Universal Material Testing Research Articles

Process and effects of heat treatment on mechanical properties of Co-Cr alloy manufactured by selective laser melting

The selective laser melting (SLM) process of cobalt-chromium alloy and the effect of heat treatment on microstructure, mechanical properties were systematically studied. The orthogonal experiment was designed to optimize the process parameters by using EOS M290 SLM equipment. The microstructure, phase and mechanical properties were observed and tested by XRD, SEM, hardness tester and universal material testing machine. The results show that the optimum hatch distance is 0.08 mm, the scanning speed is 1110 mm/s, the laser power is 335W, the energy density is 4.8 J/mm2, the density is as high as 99.18%, and the optimum hatch angle is 67. The phase of Co-Cr alloy formed by SLM is mainly composed of (fcc) and a small amount of (hcp) phases, and the microstructure of the alloy consists of fine uniform cell crystal and columnar crystal. The hardness, tensile strength and elongation of the Co-Cr alloy formed by SLM are 41.0 HRC, 1032 MPa, 10%, and the main fracture is transgranular ductile fracture. After heat treatment, the phase transition will occur, the microstructure is mainly composed of phase and a small amount of phase, and produces a small amount of an enhanced phase M23C6(M=Cr, Mo, W); the hardness, tensile strength and elongation are increased by 6.1%, 35.9% and 17.6%, respectively; the main fracture is quasi-cleavage fracture.

Axial crushing of tubes fabricated by metal sheet bending

Energy absorption characteristics of thin-walled tubes fabricated by bending of metal sheets are studied in this work. Square tubes are prepared by folding aluminum alloy 3003 H12 sheets and quasi-static axial crushing tests are then performed with universal material testing machine. The energy absorption capacity and deformation of these folded tubes are analyzed and compared with traditional square tubes. Nonlinear finite element code LS-DYNA is employed to simulate the crushing tests and the numerical results are compared with the experiment. The influences of various factors, including the boundary condition, loading speed, fillet radius and sectional shape, on the crushing force and deformation of the folded tubes are investigated numerically. In addition, folded tubes with multi-cell sections are also analyzed and compared with traditional tubes. Some suggestions are provided for the design of folded single or multi-cell tubes. Since the folded tubes are easily prepared, cost-effective for small-scale production and flexible in both sectional shape and geometric parameters, they are quite promising to be applied widely in various engineering fields.

Properties of MWCNT–glass fiber fabric multiscale composites: mechanical properties, interlaminar adhesion, and thermal conductivity

In this study, multiscale MWCNT–glass fiber fabric (MGFf) preforms with multiwalled carbon nanotubes (MWCNTs) dispersed onto commercial E-glass fiber fabric (GFf) was used to fabricate the MGFf multiscale composites. The mechanical properties, interlaminar shear strength (ILSS), dynamic viscoelasticity and thermal conductivity of MGFf multiscale composites were investigated using a universal material testing machine, dynamic mechanical thermal analyzer and transient plane source method. Furthermore, the reinforcing mechanisms of MWCNTs on interlaminar adhesion of MGFf multiscale composites were explored using scanning electron and transmission electron microscopy and energy dispersive X-ray spectrometry. Compared with the GFf composite, the ILSS and thermal conductivity of MGFf multiscale composites were increased by 40.5% and 55.3%, respectively; both of the tensile and flexural properties of MGFf multiscale composites were significantly enhanced; the glass transition temperature of MGFf multiscale composites was also raised. In addition, the interface thickness was increased with the addition of MWCNTs, and MWCNTs in MGFf multiscale composites behaved as hooked fibers to improve the interlaminar adhesion. The work demonstrates the great promise of MGFf preforms toward practical industrial application in manufacturing multifunctional fiber composites with high strength and modulus, high shear resistance and good thermal conductivity.

The Effect of Al on the Mechanical Properties and Microstructure of Copper-based Metallic Glass

An investigation was carried out into the effect of different amounts of Al on the mechanical properties, and glass-forming ability, of a three component alloy (Cu–Zr–Al). The mechanical properties were studied using a universal materials tester and a Split-Hopkinson bar tester. A series of amorphous alloys with different Al content were subjected to static compression and dynamic high-speed impact tests at 10−1 s−1, 10−2 s−1, and 10−3 s−1 for the static condition and 2000 s−1, 3000 s−1, and 4000 s−1 for the dynamic condition. Experiment showed that the flow stress value and the strain rate sensitivity coefficient of the copper-based amorphous alloys varied with changes of strain and strain rate. An increase in the rate of strain caused the flow stress value and the sensitivity coefficient of the strain rate to rise. When the Al content in an amorphous alloy Cu47.5Zr45.5Al7 was 7%, both the flow stress value and the strain were improved and effectively upgraded the mechanical properties of the material.

Effect of Bamboo Flour Grafted Lactide on the Interfacial Compatibility of Polylactic Acid/Bamboo Flour Composites.

Bamboo flour (BF) was grafted onto lactide (LA) in the molten state using stannous octoate as a catalyst to form BF-g-LA. Then, polylactic acid (PLA) was blended with BF (PLA/BF, 85/15 wt %) to prepare PLA/BF/BF-g-LA composites using BF-g-LA as a compatibilizer. The grafting rate of BF was characterized using infrared testing and elemental analysis. To investigate the effect of BF-g-LA on the performance of PLA/BF/BF-g-LA composites, the phase morphology, thermal stability, and mechanical properties of the composites were characterized using scanning electron microscopy, thermogravimetric analysis, and universal material testing, respectively. The addition of BF-g-LA improved the interface compatibility between PLA and BF. When the BF-g-LA content was 2 phr, the tensile and impact strengths of PLA/BF/BF-g-LA composites were 55.3 MPa and 9.56 kJ/m2, representing 30% and 27% increases, respectively, relative to corresponding values for PLA/BF composites.

Study on impact of UV curing process of digital light processing 3-D printer on the mechanical properties and dimensional accuracies

In the last decade, there has been an exponential increase of the scientific interest for smart additive manufacturing (AM) technology. Among the different AM techniques, the most commonly applied processes are digital light processing (DLP). DLP is a laser-based process that works with photopolymer resins, which react with the ultraviolet (UV) and is cured to form a solid in a very precise way to produce parts with high dimensional accuracy. However, because of the scattering effect when UV light passes through the transparent vat and different polymerization characteristics and curing depth of photopolymer resins, there are lots of parameters of DLP printers need to be optimized. Among these, exposure time affects the quality of the 3D printed specimen. If it is not optimized, it brings about problems such as poor mechanical properties and poor dimensional accuracy. Therefore, this study examinedoptimal exposure time. With a same specimen and layer thickness, the photopolymer resin was exposed to the UV light in different times to evaluate the influence of it. The UV mercury lamp, 240 W and wavelength of 385-650nm is used. To investigate the effect of exposure time on the mechanical strength, the tensile strength and young’s modulus were experimentally determined using universal material test machine.

Effects of cold deformation on microstructure and mechanical properties of Ti–35Nb–2Zr–0.3O alloy for biomedical applications

The Ti–35Nb–2Zr–0.3O (mass fraction, %) alloy was melted under a high-purity argon atmosphere in a high vacuum non-consumable arc melting furnace, followed by cold deformation. The effects of cold deformation process on microstructure and mechanical properties were investigated using the OM, XRD, TEM, Vicker hardness tester and universal material testing machine. Results indicated that the alloy showed multiple plastic deformation mechanisms, including stress-induced α” martensite (SIM α”) transformation, dislocation slipping and deformation twins. With the increase of cold deformation reduction, the tensile strength and hardness increased owing to the increase of dislocation density and grain refinement, and the elastic modulus slightly increased owing to the increase of SIM α” phase. The 90% cold deformed alloy exhibited a great potential to become a new candidate for biomedical applications since it possessed low elastic modulus (56.2 GPa), high tensile strength (1260 MPa) and high strength-to-modulus ratio (22.4×10−3), which are superior than those of Ti–6Al–4V alloy.

Enhanced ACL Graft Incorporation by Novel Minimally Invasive Activation of Endogenous Stem Cells

Objectives:The ultimate healing of a ligament graft to bone is a lengthy process that results in reparative tissue that is distinctly different from a native ligament insertion. This known structural aberration results in inferior biomechanical properties and can contribute significantly to recurrent injury as well as compromised function. Thus, technology allowing for accelerated biologic incorporation as well as the recapitulation of a native insertion would be of great benefit to patients. We hypothesized that the treatment of anterior cruciate ligament (ACL) reconstruction bone tunnels with bone morphogenetic protein (BMP) DNA combined with a pulse of ultrasound (US) energy would lead to activation of endogenous stem cells and result in enhanced graft incorporation.Methods:Soft tissue allograft ACL reconstruction was performed in nine mini-pigs using cortical screw post fixation. A collagen scaffold was added to the terminus of each tendon graft limb contained within the corresponding bone tunnel. On post-operative day 14, a lipid microsphere solution containing DNA encoding either green fluorescence protein (GFP, n=3 pigs) or BMP-6 (n=6 pigs) was delivered into the bone tunnels percutaneously under fluoroscopic guidance. The bone tunnels in the US treated group were then immediately treated with a transcutaneous US energy pulse at the site of the bone tunnels, whereas the control group did not receive US delivery. At five days post-treatment the cells occupying the bone tunnels of the GFP treated pigs (n=3) were harvested and subjected to fluorescence-activated cell sorting (FACS) analysis to assess for expression of GFP as well as known mesenchymal stem cell (MSC) markers (CD29, CD44, CD90). Six weeks post-treatment the BMP/US treated pigs (n=3) and control pigs (n=3) were sacrificed and their knee joints were scanned using microCT. Biomechanical testing of anterior-posterior (AP) knee laxity was performed via application of sinusoidal AP-directed shear loads for 12 cycles. Load to failure was assessed by removal of the joint capsule, menisci, collateral ligaments, and the PCL leaving only the ACL graft intact. The tibia and femur were then mounted on a universal material testing machine with a 5kN load cell and distracted until failure of the ACL graft or graft-bone interface.Results:FACS analysis done 5 days after GFP gene delivery showed that 40-50% of the cells occupying the US treated bone tunnels expressed GFP and this was significantly more than the cells in untreated bone tunnels (p< 0.05). In addition, 12-22% of the cells in the bone tunnels expressed MSC markers. Quantification of bone volume in ACL reconstruction tunnels showed significantly higher values in BMP-6/US treated animals (fig 1A,B,C; *p<0.05, t-test). AP laxities at ±20N of BMP-6/US treated pigs were lower than untreated pigs (fig 1D). The linear stiffness (fig 1E) and maximum load to failure (fig 1F) were both significantly higher than untreated pigs, demonstrating stronger graft-bone integration among the treated animals. (*p<0.05, t-test).Conclusion:Endogenous stem cell gene expression can be altered in a large animal model via novel minimally invasive techniques and this can result in enhanced ligament biomechanical properties. Minimally invasive biologic technology such as this would likely be of significant benefit to the treatment of patients undergoing ligament reconstruction procedures and more research regarding these technologies is certainly warranted.

Microstructure and fracture behavior of laser welded joints of DP steels with different heat inputs

800MPa strength cold rolled annealed DP steels was welded by different heat inputs (6–66J/mm) using 6kW fiber laser, to study the microstructure and fracture behavior of laser welded joints with sub-micron scale soften zone. The microstructure and fracture morphology of welded joints were observed by scanning electron microscope (SEM) and optical microscope (OM). Hardness, tensile properties and formability of welded joints were tested using microhardness tester, universal material testing equipment and Erichsen test machine. The results showed that the microstructure of welded joints was similar, but decomposition of martensite and precipitation of carbides was significant gradually with heat input increased such that the hardness was decreased. For the complete penetration of DP780 laser welded joints, the soften zone was impossible to eliminate by adjusting the heat input. When the size of soften zone was controlled within 539µm, the tensile properties and formability of welded joints were more than 95% of BM, due to the double effect of the size and microstructure of soften zone.

Effect of nano-SiO2 particles on the carbon fabric/resin friction materials by microwave-hydrothermal treatment

Nano-SiO2 was grafted onto the carbon fabric surface under microwave-hydrothermal condition to improve the tribological properties of carbon fabric/resin friction materials with different treatment temperature. The carbon fibers and prepared samples were characterized by the Fourier transform infrared spectrophotometer, contact angle instrument, energy dispersive spectroscopy, universal material testing machine and field emission scanning electron microscopy. The tribological behaviors of the carbon fabric/resin friction materials were evaluated by a friction tester. The results indicated that nano-SiO2 particles were successfully grafted onto carbon fabric surface under microwave-hydrothermal condition, especially at 200℃ (contact angle was almost close to 0°), which obviously improved the hydrophilicity of carbon fabric surface. The wear rate of carbon fabric/resin friction materials with microwave-hydrothermal temperature of 200℃ reduced by 81.4%, ranging from 4.3 × 10−5 mm3J−1 to 0.8 × 10−5 mm3J−1. It could effectively enhance the bonding strength of carbon fabric and resin, which improved the friction-reduction and anti-wear abilities of the friction materials.

Microstructure, texture evolution and mechanical properties of cold rolled Ti-32.5Nb-6.8Zr-2.7Sn biomedical beta titanium alloy

Ti-32.5Nb-6.8Zr-2.7Sn (TNZS, wt%) alloy was produced by using vacuum arc melting method, followed by solution treatment and cold rolling with the area reductions of 50% and 90%. The effects of cold rolling on the microstructure, texture evolution and mechanical properties of the experimental alloy were investigated by optical microscopy, X-ray diffraction, transmission electron microscopy and universal material testing machine. The results showed that the grains of the alloy were elongated along rolling direction and stress-induced α″ martensite was not detected in the deformed samples. The plastic deformation mechanisms of the alloy were related to {112}〈111〉 type deformation twinning and dislocation slipping. Meanwhile, the transition from γ-fiber texture to α-fiber texture took place during cold rolling and a dominant {001}〈110〉α−fiber texture was obtained after 90% cold deformation. With the increase of cold deformation degree, the strength increased owing to the increase of microstrain, dislocation density and grain refinement, and the elastic modulus decreased owing to the increase of dislocation density as well as an enhanced intensity of {001}〈110〉α−fiber texture and a weakened intensity of {111}〈112〉γ−fiber texture. The 90% cold rolled alloy exhibited a great potential to become a new candidate for biomedical applications, since it possesses low elastic modulus (47.1GPa), moderate strength (883MPa) and high elastic admissible strain (1.87%), which are superior than those of Ti-6Al-4V alloy.

The effects of fiber orientation on failure behaviors of 2D C/SiC torque tube

Different failure behaviors were observed in the 2D C/SiC torque tubes which were fabricated by chemical vapor infiltration (CVI) with different fiber orientations (0°/90° and ±45°). CT test was implemented to characterize the density heterogeneity of the ceramic matrix composite (CMC) torque tubes. With the density value measured by Archimedes drainage method, FEM software was implemented to simulate the stress distribution of the ceramic matrix composite torque tubes and calculate the failure stress. Torsional tests were conducted using special attachments to a universal material test machine. Different torsional behaviors of CMC torque tubes with two different fiber orientations were presented in the stress-strain curves. The fracture morphologies were observed by SEM, and the predominant factors of failure were analyzed. CMC torque tubes with fiber orientation of ±45° have a higher torque capacity and modulus. In failure analysis, we found that ±45° fiber orientation CMC torque tubes have reasonable fracture morphologies.

Biomechanical study of the lateral wall of the femur in the treatment of femoral intertrochanteric fracture with intramedullary or extramedullary fixation

To observe the biomechanical effects of the lateral wall of the femur in treating femoral intertrochanteric fractures with intramedullary or extramedullary fixation to guide the choice of clinical fixed methods. Twelve adults femur specimens of intertrochanteric fractures were belong to the type A1 of the AO fracture classification and randomly divided into the lateral wall complete PFNA group, the lateral wall complete PF-LCP group, the lateral wall breakage PFNA group, lateral wall breakage PF-LCP group, every group had 3 specimens. The four groups of specimens were subjected to compressive loading experiment with Universal Material Testing Machine. The maximum loading force was observed. The distance between fracture ends, the distance of fracture dislocation and the sliding distance of the fracture fragments along the intertrochanteric were measured with Calipers. The maximum loading force of lateral wall complete PFNA group were larger than that of lateral wall complete PF-LCP group, and the maximum loading force of lateral wall breakage PFNA group were larger than that of lateral wall breakage PF-LCP group, there were significant differences (P<0.05). The distance between fracture ends of the four groups before compression were not significant differences(P>0.05). The distance between fracture ends, the distance of fracture dislocation and the sliding distance of the fracture fragments were not significant differences between lateral wall complete PFNA group and lateral wall complete PF-LCP group after compression (P>0.05). But the distance between fracture ends, the distance of fracture dislocation and the sliding distance of the fracture fragments of lateral wall breakage PFNA group were less than that of lateral wall breakage PF-LCP group(P<0.05). Intramedullary fixation of intertrochanteric fractures have stronger loading force. Both intramedullary and extramedullary fixation of intertrochanteric fractures have strong stability when the lateral wall of the femur is complete, but intramedullary fixation of intertrochanteric fractures is stronger stability than extramedullary fixation when the lateral wall of the femur is broken. So the intramedullary fixation is the first choice for the treatment of intertrochanteric fracture.

Microstructure and Final Properties of Cold-Rolled Ti-32.5Nb-6.8Zr-2.7Sn-0.3O Biomedical β Titanium Alloy

Ti-32.5Nb-6.8Zr-2.7Sn-0.3O (TNZSO, wt%) alloy was melted under a high-purity argon atmosphere in an electric arc furnace, followed by cold-rolling. The effects of rolling process on microstructures and final properties were investigated using OM, XRD, TEM, TMA and universal material testing machine. Results show that no stress-induced α" martensite transformation occurred after cold-rolling. The plastic deformation mechanisms of the alloy were related to {112}〈111〉 type deformation twins and dislocation slip. With the increase of cold deformation reductions, the elastic modulus slightly decreased owing to the increase of dislocation density. The 90% cold deformed sample exhibited a great potential to become a new candidate for biomedical applications since it possesses low elastic modulus (55.3 GPa) and high tensile strength (1093 MPa), which are superior than those of Ti-6Al-4V alloy. The coefficient of thermal expansion was also low (~6×10-6°C-1 between 25 and 320°C) in the 90% CR alloy.

The influence of chemical treatment on the mechanical properties of windmill palm fiber

Bleached palm fiber without lignin, alkalized palm fiber without hemicelluloses and raw windmill palm fiber were prepared. Then, the chemical composition and the mechanical properties of the windmill palm fiber were investigated. Scanning electron microscopy, Fourier transform infrared spectroscopy and Raman microscopy were employed to characterize the structure and chemical composition. A universal material tester, nanoindentation and dynamic mechanical analysis were used to study the mechanical property of these samples. According to the results, bleach treatment removed most of the silica bodies as well as the lignin, smoothed the fiber surfaces and increased the hollowness to 50%. Alkali treatment removed most of the hemicelluloses, increased the surface roughness, and reduced the hollowness to 28%. Alkalized fibers have the highest tensile strength, elongation at break and elastic modulus, with values of 119.37 ± 27.21 MPa, 30.58 ± 5.87% and 10.75 ± 4.30 GPa, respectively. The raw material without treatment has the highest stiffness, while the alkalized samples are the most flexible fibers and sensitive to temperature.

Biomechanical comparison between cortical screw-rod construct versus pedicle screw-rod construct in transforaminal lumbar interbody fusion.

To compare construct stiffness of cortical screw (CS)-rod transforaminal lumbar interbody fusion (TLIF) construct (G2) versus pedicle screw (PS)-rod TLIF construct (G1) in the standardized porcine lumbar spine. Six porcine lumbar spines (L2-L5) were separated into 12 functional spine units. Bilateral total facetectomies and interlaminar decompression were performed for all specimens. Non-destructive loading to assess stiffness in lateral bending, flexion and extension as well as axial rotation was performed using a universal material testing machine. PS and CS constructs were significantly stiffer than the intact spine except in axial rotation. Using the normalized ratio to the intact spine, there is no significant difference between the stiffness of PS and CS: flexion (1.41 ± 0.27, 1.55 ± 0.32), extension (1.98 ± 0.49, 2.25 ± 0.44), right lateral flexion (1.93 ± 0.57, 1.55 ± 0.30), left lateral flexion (2.00 ± 0.73, 2.16 ± 0.20), right axial rotation (0.99 ± 0.21, 0.83 ± 0.26) and left axial rotation (0.96 ± 0.22, 0.92 ± 0.25). The CS-rod TLIF construct provided comparable construct stiffness to a traditional PS-rod TLIF construct in a 'standardized' porcine lumbar spine model.

Multiple Solution and Aging Treatment Technology Improves Microstructures and Properties of Ti53 Alloy

The effect of multiple solution and aging treatment on microstructures and room-mechanical properties of Ti-53 alloy is studied by OM, SEM and universal material testing machine. The results show that the quantity of secondary α lamella, hardness, strength, and plasticity of Ti-53 alloy decrease after the peak value with the cycling times of multiple solution and aging treatment increasing. In the process of double solid solution aging treatment, the numerical values of room-mechanical properties reached the highest level. Multiple solution and aging treatment modulates morphology effectively, which can make martensite lamellas with different Berlese’s vectors merge or decompose. Therefore, the excellent match of strength and plasticity can be obtained.

Mirostructure and properties of laser welded joints of dual phase and press-hardened steels

Abstract Tailor welding of 1000MPa-grade dual phase (DP) steels and 1500MPa-grade press-hardened steels (PHS) (22MnB5) with/without Al-Si coating was carried out using high power fiber laser. OM and SEM were used to observe the microstructure of welded joints. The microstructure of welded seam consisted of lath martensite and δ -ferrite because of the diffusion of Al-Si coating. Al element occurred segregaion in fusion line to form Fe-Al intermetallic compounds. The microstructural evolution in heat affected zone (HAZ) of two sides of dissimilar welded joints was similar: lath martensite (Coarse-grained HAZ) →lath martensite (Fine-grained HAZ) →martensite and ferrite (Intercritically HAZ) →tempered martensite and ferrite (Sub-critical HAZ). Softening occurred in both HAZs of dissimilar welded joints due to the forming of tempered martensite. Microhardness was tested by nano-indentation to evaluate the nano-mechanical properties of each phase in welded joints. Mechanical properties was measured by universal material testing machine. Both of the dissimilar welded joints, tensile fracture was at BM of DP980 side although Al-segregaion occurred at fusion line of DP980-PHS with Al-Si coating.

Evaluation of the osteoconductive potential of poly(propylene carbonate)/nano-hydroxyapatite composites mimicking the osteogenic niche for bone augmentation

Nano-hydroxyapatite (n-HA) reinforced poly(propylene carbonate) (PPC) composites were prepared for bone repair and reconstruction. The effects of reinforcement on the morphology, mechanical properties and biological performance of n-HA/PPC composites were investigated. The surface morphology and mechanical properties of the composites were characterized by scanning electron microscopy (SEM) and universal material testing machine. The analytical data showed that good incorporation and dispersion of n-HA crystals could be obtained in the PPC matrix at a 30:70 weight ratio. With the increase of n-HA content, the tensile strength increased and the fracture elongation rate decreased. In vitro cell culture revealed that the composite was favorable template for cell attachment and growth. In vivo implantation in femoral condyle defects of rabbits confirmed that the n-HA/PPC composite had good biocompatibility and gradual biodegradability, exhibiting good performance in guided bone regeneration. The results demonstrates that the incorporation of n-HA crystals into PPC matrix provides a practical way to produce biodegradable and cost-competitive composites mimicking the osteogenic niche for bone augmentation.

Bending strength and wear behavior of Fe-Cr-C-B hardfacing alloys with and without rare earth oxide nanoparticles

The aim of this paper was to investigate the effect of rare earth oxide (REO) nanoparticles on the bending strength and wear behavior of Fe-Cr-C-B hardfacing alloys. Fe-based hardfacing alloys with different content of REO nanoparticles were prepared. Optical microscope and scanning electron microscope were used to observe the microstructure of the Fe-based hardfacing alloys. X-ray diffractometer was used to study the phases of the hardfacing alloys. Energy dispersive spectrometer and X-ray photoelectron spectroscopy were used to study the chemical composition. HXA-1000 Vickers micro-hardness tester and Instron universal material test machine were used to study the mechanical properties of the Fe-based hardfacing alloys. Pin-on-disk wear testing machine was used to study the wear behavior of the Fe-based hardfacing alloys. The experimental results showed that REO nanoparticles refined the primary carbide and increased the volume fraction of primary carbide. REO nanoparticles increased the fracture toughness of primary carbide. REO nanoparticles improved the bending strength of the hardfacing alloys. The bending strength of the hardfacing alloy with 0.288wt.% REO nanoparticles increased by 46.4% compared to that of the hardfacing alloy without REO nanoparticles. The wear resistance of the hardfacing alloy was improved significantly by adding 0.288wt.% REO nanoparticles. The main mechanisms were abrasion wear and mild oxidative wear when normal load was 5N. When normal load was 30N, the main mechanisms were abrasion wear and severe oxidative wear accompanied by severe adhesion.