铁基高密度烧结材料的摩擦磨损性能研究

采用烧结热锻工艺获得高密度和高硬度的铁基粉末烧结冶金材料,研究了铁基粉末中的铬含量和施加在烧结材料上的载荷对材料摩擦磨损性能的影响,并借助于扫描电镜观察和分析了粉末冶金烧结材料的磨损形貌、探讨其摩擦磨损机制.结果表明,在铁基粉末中加入0.6%铬时,该粉末材料的硬度、密度和耐磨性最好.主要磨损机制为氧化磨损、粘着磨损和磨粒磨损.     

高铝锌基合金粉末冶金材料及其摩擦学特性初探

初步研究了高铝锌基合金的粉末冶金工艺及其材料的摩擦磨损性能。通过气喷气冷法制取合金粉末，用压制后真空烧结的方法制备高铝锌基合金粉末冶金材料。实验结果表明，高铝锌基合金的粉末冶金试样在干摩擦和油润滑条件下的磨损率及摩擦系数均小于同一合金的铸造试样，但其压溃强度有待提高。在实验的基础上还探讨了该材料的耐磨减摩机理     

碳对铜基粉末冶金摩擦材料性能的影响

借助混料-成形-烧结等工艺和性能测试、扫描电镜(SEM)的观察和分析,研究了不同种类和粒度的碳对铜基粉末冶金摩擦材料性能的影响。结果表明:由于其制造过程不同,不同形态的碳自身的物理力学性能存在较大的差别,而在同种形态的碳中粉末的粒度和个体的区别导致不同形态碳对铜基摩擦材料的密度、孔隙度的影响具有不同的表象,进而影响到摩擦材料的摩擦磨损性能。试验研究证明,在铜基粉末冶金摩擦材料中采用具有一定粒度组成的鳞片石墨具有较好的综合摩擦磨损性能。     

Fe3Al基复合材料的制备及其摩擦磨损行为

用球磨机械合金化工艺制备Fe3Al粉末，采用粉末冶金工艺，选择不同的烧结温度和烧结压力，获得了Fe3Al基复合材料。对材料的物理力学性能、摩擦磨损性能和微观结构进行分析测试，借助磨损表面扫描图像，分析了该材料的磨损形式，探讨了其磨损机理。结果表明：在烧结温度为1050℃，烧结压力为10～15MPa的工艺条件下制得的Fe3Al基复合材料有较好的摩擦磨损性能。其摩擦机理为：疲劳磨损和磨粒磨损为主，兼有磨粒和粘着磨损混合形式。     

碳对铜基粉末冶金摩擦材料性能的影响

借助混料-成形-烧结等工艺和性能测试、扫描电镜（SEM）的观察和分析，研究了不同种类和粒度的碳对铜基粉末冶金摩擦材料性能的影响。结果表明：由于其制造过程不同，不同形态的碳自身的物理力学性能存在较大的差别，而在同种形态的碳中粉末的粒度和个体的区别导致不同形态碳对铜基摩擦材料的密度、孔隙度的影响具有不同的表象，进而影响到摩擦材料的摩擦磨损性能。试验研究证明，在铜基粉末冶金摩擦材料中采用具有一定粒度组成的鳞片石墨具有较好的综合摩擦磨损性能。     

西北有色金属研究院粉末冶金钛过滤材料的研究与应用进展

西北有色金属研究院对粉末冶金钛过滤材料的研究始于60年代，当时主要研究了钛粉末的成型方法，如模压、冷热等流压、扭浆浇铸、增塑挤压以及相应的烧结工艺等．对年代开始进行标本轧制钛过滤材料的工艺研究，并逐步建立起系统的项末冶金过滤材料过滤性能的分析及检测方法与手段．由此取得的丰硕研究成果，为后来的推广应用奠定了坚实的基础．80年代，建起粉末冶金过滤材料的专业生产线，从而具备了批卫生产能力，使粉末冶金钛过滤材料在各行各业开始得到推广应用．如用于化工行业中的J酸过滤、冶金工业中的湿法炼锌等．在医药行业，粉末冶…     

烧结金属摩擦材料

摩擦是自然界普遍存在的现象。有时候人们需要减小摩擦力,有时候却需要增大摩擦力。无论是在各类工程机械中,还是在民用品的自行车、洗衣机中,摩擦材料都是动力传递或制动减速不可缺少的材料。作为摩擦式离合器与制动器的关键,摩擦材料应具有强度高,摩擦因数适中且稳定,导热性能良好,工作平稳、可靠,耐磨与污染较少,不易与对偶材料发生咬合等一系列优良特性。烧结金属摩擦材料是用粉末冶金技术制备的,在以金属或合金为基础的材料中添加润滑与摩擦组元后制备的一种复合材料。烧结金属摩擦材料是现代摩擦材料家族之中使用量最大、应用面最广的材料,广泛应用于工业机械、铁道车辆、飞机、汽车等行业。烧结金属摩擦材料的制造工艺主要为:制备粉末—配料—混合—压制成形—烧结。     

粉末冶金铝青铜基制动闸片烧结工艺研究

采用粉末冶金烧结工艺制备铝青铜基制动闸片。对烧结工艺和材料性能的研究结果表明,烧结工艺是影响材料密度的关键因素。最佳烧结工艺是烧结温度为910～960℃,烧结压力为3MPa,保温时间为1～4h。复压复烧能够提高摩擦材料的密度及性能。采用模具烧结,并在保温结束后大幅度提高烧结压力可进一步提高材料的密度和性能。     

纳米Al2O3p化学镀铜复合粉末的烧结致密化

化学镀是制备纳米颗粒增强金属基复合材料的有效方法.对纳米Al2O3p化学镀铜粉末的烧结致密化特点进行了研究,分析了化学镀粉末的预处理、成型压力、烧结温度、保温时间、复压复烧工艺等对致密化的影响.在优化各影响因素的情况下,对Al2O3含量为10%的化学镀铜粉末采用常规粉末冶金工艺得到了相对致密度达94%的试样.     

粉末短流程成形固结技术的研究及展望

针对粉末冶金行业最新发展的几种短流程成形固结新技术,结合华南理工大学近十多年来在粉末材料-工艺-装备-零件一体化方面开展的研究,重点阐述了粉末冶金温压成形、高速压制成形、喷射成形、多场作用下粉末成形与烧结一体化技术的研究进展及应用情况。指出在粉末冶金成形固结研究领域,合理拓展现有粉末冶金技术规范的空间,有望给传统粉末冶金成形固结技术注入新的活力。粉末冶金成形固结新技术的不断出现,必将促进先进制造业和高技术产业的快速发展,也必将给材料工程和制造业带来更加光明的前景。     

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。