应变水平对锆合金动载下塑性变形机制的影响

基于实验设计研究了应变参数对锆合金动载下塑性变形机制的影响。通过控制应变速率,采用应变限位环的方法实现了锆合金高应变速率下应变参数的单一分离,应变速率为2300 s~(-1)时,获得了4个不同的应变水平:0.11、0.21、0.30、0.33。基于锆合金高应变速率不同应变下微观组织的表征,预测了应变参数对锆合金动载下塑性变形过程的影响。结果表明:形变带和转变带是锆合金不同应变阶段塑性变形的重要方式,形变带内部由严重变形的晶粒组成,而转变带内部主要由100~300 nm的细小等轴晶粒组成。在变形初始阶段,锆合金变形以柱面滑移和锥面滑移为主,以孪生为辅;随着应变的增加,位错持续增殖,位错的塞积导致应力增加,直至最大抗压强度;当应变达到一个临界值时,形成形变带;随应变继续增加,形变带发生动态再结晶,演化为转变带;应变继续增加,便会在剪切带内部诱发微空洞、微裂纹,直至材料断裂。     

应变速率对锆合金塑性变形机制的影响

通过控制应变水平,采用热模拟准静态压缩和霍普金森压杆高应变速率压缩相结合的技术,实现了锆合金不同应变速率条件下的塑性变形。结果表明:锆合金准静态压缩和高应变速率压缩的主要区别在于变形后期。准静态压缩时,位错在晶粒内部塞积成为锆合金塑性变形的主要方式,导致基体晶粒内部累积取向差逐渐增加;而高应变速率压缩时,剪切带成为锆合金塑性变形的主要方式。剪切带塑性变形方式的出现,部分协调了锆合金的塑性变形,导致基体晶粒内部累积取向差较低。     

锆合金剧烈塑性变形组织演变的研究进展

综述了锆合金剧烈塑性变形行为的研究进展,系统阐述了锆合金剧烈塑性变形技术,包括等径转角挤压、高压扭转、累积叠轧、扭转挤压及多向锻造。重点介绍以上方法在纯锆、Zr-Nb系合金及Zr-Sn-Nb系合金中的应用。详细介绍锆了合金微观组织及性能演变行为的研究现状,全面描述了锆合金组织和织构的演变。     

锆及锆合金的疲劳行为及其变形机理

研究了室温,４００℃和６００℃下锆及锆－４合金的低周疲劳行为,其循环应力响应曲线表明：锆及锆－４均表现为循环初期硬化,随后饱和,再逐渐软化,与平面状滑移材料类似,密排六方金属锆的循环变形行为对加载历史敏感。     

锆—4合金的时间相关低周疲劳

研究了锆－４合金在不同应变速率下的低周疲劳和带应变保持时间相关低周疲劳行为。结果表明：在不同加载方式下，锆－４合金均表现为循环硬化，应变保持和应变速率降低均进一步提高环孢和应力。应变保持降低材料的疲劳寿命，特别是在高应变幅区域。随着应变速率降低、材料疲劳寿命降低。疲劳变形亚结构观察表明：锆－４合金时间相关疲劳过程中以｛１０１↑－０｝柱面滑移和晶界滑移方式变形。     

锆－4合金的时间相关低周疲劳

研究了锆－４合金在不同应变速率下的低周疲劳和带应变保持时间相关低周疲劳行为。结果表明：在不同加载方式下，锆－４合金均表现为循环硬化，应变保持和应变速率降低均进一步提高循环饱和应力。应变保持降低材料的疲劳寿命，特别是在高应变幅区域。随着应变速率降低，材料疲劳寿命降低。疲劳变形亚结构观察表明：锆－４合金时间相关疲劳过程中以柱面滑移和晶界滑移方式变形。     

氢化物对N18锆合金原位拉伸变形的影响

采用扫描电镜下原位拉伸方法,观察研究了电解渗氢后的N18锆合金中氢化物的变形过程和基体的滑移行为,分析了氢化物对拉伸性能的影响。研究发现,锆合金基体的塑性变形是由多滑移引起的,氢化物可随基体发生较大变形。稀疏分布的带状氢化物簇对滑移的阻碍小,滑移线能够穿过而不改变方向,但尺寸较大的氢化物簇会阻碍滑移带的穿过而改变滑移方向。氢化物使抗拉强度略有增加,伸长率显著下降,但氢含量达到623μg/g的N18锆合金的伸长率仍然达到了13.1%,具有较好的塑性。     

第二相粒子的析出演变及其对锆合金的影响研究进展

锆合金因具有低的热中子吸收截面、优异的抗腐蚀、蠕变及辐照性能，已广泛应用于核燃料组件中。为提高锆合金服役性能，通常加入微量Sn、Nb、Fe、Cr、Cu和Ni等合金元素，其中大部分合金元素在α-Zr中的固溶度较低，经过热机械加工后往往以金属间化合物的形式析出，形成第二相粒子(SPPs)。SPPs对锆合金的组织演化、力学性能等具有重要影响，细小且均匀分布的SPPs能有效提升锆合金的综合性能。本文结合锆合金的加工工艺，综述了国内外关于锆合金SPPs析出演变规律的研究进展，并提出了针对SPPs尺寸和分布的工艺优化方法；梳理了SPPs的类型、尺寸与分布以及晶体学特征，并阐明了SPPs析出后对锆合金塑性变形过程和再结晶行为以及力学性能的影响。最后，总结梳理了锆合金SPPs研究存在的问题及发展趋势，以期对锆合金的加工工艺优化提供参考。     

工业级锆及锆合金焊接的最新研究进展

锆及锆合金是一种性能优良的耐蚀结构材料,在核工业和化学工业具有广阔的应用前景,优良的焊接性能对设备的使用寿命和可靠性至关重要。在分析锆材焊接特性的基础上,对锆及锆合金焊接工艺、力学性能、残余应力分布、耐蚀性能和腐蚀机理等方面的最新研究进展进行了综述,并展望了锆及锆合金焊接在工业中的应用前景。     

超声滚压剧烈塑性变形诱导金属材料结构演变的研究进展

首先,对表面完整性的基本概念和内涵进行了概述,同时简要介绍了超声实现滚压技术的基本原理及其优点。随后,对比分析了不同剧烈塑性变形方法的特点和局限性,引出了实现表面完整性的相关剧烈塑性变形协调机制。在此基础上,随后结合其他剧烈塑性变形强化工艺,重点总结了超声滚压剧烈塑性变形对金属材料表面微观结构演变的影响。具体探讨了剧烈塑性变形诱导晶粒细化机制、晶粒生长机制以及合金元素偏聚机制等,主要分别论述了不同层错能的面心立方、体心立方以及密排六方等不同金属晶体结构的晶粒细化机制(以位错滑移、变形孪晶为主导)、晶粒长大机制(以晶界迁移、晶粒旋转为主要)与合金元素偏聚机制(晶界偏聚、位错核心偏聚)等。最后,对以上内容进行了综合总结,并针对超声滚压技术研究中存在的问题给出进一步研究和发展的建议,从而为实现超声滚压金属材料的表面完整性的主动精准控制及提高其服役寿命与可靠性提供一定的参考。     

Effect of {332}< 113 > Twins Combined with Isothermal omega-Phase on Mechanical Properties in Ti-15Mo Alloy with Different Oxygen ContentsEI北大核心CSCD

beta-type alloys have a wide application prospect in aerospace, biomedical and marine engineering and other fields, owing to their high specific strength, good corrosion resistance and low elastic modulus. Their yield strength and uniform elongation are affected by the second phase precipitation, plastic deformation mode and interstitial element, especially the oxygen element. In this work, the effect of tensile pre-deformation induced {332}< 113 > twins combined with isothermal w-phase after subsequent ageing on the mechanical properties of beta-type Ti-15Mo alloy with different oxygen contents from 0.1% to 0.5% (mass fraction) was examined by OM, XRD, TEM and DSC, Vickers hardness tester and tensile testing machine. The results indicated that with increasing the oxygen content, the formation of mechanical twins and isothermal omega-phase in the alloy was suppressed, and the effect of pre-deformation induced twins on the precipitation of isothermal omega-phase was negligible. After pre-deformation combined with subsequent ageing, the alloy with low oxygen content had the relatively high yield strength and large uniform elongation, but it with high oxygen content exhibited the brittle fracture. A good combination of strength with ductility in the alloy with low oxygen content was contributed to the twinning and dislocation slip coupled deformation. The high yield strength was mainly dominated by the dislocation slip, and the large uniform elongation was due to the static and dynamic grain refinement effects, which were caused by the pre-deformation induced twins and subsequent twinning deformation, respectively. Through utilizing the alloying element of oxygen effectively, and changing the plastic deformation mode and phase precipitation behavior based on the reasonable process of pre-deformation and heat treatment, the combination of strength and ductility can be controlled in a large range for the beta-type titanium alloys.     

GH690合金拉伸变形行为的温度敏感性

通过拉伸试验研究了GH690合金从298～623K的变形行为,用光学显微镜、扫描电镜和透射电镜观察了变形组织。结果表明,合金在298K拉伸时能够通过孪生协调变形,生成的形变孪晶阻碍了位错的滑移,从而使合金获得了较高的加工硬化速率,导致合金的强度和塑性较高。随着形变温度的升高,合金通过孪生协调变形的能力降低,变形机制由孪生转变为滑移,滑移产生的加工硬化效应小于孪生,因此合金的强度和塑性随之降低。     

Microstructure and mechanical properties of 7005 aluminum alloy processed by one-pass equal channel reciprocating extrusion

An equal channel reciprocating extrusion (ECRE) was proposed first to obtain a severe plastic deformation (SPD) of 7005 alloy. The microstructure and mechanical properties of one-pass ECREed (ECRE processed) 7005 alloy were investigated. The results show that SPD occurring in ECRE leads to a mixed microstructure. ECREed 7005 alloy exhibits a significant improvement of ultimate tensile strength (UTS) and elongation. Mechanical properties in the region undergoing a complete ECRE process are higher than those in the region undergoing an incomplete ECRE process due to larger dislocation strengthening effect. Yield strength (YS) and UTS first decrease and then increase with an increase of extrusion temperature. The YS of 359.2 MPa, UTS of 490 MPa and elongation of 17.7% are obtained after T6 treatment. Fine-grain strengthening, dislocation strengthening and precipitation strengthening in the T6-treated ECREed sample all play important roles in improving the mechanical properties.     

大塑性变形制备超细晶铝锂合金的组织及力学性能研究进展

综述了大塑性变形工艺制备超细晶铝锂合金的显微组织及其力学性能,分析了大塑性变形过程中铝锂合金的组织演变及其影响因素。铝锂合金的强化机制主要是基于析出强化,结合大塑性变形得到的超细晶粒组织可以显著提高强度和塑性,并得到优异的超塑性。表明大塑性变形加工铝锂合金,尤其是等通道挤压制备的超细晶铝镁锂合金在超塑性工业具有广阔的发展前景。     

冷拔Co40NiCrMo合金的显微组织和抗拉伸性能

对冷拔态Co40NiCrMo合金的微观组织、抗拉伸性能进行了研究。结果表明：经固溶和冷拔处理的Co40NiCrMo合金室温呈面心立方结构：冷拔过程的塑性变形为孪生和滑移，孪生为主要变形机制：孪晶细化和碎化是大变形量冷拔态Co40NiCrMo合金获得良好的综合力学性能的主要原因。     

冷轧对新型Ni-W-Co-Ta高密度合金组织与性能的

在室温环境中对新型Ni-W-Co-Ta高密度合金进行冷轧变形，借助金相显微镜、扫描电镜、透射电镜、X射线衍射仪、背散射电子衍射、电子万能试验机及显微硬度计对新型Ni-W-Co-Ta高密度合金变形过程中的微观组织及力学性能演变规律进行表征。结果表明：随着变形量的增加，新型Ni-W-Co-Ta高密度合金等轴晶粒沿轧制方向不断被拉长，同时产生大量的滑移带协调剧烈的塑性变形，并最终形成纤维组织。变形量的增大导致位错密度急剧增加，位错交互作用显著加强，进而将晶粒尺寸细化至25.5 nm。经过90%的严重塑性变形后，抗拉强度提高到1953 MPa；屈服强度提升至1806 MPa，硬度增加至534 HV，伸长率则急剧下降至9.1%。断口形貌则由韧性断裂向韧性-准解理混合型断裂转变。     

LOW CYCLE FATIGUE BEHAVIORS AND MICROSTRUCTURES OF Ti–2Al–2.5Zr WITH FINE GRAIN AT RT AND 77 K

对细晶Ti--2Al--2.5Zr合金进行了室温/低温(77 K)疲劳实验及微观组织观察. 结果表明: 室温低应变幅Δε_t/2(=0.5%, 1.0%)下,合金表现为循环软化; 室温高应变幅(1.5%, 2.0%)下, 则表现为循环应力饱和; 77 K时, 不同应变幅下均表现为循环硬化, 且随应变幅升高, 循环硬化程度增强. 疲劳寿命测试结果表明: 低温疲劳寿命始终高于室温. 断口SEM观察表明, 室温和低温下, 疲劳裂纹扩展区均有明显的疲劳条纹,疲劳裂纹以穿晶方式扩展, 室温下伴随有大量二次裂纹, 低温下的二次裂纹数量明显减少. TEM观察表明: 低温下孪生是合金主要的变形方式, 包括{1011}和{1121}型孪晶. 疲劳变形位错组态为: 室温较低应变幅(0.5%, 1.0%)下, 形成位错线和局部位错缠结; 室温下应变幅提高到1.5%和2.0%时,\{1010}柱面和{1121}锥面滑移同时开动, 位错组态演化为亚晶和明显的位错胞. 77 K下, 应变幅2.0%时形成沿 柱面平行分布的位错带; 77 K下应变幅升高到4.5%时, 多滑移形成相互垂直的位错线. 低温诱发形变孪晶是Ti--2Al--2.5Zr低温疲劳寿命升高的原因.     

Orientation-Dependent Mechanical Responses and Plastic Deformation Mechanisms of FeMnCoCrNi High-entropy Alloy:A Molecular Dynamics Study

Mechanical properties of high-entropy alloys (HEAs) with the face-centered cubic (fcc) structure strongly depend on their initial grain orientations.However,the orientation-dependent mechanical responses and the underlying plastic flow mecha-nisms of such alloys are not yet well understood.Here,deformation of the equiatomic FeMnCoCrNi HEA with various initial orientations under uniaxial tensile testing has been studied by using atomistic simulations,showing the results consistent with the recent experiments on fcc HEAs.The quantitative analysis of the activated deformation modes shows that the ini-tiation of stacking faults is the main plastic deformation mechanism for the crystals initially oriented with[001],[111],and[112],and the total dislocation densities in these crystals are higher than that with the[110]and[123]orientations.Stacking faults,twinning,and hcp-martensitic transformation jointly promote the plastic deformation of the[110]orientation,and twinning in this crystal is more significant than that with other orientations.Deformation in the crystal oriented with[123]is dominated by the hcp-martensite transformation.Comparison of the mechanical behaviors in the FeMnCoCrNi alloy and the conventional materials,i.e.Cu and Fe50Ni50,has shown that dislocation slip tends to be activated more readily in the HEA.This is attributed to the larger lattice distortion in the HEA than the low-entropy materials,leading to the lower criti-cal stress for dislocation nucleation and elastic-plastic transition in the former.In addition,the FeMnCoCrNi HEA with the larger lattice distortion leads to an enhanced capacity of storing dislocations.However,for the[001]-oriented HEA in which dislocation slip and stacking fault are the dominant deformation mechanisms,the limited deformation modes activated are insufficient to improve the work hardening ability of the material.     

Effect of grain size on the mechanisms of plastic deformation in wrought Mg–Zn–Zr alloy revealed by acoustic emission measurements

The present study has clarified the roles of dislocation slip and twinning as the deformation mechanisms in magnesium alloys, as well as the effect of grain size on their relative contributions. The details of these mechanisms were studied by monitoring acoustic emission (AE) in conjunction with a novel signal categorization technique in Mg alloy ZK60. Through the analysis of AE time series the sequences of predominant deformation mechanisms in coarse grained (～70 μm) and fine grained (～2 μm) specimens of the alloy were identified with a high degree of confidence. It was found that dislocation slip and twinning occur during tensile loading simultaneously for both microstructural states of the material, while a change from one predominant mechanism to the other occurs in the course of loading. Specifically, in the fine grained material plastic deformation is initially carried by dislocation slip, but deformation twinning takes over as the lead mechanism early on. In the coarse grained variant this sequence is reversed. The implications of the changing roles of the mechanisms of plastic deformation for the overall mechanical performance of ZK60 in the two contrasting microstructural states are discussed.