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本文研究了LY12铝合金超塑变形的机理,用扫描电镜和光学显微镜观察了LY12铝合金在超塑变形过程中的表面形貌变化,半定量地研究了该合金超塑变形过程中的机理变化。研究结果表明,LY12铝合金在超塑变形Ⅱ区,其超塑变形的主要机理为晶界滑动,晶界滑动对总变形的贡献为40~70%,调节机理为晶内位错运动和扩散蠕变;在超塑变形Ⅲ区,晶内位错运动占主要地位,其对总变形的贡献为60%以上。 相似文献
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晶粒尺寸对TC4钛合金超塑性行为及变形机理的影响 总被引:1,自引:0,他引:1
研究了不同晶粒尺寸(2,8,18μm)T℃4钛合金在温度860~950℃和应变速率5×10-4~5×10-3S-1条件下的超塑性拉伸变形行为及组织演变,分析了晶粒尺寸对该合金超塑性变形行为及变形机理的影响.结果表明:在温度890℃、应变速率5×10-4S-1的变形条件下,细晶(2μm)合金超塑性变形的断后伸长率高达1 300%,而粗晶(18μm)合金的仅为450%;细晶(2~8μm)A金超塑性变形后,平均应变速率敏感指数m值在0.50左右,晶粒保持较好的等轴状,在α/α仅晶界、α晶内均未观察到明显的位错,在α/β晶界附近发现少量的位错;粗晶(18 μm)合金超塑性变形后,m值仅为0.30,晶粒等轴程度下降,在α/α晶界及α晶内均发现大量位错,且在α晶内发现亚晶. 相似文献
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采用草酸电解浸蚀试验和恒电位极化试验研究了敏化处理前后304不锈钢脉冲电流止裂处的晶间腐蚀性能,得到适合评价裂纹止裂处晶间腐蚀性能的方法。结果表明:经脉冲电流止裂后,止裂处的凝固区、细晶区、形变马氏体区晶界处均未析出碳化物,而经恒电位极化后,晶界处的钝化膜完整,未发生晶间腐蚀;经草酸电解后,敏化试样止裂处不同区域的晶界处均发生了腐蚀,说明草酸电解法不能区分脉冲止裂后不同微区晶间腐蚀性能的差异;经恒电位极化后,敏化试样止裂处凝固区和细晶区晶界处的钝化膜稳定性较好,具有一定的耐晶间腐蚀能力,形变马氏体区发生了严重的晶间腐蚀;恒电位极化法是评价奥氏体不锈钢脉冲电流止裂处晶间腐蚀性能的一种有效方法。 相似文献
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基于Poisson-Voronoi和Monte Carlo方法构建了多晶铜分子动力学模型,研究了纳米切削中多晶铜材料去除、切削力变化及晶界与位错间的相互转化机制。研究结果表明:晶界的阻碍作用使得切屑流向发生了改变,并在已加工表面形成凹槽和毛刺;切削过程中晶界前方材料变形能的逐渐积聚及晶界的最终断裂,造成了切削力发生由最大峰值到最小谷值的大幅波动;晶界附近的材料去除经历了材料变形积聚、位错穿越晶界、晶界转变为位错及晶界最终断裂等过程。通过详细分析多晶铜纳米切削中位错与晶界间的演化过程,揭示了晶界与位错间的相互转化机制,丰富了多晶铜亚表层损伤机理的内涵。 相似文献
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针对航空铝合金7475典型件在加工中易引起弯曲变形,导致加工精度超差,成品率低下等问题,利用解析法和工程力学理论研究其初始残余应力在单面剥层和正反面剥层两种情况下每剥一层后残余应力的重新分布规律和对应的工件变形情况,利用实验进行验证此解析方法计算结果是正确的.通过解析值可知,单面剥层时,在剥层超过板厚一半多时工件向相反方向翘曲变形,而正反面剥层时始终沿一个方向弯曲,而且工件变形值比单面剥层时的变形值小.这种解析方法可以通过残余应力的变化规律及工件变形情况来有效地控制工件变形,同时适用于其他材料相关分析,是一个通用性强的方法. 相似文献
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针对铝合金激光熔化沉积件强韧性差等问题,提出一种溶剂蒸发法制备具有粉末球形度高、流动性好、激光吸收率高且氧化石墨烯(Graphene oxide,GO)均匀分散的GO/AlSi10Mg复合粉末,采用激光溶化沉积技术(Laser melting deposition,LMD)分别打印AlSi10Mg成形件和GO/AlSi10Mg成形件,对比分析两种LMD成形件的微观组织和力学性能,探究GO调控AlSi10Mg合金成形件强韧性的机理。结果表明,添加0.1%GO的LMD成形复合材料抗拉强度提升了10.3%,延伸率提高了170%,硬度提高了5.8%,拉伸断口从脆性断裂特征转变成韧性断裂特征。GO在高能激光的作用下发生还原反应生成石墨烯,石墨烯对复合材料起到了晶粒细化的效果。拉伸试验过程中位错在石墨烯附近聚集并缠结,石墨烯在铝基体中的钉扎作用阻碍了位错的移动、促进了位错增殖,而且石墨烯与Al基体有较强界面结合,起到载荷转移和桥接作用。由于晶粒细化、位错强化、载荷转移强化以及桥接作用,提出的GO/AlSi10Mg激光熔化沉积技术提高了铝合金成形件的强韧性,为铝合金激光熔化沉积技术的应用和发展提供了... 相似文献
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Kanwer S. Arora Sunil Pandey Michael Schaper Rajneesh Kumar 《The International Journal of Advanced Manufacturing Technology》2010,50(9-12):941-952
In this work, successful friction stir welding of aluminum alloy 2219 using an adapted milling machine is reported. The downward or forging force was found to be dependent upon shoulder diameter and rotational speed whereas longitudinal or welding force on welding speed and pin diameter. Tensile strength of welds was significantly affected by welding speed and shoulder diameter whereas welding speed strongly affected percentage elongation. Metallographic studies revealed fine equiaxed grains in weld nugget and microstructural changes in thermo-mechanically affected zone were found to be the result of combined and interactive influences of frictional heat and deformation. A maximum joining efficiency of 75% was obtained for welds with reasonably good percentage elongation. TEM studies indicated coarsening and/or dissolving of precipitates in nugget. For the gas metal arc weld, SEM investigations revealed segregation of copper at grain boundaries in partially melted zone. 相似文献
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Jun-Hyun Han Kwang-Koo Jee Kyu Hwan Oh 《International Journal of Mechanical Sciences》2003,45(10):1613-1623
Microstructural evolutions and orientation rotation behavior taking place during uniaxial tensile deformation at room temperature are studied in polycrystalline 1050 aluminum alloy. Specimens are elongated in an in situ deformation stage equipped in a high-resolution electron backscattered diffraction (HR-EBSD) system. Variations in grain boundary characteristics, such as misorientation and grain boundary distribution, during in situ tensile deformation are analyzed statistically using HR-EBSD. Orientation rotation behavior in individual grains is traced during the whole deformation process. A large number of grains in polycrystalline 1050 aluminum alloy rotate during deformation and are divided into subgrains due to multiple slip. The plane normal directions of individual grains show no remarkable tendency of the orientation rotation during in situ tensile deformation, while the orientation rotation of the tensile direction is found to be strongly dependent on the initial orientation of each grain prior to deformation. 相似文献
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Large angle convergent beam electron diffraction (LACBED) is used to analyse secondary dislocations in sigma3 and sigma9 grain boundaries in silicon. By selecting reflections from crystal planes common to the adjoining grains, LACBED images are insensitive to the boundaries except where dislocations are present. The dislocation images are closely similar to those for dislocations in single crystals and can be analysed by standard Cherns-Preston rules. It is shown that, for both boundaries, sufficient common reflections can be selected for a complete analysis, and that dislocations can be analysed assuming integer values of g x b, implying that the Burgers vectors are Displacement Shift Complete (DSC) lattice vectors. For both sigma3 and sigma9 boundaries, DSC dislocations are identified which are specific to these boundaries. The experimental conditions for the analysis of grain boundaries are explained, and the extension of the method to other coincidence boundaries is discussed. 相似文献
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针对传统回归再时效(Retrogression and re-aging,RRA)工艺并不能充分发挥合金综合性能的缺点,通过拉伸试验、电导率测试、透射电镜观察等手段,研究适合喷射成形7075铝合金的回归再时效处理工艺。结果表明:120℃,16 h的欠预时效处理更有利于合金晶内析出相在回归处理过程中的回溶,有利于合金再时效后强度的提升;200℃,8 min的回归处理可有效地粗化晶界析出相并使其断开明显,使合金的耐蚀性大幅提升;120℃再时效24 h可再次强化合金的力学性能。采用上述RRA处理工艺可得抗拉强度、屈服强度、伸长率和电导率分别为791 MPa、736 MPa、8.5%和22.9 MS/m的高性能喷射成形7075合金,比传统RRA处理的合金在强度与耐蚀性上均有明显提高。 相似文献