolution, early medium compaction–medium calcite and dolomite cementation–weak dissolution. The medium-pore fine throats and fine-pore fine throats are mainly developed in shallow lakes and semi-deep lakes. They are characterized by the diagenetic assemblage type of strong compaction–strong calcite cementation–weak dissolution diagenesis. This study provides a comprehensive understanding of the pore throat structure and the genetic mechanism of a complex shale oil reservoir and benefits the exploration and development of shale oil. [ABSTRACT FROM AUTHOR]

The wave propagation and vibration transmission in metamaterial-based elastic rods with periodically attached multi-degree-of-freedom (MDOF) dynamic anti-resonant vibration isolator (DAVI) resonators are investigated. A methodology based on a combination of the transfer matrix (TM) method and the Bloch theorem is developed, yielding an explicit formulation for the complex band structure calculation. The bandgap behavior of the periodic structure arrayed with single-degree-of-freedom (SDOF) DAVI resonators and two-degree-of-freedom (2DOF) DAVI resonators are investigated, respectively. A comparative study indicates that the structure consisting of SDOF DAVI resonators periodically jointed on the metamaterial-based elastic rod can obtain an initial locally resonant band gap 500 Hz smaller than the one given in the published literature. The periodic structure containing 2DOF DAVI resonators has an advantage over the periodic structure with SDOF DAVI resonators in achieving two resonance band gaps. By analyzing the equivalent dynamic mass of a DAVI resonator, the underlying mechanism of achieving a lower initial locally resonant band gap by this periodic structure is revealed. The parameters of the 2DOF DAVI resonator are optimized to obtain the lowest band gap of the periodic structure. The numerical results show that, with the optimal 2DOF DAVI parameters, the periodic structure can generate a much lower initial locally resonant band gap compared with the case before the optimization. [ABSTRACT FROM AUTHOR]

This article investigated the effect of different ultrasonic surface rolling (USR) processing parameters on microstructure, surface layer properties, and fretting wear properties of a kind of high strength and high toughness titanium alloy Ti5Al4Mo6V2Nb1Fe. With the aid of SEM, TEM, EDS, and 3D-profile scanning, the surface layer of specimens was characterized and analyzed. The experimental results showed that the severe plastic deformation took place on the specimen surface layer. The thickness of plastic deformation layer could reach more than 230 μm. The grains in the surface layer were refined, which was induced by dislocations of high density, such as dislocation tangles and dislocation walls. The surface layer properties were improved compared with untreated specimen: the surface roughness decreased from 0.18 μm of untreated specimen to 0.06 μm; the microhardness of surface increased about 20%; the compressive residual stress about −1000 MPa occurred. The wear rate reduced about 70% after USR and the fretting wear resistance was improved. • The paper studies the ultrasonic surface rolling (USR) of a high strength and high toughness Ti alloy Ti5Al4Mo6V2Nb1Fe. • The effects of USR on the surface layer microstructure, properties, and fretting wear properties are investigated. • The surface layer properties and fretting wear resistance are promoted after USR treatment. [ABSTRACT FROM AUTHOR]

In this work, the shot peening (SP) treatment with different processing parameters was introduced to 17Cr2Ni2MoVNb steel. The finite element model (FEM) was performed in the same experimental conditions and the simulative results were compared with experimental results to study the residual stress distribution. In addition, the microhardness, surface morphology and tribological behaviors of SP treated samples were investigated and evaluated. Results showed that compressive residual stress was positively proportional to the SP velocity. During the tribological tests, the SP treated samples could obtain lower coefficient of friction (COF) and better wear resistance than the untreated samples. Moreover, the wear mechanisms of untreated and SP treated samples were ploughing and abrasive wear, respectively. • Using the Johnson-Cook model, the multi-shot cases are established based on the calculation results of the single shot. • The effects of shot peening parameters on residual stress distribution are studied by experiments and simulation. • The treated samples shows lower COFs and better wear resistance. • The main wear mechanisms of untreated and SP samples are ploughing and abrasive wear, respectively. [ABSTRACT FROM AUTHOR]

Due to their design, hollow cavity and filled sodium, hollow head and sodium filled engine valves (HHSVs) have superior performance to traditional solid valves in terms of mass and temperature reduction. This paper presents a new manufacturing method for 42Cr9Si2 steel hollow head and sodium filled valves. An inertia friction welding process parameter optimization was conducted to obtain a suitable process parameter range. The fatigue strength of 42Cr9Si2 steel at elevated temperatures was evaluated by rotating bending fatigue test with material specimens. Performance evaluation tests for real valve components were then carried out using a bespoke bench-top apparatus, as well as a stress evaluation utilizing a finite element method. It was proved that the optimized friction welding parameters of HHSV can achieve good welding quality and performance, and the HHSV specimen successfully survived defined durability tests proving the viability of this new method. The wear resistance of the HHSV specimens was evaluated and the corresponding wear mechanisms were found to be those classically defined in automotive valve wear. [ABSTRACT FROM AUTHOR]

Titanium and its alloys are one of the mainstream materials for the manufacture of intervertebral cages. With the application on clinical, the problems of elastic modulus is relatively high, subsidence of adjacent vertebral implants and stress shielding after surgery have gradually exposed. In this paper, metal rubber made from titanium alloy wire was used to prepare cervical fusion cage (CFC), which was a porous material with buffering and vibration damping properties. The C5/C6 segment of the goat cervical vertebra was used as the research object. The shape parameters of the CFC were determined by combining the three-dimensional model data of the cervical vertebra and the structural characteristics of the natural intervertebral disc. The force of CFC under different working conditions were simulated and analyzed by finite element simulation. Then three kinds of metal rubber core (MRC) were prepared by medical titanium alloy wire (TC4), and their mechanical properties and fatigue strength were experimentally studied. With the increases of density, the mechanical properties of MRC improved. The variation range of the loss factor η under different amplitudes and frequencies were 20% and 16.3%, respectively. After one million vibrations, the wear rate was 0.131 g/MC; after five million vibrations, the wear rate was 0.158 g/MC, which was similar to the existing clinical prosthesis wear rate. The MRC has sufficient mechanical strength. Compared with the existing clinical prostheses, it has a longer service life and has broad application prospects. [ABSTRACT FROM AUTHOR]

The influence of ultrasonic surface rolling (USR) treatment on microstructures, residual stress, microhardness and fretting wear behaviors of 20CrMoH steel under different quenching temperatures (740, 840 and 940 °C) was systematically investigated. The results indicated that the maximum hardening layer depth of the USR treated specimen quenched at 740 °C was about 130 μm, accompanied by grain refinement and high-density dislocations. Simultaneously, the microhardness was mostly increased by 212 HV 0.2 and the highest surface residual compressive stress (RCS) was up to −649 MPa. The fretting wear mechanisms of the specimens in different treatment states were mainly delamination and oxidative wear. The volume wear loss of the USR treated specimen quenched at 940 °C was reduced by 48% compared with the untreated specimen quenched at 740 °C. This could be benefited from the protection of the oxide layer and the effective prevention of cracks source by the higher surface RCS, as well as the grain refinement and the increase in dislocations caused by USR treatment. • The maximum hardening layer depth of the USR treated specimen is 130 μm. • The surface RCS is 256.52% higher than the corresponding untreated specimen. • The surface roughness Ra value is reduced from 1.03 μm to 0.36 μm. • The average surface grain size of the USR treated 20CrMoH reaches 17 nm. • The USR treated 20CrMoH quenched at 940 °C obtains the best wear resistance. [ABSTRACT FROM AUTHOR]

Rolling contact fatigue (RCF) characteristics of 0.1C–3Cr–2W–V nitrided and untreated steel have been investigated at ambient temperature. The results indicate that the friction coefficients of the nitrided specimens decreased from 6% to 29%, and the RCF life of the nitrided specimens have been significantly prolonged. The failure modes of the nitrided surface could be classified as spalling and delamination within the layer, and the inner defects generated by the plasma nitriding play an important role in the surface and subsurface initiated RCF. Meanwhile, decreased surface roughness and better wear-resistance are demonstrated to be useful to improving the RCF performance. [ABSTRACT FROM AUTHOR]

• RCF behaviors of combined treated sample under different stresses were studied. • Surface roughness and surface RCS are important factors for anti-RCF failure. • The RCF life of untreated samples was extended by 100% after the combined treatment. • The effectively synergistic influence range on the RCF life was about 1.69–2.36 GPa. • RCF failure mode changed from spalling to delamination after modification treatment. Ultrasonic surface rolling (USR), carburizing and the combined (Carburizing + USR) strengthening method were applied on the 20CrMoH steel, and the rolling contact fatigue (RCF) mechanisms of 20CrMoH steel subjected to different strengthening methods are analyzed. Results indicated that the combined strengthening method effectively increased the surface hardness value from 370 HV 0.2 to 900 HV 0.2 , produced the highest residual compressive stress (RCS) value of −920 MPa and markedly reduced the surface roughness value to 0.48 μm. Under the Hertz contact stress of 2.02 GPa, the RCF life of the combined treated samples increased by 100% compared to the carburized samples, and the delamination mainly occurred. Surface roughness and RCS are important factors for anti-RCF failure. [ABSTRACT FROM AUTHOR]

The discrete laser surface hardening (DLSH) parameters of 25CrNi2MoV steel were synthetically optimized and employed to enhance the surface sliding wear resistance under starved lubrication. Results showed that the DLSH treatment changed the sample's surface microstructures, local hardness and residual compressive stress. The proper surface quality and hardening depth can be obtained in the laser power range of 400–500 W. DLSH treatment delayed the occurrence time of severe scuffing failure and decreased the wear loss. The formed arc-shaped dimples in substrate zone between the hardened spots helped to reduce the coefficient of friction. Different matching strategies of laser power and irradiation time caused the differences of surface wear mechanism. • Laser surface hardening parameters of 25CrNi2MoV steel was synthetically optimized. • Hardness of hardened spots was 31.1–35% higher than that of the untreated samples. • DLSH treatment delayed the occurrence time of severe scuffing failure during wear. • Combined high laser power and short irradiation time had a better wear resistance. • DLSH treatment may increase the degree of delamination wear or adhesive wear. [ABSTRACT FROM AUTHOR]

Herein, shot peening (SP) using different parameters is performed on 4Cr9Si2 martensite engine valve steel at elevated temperatures. The microstructure of the modified layer is characterized via optical microscopy (OM), transmission electron microscopy (TEM), and X‐ray diffraction (XRD). High‐temperature wear tests are performed under dry sliding conditions at 450 °C using a pin‐on‐disc wear tester, and the worn surface is evaluated via scanning electron microscopy (SEM) and energy‐dispersive spectroscopy (EDS). The results show that SP refines the grains on the top surface to 19.8 nm and yields numerous dislocations. Meanwhile, the compressive residual stress and microhardness of the treated surface increase to −575 MPa and 486.33 HV0.2, respectively. At elevated temperatures, the increase in hardness provides resistance to plastic deformation and improves the performance of the oxide film. Compared with an untreated sample, sample SP4 shows a 65.23% decrease in wear rate and its wear resistance improves significantly at elevated temperatures. In addition, the wear mechanisms of SP‐treated samples are primarily oxidation wear and delamination. [ABSTRACT FROM AUTHOR]

• USR process prepared gradient nano/ultrafine grain layer on DLSH treated surface. • Severe deformation at hardened spot edge relieved the contact stress concentration. • High compressive residual stress obtained via plastic deformation of hardened zone. • Rolling contact fatigue life of DLSH samples obviously enhanced by USR treatment. • USR process did not changed the dominate failure mode at the laser hardened spot. In this paper, the effect of a novel surface treatment method that combing the discrete laser surface hardening (DLSH) and ultrasonic surface rolling (USR) on the material properties (surface roughness, microstructures, microhardness and residual stress) and rolling contact fatigue (RCF) behaviors of 25CrNi2MoV steel were investigated. A continuous-wave diode laser with a maximum output power of 2 kW was used to fabricate four different types of DLSH density samples with a size of Φ42 mm × 6 mm. The results showed that the combined USR treatment improved the surface quality (including roughness and oxide layer) of the DLSH samples, increased surface hardness, and obtained a beneficial surface compressive residual stress of up to 1240 ± 91 MPa. The severe plastic deformation introduced a gradient nano/ultrafine grain layer on both hardened zone (HZ) and substrate zone (SZ) surfaces of DLSH group samples, and the deformation depth decreased with the increase of DLSH density within 24.3–65.3 μm. Accumulation of plastic deformation below and around the HZ edge resulted in a gradient drop in hardness from HZ to SZ, which helps to relieve the occurrence of stress concentration at the surface HZ edge. Benefit from favorable factors, the RCF life of combined treated samples with hardened spot densities of 28%, 50%, 79% and 100% was increased by 82.2%, 123%, 143.6% and 171.9% compared with that of the untreated samples, respectively. After USR treatment, the failure mode within the SZ changed from spalling to delamination, but it remained as spalling failure within the HZ. [ABSTRACT FROM AUTHOR]

Laser surface texturing (LST) followed by ultrasonic surface rolling (USR) was applied to 20CrMoH steel to improve the friction and wear behavior. In this paper, the fretting friction and wear mechanisms of the modified (USR, LST + USR) 20CrMoH steel under different loads and lubrication conditions were systematically investigated. Results indicated that the regular coupling distribution of micro-texture and gradient nanostructure (GNS) was formed on the surface layer of the combined treated material. Simultaneously, the depth of the GNS was up to 22 μm and the surface microhardness was increased from 800 HV 0.2 to 860 HV 0.2. Besides, the surface roughness Ra value was decreased from 0.24 μm to 0.01 μm and the maximum residual compressive stress (RCS) value was −610 MPa. Under dry friction and high load conditions, compared with the untreated specimen, the average friction coefficient and worn losses of the combined treated specimen were reduced by about 10% and 30%, respectively. In comparison with the untreated specimen, the average friction coefficient of the combined treated specimen was decreased by 26% under the conditions of low load and oil lubrication. Especially, the fretting wear resistance was obviously improved and its worn loss was significantly reduced by 92.05% compared with the untreated material. The predominant wear mechanisms of the combined treated material under dry friction and oil lubrication were oxidation wear and abrasive wear, respectively. • The three-dimensional coupled surface was formed after the combined treatment. • Wear loss of untreated specimen was reduced by 92.05% after the combined treatment. • The combined treated sample obtained best wear resistance in low-load oil lubrication. • Oxidation wear mainly occurred for the combined treated specimen in dry friction. • Abrasive wear mainly occurred for the combined treated specimen in oil lubrication. [ABSTRACT FROM AUTHOR]

Ultrasonic rolling processing (URP) can strengthen the material surface layer and enhance the material properties. However, the surface layer of work hardening induced by URP behaves like a hard shell that can restrict further strengthening of deeper material. The URP of Ti alloy Ti5Al4Mo6V2Nb1Fe strengthened its surface layer properties, but the material performance did not improve to a greater extent. In this study, electric pulse aided ultrasonic rolling processing (EPAURP) was utilized for the nanocrystallization of the surface layer and further improvement of the Ti5Al4Mo6V2Nb1Fe properties such as wear resistance, mechanical properties, and fatigue properties. The experimental results revealed the nanocrystallization of the surface layer through the introduction of electric pulse. The nanocrystallized surface layer was approximately 300 nm thick, and the size of the nanocrystalline was about 30 nm. In addition, the EPAURP induced the formation of a serious plastic deformation (SPD) surface layer, with thickness greater than that induced by the URP. The EPAURP reduced the defects and cracks in the surface and improved the fretting wear resistance, attributing to work-hardening and nanocrystallization. The tensile properties and fatigue properties improved after EPAURP owing to the smooth surface, higher compressive residual stress, and the nanocrystallization. • EPAURP can strengthen titanium alloy Ti5Al4Mo6V2Nb1Fe better than URP. • Nanocrystallization surface layer of 300 nm thick is caused by EPAURP. • The size of nanocrystalline grains is about 30 nm. • The mechanical behaviors and fretting wear resistance can be enhanced by EPAURP. • The fatigue resistance is raised because of better properties of surface layer. [ABSTRACT FROM AUTHOR]

• Low surface roughness relieved the local stress concentration caused by asperities. • Strengthened microstructures and compressive residual stress enhanced failure life. • Failure under high lubricant viscosity was improved by ultrasonic surface rolling. • Ultrasonic surface rolling changed the failure mode from spalling to delamination. Ultrasonic surface rolling (USR) treatment was subjected to the 25CrNi2MoV shaft steel surface. The rolling contact fatigue (RCF) properties of treated samples under different lubricant viscosities were investigated. Results showed that the USR treatment significantly refined the surface grains, improved the surface hardness and generated a compressive residual stress (CRS) field in the subsurface layer. Reduced surface roughness changed the lubrication regime between contact pairs and relieved the local surface stress concentration. USR treatment is an effective way to improve the RCF life under high lubricant viscosity. Moreover, the dominant failure mode of USR treated sample was delamination. [ABSTRACT FROM AUTHOR]

• A combined treatment of ultrasonic surface rolling and shot peening was proposed. • Grain size refinement was the finest after combined treatment. • Microhardness and residual stress were the highest after combined treatment. • Combined treatment can improve rolling contact fatigue life. • Surface quality determined the type of failure mechanisms of the combined samples. A novel surface treatment method of combining ultrasonic surface rolling (USR) and shot peening (SP) in different sequences was proposed. The microstructures and rolling contact fatigue (RCF) behaviors of 17Cr2Ni2MoVNb steel were investigated after USR treatment, SP treatment and combined (USR + SP + USR) treatment. Results showed that the combined treatment can significantly generate ultra-fine grains, improve surface microhardness and induce high intensity residual compressive stress in material surface layer. The samples after combined treatment with the lowest surface roughness exhibited the maximum mean RCF life of 6.610 × 106 cycles and the fatigue damage mechanism was spalling. [ABSTRACT FROM AUTHOR]