车轴的微动摩蚀与对策

微动摩蚀能引起一种或多种形式的破坏，如微动磨损、微动疲劳。微动量、滑移区域的大小与轮座的型式、轮毂刚度、法向力的大小等因素有关。试验表明，微动摩蚀可使构件的疲劳强度降低３０％～８０％，实物轮轴试验结果验证，车轴压装的裂纹或断裂都是由于微动摩蚀所致。在微动区域加保护层可有效地防止微动摩蚀。预处理工艺选择恰当，可使其疲劳强度提高５０％，实物轴已装车运行４０多万公里，情况良好。

达尔其油田油井摩蚀与防治措施

达尔其油田达14和达33区块油井发现偏摩和腐蚀现象,腐蚀因素包括pH值、氯离子、硫酸盐还原菌和总铁含量等.实验表明,油井的平均腐蚀速率为0.1 mm/a,腐蚀产物包括钙铁氧化物Ca_4Fe_9O_(17)和碳酸盐Mg_3Ca(CO_3)_4等,对偏摩和腐蚀的相互作用机理进行了分析,发现在油井中管杆腐蚀和磨损之间相互促进,针对以上情况提出加注杀菌剂和缓蚀剂、井斜段抽油杆使用双向保护接箍等针对摩蚀的防治措施,SRB由104个/mL降至10个/mL,平均腐蚀速率也下降到0.045 mm/a,达14区块的平均检泵周期从原来的平均216 d延长到478 d,延长一倍以上。

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.

Fabrication, tribological and corrosion behaviors of detonation gun sprayed Fe-based metallic glass coating

A metallic glass coating with the composition of Fe51.33Cr14.9Mo25.67Y3.4C3.44B1.26 （mole fraction, %） on the Q235 stainless steel was developed by the detonation gun （D-gun） spraying process. The microstructure and the phase aggregate were analyzed by scanning electron microscopy and X-ray diffractometry, respectively. Microhardness, wear resistance and corrosion behavior were assessed using a Vickers microhardness tester, a ball-on-disk wear testing machine and the electrochemical measurement method, respectively. Microstructural studies show that the coatings possess a densely layered structure with the porosity less than 2.1%. The tribological behavior of the coatings examined under dry conditions shows that their relative wear resistance is five times higher than that of the substrate material. Both adhesive wear and abrasive wear contribute to the friction, but the former is the dominant wear mechanism of the metallic glass coatings. The coatings exhibit low passive current density and extremely wide passive region in 3.5% NaCl solution, thus indicating excellent corrosion resistance.

Microstructural evolution and delayed hydride cracking of FSW-AZ31 magnesium alloy during SSRT

Evolution of microstructure including texture and fractography in a friction-stir welded（FSW） AZ31 magnesium alloy was investigated. The texture was measured using a neutron diffractometer. The microstructure and fractography of stress corrosion cracking（SCC） samples were observed by optical and scanning electron microscopy, respectively. An X-ray diffraction study was carried out on the fractured surfaces of the SCC specimens. The results indicated that a strong basal fiber was formed on the base material, whereas the grains in the stir zone were reoriented with their most basal planes tilted 25 o to the welding direction. Feather-like twins and hydride formed under slow strain rate tensile（SSRT） stress in air and aggressive solutions, respectively. Transgranular cracks propagated and finally failed on the retreating side in the solution. The hydride phase confirmed to sit on the fracture surface demonstrated the delayed hydride cracking（DHC） mechanism of the alloy.

Corrosion and wear resistance of AZ31 Mg alloy treated by duplex process of magnetron sputtering and plasma electrolytic oxidation

In order to improve the wear and corrosion resistance of AZ31 magnesium alloy,a magnetron-sputtered Al layer with a thickness of 11μm was firstly applied on the alloy,and then treated by plasma electrolytic oxidation(PEO)in an aluminate and silicate electrolytes,respectively.The performance of PEO coatings was investigated by dry sliding wear and electrochemical corrosion tests.The aluminate coating exhibits excellent wear resistance under both 10 and 20 N loads.The silicate coating only shows low wear rate under 10 N,but it was destroyed under 20 N.Corrosion tests show that the Al layer after magnetron sputtering treatment alone cannot afford good protection to the Mg substrate.However,the duplex layer of PEO/Al can significantly improve the corrosion resistance of AZ31 alloy.Electrochemical tests show that the aluminate and silicate coatings have corrosion current densities of-1.6×10^(-6) and-1.1×10^(-6) A/cm^(2),respectively,which are two orders lower than that of the un-coated AZ31 alloy.However,immersion tests and electrochemical impedance spectroscopy(EIS)show that the aluminate coating exhibits better long-term corrosion protection than silicate coating.

Effect of SiC content on dry sliding wear, corrosion and corrosive wear of Al/SiC nanocomposites

The corrosion, corrosive wear and dry sliding wear of nanocomposites, are extremely complicated and involve various chemical, physical anbd mechanical factors. The aim of this work is to investigate the effects of nanosized SiC content on the hardness, dry sliding wear, corrosion and corrosive wear of Al/SiC nanocomposites synthesized by mechanical milling cold pressing and hot extrusion. The corrosion resistance of these composites in 3%NaCl solution was investigated by electrochemical polarization testing and their dry sliding as well as corrosive wear resistance in the same solution was evaluated using a pin-on-disc tester. The microstructures of the samples and their worn surfaces were examined using scanning electron microscopy. It was shown that the dry sliding wear and corrosion resistance of these nanocomposites were improved with the increase of SiC content. It was concluded that due to the lubrication effect of the solution, both the friction coefficient and frictional heat that might soften the material were reduced. In addition, the improved strength of the nanocomposites combined with their better corrosion resistance contributed to their increased corrosive wear resistance, compared with the base alloy. The prominent wear mechanism in the unreinforced alloy was adhesive wear, in the Al/SiC nanocomposites, the wear mechanism changed to abrasive.

Corrosion behaviour of friction stir welded AZ61A magnesium alloy welds immersed in NaCl solutions

The extruded AZ61A magnesium alloy plates of 6 mm thickness were butt welded using friction stir welding（FSW） process.The corrosion behavior of the welds was evaluated by conducting immersion test in NaCl solution at different pH value,immersion time and chloride ion concentrations.An empirical relationship was established incorporating pH value,immersion time and chloride ion concentration to predict the corrosion rate of friction stir welds of AZ61A magnesium alloy at 95% confidence level.Three-factor,five-level central composite rotatable design was used to minimize the number of experimental conditions.Response surface method was used to develop the relationship.The results show that the corrosion resistance of AZ61A magnesium alloy welds in the alkaline solution is better than that in the acidic and neutral solutions,moreover,low corrosion rate is found at low concentrated solution and longer exposure time,and the corrosion morphology is predominantly influenced by the distribution of β-phase.

Effects of processing parameters on corrosion properties of dissimilar friction stir welds of aluminium and copper

The influence of friction stir welding processing parameters on dissimilar joints conducted between aluminium alloy （AA5754） and commercially pure copper （C11000） was studied. The welds were produced by varying the rotational speed from 600 to 1200 r/min and the feed rate from 50 to 300 mm/min. The resulting microstructure and the corrosion properties of the welds produced were studied. It was found that the joint interfacial regions of the welds were characterized by interlayers of aluminium and copper. The corrosion tests revealed that the corrosion resistance of the welds was improved as the rotational speed was increased. The corrosion rates of the welds compared to the base metals were improved compared with Cu and decreased slightly compared with the aluminium alloy. The lowest corrosion rate was obtained at welds produced at rotational speed of 950 r/min and feed rate of 300 mm/min which corresponds to a weld produced at a low heat input.

Effect of friction stir processing on corrosion of Al-TiB2 based composite in 3.5 wt.% sodium chloride solution

The microstructure and corrosion behavior of as-cast and friction stir processed in-situ Al-TiB2 based composite in 3.5 wt.% sodium chloride solution were investigated. The microstructure was characterized using X-ray diffractometry, scanning electron microscopy and electron backscattered diffraction technique while corrosion behavior was evaluated using linear/cyclic potentiodynamic, electrochemical impedance spectroscopy and ASTM–G67 tests. The composite contains sub-micron TiB2 particles in an aluminum matrix with both blocky and fine clusters of Al3Ti agglomerated around TiB2 and displays a low uniform corrosion rate. It is also resistant to pitting as substantiated by the absence of a positive loop in cyclic potentiodynamic tests. This is due to the non-conductive nature of TiB2 particles and a controlled amount of blocky Al3Ti phase. However, both friction stir processed and as-cast composites are susceptible to inter-granular corrosion where Al3Ti and TiB2 at grain boundaries provide initiation sites for corrosion. Electrochemical impedance study attributes this to the adverse effect of Al3Ti and TiB2 on the protective oxide surface film, which increases with immersion time.

Effects of titanium addition on structural, mechanical, tribological, and corrosion properties of Al-25Zn-3Cu and Al-25Zn-3Cu-3Si alloys

To investigate the effect of grain refinement on the material properties of recently developed Al-25 Zn-3 Cu based alloys,Al-25 Zn-3 Cu,Al-25 Zn-3 Cu-0.01 Ti,Al-25 Zn-3 Cu-3 Si and Al-25 Zn-3 Cu-3 Si-0.01 Ti alloys were produced by permanent mold casting method.Microstructures of the alloys were examined by SEM.Hardness and mechanical properties of the alloys were determined by Brinell method and tensile tests,respectively.Tribological characteristics of the alloys were investigated by a ball-on-disc type test machine.Corrosion properties of the alloys were examined by an electrochemical corrosion experimental setup.It was observed that microstructure of the ternary A1-25 Zn-3 Cu alloy consisted ofα,α+ηandθ(Al2Cu)phases.It was also observed that the addition of 3 wt.%Si to A1-25Zn-3Cu alloy resulted in the formation of silicon particles in its microstructure.The addition of 0.01 wt.%Ti to the Al-25Zn-3Cu and Al-25 Zn-3 Cu-3 Si alloys caused a decrement in grain size by approximately 20%and 39%and an increment in hardness from HRB 130 to 137 and from HRB 141 to 156,respectively.Yield strengths of these alloys increased from 278 to 297 MPa and from 320 to 336 MPa while their tensile strengths increased from 317 to 340 MPa and from 334 to 352 MPa.Wear resistance of the alloys increased,but corrosion resistance decreased with titanium addition.

Influence of welding speed on corrosion behaviour of friction stir welded AA5086 aluminium alloy

The plates of AA5086 aluminium alloy were joined together by friction stir welding at a fixed rotation speed of 1000 r/min various welding speeds ranging from 63 to 100 mm/min.Corrosion behavior of the parent alloy(PA),the heat affected zone(HAZ),and the weld nugget zone(WNZ)of the joints were studied in 3.5%(mass fraction)aerated aqueous Na Cl solution by potentiodynamic polarization and electrochemical impedance spectroscopy(EIS).The corrosion susceptibility of the weldments increases when the welding speed increases to 63 and 100 mm/min.However,the value of corrosion rate in the weldments is lower than that in the PA.Additionally,the corrosion current density increases with increasing the welding speed in the HAZ and the WNZ.On the contrary,the corrosion potential in the WNZ appears more positive than in the HAZ with decreasing the welding speed.The WNZ exhibits higher resistance compared to the HAZ and the PA as the welding speed decreases.The results obtained from the EIS measurements suggest that the weld regions have higher corrosion resistance than the parent alloy.With increasing the welding speed,the distribution and extent of the corroded areas in the WNZ region are lower than those of the HAZ region.In the HAZ region,in addition to the pits in the corroded area,some cracks can be seen around the corroded areas,which confirms that intergranular corrosion is formed in this area.The alkaline localized corrosion and the pitting corrosion are the main corrosion mechanisms in the corroded areas within the weld regions.Crystallographic pits are observed within the weld regions.

Tribocorrosion behaviour of Ti6Al4V under various normal loads in phosphate buffered saline solution

Tribocorrosion tests were conducted on Ti6 Al4 V against alumina in phosphate buffered saline solution under normal loads of 3-30 N(corresponding to the maximum Hertzian contact pressures of 816-1758 MPa) using a ball-on-disk tribometer. Nano-hardness measurements revealed the formation of work-hardened layers on the pure wear and tribocorrosion surfaces. As the normal load increased from 15 to 30 N during the pure wear, the surface hardness was increased by about 100%. However, a lower generation of wear debris resulted in a lower wear rate under a normal load of 30 N. The presence of corrosion caused an increase in the wear rates by 28%-245% under various normal loads. The corrosion current density acquired from polarization curves was increased by three orders of magnitude and the open circuit potential(OCP) shifted to more negative potentials during tribocorrosion compared with the stagnant condition. The successive formation and removal of tribofilms, which consisted of oxygen and phosphorous compounds, resulted in peaks in the OCP trend and lower fluctuations in coefficient of friction under normal loads higher than 3 N.

Mechanism of corrosion fatigue fracture of friction stir welding joints of 7075 aluminium alloy in 3.5% NaCl solution

The corrosion fatigue fracture mechanism of friction stir welding(FSW) joints of 7075 aluminium alloy in3.5% NaCl solution is investigated. The corrosion fatigue crack source originates from the junction of nugget zone(NZ)and thermo-mechanical affected zone(TMAZ). Multiple crack sources are developed at the same time, and they merge into large cracks along the boundary line of NZ and TMAZ during the propagation stage. Furthermore, a mutual reinforcement coupling always exists between corrosion and cyclic loading during the initiation and propagation of corrosion fatigue crack. It is necessary to consider the effect of welding residual stress for understanding the mechanism of corrosion fatigue fracture of FSW joints.

New insights into enhancement of sodium hypochlorite on formation and properties of anodic films on Ti6Al4V alloy

Anodic films were successfully fabricated on Ti6A14V alloy by anodic oxidation method in an environmental friendly electrolyte with and without sodium hypochlorite. The anodic films were characterized by means of the scanning electron microscope （SEM） and energy dispersive spectrometer （EDS）. Results revealed that the addition of sodium hypochlorite leads to the ultrafast growth of oxide films, and results in the significant changes of morphology and thickness. The influence of sodium hypochlorite on formation and crystallization of oxide films as a function of anodizing time was discussed. Meanwhile, potentiodynamic electrochemical tests and dry sliding wear tests were performed to evaluate the corrosion resistance and tribological properties of oxide films. It was found that the oxide film fabricated with the existence of sodium hypochlorite had improved corrosion resistance and tribological properties than the one formed without sodium hypochlorite. Moreover, the effect mechanism of sodium hypochlorite on the growth rate and surface morphologies of oxide films during the anodizing process was discussed. It was found that hypochlorite ions participated in the reaction on anode which causes the rapid growth of oxide films and then affect the whole anodizing process.

Tribological behavior of Cu-15Ni-8Sn/graphite under sea water, distilled water and dry-sliding conditions

The tribological behaviors of Cu-15Ni-8Sn/graphite composites with the graphite content of 38 vol.%against AISI321 stainless steel under dry-sliding,deionized water and sea water were investigated on a block-on-ring configuration.The results indicated that the friction coefficient was the lowest under dry-sliding,and the highest in deionized water.The wear rate decreased to reach the minimum value of 1.39×10-15 m3/(N·m)in sea water and in deionized water,it increased to the maximum value of 5.56×10-15 m3/(N·m).The deionized water hindered the formation of tribo-oxide layer and lubricating film,which resulted in the largest friction coefficient and wear rate.In sea water,however,the corrosion products comprised of oxides,hydroxides and chlorides were found on the worn surface,and the compacted layer composed of corrosion products and graphite played an important role in keeping the excellent wear resistance.It was elucidated that the tribological behaviors of Cu-15Ni-8Sn/graphite composite were powerful influenced by the friction environments.

Stiffness identification of four-point-elastic-support rigid plate

As the stiffness of the elastic support varies with the physical-chemical erosion and mechanical friction, model catastrophe of a single degree-of-freedom(DOF) isolation system may occur. A 3-DOF four-point-elastic-support rigid plate(FERP) structure is presented to describe the catastrophic isolation system. Based on the newly-established structure, theoretical derivation for stiffness matrix calculation by free response(SMCby FR) and the method of stiffness identification by stiffness matrix disassembly(SIby SMD)are proposed. By integrating the SMCby FR and the SIby SMD and defining the stiffness assurance criterion(SAC), the procedures for stiffness identification of a FERP structure(SIFERP) are summarized. Then, a numerical example is adopted for the SIFERP validation, in which the simulated tested free response data are generated by the numerical methods, and operation for filtering noise is conducted to imitate the practical application. Results in the numerical example demonstrate the feasibility and accuracy of the developed SIFERP for stiffness identification.

Comments on process of duplex coatings on aluminum alloys

Despite the great achievements made in improvement of wear resistance properties of aluminum alloys, their applications in heavy surface load-bearing are limited. Single coating is insufficient to produce the desired combination of surface properties. These problems can be solved through the duplex coatings. The aim of the present study is to overview the research advances on processes of duplex coatings on (aluminum) alloys combined with micro plasma oxidation process and with other modern processes such as physical vapour deposition and plasma assisted chemical vapour deposition and also to evaluate the performance of micro plasma oxidation coatings in improving the load-bearing, friction and wear resistance properties of aluminum alloys in comparison with other coatings. Wherein, a more detailed presentation of the processes and their performances and disadvantages are given as well.

Effect of cooling conditions on corrosion resistance of friction stir welded 2219-T62 aluminum alloy thick plate joint

Friction stir welding (FSW) with water cooling and air cooling was used to weld 2219-T62 aluminum alloy joints with a thickness of 20 mm. The effect of cooling conditions on the corrosion resistance of joints in 3.5% NaCl solution was investigated using the open circuit potential (OCP), the potentiodynamic polarization, and the corrosion morphology after immersing for different time. And the precipitates distribution was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results reveal that the weld nugget zone (WNZ) owning positive potential, lower corrosion current density and fine and uniform precipitates, is much more difficult to corrode than the heat affected zone (HAZ) and the base metal (BM). Compared with air-cooled joint, the water-cooled joint has better corrosion resistance. In addition, the results of microstructure observation show that the potential, distribution and size of second phase particles determine the corrosion resistance of FSW AA2219 alloy joints in chlorine-contained solution.

Corrosion performance and tribological behavior of diamond-like carbon based coating applied on Ni−Al−bronze alloy

The effect of diamond-like carbon(DLC)coating(fabricated by cathodic arc deposition)on mechanical properties,tribological behavior and corrosion performance of the Ni−Al−bronze(NAB)alloy was investigated.Nano-hardness and pin-on-plate test showed that DLC coating had a greater hardness compared with NAB alloy.Besides,the decrease in friction coefficient from 0.2 for NAB substrate to 0.13 for the DLC-coated sample was observed.Potentiodynamic polarization and EIS results showed that the corrosion current density decreased from 2.5μA/cm2 for bare NAB alloy to 0.14μA/cm2 for DLC-coated sample in 3.5 wt.%NaCl solution.Moreover,the charge transfer resistance at the substrate−electrolyte interface increased from 3.3 kΩ·cm2 for NAB alloy to 120.8 kΩ·cm2 for DLC-coated alloy,which indicated an increase in corrosion resistance due to the DLC coating.