Fatigue damage generation in ECAPed oxygen free copper

In order to understand the fatigue damage generation of ultra-fine grained copper, rotating bending fatigue tests were carried out. After the 4 and 8 pass of ECAP (equal channel angular pressing) with B_c route, grains with about 300 nm diameter were formed. The damage profile of fatigued surfaces between annealed pure copper and ECAPed one had substantial difference in morphology was observed. To clarify the formation process of surface damage, morphological change in surface caused by cyclic stresses was monitored successively by using optical microscope. It was found that the surface damages for the ECAPed copper propagated along the projected direction of shear plane in ECAP process.     

ECAP铜基原位复合材料的组织与性能研究

室温下采用等通道变形(ECAP)制备了 Cu-5.7%Cr原位复合材料,研究了其力学性能,电导率以及原位纤维的演变.结果表明:经过ECAP后,第二相Cr发生了旋转和伸长,逐渐演变为细小的纤维,且纤维逐渐倾向于与x轴平行.Cu-5.7%Cr合金的硬度,抗拉强度在2道次前显著增加,延伸率则迅速下降.2道次以后,硬度和抗拉强度的增加缓慢,延伸率则保持在20%左右.随着变形道次的增加,电导率逐渐降低,4道次后趋于稳定,8道次后达到80%LACS.     

固溶-大变形-时效下7085铝合金的强化机理

以固溶—时效和固溶—大变形(压缩、ECAP)—时效加工的7085铝合金为实验对象,分别采用拉伸试验机、X射线衍射仪(XRD)和晶体微区取向分析技术(EBSD)对7085铝合金的拉伸性能、内部的位错密度、单元边界(小角度晶界)和晶粒边界(大角度晶界)进行研究,结合拉伸试验测得的屈服强度,定量计算强化项对不同状态下铝合金的强化贡献。结果表明,相比常规固溶—时效工艺,固溶—大变形—时效工艺加工的7085铝合金的拉伸强度从381.2MPa分别提升到475.6和543.3 MPa;位错强化显著提高,从零分别提高到107.4和180.6 MPa;小角度强化显著提高,从10.4 MPa分别提高到89.1和116.4 MPa。7085铝合金强度提高来源于材料内部的位错和小角度晶界;固溶后的大变形加速了时效,降低了时效沉淀强化。并且发现强烈塑性变形加工(ECAP)的强化效果高于传统塑性变形加工(压缩变形)的效果。     

6061铝合金等通道挤压工艺数值模拟

采用有限元技术模拟6061铝合金在室温下等通道转角挤压(ECAP)过程,分析了模具圆心角、摩擦因数对ECAP过程的影响。结果表明,圆心角减小,试样等效应变值增大且较为均匀,但是挤压载荷增加;摩擦对载荷的影响明显。单道次挤压后,试样变形不均匀。     

基于Normalized C&L准则的ECAP裂纹萌生趋势的数值模拟

根据Normalized Cockcroft&Latham韧性断裂准则,利用Deform-2D对6061Al等径角挤压过程进行了裂纹萌生趋势的模拟,在一道次模拟中,得出了模具拐角φ、外转角半径r与背压对试样裂纹损伤分布的影响:模具拐角越大,裂纹损伤值越小;外转角半径r=6 mm为最佳,大于6 mm时裂纹损伤值增大;施加背压有利于减少裂纹的产生,背压越大,裂纹损伤值越小,但是,考虑到ECAP的效率,背压值不能选择太大的数值。对多道次ECAP进行数值模拟,并与实验结果进行对比验证。结果表明,三道次、A路线挤压后裂纹损伤值在上表层最大。     

钛及钛合金ECAP变形研究进展

综述了等径变曲通道变形(Equal channel angular pressing,ECAP)技术制备超细晶(Ultra fine grain,UFG)钛及钛合金的研究进展。总结了模具参数、变形工艺参数对钛及钛合金ECAP变形及组织的影响,以期通过制定合理的变形工艺制备出组织均匀、性能优良的超细晶钛及钛合金,同时汇总了钛及钛合金ECAP变形组织变形机理、演变机理、ECAP变形组织稳定性及超细晶材料性能(超塑性、疲劳强度、耐腐蚀性等)的研究进展,最后指出ECAP制备超细晶钛及钛合金的研究方向。     

Evolution of precipitates of Al-Cu alloy during equal-channel angular pressing at room temperature

The evolution of precipitates and hardness changes in Al-Cu alloys during equal-channel angular pressing（ECAP） at room temperature were investigated by hardness measurement, X-ray diffraction analysis and transmission electron microscopy. The results show that with the increase of the total equivalent strain during ECAP from 0 to 8.4, the hardness of specimens with metastable θ″ phase increases first and decreases in later period. The hardness increases successively in specimens containing metastable θ′ phase and equilibrium θ phase. It is believed that the evolutions of hardness are related to the mechanism of re-dissolution of precipitates. A critical nuclei size concept is provided to express the mechanism of such re-dissolution of three precipitates in Al-Cu alloys.     

室温复合加工及热处理对Ti53Nb组织及性能的影响

采用室温ECAP+冷轧+冷旋锻复合变形方法制备了Ti-53Nb 合金棒材,通过金相显微镜、扫描电子显微镜、单向拉伸实验等研究了合金室温及热处理后组织演变以及β晶粒的长大行为,并分析了加工硬化和细晶强化效应。研究结果表明：室温抗拉强度由变形前的 380MPa,提升到了变形后的 553MPa,提高了45.53%,延伸率也在 16%以上。随固溶温度升高,β晶粒长大速率加快；晶粒尺寸对合金的强化作用满足Hall-Petch 关系式。在700℃,保温60min的条件下,组织均匀呈细小等轴状,可以获得良好的强塑性匹配。