Evolution of linear edge dislocation in atmospheric turbulence and free space

In accordance with the extended Huygens–Fresnel principle, the evolution of linear edge dislocation propagating through atmospheric turbulence is studied, and the effects of waist width and the slope of linear edge dislocation are investigated. It is shown that when linear edge dislocation beams propagate through atmospheric turbulence, if the waist width is not equal and the slope is not zero, then the linear edge dislocation vanishes and transforms into an optical vortex with a topological charge of ?1 or +1. The optical vortex and an optical vortex that is created annihilate when the transmission distance is far enough. The linear edge dislocation vanishes when the slope is zero. If the waist width is equal, then the linear edge dislocation will vanish regardless of the slope value. For linear edge dislocation beams in free space, when selecting specific parameters, linear edge dislocation always exists.     

Solids Under Extreme Shear: Friction‐Mediated Subsurface Structural Transformations

Tribological contacts consume a significant amount of the world's primary energy due to friction and wear in different products from nanoelectromechanical systems to bearings, gears, and engines. The energy is largely dissipated in the material underneath the two surfaces sliding against each other. This subsurface material is thereby exposed to extreme amounts of shear deformation and often forms layered subsurface microstructures with reduced grain size. Herein, the elementary mechanisms for the formation of subsurface microstructures are elucidated by systematic model experiments and discrete dislocation dynamics simulations in dry frictional contacts. The simulations show how pre‐existing dislocations transform into prismatic dislocation structures under tribological loading. The stress field under a moving spherical contact and the crystallographic orientation are crucial for the formation of these prismatic structures. Experimentally, a localized dislocation structure at a depth of ≈100–150 nm is found already after the first loading pass. This dislocation structure is shown to be connected to the inhomogeneous stress field under the moving contact. The subsequent microstructural transformations and the mechanical properties of the surface layer are determined by this structure. These results hold promise at guiding material selection and alloy development for tribological loading, yielding materials tailored for specific tribological scenarios.     

Assessment of plastic damage in high strength structural steel using electromagnetic technique

ABSTRACT

High strength structural (HSS) steels are widely used in many construction equipment and infrastructures. Currently, there is a substantial demand of Non-Destructive Testing of these steel structures. In this research, the electromagnetic technique was utilised to assess the plastic damage in a typical HSS steel (i.e. Q690 steel). The results showed that the magnetic hysteresis loop of this material changed apparently after the tensile deformation, and the relevant magnetic parameters such as coercivity, remanence, and maximum permeability were sensitive to the cumulative plastic strain. The results demonstrated that there is a good coherence between the plastic damage evolution and the magnetic parameters variation, which indicated that the electromagnetic technique is an effective method to assess the plastic damage of HSS steel.     

Synergistic effects of anisotropy and image force on TEM diffraction contrast of dislocation loops

Based on column approximation (CA) assumption, many-beam Schaeublin–Stadelmann diffraction equations are employed for simulating the transmission electron microscopy (TEM) diffraction image contrast of dislocation loops within thin TEM foil of finite thickness, and two beam and many beam diffraction conditions are compared. Moreover, the effects of materials anisotropy and free surface relaxation induced elastic fields distortion of dislocation loops on the black-white image contrast are specially focused. It is found that anisotropy has a remarkable impact on the TEM image contrast of dislocation loop, and free surface relaxation induced image forces can change the black-white contrast features when dislocation loops are near TEM foil free surfaces. Thus, in order to make reliable judgment on the nature of defects, effects of free surface and anisotropy should be included when analysing irradiation induced dislocation loops and other type of defects in in-situ electron, proton, heavy-ion irradiation experiments under TEM environments.     

双模晶体相场研究六方四方相变过程晶界和位错演化

对于晶粒，晶界，应力和位错的交互作用的深入理解有助于优化材料组织和提升材料性能。本文采用双模晶体相场法研究六方相向正方相的转变。分别针对倾侧角为0°，15°，30°，和 45°，晶粒取向差为6°的六方相体系做了系统研究。六方晶粒长大、溶合、并形成共格晶界，位错组沿六方晶界均匀分布，并有两种取向。正方相在位错组处形核，并且其取向取决于位错组取向。每一种倾侧角的体系种均形成两个取向正方相的变体。针对倾侧角为0 °，15°，30°，和 45°的六方相体系生成的四方相相变体之间的取向差分别为30°, 30°, 10°, 和5°。不同取向的正方相晶粒长大熟化的方式有差异，位于有利取向的晶粒将会优先生长占据主导地位。以共格晶界形式长大的晶粒，晶界处有位错组生成以松弛晶粒长大的应力集中。     

Hydrogen embrittlement behavior in interstitial Mn–N austenitic stainless steel

The susceptibility to hydrogen embrittlement behavior was investigated in an interstitial Mn–N austenitic steel HR183 and stainless steel 316L. Hydrogen was introduced by cathodic hydrogen charging at 363 K. HR183 has stronger austenite stability than 316L despite its lower nickel content, the addition of manganese and nitrogen inhibited martensitic transformation during the slow strain rate tensile deformation. Due to the diffusion of hydrogen being delayed by the interstitial solution of nitrogen atoms and the uniform dislocation slips, hydrogen permeates more slowly in HR183 than 316L, contributing to an 84.79 μm thinner brittle fracture layer in HR183 steel. Hydrogen charging caused elongation losses in both 316L and HR183 steels associated with the hydrogen-enhanced localized plasticity (HELP) and hydrogen-enhanced decohesion (HEDE) mechanism. However, the hydrogen embrittlement susceptibility of HR183 is 3.4 times lower than that of 316L according to the difference in elongation loss between the two steel after hydrogen charging. Deformation twins trapped a lot amount of hydrogen leading to brittle intergranular fracture in 316L. The multiple directions of slip in HR183 steel suppressed the strain localization inside grains and delayed the adverse effects conducted by HELP and HEDE mechanism, eventually inhibiting server hydrogen embrittlement in the HR183 steel. This study is assisting in the development of low-cost stainless steel with excellent hydrogen embrittlement resistance that can be used in harsh hydrogen-containing environments.     

屯留矿井测量工作必要精度的确定

在生产矿井中所进行的全部测量工作,是指导采矿生产正确、安全和顺利进行的保证。矿井测量工作是否及时,测量精度是否能满足采矿生产的要求,会给矿井生产以直接的影响。因此,必须对矿井测量工作的必要精度进行确定,从而提出正确的测量方案,克服盲目性。     

Estimate of stress state in rock masses adjacent to open pit walls

It is proposed to study the action exerted by the tectonic stresses on stability of open pit walls by using the method of core disking in exploratory holes and the tectono-physical method based on the analysis of tectonic structure of a rock mass. __________ Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 3, pp. 36–44, May–June, 2007.     

T1相(Al2CuLi)对铝锂合金各向异性的贡献

在分析T1相基本特性的基础上，结合相关工作，论述T1相与位错的交互作用、T1相与结构的相互影响、T1相对合金各向异性的贡献及稀土Ce的作用。结果表明，T1相因其分布及形貌而难以有效阻碍共面滑移；T1相对形变织构的形成起调整作用；织构的存在使T1相的分布及其与位错的作用发生变化，从而使其强化贡献具有各向异性。Ce影响形变织构的形成和合金的时效析出，并对共面滑移具有双重作用，从而改变T1相强化的各向异性。     

福建省漳平电厂发电机护环开裂的研究

就基体材料的组织特征以及是否由于基体材料本身问题导致护环开裂进行研究。利用金相显微镜和电子显微镜对福建省漳平电厂发电机护环的金相样品进行观察与分析 ,发现护环材料运行一定时间后 ,奥氏体基体组织中出现滑移带。在电镜下可观察到位错缠结和位错胞 ,并伴有少量马氏体和形变孪晶。研究表明 :该基体材料的组织特征属于正常运行的组织转变 ,不会产生裂纹等异常现象。