稀土复合薄膜的制备及其微摩擦学性能

在羟基化的单晶硅片上制备了3-巯丙基三甲氧基硅烷-稀土(MPTS-RE)复合薄膜。利用接触角测量仪、X射线光电子能谱仪(XPS)分析了MPTS-RE复合薄膜接触角及其表面典型化学元素的状态;运用原子力显微镜(AFM)观察了MPTS-RE复合薄膜的表面形貌并研究了其微摩擦学性能。结果表明:稀土成功组装到磺化后的MPTS薄膜表面;随着探针的滑动速率和载荷的增加,针尖与样品间摩擦力增加;硅基片和MPTS-RE复合薄膜表面的黏附力随着相对湿度的增加而增加;MPTS-RE复合薄膜具有较低的摩擦系数和黏附力。

烧结型NdFeB永磁体表面有机纳米复合膜的制备及性能

采用自组装分子膜技术在烧结型NdFeB永磁体表面制备了三嗪硫醇三乙基硅烷(TES)自组装分子膜(TES-SAMs),在TES-SAMs的基础上利用自主开发的有机镀膜技术制备了具有含氟官能团的三嗪硫醇(ATP)有机纳米复合薄膜(TES-ATP).通过X射线光电子能谱仪(XPS)、傅里叶变换红外(FTIR)光谱仪、椭圆偏振光谱仪、原子力显微镜(AFM)和接触角测量仪对薄膜的表面状况进行评价,使用UMT-2型摩擦磨损试验机研究TES-SAMs和TES-ATP的微摩擦学性能.研究结果表明:TES-SAMs和TES-ATP的膜厚分别是5.08和29.78nm;表面自由能从基体的73.13mJ·m-2下降到TES-SAMs的63.69mJ·m-2和TES-ATP复合膜的10.19mJ·m-2,且TES-ATP复合膜对蒸馏水的接触角为123.5°,成功实现了NdFeB表面由亲水到疏水的转换.TES-SAMs和TES-ATP均能有效降低摩擦系数,TES-SAMs的摩擦系数为0.22,TES-ATP的摩擦系数为0.12,而基体的摩擦系数为0.71;同时,TES-ATP还表现出良好的抗磨性能.TES-ATP复合膜为微机电系统中的摩擦磨损问题的解决提供了一种新思路.

Preparation and tribological properties of surface modified Cu nanoparticles

Cu nanoparticles surface-modified by dioctylamine dithiocarbamate （DTC8） were synthesized using a two-phase extraction route. The size, morphology and structure of resultant surface-capped Cu nanoparticles （coded as DTC8-Cu） were analyzed by means of X-ray diffraction, transmission electron microscopy and infrared spectrometry. The tribological behavior of DTC8-Cu as an additive in liquid paraffin was evaluated with a four-ball machine, and the surface topography of the wear scar was also examined by means of scanning electron microscopy. Results show that Cu nanoparticles modified by DTC8 have a small particle size and a narrow size distribution. Besides, DTC8-Cu as an additive in liquid paraffin has excellent antiwear ability, due to the deposition of nano-Cu with low melting point on worn steel surface leading to the formation of a self-repairing protective layer thereon.

Influence of Ti target current on microstructure and properties of Ti-doped graphite-like carbon films

Ti-doped graphite-like carbon （Ti-GLC） films were synthesized successfully by magnetron sputtering technique. The compositions, microstructures and properties of the Ti-doped GLC films dependent on the parameter of Ti target current were systemically investigated by Raman spectra, X-ray photoelectron spectroscopy （XPS）, X-ray diffraction （XRD）, scanning electron microscopy （SEM）, atomic force microscopy （AFM）, nanoindentation and ball-on-disk tribometer. With the increase of the Ti target current, the ratio of sp2 bond and the content of Ti as well as the film hardness and compressive internal stress increase, but the high content of the Ti would result in the loose film due to the formation of the squamose structure. Less incorporated Ti reduces the friction of the GLC film in dry-sliding condition, while pure GLC film exhibits the lowest friction coefficient in water-lubricated condition. Ti-GLC film deposited with low Ti target current shows high wear resistance in both dry-sliding and water-lubricated conditions.

Structure and mechanical properties of thick Cr/Cr_2N/CrN multilayer coating deposited by multi-arc ion plating

A Cr/Cr2N/CrN multilayer coating with a thickness of 24.4 μm was deposited by multi-arc ion plating. The coating was systematically characterized by field emission scanning electron microscopy(FESEM), X-ray photoelectron spectrometry(XPS), energy dispersive spectroscopy(EDS), X-ray diffraction(XRD) and transmission electron microscopy(TEM). Hardness and adhesion were tested by nanoindentation and scratch tester, respectively. The friction properties were investigated by a reciprocating UMT-3MT ball-on-disk tribometer in air and seawater. The results showed that the multilayer coating consisted of three different layers, with Cr,Cr2N and CrN phases, respectively. Compared with CrN single layer coating, the adhesion of the multilayer coating was improved significantly, the hardness of the multilayer coating was(21±2) GPa. The corrosion resistance of the multilayer coating was also improved in artificial seawater. The friction coefficient of multilayer coating was lower than that of CrN single layer coating both in air and seawater.

Microstructure and mechanical properties of dissimilar pure copper/1350 aluminum alloy butt joints by friction stir welding

The dissimilar friction stir welding of pure copper/1350 aluminum alloy sheet with a thickness of 3 mm was investigated. Most of the rotating pin was inserted into the aluminum alloy side through a pin-off technique, and sound welds were obtained at a rotation speed of 1000 r/min and a welding speed of 80 mm/min. Complicated microstructure was formed in the nugget, in which vortex-like pattern and lamella structure could be found. No intermetallic compounds were found in the nugget. The hardness distribution indicates that the hardness at the copper side of the nugget is higher than that at the aluminum alloy side, and the hardness at the bottom of the nugget is generally higher than that in other regions. The ultimate tensile strength and elongation of the dissimilar welds are 152 MPa and 6.3%, respectively. The fracture surface observation shows that the dissimilar joints fail with a ductile-brittle mixed fracture mode durin~ tensile test.

Microstructure and mechanical properties of dissimilar Al-Cu joints by friction stir welding

Dissimilar friction stir welding between 1060 aluminum alloy and annealed pure copper sheet with a thickness of 3 mm was investigated. Sound weld was obtained at a rotational speed of 1050 r/min and a welding speed of 30 mm/min. Intercalation structure formed at the crown and Cu/weld nugget （WN） area promotes interracial diffusion and metallurgical bonding of aluminum and copper. However, corrosion morphology reveals the weak bonding mechanism of internal interface, which causes the joint failing across the interface with a brittle-ductile mixed fracture mode. The tensile strength of the joint is 148 MPa, which is higher than that of the aluminum matrix. Crystal defects and grain refinement by severely plastic deformation during friction stir welding facilitate short circuit diffusion and thus accelerate the formation of A14Cu9 and A12Cu intermetallic compounds （IMCs）. XRD results show that A14Cu9 is mainly in Cu/WN transition zone. The high dislocation density and formation of dislocation loops are the major reasons of hardness increase in the WN.

Microstructure and mechanical properties of friction stir welded AA7075-T651 aluminum alloy thick plates

Friction stir butt welding of AA7075-T651 plates with thicknesses of 10 and 16 mm was investigated. Defect-free, full- penetration welds were obtained after careful process parameter selection. While the nuggets in both welds exhibited very fine reerystallized grains, and finer grains were observed in welds made on 10 mm thick plates. Microhardness surveys revealed that significant loss in hardness occurs in the heat-affected zone. The reduction in hardness due to the welding process is higher in the case of welds made on 16 mm thick plates. Welds made on 10 mm thick plates exhibited superior tensile properties compared with those made on 16 mm thick plates. Fracture during tensile test occurred in the heat-affected zone in both cases. TEM images of specimens revealed that the heat-affected zone consisted of widened precipitate-free zones along grain boundaries and partial dissolution of precipitates in the grain interiors. It is concluded that defect-free single pass welds can be made on AA7075-T651 thick plates using friction stir welding and the welds made on 10 mm thick plates exhibit high joint efficiency.

Microstructure and mechanical properties of dissimilar pinless friction stir spot welded 2A12 aluminum alloy and TC4 titanium alloy joints

The microstructure and mechanical properties of dissimilar pinless friction stir spot welded joint of2A12aluminum alloy and TC4titanium alloy were evaluated.The results show that the joint of Al/Ti dissimilar alloys can be successfully attained through pinless friction stir spot welding(FSSW).The joint can be divided into three zones(SZ,TMAZ and HAZ).The microstructure of joint in Al alloy side changes significantly but it basically has no change in Ti alloy side.At the same rotation speed,the maximum load of welded joints gradually rises with the increase in dwell time.At the same dwell time,the maximum load of the welded joint increases with the increase of the rotational speed.In addition,optimal parameters were obtained in this work,and they are rotation speed of1500r/min,plunge speed of30mm/min,plunge depth of0.3mm and dwell time of15s.The fracture mode of welded joints is interfacial shear fracture.The microhardness of the joint on the Al side distributes in a typical“W”type and is symmetry along the weld center,but the distribution of the microhardness on the Ti side has no obvious change.

Effect of ultrasonic assisted friction stir welding on microstructure and mechanical properties of AZ91-C magnesium alloy

The influence of ultrasonic vibrations on microstructure and mechanical properties of the AZ91-C magnesium alloy after ultrasonic assisted friction stir welding(UaFSW)in comparison with conventional friction stir welding(FSW)was investigated.The FSW was applied at the rotational speed of 1400 r/min and welding speed of 40 mm/min and no defects were observed.Using the same welding parameters,the process was carried out with inducing ultrasonic vibrations to the weld line at the amplitude of 15μm.The microstructure of the specimens was observed with optical and scanning electron microscopy.The results indicate that a very fine microstructure is obtained in UaFSW with respect to that of conventional FSW.Moreover,β-Mg17Al12 coarse dendrites are segregated to very fine and partly spherical particles that homogeneously distribute inα-Mg matrix.This remarkably-modified morphology of microstructure attributed to severe plastic deformation comes from ultrasonic vibration and friction stirring effect.Tensile and hardness tests were performed to evaluate the mechanical properties of the welds.According to the results,the vibration greatly improves the mechanical properties of the conventional FSW joint.The tensile strength and hardness are increased from 195 MPa and HV 79 in conventional FSW to 225 MPa and HV 87 in UaFSW,respectively.

Effects of heat input in friction stir welding on microstructure and mechanical properties of AA3003-H18 plates

The non-heat-treatable AA3003-H18 plates were joined by friction stir welding（FSW） to achieve a proper joint by optimizing the welding parameters.For this purpose,the effects of heat input on microstructure and mechanical properties of the welded samples were investigated by changing the ratios of rotational speed（800-1200 r/min） to travel speed（40-100 mm/min）（w/v）.It was revealed that the grain growth rate was strongly increased with the increase of the heat input by rotational speed at constant travel speed,while the grain growth rate was slightly increased with the increase of the heat input by travel speed at constant rotational speed.Subsequently,hardness reduction was observed in the stir zone at higher rotational speed compared with that at lower one.An interesting observation was that various welding parameters do not have noticeable effect on the tensile strength of the FSW joints.Also,it has been observed that the fracture location of tensile test specimens was placed in the heat-affected zone（HAZ）on the advancing side at lower travel speed,while at higher travel speed,it was placed at the HAZ/thermomechanical affected zone（TMAZ） interface on the retreating side.

Effect of arc re-melting on microstructure,mechanical and tribological properties of commercial 390A alloy

To investigate the effect of the arc re-melting on the microstructure,mechanical and tribological properties of the 390 A alloy,its ingot produced by the conventional induction melting method was subjected to the arc re-melting process.The microstructure of the 390 A alloy was examined by OM and SEM.Mechanical properties of the 390 A alloy were determined by the Brinell method and tensile tests.Tribological properties were investigated with a ball-on-disc type tester.It was observed that the microstructure of both conventional induction melted and arc re-melted 390 A alloys consisted ofα(Al),eutectic Al-12 Si,primary silicon particles,θ-CuAl_(2),β-Al_(5) FeSi,δ-Al_(4) FeSi_(2),andα-Al_(15)(FeMnCu)3 Si_(2) phases.Re-melting with the arc process caused grain refinement in these phases.In addition,after this process,theα(Al)phase and primary silicon particles were dispersed more uniformly,and sharp edges of primary silicon particles became round.The arc re-melting process resulted in an increase in the hardness of the 390 A alloy produced by the conventional method from 102 HB to 118 HB and the tensile strength from 130 to 240 MPa.It also caused an increase in the wear resistance of the 390 A alloy and a decrease in the friction coefficient.

Application of vibration to enhance efficiency of friction stir processing

Friction stir processing (FSP) is a solid-state modification method to process the surface of metals. In this process, due to rotation and traverse motions of a non-consumable tool, metal surface microstructure is refined and its mechanical characteristics are improved. Different methods have been applied to improving the efficiency of FSP. In this research, a new method entitled friction stir vibration processing (FSVP) was presented to enhance the efficiency of FSP. In this method, metal workpiece was vibrated normal to processing line during FSP. Microstructure and mechanical properties including hardness, ultimate tensile strength (UTS) and elongation of Al5052 alloy specimens processed using FSP and FSVP methods were analyzed and compared. The results showed that grain size decreased by about 33% as vibration was applied. It was also observed that ultimate tensile strength as well as hardness increased by about 7% as FSVP was applied. This was related to the enhanced straining of metal surface material as vibration was applied. The increase in straining results in the increase of dislocation density. It leads to more development of high angle grain boundaries due to dynamic recrystallization. The results also showed that UTS and elongation of FSV processed specimens increased as vibration frequency increased.

Effect of reverse dual rotation process on properties of friction stir welding of AA7075 to AISI304

The friction stir lap welding of AISI304 stainless steel to AA7075 aluminium alloy was investigated using the conventional friction stir welding (C-FSW) and the reverse dual rotation friction stir welding (DR-FSW) processes. In order to reduce the heat input, a dual rotation tool with a lower shoulder rotating speed was used. The results showed that both processes provide welds with excellent appearance and free of internal defects. The use of the DR-FSW process with the tool shoulder rotating reversely at low speed results in larger grain refinement in the nugget and less change in the microstructure of the aluminium alloy than using the C-FSW. The use of DR-FSW process at low speed of rotation allows to reduce the amount of intermetallic compounds in the welding interface, but does not prevent their formation. Although DR-FSW welding exhibits tensile strength superior to that achieved with the conventional process (C-FSW), both exhibit brittle behaviour with fracture at the weld interface.

Effects of TaN nanoparticles on microstructure,mechanical properties and tribological performance of PEEK coating prepared by electrophoretic deposition

In order to solve the friction,wear and lubrication problems of titanium,a series of TaN/ployether−ether−ketone(PEEK)coatings were developed by electrophoretic deposition,and the effects of TaN nanoparticles on the microstructure,mechanical properties and tribological performance of coatings were explored.Results manifest that the introduction of TaN nanoparticles into PEEK coatings could improve the deposition efficiency,enhance the resistant deform capacity,increase the hardness,elastic modulus and adhesive bonding strength.Compared with the pure PEEK coating,the friction coefficient of P-TN-3 was greatly reduced by 31.25%.The wear resistance of P-TN-3 was also improved in huge boost,and its specific wear rate was decreased from 9.42×10^(−5) to 1.62×10^(−5) mm^(3)·N^(−1)·m^(−1).The homogeneous composite TaN/PEEK coatings prepared by electrophoretic deposition were well-adhered to the titanium alloy substrate,TaN nanoparticles could improve the strength of PEEK coating,and provide wear-resistance protection for titanium alloys.

Achieving High-Quality Aluminium Alloy Welded Joint with Fine Grains Using Submerged Friction Stir Welding

The purpose of this study is to reveal the microstructure and mechanical properties of friction stir welding(FSW)joints prepared in water/air.For comparable analysis,the submerged FSW(SFSW)and conventional FSW are both conducted on 6061-T6 aluminum alloy plates at the combination rotation speed of 800 r/min and the traverse rate of 50 mm/min.The results show that a greatest grain refinement is achieved by SFSW,which is remarkably smaller than that of the base material(BM)and air FSW(AFSW)samples,leading to a significant improvement of tensile strength from 202.5 MPa in the AFSW sample to 232 MPa in the SFSW sample.

Microstructure and mechanical properties of continuous drive friction welded Ti_(2)AlNb alloy under different rotational rates

Ti_(2)AlNb-based alloy was joined in a continuous drive friction welding machine under different rotational rates(500,1000 and 1500 r/min).The microstructure and mechanical properties of the joints were investigated.It is shown that the weld zone(WZ) is fully composed of recrystallized B2 phase,and the grain size decreases with increasing rotational rate.The thermo-mechanically affected zone(TMAZ) suffers severe deformation during welding,due to which most of original precipitation phase is dissolved and streamlines are present.In the heat affected zone(HAZ),only the fine O phase is dissolved.The as-welded joint produced using 1000 r/min has the best mechanical properties,whose strength and elongation are both close to those of the base metal,while the as-welded joint obtained using 500 r/min exhibits the worst mechanical properties.Post-weld annealing treatment annihilates the deformation microstructure and fine O phase precipitates in the joints,consequently improving the mechanical properties significantly.Decomposed α_(2) phase is a weakness for the mechanical performance of the joint since microcracks are apt to form in it in the tensile test.

Effect of oxide film on nanoscale mechanical removal of pure iron

In this paper, the properties of an oxide film formed on a pure iron surface after being polished with an H2O-based acidic slurry were investigated using an atomic force microscope （AFM）, Auger electron spectroscopy （AES）, and angle-resolved X-ray photoelectron spectroscopy （AR-XPS） to partly reveal the material removal mechanism of pure iron during chemical mechanical polishing （CMP）. The AFM results show that, when rubbed against a cone-shaped diamond tip in vacuum, the material removal depth of the polished pure iron first slowly increases to 0.45 nm with a relatively small slope of 0.11 nm/μN as the applied load increases from 0 to 4 μN, and then rapidly increases with a large slope of 1.98 nm/μN when the applied load further increases to 10 μN. In combination with the AES and AR-XPS results, a layered oxide film with approximately 2 nm thickness （roughly estimated from the sputtering rate） is formed on the pure iron surface. Moreover, the film can be simply divided into two layers, namely. an outer layer and an inner layer. The outer layer primarily consists of FeOOH （most likely α-FeOOH） and possibly Fe2O3 with a film thickness ranging from 0.36 to 0.48 nm （close to the 0.45 nm material removal depth at the 4 μN turning point）, while the inner layer primarily consists of Fe304. The mechanical strength of the outer layer is much higher than that of the inner layer. Moreover, the mechanical strength of the inner layer is quite close to that of the pure iron substrate. However, when a real CMP process is applied to pure iron, pure mechanical wear by silica particles generates almost no material removal due to the extremely high mechanical strength of the oxide film. This indicates that other mechanisms, such as in-situ chemical corrosion-enhanced mechanical wear, dominate the CMP process.