Representation of Crack-Tip Plasticity in Pressure Sensitive Geomaterials: Large Scale Yielding

We model large scale Mohr-Coulomb yielding that accompany fractures in weak rocks, by means of dislocations. The basic equations are derived from a simple model of the crack tip plasticity which represents the plasticity by superdislocations placed at the effective centres of the crack tip process zone.     

Comments on “An alternative physical explanation of the Hall–Petch relation”

Bata and Pereloma describe a physical model that proposes to explain the Hall–Petch relationship. The model is based on an averaging process for the work required to emit a dislocation from a tilt boundary. The purpose of the present comment is to examine several assumptions at the heart of the proposed model. Consideration is first directed at the fundamental premise that application of an average stress is sufficient to induce emission of a straight dislocation from a boundary, even though that stress is far below the stress required to overcome the highest energy barrier. The averaging process is also shown to emphasize the weak long-range interaction of the emitted dislocation with the original boundary, the consequences of which are considered.     

AlN基板与金属化层界面的分析电镜研究

利用各种分析电镜观察了掺杂助烧剂和未掺杂助烧剂的ＡｌＮ陶瓷的微观结构特征，鉴别了ＡｌＮ中的第二相，研究了ＡｌＮ基板上薄膜（Ａｕ－Ｐｔ－Ｔｉ）和厚膜（Ｍｏ－Ｍｎ）金属化界面的结构。     

深冷处理对W6Mo5Cr4V2钢强度和冲击磨损性能影响的研究

研究了深冷处理对W6Mo5Cr4V2钢的抗弯强度和冲击磨损性能的影响。研究结果表明明，随深冷时间的延长，晶体中空位密度有所增加。经透射电镜观察，深冷处理后在马氏体的孪晶带上弥散折出颗粒为3-6nm的碳化物。经深冷处理的W6Mo5Cr4V2钢其冲击磨损性能得到了提高。     

Molecular dynamics simulation of dislocation nucleation and motion at γ/γ′ interface in Ni-based superalloy

Molecular dynamics simulations are conducted on the dislocation behavior at the apices and edges of cuboidal Ni₃Al precipitate in a pure Ni matrix, or the idealized γ/γ′ microstructure in a Ni-based superalloy. A tensile simulation of the [001] direction is implemented with a periodic cell that has eight cubic precipitates in order to investigate the nucleation site of dislocation in the idealized microstructure with no defects other than the γ/γ′ interfaces. The effect of residual internal stresses on the stability of the interfaces is also discussed. Other simulations are conducted on the behavior of edge dislocations nucleated from a free surface and proceeding in the γ matrix toward γ′ precipitates under shear force. Dislocation pinning at γ′ precipitates, bowing-out in the γ channel, pile-up and nucleation of superdislocation in the γ′ precipitate are simulated and inspected in detail. Discussions on the size of the γ/γ′ microstructure and the sharpness of the edge of the γ′ precipitate are also presented.     

影响碲镉汞晶体电子迁移率的主要因素

通过把迁移率的实测值与影响ＨｇＣｄＴｅ晶体电子迁移率的主要散射机构进行对比，得出结论：位错是ＨｇＣｄＴｅ晶体低温电子迁移率降低的主要原因。     

Comparison of spatial compositional uniformity and dislocation density for organometallic vapor phase epitaxial Hg1−x CdxTe grown by the direct alloy and interdiffused growth processes

Etch pit density and spatial compositional uniformity data are presented for organometallic vapor phase epitaxial Hg_1−x Cd_x Te grown by the direct alloy and interdiffused growth methods. For alloy growth, composition variation is as low as Δx=0.004 and 0.02 over 2- and 3-in diam areas, respectively; while for growth on CdZnTe substrates, etch pit density values lower than 2×10⁵ cm⁻² have been achieved. For interdiffused growth on CdZnTe, etch pit density values lower than 5×10⁵ cm⁻² have been obtained, while the composition variation is usually Δx≤0.004 and 0.014 over 2- and 3-in diam areas, respectively. Data demonstrate that the choice of particular CdZnTe substrate strongly affects the subsequent etch pit density measured in the layer. Reasonably uniform n-type doping over 3-in diam area using the source triethylgallium is also reported for both growth methods.     

较大直径、低位错锑化铟单晶的研制

本文简要介绍了用ＴＤＫ－３６单晶炉拉制的较大直径（φ＝２５ｍｍ）、低位错（＜１００ｃｍ￣（－２））的锑化铟单晶的理论和实践。通过对晶体生长室内温场，特别是内外坩埚尺寸的调整及对循环水流量的控制，成功地拉制出较大直径、低位错的锑化铟单晶。     

Elevated temperature deformation behavior in an AZ31 magnesium alloy

An AZ31 magnesium alloy was tested at constant temperatures ranging from 423 to 473 K (0.46 to 0.51T _m ) under constant stresses. All of the creep curves exhibited two types depending on stress levels. At low stress (σ/G<4×10⁻³), the creep curve was typical of class A (Alloy type) behavior. However, at high stresses (σ/G>4×10⁻³), the creep curve was typical of class M (Metal type) behavior. At low stress level, the stress exponent for the steady-state creep rate was of 3.5 and the true activation energy for creep was 101 kJ/mole which is close to that for solute diffusion. It indicates that the dominant deformation mechanism was glide-controlled dislocation creep. At low stress level wheren=3.5, the present results are in good agreement with the prediction of Fridel model.     

Rate mechanisms of plasticity in semi-crystalline polyethylene

Based on our experiments on polyethylene where we have observed a constant level of plastic resistance, independent of lamella thickness exceeding 40 nm, we have fundamentally re-considered the rate controlling mechanisms of crystal plasticity in semi-crystalline polymers. In this we have not only re-examined and made modifications to the widely accepted mechanism of Young (Young RJ. Mater Forum 1988;11:210.) of monolithic nucleation of screw dislocations from edges of crystalline lamellae predicting an increase in plastic resistance with increasing lamella thickness, but we are proposing here two new modes of nucleation of both edge and screw dislocation half loops from lamella faces that are independent of lamella thickness. These two new modes of dislocation nucleation explain well the observed transition from a plastic resistance increasing with lamella thickness to one of constant resistance above a lamella thickness of ca. 35 nm in polyethylene. They also provide a more satisfactory framework to explain the temperature and strain rate dependence of the plastic resistance of polyethylene and predict the observed levels of activation volumes determined by us.