不同晶粒尺寸Ni—P合金纳米晶体的界面过剩体积研究

用非晶晶化法制备尺寸为１３－１０７ｎｍ的Ｎｉ－Ｐ合金纳米晶体，利用正电子湮没技术研究了尺寸不同的纳米晶体中界面缺陷类型及其分布，发现单位体积界面的缺陷含量随晶粒减小而降低。由精细的密度测量和界面结构特征估算纳米晶体样品中的界面积过剩率随晶粒减小而显著降低，发生致密化现象，这一结果与正电子湮没实验及其它性能测试结果十分吻合。     

不同晶粒尺寸Ni－P合金纳米晶体的界面过剩体积研究

用非晶晶化法制备尺寸为１３－１０７ｎｍ的Ｎｉ－Ｐ合金纳米晶体．利用正电子湮没技术研究了尺寸不同的纳米晶体中界面缺陷类型及其分布，发现单位体积界面的缺陷含量随晶粒减小而降低．由精细的密度测量和界面结构特征估算纳米晶体样品中的界面体积过剩率随晶粒减小而显著降低，发生致密化现象，这一结果与正电子湮没实验及其它性能测试结果十分吻合．     

非晶态合金向纳米晶体的相转变

利用非晶态合金的晶化过程可以形成纳米尺寸晶粒的多晶体材料（即纳米晶体），这种制备纳米晶体的方法近年来得到了广泛重视和深入研究，本文对这种制备方法和非晶态合金向纳米晶体的相转变动力学，热力学及转变机理等方面进行综述。     

非晶态合金向纳米晶体的相转变

利用非晶态合金的晶化过程可以形成纳米尺寸晶粒的多晶体材料（即纳米晶体），这种制备纳米晶体的方法近年来得到了广泛重视和深入研究，本文对这种制备方法和非晶态合金向纳米晶体的相转变动力学、热力学及转变机理等方面进行综述．     

纳米晶体Se的微观结构特征

本文采用Ｘ射线衍射和透射电子显微镜研究了纳米晶体Ｓｅ的微观结构特征，通过测定不同晶粒尺寸的纳米晶体Ｓｅ的点阵参数ａ和ｃ，发现纳米晶体Ｓｅ中存在晶格畸变，畸变量与晶粒尺寸有关，得到了纳米晶体Ｓｅ中晶胞体积变化与晶粒尺寸的关系，并由点阵参数计算出纳米晶体Ｓｅ的键长，用非晶态Ｓｅ中的无规链折叠的晶化机制解释了纳米晶体Ｓｅ中晶格畸变现象。     

纳米晶体Se的微观结构特征

本文采用Ｘ射线衍射和透射电子显微镜研究了纳米晶体Ｓｅ的微观结构特征．通过测定不同晶粒尺寸的纳米晶体Ｓｅ的点阵参数ａ和ｃ，发现纳米晶体Ｓｅ中存在晶格畸变，畸变量与晶粒尺寸有关．得到了纳米晶体Ｓｅ中晶胞体积变化与晶粒尺寸的关系．并由点阵参数计算出纳米晶体Ｓｅ的键长．用非晶态Ｓｅ中的无规链折叠的晶化机制解释了纳米晶体Ｓｅ中晶格畸变现象．     

纳米陶瓷材料弹性模量的尺度效应

针对纳米陶瓷的界面现象，在三相模型基础上，考虑纳米晶粒与界面相的相互作用，将其改进为复合材料刚度预报的四相模型法，根据有效自恰方法推导出纳米晶粒与界面相内的有效应力，进而得到柔度增量的隐性表达式，再利用相互作用直推法，得到纳米陶瓷材料的柔度增量的显性形式，它具有：1）简单的解析形式；2）适合任何形状的纳米晶粒；3）适合各向同性和各向异性纳米晶粒；4）将复合材料的弹性性能与纳米晶粒尺寸联系起来。结果表明：当纳米晶粒尺寸小于50nm时，纳米陶瓷材料的弹性模量随纳米晶粒尺寸的减小而下降，当纳米晶粒尺寸超过50nm以后，纳米陶瓷材料的弹性模量基本保持不变。     

纳米多晶Ni微观结构与力学性能的分子动力学模拟

运用分子动力学技术,结合分析型嵌入原子方法(AEAM)模拟计算了平均晶粒尺寸为2.09～5.23 nm的纳米多晶Ni的微观结构和力学性能.从原子能量分布、径向分布函数(RDF)、局域晶序结构的角度分析了纳米多晶Ni的晶界和晶粒结构,发现晶界部分所占的比例随晶粒尺寸的减小明显提高,结构与普通微晶的相似,纳米晶体的结合能较普通晶体的低.单向拉伸模拟结果表明:纳米多晶Ni的强度与晶粒尺寸之间出现反常Hall-Petch关系;弹性模量的降低与纳米尺度结构特征相关.     

Al-TiB2纳米晶薄膜中的反Hall-Petch效应

多种微结构因素作用的相互交织使纳米晶合金中是否存在与纯金属类似的反Hall-Petch现象难以得到实验证实。选用Al-TiB_2体系,采用二维结构纳米多层膜的方法,实现了对晶粒尺寸因素的孤立和使其独立地改变,研究了晶粒尺寸对薄膜力学性能的作用规律。结果表明:Al-TiB_2过饱和固溶纳米晶薄膜也与纳米晶纯金属Al一样,存在硬度随晶粒尺寸减小从遵从Hall-Petch关系提高转变为偏离Hall-Petch关系,并进一步出现反Hall-Petch效应的3个阶段,实验得到了偏离Hall-Petch关系为32 nm,产生反Hall-Petch现象的临界晶粒尺寸为8 nm,这2个临界晶粒尺寸与分子动力学方法对纳米晶纯金属A1计算的结果相当。     

纳米金属材料的界面力学行为研究

将常规多晶材料的粗晶粒尺寸缩小到纳米尺度时,这些纳米晶体材料会呈现出与其对应的粗晶材料迥异的物理现象.与材料力学行为最相关的是强度及塑形变形机理这两个方面.考虑到晶界的变形与破坏可能是纳米晶体材料低塑性的根源,克服纳米晶体材料中强度与韧性之间存在的"熊掌和鱼不可兼得"的问题,也通常称为晶界工程.在众多的晶界中,孪晶界面被发现可同时保持材料的强度和韧性.本文主要就纳米金属材料中界面的力学行为做一个简要综述,包含晶界的强化力学机理以及新型孪晶界面的力学行为与揭示内在尺度效应的模型研究.     

Numerical simulation of influence of material parameters on splitting spinning of aluminum alloy

During the splitting spinning process, the material parameters of disk blank have a significant effect on the determination of forming parameters and the quality of deformed blank. The influence laws of material parameters, including yield stress, hardening exponent and elastic modulus, on splitting spinning force, splitting spinning moment, degree of inhomogeneous deformation and quality of flange （average thickness and average deviation angle） were investigated by 3D-FE numerical simulation based on elasto-plastic dynamic explicit FEM under ABAQUS/Explicit environment. The results show that, the splitting spinning force and the splitting spinning moment increase with the increase of yield stress, hardening exponent and elastic modulus. The degree of inhomogeneous deformation increases with the decrease of yield stress and hardening exponent and the increase of elastic modulus. The average thickness of flange increases with the decrease of yield stress and the increase of hardening exponent and elastic modulus. The average deviation angle of upper surface increases with the increase of yield stress and the decrease of hardening exponent and elastic modulus. The average deviation angle of lower surface increases with the decrease of yield stress, hardening exponent and elastic modulus. Meanwhile, the corresponding variation ranges are given. The achievements may serve as an important guide for selecting the reasonable processing parameters of splitting spinning based on different aluminum alloys, and are very significant for optimum design and precision control of the splitting spinning process.     

纯铜动态再结晶过程的元胞自动机模拟

基于热加工过程金属学原理,建立了一类改进动态再结晶二维元胞自动机模型,模拟了加工硬化,动态回复、形核及再结晶晶粒长大等一系列过程.利用该模型可得到整个热加工过程流变应力变化,晶粒的形态、晶粒取向及大小.流变应力的大小可由基体与再结晶晶粒位错密度的平均值计算.采用该模型对不同应变,应变率及温度下纯铜动态再结晶过程进行了模拟,模拟结果与相同热变形条件下纯铜实验结果吻合较好.     

磁记录Fe,Co,Ni纳米晶体的熔化温度

本文提出了一个无自由参数的晶体熔化温随尺寸变化的模型。模型指出纳米金属晶体的熔化温度随着纳米晶的尺寸的减小而降低。     

MECHANICAL PROPERTIES OF Ti_3SiC_2 AT HIGH TEMPERATURE

Creep and stress relaxation behavior, the elastic modulus and fracture toughness of machinable Ti3SiC2 at various temperatures from 20 to 1250℃ were investigated by means of three-point bending tests. The experiments were performed respectively at: (i) fixed stress and changed temperatures, and (ii) fixed temperature and changed stresses. A creep resistance parameter that represents the probability of creep deformation in a given condition was defined as a function of both applied stress and the threshold stress, varying in a range from 0 to 1. Elastic modulus at high temperatures was measured through comparing relative slopes of loading curves in cyclic loading curve. The fracture toughness measured by SENB method showed a stable value in the range of 25-1000℃, but over 1000℃, it declined abruptly from -6.7MPa·m1/2 to -2.0MPa·m1/2 at 1200℃.     

MECHANICAL PROPERTIES OF TiaSiC2 AT HIGH TEMPERATURE

Creep and stress relaxation behavior, the elastic modulus and fracture toughness of machinable Ti3SiC2 at various temperatures from 20 to 1250℃ were investigated by means of three-point bending tests. The experiments were performed respectively at: (i) fixed stress and changed temperatures, and (ii) fixed temperature and changed stresses. A creep resistance parameter that represents the probability of creep deformation in a given condition was defined as a function of both applied stress and the threshold stress, varying in a range from 0 to 1. Elastic modulus at high temperatures was measured through comparing relative slopes of loading curves in cyclic loading curve. The fracture toughness measured by SENB method showed a stable value in the range of 25-1000℃, but over 1000℃, it declined abruptly from ～6.7MPa.m^1/2 to～2.0MPa.m^1/2 at 1200℃.     

Der Einfluß der Strahlenschädigung durch schnelle Neutronen auf die Spannungsrißkorrosion (SKR) von Eisen-Chrom-Nickel-Stählen

Influence of radioactive deterioration by fast neutrons on stress corrosion cracking of chromium-nickel steels Neutron irradiation has a bearing on the mechanical properties of the pure and industrial steels investigated. The creep limit is increased while the range of uniform elongation is reduced. Under an integral fast neutron flux of about 2.5.10¹⁹ n/cm² there is a defined yield strength increasing the stress corrosion susceptibility and there are indications of intercrystalline cracking in some cases. The industrial alloy has exclusively transcrystalline cracks een after neutron irradiation; the crack density is higher than in the pure alloy.     

20CrMnMo钢不同渗碳淬硬层深度的组织与应力分布

以三种渗碳淬硬层深度不同的20CrMnMo齿轮钢试样为研究对象,对其显微组织和硬度梯度进行检测,采用电化学剥层技术,借助X-350A型X射线应力仪,测量各试样深层渗碳淬硬层的残余应力及其分布,将硬度梯度与残余应力的分布进行对照,认为20CrMnMo钢渗碳淬硬层硬度小于400 HV1,均为残余压应力,之后才转换为残余拉应力,这一结果为确保齿面具有可靠的抗接触疲劳性能,合理地确定重载大模数齿轮有效硬化层深度提供技术支撑。     

On the similarity of plastic flow processes during smooth and jerky flow in dilute alloys

The jerky flow of dilute alloys, or the Portevin-Le Chatelier effect, has a burst-like intermittent character at different fluctuation size levels. Multifractal analysis is applied to both the macroscopic stress serrations and the acoustic emission accompanying the plastic deformation. Multifractal scaling is found for both kinds of time series. The scaling range of the stress serrations is limited from below by their characteristic frequency. Unexpectedly, the scaling range for acoustic bursts not only covers this range but spreads to much shorter time scales with the same scaling exponent. This result testifies that the deformation processes revealed by the acoustic emission at a mesoscopic scale have a similar nature during both stress serrations and smooth plastic flow. The implications on the crossovers in the dynamics of jerky flow are discussed.     

Evaluation of the mechanical properties of conventionally-cast Al matrix composites reinforced by quasicrystalline Al-Cu-Fe particles using continuous ball indentation technique

Room temperature mechanical properties of the Al/(AlCuFe)_p and Al₉₆Cu₄/(AlCuFe)_p cast composites were estimated from uniaxial compressive test and continuous ball indentation technique. Values of the Young’s modulus and yield stress determined from continuous ball indentation tests were slightly overestimated, suggesting a surface effect on the mechanical properties. However, it was shown that the Al-Cu-Fe particles provided a significant increase of the elastic modulus, yield stress, and strain hardening, especially in the range up to 10% volume fraction of reinforcements. Also, determination of the hardness by continuous-ball-indentation tests revealed a strong influence of the matrix strength on the mechanical properties of the conventionally cast composites.     

针状铁素体钢的高温屈服应力及弹性模量

用热模拟试验机研究了C-Mn-Mo-Nb针状铁素体钢的相变特性,采用拉伸和压缩方法检测了试验钢在奥氏体化加热后冷却至不同温度时的屈服应力和弹性模量,采用高温拉伸试验机对比检测了加热至奥氏体化以下,试验温度时钢的屈服应力和弹性模量。结果表明：在奥氏体化后冷却过程中,钢的屈服应力在650～500℃相变温度范围内从约75 MPa提高至约450 MPa,但弹性模量在针状铁素体相变温度区间（600℃左右）出现谷值。在550℃以上,从室温加热至试验温度拉伸方法获得钢的屈服应力和弹性模量较奥氏体化加热法的高。相变过程中,晶体结构转变及位错密度增加是弹性模量波谷产生的主要原因;晶体结构转变、位错密度增加和析出使屈服应力急剧增加。而相同组织状态下,钢的屈服强度和弹性模量主要受温度影响。不同测试方法所得数据的差异,主要是由不同的组织结构转变而非测试方法造成。