石墨烯微片对放电等离子烧结制备铜基摩擦材料性能的影响

采用放电等离子烧结技术(spark plasma sintering,SPS)制备铜基粉末冶金摩擦材料,研究石墨烯微片含量对铜基粉末冶金摩擦材料物理性能和摩擦磨损性能的影响.结果表明:当石墨烯微片质量分数低于4％时,材料的密度、孔隙率和抗剪切强度随石墨烯微片含量的增加而升高;当石墨烯微片质量分数超过4％后,材料的密度、...     

湿式铜基烧结金属摩擦片胶粘工艺研究

烧结金属摩擦片摩擦层与芯板的联接通常是通过加压烧结来实现,该工艺虽然结合强度较高,但存在若干缺点,如:钢芯板经烧结后发生退火,硬度和强度显著降低;另一方面,加压烧结时必须用传压垫板,增加了能耗,同时产品易出现压偏的情况,摩擦层内的低融点成分易被挤压而流出,从而降低摩擦性能,产品的外观质量也受到影响.本文研究了一种湿式铜基烧结金属摩擦片摩擦层与芯板连接的新工艺-胶粘工艺,旨在克服压烧工艺的上述缺点,以提高生产效率,降低生产成本.     

烧结气氛对铜基粉末冶金摩擦材料性能的影响

本文分别在N2、H2和N2+H2:混合气三种气氛下,采用热压烧结法制备了合金强化铜基粉末冶金摩擦材料,并观察了微观形貌,测试了物理力学性能和摩擦磨损性能.结果表明:不同烧结气氛下制备的材料的显微组织相似,但抗压强度和摩擦磨损性能有显著区别:H2气氛烧结的材料挤压强度最低,摩擦系数随转速和制动压力的增加波动较大,且磨损严...     

铝代铅新型铜基自润滑材料的摩擦磨损性能

采用粉末松装烧结法,以A1代替Pb制备新型无铅铜基自润滑材料,研究Al含量(w(Al)为2％～12％)对该材料摩擦磨损性能的影响.结果表明:随着Al含量增加,材料硬度逐渐降低,摩擦因数呈现先降低后增加的趋势.当Al质量分数为6％时,该材料在油摩擦环境下(载荷50 N,转速900 r/min)的摩擦因数为0.089 85,磨痕宽度为1 095 μm,摩擦面较光滑、平整,具有较好的摩擦磨损性能,且自润滑层与钢背的结合强度较高;实验结果表明用Al替代Pb制备新型无铅铜基自润滑材料是可行的,为绿色环保双金属自润滑材料的研究提供了参考依据.     

钨含量对铜基摩擦材料性能的影响

为了探究钨含量对制动用铜基摩擦材料性能的影响,采用热压烧结工艺制备了不同钨含量的铜基摩擦材料,对其物理性能、力学性能和摩擦磨损性能进行了测试.研究表明,铜基摩擦材料的密度随着钨含量的增加而增大,而剪切强度和硬度先增大后减小.钨提高了材料磨损表面微凸体接触的结点强度,从而提高了材料的摩擦因数.适量的钨可以有效地减少磨损表...     

真空烧结温度对铜基减磨材料性能的影响

以铜粉、锡粉、铅粉等为原料,采用“压制-烧结”工艺制备了铜基减磨材料,烧结采用真空无压烧结和还原气氛保护烧结两种工艺方法.运用对比试验的方法,探讨了真空无压烧结工艺中不同烧结温度对铜基减磨材料烧结体性能的影响.结果表明:真空烧结工艺与还原气氛保护烧结工艺相比,相同的烧结温度下材料的孔隙度、抗拉强度、抗压强度和硬度变化不...     

铁铜基湿式烧结摩擦材料

研究了铁粉含量对烧结湿式铜基摩擦材料的影响,获得一种铁铜基湿式烧结摩擦材料。将该材料在MH-2试验台上与铜基湿式摩擦材料进行了摩擦磨损性能对比试验。     

冷压烧结法制备碳纤维增强铜基复合材料的研究

以碳纤维和Cu粉为原材料,采用冷压烧结法制备了碳纤维增强铜基复合材料,研究了压制压力、烧结温度和烧结时间对复合材料性能的影响。结果表明:随着压力的增加,冷成形压坯的密度和压溃强度均先快速提高,而后缓慢增长,较合理的压制压力为238~286 MPa;碳纤维增强铜基复合材料的密度和强度都随着烧结温度的增大而快速提高,但在800℃以上,密度基本不变,强度开始下降;提高烧结温度可提高复合材料的抗摩擦性能,当烧结温度超过750℃时,摩擦性能基本保持不变;碳纤维增强铜基复合材料的密度、强度和抗摩擦性能都随着烧结时间的延长而提高,但是提高速度越来越慢,当烧结时间超过40 min后,这些性能基本不再随时间变化。     

混料时间对含石墨的铜基摩擦材料性能的影响

本文采用粉末冶金方法制备了含石墨的铜基粉末冶金摩擦材料,通过调整加入石墨后的混料时间,采用布氏硬度计、摩擦磨损试验机和扫描电镜等设备研究了混料时间对含石墨的铜基摩擦材料性能的影响。研究结果表明:随着加入石墨后混料时间的增加,烧结后摩擦材料中的石墨颗粒分布更加均匀,铜基体的连续性变差,材料密度和硬度均下降,材料的摩擦因数先增大后减小,磨损量先减小后增大。加入石墨后,混料8 h的烧结体的摩擦磨损性能最佳(较其他试样摩擦因数增加了10%左右,磨损量降低了30%左右)。     

烧结压力对湿式铜基烧结摩擦材料性能的影响

研究了烧结压力对湿式铜基烧结摩擦材料性能的影响,探讨了这些影响的作用机理。研究结果表明:在一定范围内,随烧结压力增大,材料的硬度增大,能量负荷许用值增大,磨损大幅度下降,平均动摩擦因数(μ_d)则略有降低。     

Influence of the SiC content and sintering temperature on the microstructure,mechanical properties and friction behaviour of sintered self-lubricating composites

This work reports the development of a new, low-friction coefficient combined with high mechanical strength and scuffing resistance of self-lubricating composite produced by powder injection moulding process and the recently introduced plasma-assisted debinding and sintering process. We present and discuss the effect of sintering temperature and SiC content on the microstructure, mechanical and friction properties. Three different temperatures (1100,1150, 1200°C) and six different SiC contents (0–5%) were analysed. SiC content had a paramount role on the microstructure, mechanical and friction behaviour. Sintering temperature had almost no effect on the friction coefficient. However, the sintering temperature strongly influences scuffing resistance. Raman spectra obtained in the central region of the wear scar indicate the presence of turbostratic two-dimensional graphite. The misorientation between graphene planes and the increase in interlamellae distance may induce a low interaction between these atomic planes and are, probably, the origin of the low-friction coefficient.     

Optimization of Friction Welding Process Parameters for Joining Carbon Steel and Stainless Steel

 Friction welding is a solid state joining process used extensively currently owing to its advantages such as low heat input, high production efficiency, ease of manufacture, and environment friendliness. Materials difficult to be welded by fusion welding processes can be successfully welded by friction welding. An attempt was made to develop an empirical relationship to predict the tensile strength of friction welded AISI 1040 grade medium carbon steel and AISI 304 austenitic stainless steel, incorporating the process parameters such as friction pressure, forging pressure, friction time and forging time, which have great influence on strength of the joints. Response surface methodology was applied to optimize the friction welding process parameters to attain maximum tensile strength of the joint. The maximum tensile strength of 543 MPa could be obtained for the joints fabricated under the welding conditions of friction pressure of 90 MPa, forging pressure of 90 MPa, friction time of 6 s and forging time of 6 s.     

7075铝合金板材热冲压成形中的高温摩擦

采用自制的板带高温摩擦试验机模拟实际固溶–冲压–淬火一体化热成形工艺下7075铝合金的高温摩擦过程,分别对上下摩擦头进行冷却和加热以模拟实际热冲压过程对模具和压边圈的冷却和加热,分析了下模加热温度、法向载荷和滑动速度对7075铝合金摩擦行为及磨损机理的影响。结果表明:铝合金摩擦系数随着下模加热温度的升高而增大,磨损机制由300 ℃时的黏着磨损转变为500 ℃时的黏着磨损、氧化磨损和磨粒磨损;施加法向载荷越大,摩擦系数越大,不同载荷下磨损机制均为黏着磨损及轻微的磨粒磨损,且随着载荷增大,黏着磨损程度有所加深;高滑动速度导致了磨损表面局部氧化物的生成,使摩擦系数随着滑动速度增大而减小,滑动速度为30 mm·s?1时,磨损机制主要是氧化磨损、磨粒磨损和黏着磨损。      

韶冶铅锌硫化矿高料层烧结焙烧应用研究

介绍了韶关冶炼厂铅锌硫化矿烧结机焙烧实施高料层生产的相关情况，生产实践证明，采用高料层工艺操作模式能有效地提高烧结机的产能和烧结块强度，降低了其对原料的依赖程度，提高了氧化物料的处理量，经济效益显著。     

Experimental Analysis on the Frictional Behaviour of Drawbeads in Sheet Metal Forming

In sheet metal forming, drawbeads are commonly used to control uneven material flow, which may cause defects such as wrinkles, fractures, surface distortion and springback. Although friction may not directly change the limiting strain of steel sheets, the tribological conditions in the contact zone between the sheet surface and the tool surface play an important role in determining the limits of the forming process. Friction in the drawbead contact zones affects the flow of the material in the tool and is used deliberately to control the stamping process. Therefore in this study, the frictional behaviour of drawbeads is experimentally investigated by the drawbead friction test. To characterize the effect of processing variables on the friction coefficients, tests are performed for various sheets, lubricants and bead materials suffering different surface treatments. The results obtained from the drawbead friction test show that the friction and drawing characteristics of deforming sheets were strongly influenced by the strength of sheet, viscosity of lubricant and hardness of bead surface.     

A Study on Friction Stir Multi Spot Welding Techniques to Join Commercial Pure Aluminum and Mild Steel Sheets

To achieve significant improvement in the shear strength of dissimilar joints between aluminum and mild steel sheets, four methods of friction stir multi-spot welding processes, were investigated. Initially, in all these methods, plasticized aluminum layer was deposited on the steel side by friction surfacing. Subsequently, the deposited aluminum was compacted by friction forming. After dressing, spot welding with different tool configurations was performed. Tool rotational speeds of 900, 1120, 1400 and 1800 rpm were used to analyze their effects on the weld nugget. Different mechanical and metallurgical characterizations were done on the welds thus made. The process with aluminum layer on grooved mild steel followed by friction stir multi-spot welding using concave tipped welding tool resulted in welds. These welds had better metallurgical bonding characteristics and higher shear strength, which at a rotational speed of 1120 rpm was more than twice that of the welds made with conventional friction stir spot welding.     

Taguchi Optimisation of Friction Stir Processing Parameters to Achieve Maximum Tensile Strength of Mg AZ31B Alloy

In this investigation, the effect of friction stir processing process variables such as rotational speed, traverse speed and tool tilt angle on the tensile strength of magnesium alloy AZ31B was studied. The experiments were carried out according to the Taguchi parametric design L9 at various combinations of process parameters and statistical optimization technique ANOVA was used to determine the optimum levels and to find the percentage of contribution of the process parameters. The results indicate that the rotational speed is the most significant factor followed by the traverse speed and tool tilt angle for maximising the tensile strength of the friction stir processed magnesium alloy.     

High strength aluminium alloys prepared by nanocrystallisation of amorphous powders using spark plasma sintering

Al based nanocrystalline alloys with high fracture strength are fabricated using consolidation and controlled crystallisation strategy of amorphous powder precursors. The sintered product exhibits high specific strength of 3.18?×?10⁵?Nm?kg^??1. The compacted microstructure and ultrafine grains caused by sufficient densification and crystallisation of Al based amorphous powders are responsible for considerable properties of the sample. Furthermore, the densification process and mechanical behaviour of the sintered Al based nanocrystalline alloy are investigated in detail. The Al based nanocrystalline alloys prepared by synergetic process of powder consolidation and crystallisation of amorphous can exhibit much improved mechanical properties compared with conventional Al alloys, which can have potential engineering applications.     

A process model for friction welding of AlMgSi alloys and AlSiC metal matrix composites—II. Haz microstructure and strength evolution

The present investigation is concerned with the development of an overall process model for the microstructure and strength evolution during continuous drive friction welding of AlMgSi alloys and AlSiC metal matrix composites. In Part II the heat and material flow models presented in the first paper (Part I) are utilized for prediction of the HAZ subgrain structure and strength evolution following welding and subsequent natural ageing. The modelling is done on the basis of well established principles from thermodynamics, kinetic theory and simple dislocation mechanics. The models are validated by comparison with experimental data, and are illustrated by means of novel mechanism maps. These show the competition between the different process variables that contribute to microstructural changes and strength losses during friction welding of AlMgSi alloys and AlSiC metal matrix composites.     

一种双金属轴套制造工艺研究

通过实验介绍了一种可适应不同批量生产的钢/紫铜双金属轴套的生产方法、生产工艺和设备。实验结果表明,选择合理的摩擦焊工艺参数,可得到良好的钢/紫铜接头,接头界面结合强度可达200 MPa左右,符合国家标准。