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文中进行了脉冲电流对2A12铝合金预制裂纹的修复试验,观察了脉冲电流处理前后试样的微观组织变化,测试了脉冲电流对试件硬度和抗拉强度的影响。试验结果表明,峰值电流为295 A,410 A和656 A,作用时间分别为1.5 s, 1.5 s和2.25 s,电压为4 V的脉冲电流均可使裂纹呈愈合趋势。峰值电流为410 A的脉冲电流裂纹愈合效果最好,裂纹尖端周围区域晶粒得到细化。脉冲电流处理前、后试件硬度平均值分别趋近于130 HV,125 HV,脉冲电流在裂纹尖端区域的焦耳热效应使该区域发生回复与再结晶,内应力消除,硬度降低。脉冲电流处理前、后试件的平均抗拉强度分别为273 MPa, 281.7 MPa,裂纹区域的高密度脉冲电流加速位错移动,使抗拉强度提高了3.19%。文中使用参数调控简便的UN1-1型对焊机作为脉冲电流处理电源,采用了锤击预制裂纹方法,得到的裂纹与实际更为接近,并通过试验验证了2A12铝合金裂纹脉冲电流修复的可行性。 相似文献
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采用压痕法在热压烧结的SiC/Al2O3复合陶瓷试样表面制造裂纹,对含有裂纹的试样在1 000~1 400℃进行不同时间的愈合处理,研究了愈合工艺对材料抗弯强度的影响规律,同时探索了愈合机理.结果表明,随着愈合处理温度的升高和时间的延长,表面裂纹逐渐愈合,长度缩短,材料的抗弯强度逐渐恢复.经1 300℃保温4 h愈合处理后,抗弯强度恢复至583.6 MPa,与完好试样的抗弯强度值(600.6 MPa)非常接近.继续提高处理温度或和延长时间,生成的大量CO(或CO2)气体难以从试样中逸出或在表面产生气孔,在试样表面形成新的缺陷,反而不利于抗弯强度的恢复;抗弯强度的恢复反应是SiC+O2→SiO2+CO(CO2),生成的SiO2填充了裂纹. 相似文献
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《金属热处理》2017,(5)
对热作模具钢进行了脉冲电流处理,研究了脉冲电流处理阶段、脉冲电流持续时间和脉冲电流密度对热作模具钢热疲劳裂纹形貌和裂纹扩展速率的影响,并分析了热疲劳裂纹萌生和扩展的规律,探讨了其作用机理。结果表明,对热作模具钢进行脉冲电流处理可以提高模具钢的抗热疲劳性能,且在热疲劳循环过程中而不是在初始回火态下进行脉冲电流处理可以获得最佳的抗热疲劳性能;脉冲电流持续时间的延长可以有效缩短热疲劳过程中的最大裂纹长度和减少次生裂纹数量,表面龟裂现象有所减缓,还可以降低模具钢试样的热疲劳裂纹扩展速率;脉冲电流密度的增加不仅可以延长疲劳裂纹萌生的时间,还可以降低模具钢试样的热疲劳裂纹扩展速率,从而提高模具钢热疲劳循环服役寿命;经过脉冲电流处理后的模具钢在细晶强化、位错强化和弥散强化的共同作用下,热疲劳性能得到提升。 相似文献
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用钻孔压缩法在试样内部引入裂纹,然后对含内部裂纹的试样进行不同加热温度和不同保温时间的空冷处理,采用金相显微镜及扫描电镜观察分析裂纹愈合程度,研究了化学成分对结构钢裂纹愈合的影响.结果表明:单纯高温热处理条件下,20、45、20CrMnTi三种钢内部裂纹均能愈合.钢中的碳含量及合金元素对裂纹愈合存在一定的影响,主要是对愈合区的组织影响较为明显.碳化物形成元素易于形成稳定的碳化物,阻碍碳原子扩散;同时碳化物会钉扎晶界,使裂纹愈合区的再结晶晶粒比较细小. 相似文献
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采用剖分试样真空回复热处理法对低碳钢和Cr-Mo钢的氢腐蚀裂纹愈合机理进行了研究.结果表明,在单纯高温条件下,低碳钢和Cr-Mo钢氢蚀裂纹均有所减小,尤其以裂纹尖端愈合较为明显.愈合程度与裂纹尺寸有关,小尺度裂纹优先发生闭合.分析表明,氢蚀裂纹愈合的机制主要是热扩散,Fe和C在钢中的扩散是内部裂纹自愈合的必要条件.在Fe和C原子扩散足够快的情况下,氢蚀裂纹愈合的条件是塑性变形能Ea大于裂纹愈合所必须克服的表面张力能.同时,相变、应力应变等因素均对其产生重要积极的作用. 相似文献
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脉冲电流下的热喷涂层组织演变 总被引:1,自引:0,他引:1
对A3钢基材表面的热喷涂层进行脉冲电流处理,通过显微镜观察涂层组织结构变化,结果表明,在脉冲电流处理下涂层组织结构发生了变化,涂层所固的层状结构趋于愈合。 相似文献
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采用纯铝/硬铝(Al/LY12)爆炸复合板通过电子束焊接制得界面裂纹四点弯曲试样,由于强度错配,Al/LY12界面裂纹顶端局部的变形是锐化与钝化的复合型,但在疲劳载荷下其整体裂端应力应变场仍然可由纯1型应力强度因子主导,可以采用和单材料试样相同的方式进行界面裂纹的疲劳扩展行为研究,界面裂纹可在较低的外载水平下启努扩展,但爆炸焊接界面存在的波纹使得界面裂纹的扩展速率出现波动,并且阻碍裂纹的扩展,相同外载下Al/LY12界面裂纹的疲劳扩展速率低于单材料LY12的疲劳扩展速率。 相似文献
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Pan DongZhao YuguangXu XiaofengWang YitongJiang WenqiangJu Hong 《金属学报》2018,(9):1245-1252
42CrMo steel was widely used in many industry fields for its excellent hardenability and high temperature strength. Many transmission mechanisms and fasteners, such as roller and heat-resistant gear, are made of this steel. However, the ductility of 42CrMo steel is relatively low after quenching and tempering. During high tempering Mo riched carbides at grain boundary and undecomposable martensite at low tempering are the main reasons for poor ductility of 42CrMo steel. Grain refinement can enhance both strength and ductility significantly, but traditional refinement technology will cause intergranular oxidation so that strengthening effect was weak. Although thermomechanical treatment can achieve dynamic recrystallization, its refinement effect is unstable. Elecropulsing treatment, which makes significant change in microstructure and properties of metals, has been applied in many fields such as, modification of solidified microstructure of liquid metal, healing of fatigue crack, nanocrystallization of amorphous materials and so on. Moreover, this process can produce superior mechanical properties in metals. In order to improve the mechanical properties of 42CrMo steel better, high-energy and instantaneous electropulsing treatment was applied. In this contribution, 42CrMo steel was subjected to traditional and electropulsing treatment individually. It was found that EPQ treatment (480 ms electropulsing treatment, water cooled) results in finer grain, promoting the formation of retained austenite and twin martensite; EPT treatment (180 ms electropulsing treatment, air cooled) can stabilize retained austenite in EPQ specimen and induce multiphase structure. Mechanical properties results indicate that strength-ductility balance of EPQ and EPQ+EPT specimen are 32% and 13.9% higher than that of TQ (traditional quenched) and EPQ+TT (traditional tempered) specimen respectively. 相似文献
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X.G.Li C.F.Dong H.Chen School of Materials Science Engineering University of Science Technology Beijing Beijing China State Key Laboratory of Corrosion Protection Institute of Metal Research The Chinese Academy of Sciences She 《金属学报(英文版)》2002,15(4):385-390
The specimens of 304 austenite stainless steel with the hydrogen attack bubbles or cracks were heat treated at 600℃ for 6h. The SEM and TEM observations on the specimens before and after the heat treatment showed that the bubbles or cracks could be healed completely by heat treatment. The healing of hydrogen attack bubbles or cracks is closely related to heat diffusion of Fe and C atoms in austenite. The driving force of crack healing results from the plastic deforming energy Es induced by the growth of hydrogen attack bubbles or cracks. The critical condition of healing of bubbles or cracks is Es≥2γ (where γ is the surface tension, r is the radius of bubbles or half length of crack). During healing of the hydrogen attack bubbles or cracks, the recovery, polygonization and recrystallization of the sub-grain also occured. 相似文献
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Jiang F. Deng Z. L. Sun J. Wei J. F. 《Journal of Materials Engineering and Performance》2004,13(1):93-98
Bimetallic three-point-bending specimens and four-point-bending fatigue test specimens were produced from strength mismatched
stainless steel/low carbon steel bi-material. Both the J resistance curves and fatigue crack growth behavior were investigated for the bi- and bulk materials. The results showed
that a crack initiated easily at the interface, and crack growth resistance along interface was inferior to that of the corresponding
bulk materials under either static or dynamic loading conditions. 相似文献