Mg-Cu-Y块体金属玻璃的塑性变形特性

通过对Mg-Cu-Y块体金属玻璃在深过冷液体区间塑性变形特性的研究，探讨了影响其塑性变形的因素及其影响规律。结果表明，加载温度和时间均对其塑性变形有明显的影响，在深过冷液体区间，要达到合适的变形量，加载温度和时间必须适中；Mg-Cu-Y块体金属玻璃在压缩条件下能够发生流变，较好地复制模具表面的显微形貌。同时，在加载条件下，Mg-Cu-Y块体金属玻璃更容易发生晶化。     

塑性变形中晶粒变形与细化机制的影响因素

讨论了层错能、应变速率和变形温度等因素在塑性变形制备超细晶/纳米晶材料的变形过程中,对变形机制与晶粒细化机制的影响.研究表明,随着层错能的降低,晶粒的变形机制会由位错滑移向机械孪生转变,有利于晶粒的细化.应变速率的增加与变形温度的降低有利于抑制位错动态回复、增加流变应力,促使晶粒进一步细化.     

Zr-4合金管材皮尔格轧制过程数值模拟分析：宏观模型的建立、验证及塑性变形分析

皮尔格轧制变形对于锆合金管材的性能有着重要影响,受到学者们的高度重视。长期以来,由于皮尔格轧制是一个高度非线性的三维变形过程,开展实验研究不但成本高昂而且周期较长。本研究以ABAQUS/standard平台,根据多行程皮尔格轧制的运动特点,建立了Zr-4合金管材皮尔格轧制有限元模型,并开展一整个道次的轧制过程模拟。模拟结果表明:预测的管材几何尺寸与实验结果吻合良好,而模拟的轧制力与经典的舍瓦金公式计算结果也比较相符,验证了所建立模型的准确性,可用于进一步仿真分析。模拟结果还表明开口处的管坯应力状态与轧槽底部管坯的应力状态有显著的差别。此外,轧制过程中还存在有明显的剪切变形,而且还有较大幅度的周期性波动,这主要与孔型开口以及管坯回转送进有关。     

强烈塑性变形方法制备块体金属纳米材料

介绍了强烈塑性变形制备块体金属纳米材料的主要方法，分析了利用强烈塑性变形方法制备块体金属纳米材料的微观结构和性能。     

Deformation and fracture behaviors of Ti-based metallic glass under multiaxial stress state

The deformation and fracture behaviors of a Ti-based metallic glass (MG) under a multiaxial stress state were investigated using a small punch test. It was found that controlling both the initiation and propagation of a shear crack can significantly stabilize the plastic deformation of Ti-based MG by forming multiple shear bands and delaying the shear crack from reaching the critical crack length. Radial, circumferential and spiral shear band patterns and corresponding fracture modes were observed. The relationship between the shear band pattern and the stress state was established. This finding implies that a MG could be stabilized and become ductile in nature under suitable stress conditions.     

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.     

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。     

Wettability and Interfacial Reactions Between Metallic Glass Melts and Cu/Mo Used as Roller Materials for Twin-Roll Casting

Twin-roll casting has been recently revealed to be an efficient technique to produce rejuvenated metallic glass (MG) strips. Due to the high melting point and high hardness, pure Mo is considered as a good roller material as pure Cu. However, the wettability and interfacial reactions between MG melts and Cu or Mo remain largely unknown. In this work, a series of sessile droplet wetting experiments are designed to investigate the wettability and reactions between Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 (Vit.1) or (Zr_0.401Ti_0.133Cu_0.118Ni_0.101Be_0.247)₉₉Nb₁ (Nb1) MG melts and Cu/Mo substrates at temperatures of 1073, 1123 and 1173 K. It is found that the wettability and interfacial reactions of the Vit.1 and Nb1 MG melts on the Cu substrates are very similar. The equilibrium contact angles are ~ 30° at 1073 K and ~ 25°-27° at 1123 K. The MG melts completely spread out on the Cu substrates at 1173 K. Cu substrates are slightly dissolved in the MG melts event at 1073 K, and a transitional reaction layer exists between the droplet and the Cu substrate. In comparison, the Vit.1 MG melt exhibits a much improved wettability on the Mo substrate. The equilibrium contact angle of the Vit.1/Mo is only 6° at 1073 K and 5° at 1123 K. No significant diffusion of Mo into the droplet occurs even at 1173 K with a holding time of ~ 30 min. The interfaces of the Vit.1/Mo samples are sharp, and no interfacial reaction layers form. These findings indicate that pure Mo can be a good roller material for twin-roll casting at high temperatures, and the Mo-made rollers are expected of capability to produce MG strips with good quality.     

基于磁噪声和增量磁导率的塑性变形定量无损评价

针对机械结构在加工、制造和使用过程中常出现的塑性变形损伤,研究了碳素钢材料塑性变形与巴克豪森噪声及增量磁导率之间的关联性。试验结果表明,在小变形时,巴克豪森噪声信号随塑性变形变化明显;增量磁导率值随塑性变形的增大而规律性变化。不同碳素钢材料的试验结果表明,巴克豪森磁噪声和增量磁导率可用于碳素钢材料中塑性变形的定量无损评价。     

大塑性变形材料及变形机制研究进展

大塑性变形技术（SPD）具有将铸态粗晶金属的晶粒细化到纳米量级的巨大潜力。综述了SPD技术的分类、优势及其存在问题;介绍了材料在SPD加工过程中的组织转变特点,指出如果超塑性成形能够在镁合金等中得到成功的应用,则可大大拓宽其实际应用领域;描述了SPD细化铝、镁、钛等合金后的微观组织、塑性变形机制与力学性能,最后对大塑性变形技术的应用前景进行了展望。     

商业纯钛拉压塑性变形行为与机理

通过拉伸和压缩试验,获得了商业纯钛在不同温度和不同应变速率下的拉伸和压缩应力-应变关系,对比分析了拉压变形路径、变形温度和应变速率对商业纯钛塑性变形行为的影响;建立了Zener-Hollomon模型,获得了变形温度和应变速率对商业纯钛压缩变形加工硬化的作用规律及商业纯钛压缩变形加工图;基于电子背散射衍射技术,获得了商业纯钛晶粒取向分布,结合拉压变形特性阐明了商业纯钛拉伸塑性变形机理主要是滑移,压缩塑性变形机理主要分为滑移-孪生-滑移3个阶段。     

新型Cu-Fe-(C)复相合金的变形及时效析出行为对比研究

采用真空感应熔炼和快速凝固法制备了组织性能优异的新型Cu-Fe-(C)复相合金材料,并通过OM、TEM以及力学性能测试分别对熔铸态、超低温深冷轧态、时效态组织和变形行为进行了研究。结果表明,添加溶质元素C有利于避免Cu-3%Fe(质量分数)合金铸态晶界偏析,降低晶内γ-Fe相尺寸,增加其在基体内的数量密度,使得该合金屈服强度较低,而延伸率却较高;超低温深冷轧变形可使Cu-Fe-(C)合金基体内γ-Fe相发生γ-Fe→α-Fe马氏体转变,屈服强度提升至520MPa以上,但是C元素的引入,会使合金残留部分细小γ-Fe相而维持高塑性;进一步经不同温度时效1 h时,2种合金均随温度升高逐渐发生回复再结晶导致硬度降低,不过Cu-Fe-C合金经400℃/1 h处理后发生再结晶的同时,还会析出更多更细小的α-Fe沉淀相,并残留较多位错,最终导致其具有较高的强度和延伸率。此外,对不同状态的沉淀相分布进行了统计和理论强度计算,深入分析了合金强度差异的本质原因。     

Variability in the yield strength of a metallic glass at micron and submicron length scales

This work presents an in-depth investigation of the dispersion in the compressive yield strength of a Zr-based bulk metallic glass as the specimen dimensions decrease from the micron to the submicron length scale. While the investigated alloy belongs to one of the so-called “ductile” glass families, the degree of variation in strength exhibited in the submicron size range approaches that of conventional brittle ceramics. Using a three-parameter Weibull analysis, however, we find that the engineering reliability of the glass is independent of specimen size. The glass exhibits a size-independent failure-free stress of 1825 MPa, below which yielding is not expected. The three-parameter Weibull modulus is also size independent. The dispersion in yield strengths above the failure-free stress is due to the change in the sampling volume for specimens 1 μm in diameter or larger, while interactions between defects and the surface actually limit the breadth of the strength distribution observed in specimens 200–330 nm in diameter relative to what may be expected for that volume. Using an instability criterion for a penny-shaped crack under shear with interfacial friction, a relationship between yield strength and the corresponding defect size is established, and the defect concentration is estimated.     

Toughening Effects through Optimizing Cell Structure and Deformation Behaviors of Al-Mg Foams

As widely used protective materials, the application of Al foams is still limited by their low intrinsic mechanical properties caused by the brittleness of struts. The introduction of Mg is recently demonstrated effective to improve the mechanical performance of Al foams; however, the mechanism of Mg modification is still not clear. In this work, Al-Mg foams are developed through a powder metallurgy process with excellent compression performance and high energy absorption capacity. The effects of Mg modification on the cell structure, toughness, and deformation behavior are investigated systematically. As a result, the small cell size of ~ 1.8 mm and the high sphericity of 0.92 are achieved with 5% of Mg addition, delivering high compression stress of 8.5 ± 0.43 MPa and energy absorption capacity of 6.9 ± 0.36 MJ/m³, simultaneously. The synergistic mechanism for the improved mechanical performance is also demonstrated to be the combination of stress transfer and plastic deformation behavior of cells. The results provide a new strategy to develop high-performance foam materials by improving toughness and further promote the practical application.     

Molecular Dynamics Simulations of the Orientation Effect on the Initial Plastic Deformation of Magnesium Single Crystals

Molecular dynamics simulation is employed to study the tension and compression deformation behaviors of magnesium single crystals with different orientations.The angle between the loading axis and the basal a direction ranges from 0° to 90°.The simulation results show that the initial defects usually nucleate at free surfaces,but the initial plastic deformation and the subsequent microstructural evolutions are various due to different loading directions.The tension simulations exhibit the deformation mechanisms of twinning,slip,crystallographic reorientation and basal/prismatic transformation.The twinning,crystallographic reorientation and basal/prismatic transformation can only appear in the crystal model loaded along or near the a-axis or c-axis.For the compression simulations,the basal,prismatic and pyramidal slips are responsible for the initial plasticity,and no twinning is observed.Moreover,the plastic deformation models affect the yield strengths for the samples with different orientations.The maximum yield stresses for the samples loaded along the c-axis or a-axis are much higher than those loaded in other directions.     

超声波对比法测试金属塑性变形前后残余应力的变化

采用超声检测方法,通过声弹性理论可计算出残余应力的数值。但是由于实际声速很难准确测量,使得该方法在实践中的可操作性受到了限制。介绍了声速和残余应力间关系,用对比实验的方法来分析声速变化和残余应力变化之间的关系。实验表明,试件受拉伸至塑性变形,内部所受残余拉应力增大,同一试件的同一位置超声波测得的回波波峰处声程减小。若不涉及残余应力具体值,只关心应力变化的情况下,可以通过超声波对比法判断残余应力的变化。该方法具有实用性和可操作性。     

亚共晶白口铸铁塑性变形行为的观察和分析

用金相显微镜，扫描电镜和透射电镜对经锻造和轧制等塑性变形的亚共晶白口铸铁组织进行了观察和分析，提示了共晶碳化物和基体的塑性变形行为，特别展示了被认为不能性变形的硬脆相共晶碳化物在变形应力驱使下由位错的运动，晶体滑移，扭转进行塑性变形的机制。为菜氏体钢铁材料塑性变形的研究提供了科学的证据。     

激光表面处理对工业级锆基块体非晶合金塑性变形能力的影响

目的 针对工业级Zr49.7Ti2Cu37.8Al10Er0.5块体非晶合金受到原材料中杂质元素和制备环境中氧元素的影响,其本征塑性变形能力较差的问题,研究激光表面处理对工业级Zr49.7Ti2Cu37.8Al10Er0.5块体非晶合金在压缩和拉伸条件下塑性变形能力的影响。方法 采用低纯原料制备工业级母合金锭子,利用铜模铸造法在低真空环境下制备工业级非晶合金试样,采用激光法对试样进行表面处理,利用万能试验机对激光处理试样的压缩和拉伸力学性能进行测试。通过X射线衍射仪和电子探针对试样的微观组织结构进行表征,采用扫描电镜对力学测试失效后试样的形貌进行微尺度观察。结果 经激光表面处理后影响区的深度约为150 μm,在影响区内铜元素的含量有所降低,但依然为非晶结构。在压缩条件下,未经激光表面处理的工业级Zr49.7Ti2Cu37.8Al10Er0.5块体非晶合金的塑性应变为0,断裂强度为1 534 MPa。经过激光表面处理后,试样具有1%的塑性应变,屈服强度为1 337 MPa,断裂强度为1 562 MPa。在拉伸条件下,激光表面处理前后工业级块体非晶合金的塑性应变均为0,断裂强度也无明显变化,其平均值为1 379 MPa。结论 通过激光表面处理在工业级Zr49.7Ti2Cu37.8Al10Er0.5块体非晶合金试样表面引起的成分变化和引入的残余应力状态,能够有效促使压缩载荷作用下剪切带的萌生,提高其压缩塑性变形能力。     

On the source of plastic flow in metallic glasses: Concepts and models

We briefly review the state-of-the-art study on plastic flow in metallic glasses. Especially, we survey the features and behaviors, percolation, and response of the basic deformation units to the activation of stress and temperature, and various models and notions on microscopic flow in metallic glasses. The discussion, comments and perspective on possible unified notation, terminologies and models on plastic flow in metallic glasses are presented. The purpose is to reach a consensus within the community with a hope to eventually unify the notations and models on the deformations in metallic glasses.     

金属纳米多层膜力学性能研究进展

新型功能材料及器件向小型化,集成化和复合化发展的趋势,使得尺寸在纳米尺度的层状材料和柔性多层器件在使用过程中的服役行为成为其发展的关键科学问题。本文结合作者近几年对Ag/M系列和Cu/M系列多层膜力学性能的研究工作,对金属纳米多层膜的微结构特征及其对力学性能的影响进行了回顾和总结,主要包括多层膜的晶粒形貌对其强化机制和塑性变形行为的影响,组元强度错配对多层膜硬化行为的影响,界面结构与其强度极值的关系、不对称界面结构引起的异常弹性模量增强和多层膜的室温蠕变机制及界面结构对蠕变性能的影响等几个方面,并对多层膜的力学性能研究进行了展望。