Ti3SiC2系材料的载流磨损特性及机理

研究了三元层状化合物钛硅碳(Ti3SiC2)和钛铝碳(Ti3AlC2)材料的载流磨损特性,探讨了在大电流、热应力和摩擦力的交互和耦合作用下Ti3SiC2系材料的支配性磨损机理.试验在盘-块式大功率载流高速摩擦试验机上进行,用A3钢盘为对磨体;滑动速度为20 m/s,法向压强为0.4～0.8 MPa,电流强度为0,50和100 A.结果表明,在适当的速度和载荷条件下,Ti3SiC2系材料表现出良好的载流摩擦学特性.但载流条件下的磨损率都比非载流条件下的大,且随电流强度而增大.通过SEM&EDS观察、分析,载流条件下的Ti3SiC2系材料的磨损主要由微电弧烧蚀与机械摩擦的交互作用及热-力耦合作用两部分共同影响.微电弧烧蚀作用引起Ti3SiC2系材料表层氧化、熔融和分解以及亚表层裂纹,因而耐磨性发生改变.通电条件下的电热效应和摩擦热的耦合作用也对Ti3SiC2系材料的耐磨性产生影响.力-电-热的交互和耦合作用哪部分占主导机制取决于Ti3SiC2系材料的物理参数及载荷、速度等外部条件因素.     

载流条件下Ti3SiC2陶瓷材料的摩擦学特性

研究了三元层状化合物钛硅碳(Ti3SiC2)材料在载流滑动条件下的摩擦学特性.试验在盘一块式大功率载流高速摩擦试验机上进行,用A3钢盘作为对磨体;滑动速度为20～60 m/s,法向压强为0.4～0.8 MPa,电流强度为0,50和100 A.结果表明,在适当的速度和载荷条件下,Ti3SiC2陶瓷表现出良好的载流摩擦学特性.但载流条件下的摩擦系数和磨损率都比非载流条件下的大,且随电流强度的增大而增大.载流条件下,摩擦系数随法向压强和速度的增大而减小;磨损率随法向压强的增大呈下降趋势,随速度的增高而增大.SEM & XRD观察和分析结果表明,载流情况下Ti3SiC2摩擦面表层生成的TiC等硬质结晶相是导致摩擦系数增大的主要原因;而其磨损率增大主要由微电弧烧蚀与机械摩擦的交互作用及热-力耦合作用两部分共同影响所致.微电弧烧蚀作用引起Ti3SiC2表层氧化、熔融和分解,因而耐磨性发生改变.     

Ti_3AlC_2材料载流摩擦磨损性能的研究

采用反应烧结技术制备了Ti3AlC2材料,研究了该材料的载流摩擦磨损性能。结果表明,随电流强度的增大,Ti3AlC2材料的摩擦系数和磨损率均呈现增加的趋势,在80 A时分别达到最大值0.47和6.3×10-6mm3/N·m。当电流为0时,磨损以氧化膜的轻微划痕和粘着磨损为主;随着电流的增加,磨损逐渐转变为以微电弧烧蚀和机械磨损为主。     

超音速等离子喷涂Mo涂层的载流摩擦磨损性能

采用超音速等离子喷涂技术在45CrNiMoVA钢表面制备Mo涂层，利用场发射扫描显微镜（SEM）、X射线能谱分析仪（EDS）观测涂层显微形貌与组织成分，分析了载流摩擦中的电接触模型及电弧成因，利用滑动式摩擦试验机研究了电流强度对涂层粗糙度、表面温升及摩擦磨损性能的影响。结果表明：制备的Mo涂层组织致密、氧化程度低，与基体结合方式为“机械铆合”；随电流增加，摩擦副间电弧能量急剧升高，起弧率与表面粗糙度先降低，后上升。其中收缩电阻和微电容产生的自感电动势促进了电弧形成；摩擦副表面的温升由摩擦热、焦耳热、电弧热共同决定，与电流强度呈正相关；摩擦因数受表面粗糙度、材料剪切强度、表面膜等因素共同影响，随电流增加呈下降趋势。此外，载流条件下会出现黏着磨损、氧化磨损、电弧烧蚀等磨损，加剧了涂层剥落与磨粒磨损，但形成的摩擦膜可以有效保护涂层，降低磨损率。     

电流对碳纳米管增强铜基复合材料载流摩擦学性能的影响

采用粉末冶金方法在相同的工艺条件下制备纯铜和碳纳米管含量为10%（体积分数）的铜基复合材料。在一种销盘式载流摩擦磨损试验机上考察了不同电流条件下2种材料的载流摩擦磨损性能。结果表明：纯铜和铜基复合材料的摩擦系数和磨损率均随电流的增大而增大,但是电流对纯铜材料的影响更加显著;纯铜材料的主导磨损机制是电弧烧蚀磨损,而铜基复合材料的主导磨损机制是塑性流动变形;碳纳米管可以改善铜基复合材料的载流摩擦磨损性能。     

60Si2Mn钢高速电弧喷涂耐磨涂层的摩擦磨损性能

为提高旋耕刀的耐磨性并延长其使用寿命,利用高速电弧喷涂技术在旋耕刀材料60Si2Mn钢表面制备NiAl粘结层与Ni-Al2O3、Cr2O3、SiC、Cr、Ti和Fe构成的耐磨涂层。经XRD、显微组织分析及硬度测试得到,耐磨涂层由Fe9.64Ti0.36、FeAl、Al2O3和SiO2多相组成,组织均匀致密,表面硬度达到1 037 HV0.2,比传统淬火、中温回火的表面硬度提高69%,表层硬度最高达到1 202HV0.2。摩擦磨损试验结果表明,耐磨涂层与传统淬火、中温回火相比,体积磨损量下降60%,摩擦因数降低44%,电弧喷涂涂层有效的降低了摩擦和磨损,改善了材料的耐磨性。     

碳/铜载流滑动摩擦过程中摩擦学与电弧行为

在先进的多功能摩擦磨损试验机上,对碳刷/铜环在有、无电流条件下的滑动摩擦学行为进行研究,并对电弧行为进行分析。结果表明：法向载荷是载流摩擦过程中电弧产生的主要控制因素之一;电弧强度随法向载荷的降低而增强,随电流的增大而增强;摩擦过程的不稳定和摩擦系数的波动强烈地依赖于电弧;碳刷的磨损量和磨损机制受电弧影响显著;当没有电弧产生时,在有、无电流条件下碳刷的磨损量没有显著差别,此时,碳刷磨损机理主要是机械磨损;当有电弧产生时,载流条件下碳刷的磨损量远高于无电流实验的,并随着电流的增大和法向载荷的降低而迅速增大,磨损机理主要是电弧烧蚀和粘着磨损,并伴有一定的材料转移。     

弓网载流效率及其对碳滑板磨损性能影响的试验研究

目的研究纯碳滑板在高速载流条件下的滑动电接触特性。方法将纯碳受电弓滑板加工成尺寸为120 mm×34.5 mm×25 mm的长方形试样。在环-块式高速载流摩擦磨损试验机上,研究法向压力、滑动速度、电流对弓网载流效率的影响,比较了不同载流效率时碳滑板的磨损形貌。试验过程中实时采集接触副两端的电压、电流以及碳滑板表面温升。每组试验的滑动距离为150 km,试验结束后,用SEM扫描电镜观察碳滑板的表面形貌。结果在电流恒定的情况下,电弧放电能量随着载流效率的增加而降低。在电流I=150A、滑动速度v=150 km/h的条件下,载流效率随着法向压力的增加而增加。在电流I=100 A、法向压力Fn=100N的条件下,载流效率随着滑动速度的增加而减小。在电压U=7 V、滑动速度v=150 km/h的条件下,载流效率随着电流的增加而减小。碳滑板的磨损形貌显示,载流效率较高时,碳滑板以机械磨损为主并伴随着轻微的电弧烧蚀现象;载流效率较低时,碳滑板电弧烧蚀现象非常严重,有明显的烧蚀坑。结论载流效率在一定程度上反映了弓网系统的接触稳定性。载流效率越低,碳滑板磨损越严重。     

导电陶瓷Ti3SiC2-Cu-C复合材料的制备与性能研究

用粉末冶金法制备了一定含量的镀铜和不镀铜Ti3SiC2-Cu-C复合材料,以及Cu-C复合材料,对它们的物理和力学性能进行了测试,并在滑动速度为10m/s,载荷为4.9N的干摩擦条件下进行了36h磨损试验,结果表明:镀铜Ti3SiC2-Cu-C复合材料的导电性、硬度、抗弯强度和耐磨性优于不镀铜Ti3SiC2-Cu-C复合材料和Cu-C复合材料。     

Al2O3/Cu复合材料的载流摩擦磨损性能

研究了采用内氧化法制备的Al2O3／Cu复合材料在载流条件下的干滑动摩擦磨损性能，结果表明，在相同条件下，Al2O3／Cu复合材料的抗摩擦磨损性能明显优于紫铜；当电流一定时，随着速度与载荷的增加，销试样的磨损率增加，摩擦因数降低。Al2O3／Cu复合材料销试样表层发生了磨粒磨损和粘着磨损，紫铜表层主要发生了粘着磨损。在试验范围内，质量分数为0．60％的Al2O3的Cu肚复介材料比质量分数为0．24％的磨损率和摩擦因数低。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

电化学噪声数据处理方法概述

综述了常见的电化学噪声数据处理方法,介绍了直流趋势剔除、统计分析、快速傅立叶变换(FFT)法计算功率谱密度(PSD)以及小波变换处理电化学噪声信号的基本过程,并阐释了各种数学处理及所得参数的物理意义。