微织构对铜基自润滑复合材料摩擦磨损性能的影响

目的 针对活塞环在高温高压、循环往复的惯性力等工况下与气缸极易磨损的问题,以栓盘模型为试验对象,研究圆形微织构对铜基自润滑复合材料的摩擦磨损性能,以期提高两者的耐磨损性能。明确微织构在不同工况下与复合材料摩擦磨损行为之间的联系,建立表面微织构设计准则。方法 采用CT-MF20型光纤雕刻激光打标机在45#钢表面加工制备出直径为0.2 mm的圆形微织构,并通过栓-盘形式在HT-1000型摩擦磨损试验机上对圆形织构化45#钢进行摩擦性能试验,考察圆形微织构在不同载荷(2、10、20 N)及不同滑动距离(1.88 m和18.84 m)下的摩擦磨损情况,而且借助扫描电子显微镜(SEM)分析摩擦表面的显微结构和形貌,通过能谱仪(EDS)结果分析摩擦表面元素积累情况。此外,为了与之形成对比每组均设有无织构的45#钢试验。结果 在摩擦试验中,载荷为20 N、滑动距离为18.84 m时圆形织构的摩擦磨损性能最优,平均摩擦因数降幅随着滑动距离的增加从11%增加到23.5%,同时栓和盘表面形貌磨损也明显比其他条件的试件要小。在EDS结果中发现圆形织构表面的氧元素更多,集中分布在织构里。结论 当载荷为20 N、滑动距离为18.84 m时,圆形织构的减摩效果最好,摩擦因数稳定,栓盘磨损表面变得光滑,这归因于圆形织构盘表面棘轮效应明显,并形成连续稳定的转移润滑膜,从而减小磨损。     

基于压力和流量守恒收敛准则的微织构端面机械密封数值计算

目前在研究微织构端面机械密封时,离散求解雷诺方程时采用的压力收敛准则,并不能完全保证得到准确的泄漏率。提出基于压力收敛和内外径流量守恒收敛双重收敛准则的微织构端面机械密封数值计算方法,针对圆柱形微孔端面机械密封,基于考虑JFO边界条件的二维雷诺方程,建立含一个计算域的数值计算模型,并采用不同的收敛准则对开启力和泄漏率进行数值计算。结果表明:仅使用压力收敛准则不能显式判断计算是否已经满足质量守恒,不能准确计算泄漏率;仅使用内外径流量守恒收敛准则可能出现迭代初始阶段就满足收敛条件,导致错误结果;使用压力收敛准则和内外径流量守恒收敛准则相结合的双重收敛准则,可保证泄漏率计算的正确性。     

GCr15轴承钢表面的激光凹/凸微织构工艺

采用光纤激光器对GCr15轴承钢试样表面进行了激光织构加工,使用共聚焦显微镜观察了微织构的形貌,分析了功率、脉宽、重复次数对织构点形貌的影响。试验结果表明,织构点直径随脉宽的增大而增大,在一定脉宽范围内,织构点深度随脉宽的增大而明显增大;在单脉冲作用下,当脉宽为1000μs时形成凸起形貌,当脉宽增大到5000μs以上时形成凹坑形貌;随着功率的增大,织构点的直径和深度增大;随着重复次数的增加,热效应尤为明显,凹坑先逐渐变深然后部分被填平,凸起高度先不变然后急剧增大。研究验证了同一台激光器同时实现凹/凸微织构的可行性,为实现表面不同形貌的加工提供了新的思路。     

Local inhomogeneity of mechanical properties in stir zone of friction stir welded AA1050 aluminum alloy

The local inhomogeneity of the stir zone in friction stir welded face-centered cubic metal was investigated, which has multiple activated slip systems during plastic deformation, by selecting commercial AA1050 aluminum alloy as an ideal experimental material. The local inhomogeneity was evaluated by uniaxial tensile tests using small samples with a 1 mm gauge length. The corresponding microstructural parameters such as grain size, misorientation angle distribution, and micro-texture, were quantified by the backscattered electron diffraction technique. A comprehensive model was used to reveal the microstructure−mechanical property relationship. The experimental results showed that the uniaxial tensile property changes significantly across the weld. The maximum ultimate tensile strength (UTS) occurred in the center of the stir zone, which was 99.0 MPa. The weakest regions were located at the two sides of the stir zone. The largest difference value in UTS reached 14.9 MPa, accounting for 15% of the maximum UTS. The analysis on the structure−mechanical property relationship suggests that the micro-texture change with the location formed during the rotational material flow is the main reason for the local inhomogeneity.     

激光微造型中烧蚀热场及弹坑的数值模拟

在摩擦副表面激光微细加工技术中,为了确定其表面形貌,采用有限差分法对激光微造型中的烧蚀温度场和烧蚀产生的弹坑进行了数值模拟,计算模型在能量平衡方程的基础上,将入射脉冲激光在空间以高斯分布考虑,模拟出了激光微造型中靶材的温度场分布和变化规律,以及弹坑的深度和直径,进行了理论分析和实验验证,将此模拟结果(弹坑直径和深度)和现有文献中的实验进行比较,得到了良好的一致性.这对于激光微造型技术的理论研究是有帮助的.     

Multi-scale study of the polishing behaviour of quartz and feldspar on road surfacing aggregate

In this paper, the exact mechanisms as to how petrographic properties of aggregate influence the polishing behaviour quantitatively were identified. Since the aggregate is composed of the different rock-forming minerals, the analyses conducted in this research project focused not only on the aggregate but also on crystals/minerals. The hardest and most abundant rock-forming minerals found on earth – quartz and feldspar – were investigated with polishing tests with the Aachen Polishing Machine on granite aggregates from four sources which exhibit different mineralogical properties. Changes of the aggregate texture and minerals were studied based on texture measurements and skid resistance measurements obtained by means of the Pendulum Test and the Wehner/Schulze device. The influences of mineral composition and crystal size on the changes of the micro-texture and skid resistance of the aggregates were determined by comparing the four granites. The polishing and wearing behaviour of quartz and various feldspars (albite, microcline and plagioclase) were characterised quantitatively by means of a spectral analysis and abrasion analysis. The results show that the micro-texture of exposed minerals is greatly smoothened on wavelengths from 100 to 500 μm. Fine-grained quartz or feldspar crystals tend to be rougher than medium of large-sized crystals. Quartz exhibits more favourable properties than feldspar between 100 and 500 μm; this is especially true for fine quartz crystals. The correlation that more content of coarse-grained quartz leads to high friction value cannot be proved in this research.     

微织构(W,Mo)C基刀具和YG8刀具对钛合金干切削性能的影响

刀具切削钛合金时存在切削温度高、单位面积上切削力大等问题,微织构刀具可以有效减小摩擦力,减小切削力。通过正交实验法设计微织构参数,研究微织构参数对Al 2O 3/La 2O 3/(W,Mo)C无黏结相硬质合金刀具以及YG8刀具切削钛合金实验的切削性能影响。实验结果表明,合适参数的沟槽型微织构能有效降低Al 2O 3/La 2O 3/(W,Mo)C无黏结相硬质合金刀具和YG8刀具切削TC4钛合金的切削力,相同沟槽参数下,无黏结相硬质合金刀具的切削力明显低于YG8刀具的切削力;合适参数的沟槽型微织构能有效降低刀具刀屑界面的摩擦系数,相同沟槽参数下,无黏结相硬质合金刀具的摩擦系数大都低于YG8刀具的摩擦系数;沟槽深度10μm、沟槽间距100μm以及沟槽宽度30μm的沟槽参数下,切削钛合金时,无黏结相硬质合金刀具前刀面无明显磨损,后刀面只有边界磨损,YG8刀具发生崩刃,前刀面出现切屑的滞留。     

添加ZnO对高强瓷性能影响的研究

高强瓷配方中铝矾土用量较大,要兼顾工艺性能,采用继续增加矾土含量来提高瓷质强度是有困难的。采取在原高强瓷配方中添加少量的ZnO,并研究随着ZnO添加量的增加,高强瓷配方坯料和瓷质各项性能的变化情况。试验得出,在高强瓷配方中添加2%的ZnO,可以使瓷质的显微结构得到明显改善,瓷质机械强度有较大幅度的提高,最大可提高15%左右,并仍保持着良好的制造工艺、电、热等各项性能,指出利用原有工艺条件生产更高等级电瓷产品的有效途径。     

表面微织构协同热扩渗技术改善材料表面摩擦学性能的研究进展

表面微织构因其能够有效改善摩擦副之间的摩擦学性能而获得国内外学者的广泛关注。通过将表面微织构与热扩渗技术相结合,可以充分发挥2种技术的优点,进一步提高摩擦副之间的摩擦学性能,为更复杂环境下的应用提供可能。首先概述了表面微织构的常用加工方法及其所加工的织构类型,系统地归纳总结了表面织构在不同润滑工况下的减摩机理。其次,从不同的表面热扩渗技术入手,分别综述了盐浴渗氮技术、等离子渗镀技术、热氧化技术和化学气相沉积与表面织构的协同作用研究现状,根据摩擦因数、磨损量和表面硬度等性能参数,分析总结了不同复合技术的可行性以及对基体摩擦学性能的影响。相对于单一表面处理技术,复合技术能够进一步提高材料的表面硬度,延长织构的使用寿命。一般来说,复合处理表面的耐磨性显著优于单一技术处理的表面和未处理表面,但摩擦因数受工况的影响较大。最后,对该复合技术的研究发展做出总结,提出不同织构参数和热扩渗参数对基体摩擦磨损性能的影响有待进一步探究,开展极端工况下复合技术的应用基础研究,推动复合技术在摩擦领域的发展。     

Microstructure and texture of electroformed copper liners of shaped charges

The microstructures of copper liners of shaped charges prepared by electroforming technique were investigated by trans-mission electron microscopy (TEM). Meanwhile, the orientations distributing of the grains in the electroformed copper liners of shaped charges was examined by the electron backscattering Kikuchi pattern (EBSP) technique. TEM observations have revealed that these electroformed copper liners of shaped charges have the grain size of about 1-3μm and the grains have a preferential orientation distribution along the growth direction. EB SP analysis has demonstrated that the as-formed copper liners of shaped charges exhibit a micro-texture,i.e. one type of fiber texture, and the preferred growth direction is normal to the surface of the liners.