位错引起晶体熔化的统计理论

建立三维晶体中缺陷引起晶体熔化的统计理论，讨论了三维晶体中的缺陷－位错对的形成篚过程，地无相互作用位错对“成核－篚”过程的统计计算，得到了理论相变温度Ｔｃ，中还从理论上证明了此相变为一级相变，并得到了相变潜势的计算公式，最后还对理论预言进行了实验验证．。     

薄膜材料刃位错的求解

以弹性力学的平面应力模型求解了材料的刃位错,论证了此解可描述薄膜材料的位错。与体相的位错结果比较表明,薄膜材料的位错具有较低的应力和较低的弹性能。将本文的结果应用于位错引起薄膜熔化理论,得到了薄膜的熔点低于体相的熔点。将薄膜中存在位错情况与材料表面情况进行类比,得出材料表面的熔点也将低于体相的熔点。     

谈体心立方晶体{110}<1■1>滑移系全位错的滑移方式

本文从体心立方点阵中抽取一个滑移系棱锥来描述12个(110)(1(?)1)滑移系。根据滑移系棱锥可以清晰识别正交和斜交滑移面;本文讨论了在斜交{110)滑移面上螺位错和刃位错的滑移行为。     

晶体中滑移的位错机构研究

在研究岩盐型晶体的塑性变形中,用偏激光方法观察晶体中在塑性变形时出现的又折射光带,并结合用显微干涉仪对晶体表面的研究,观察到晶体中发生滑移时滑移带两端所发生的滑移距离恒不相等。根据这一结果,用腐蚀方法观察晶体中的位错排列,并和双折射光带及表面干涉图形的研究对比,全面地验证了离子型晶体中滑移过程的位错机构。此外,还证明了腐触坑和位错之间的——对应的关系,并用实验方法证明了晶体滑移面内存在着符号不同的位错。     

体心立方晶体{100}—{110}—{112}晶面上全位错反应系统

本文建立了一种晶面—晶向投影图,以揭示体心立方晶体{100)、{110)和{112)晶面簇中诸晶面以及在这些晶面上各重要晶向。根据该投影图,可以方便地获得这些晶面和晶向的位向关系,并全面确定在这些晶面上可能出现的全位错的反应类型及其具体组合方式。     

平面应力屈服行为的晶体学Taylor理论分析

本文用对偶单形法线性规划求解Taylor理论,计算了面心立方和体心立方金属在平面应力条件下各向同性屈服表面。所得结果介于Mises和Tresca屈服准则之间。面心立方金属的计算结果和B-H理论的结果吻合;体心立方金属的结果和Pensil Glide模型的结果基本一致。     

不同方法生长的蓝宝石晶体位错缺陷

采用化学腐蚀-显微镜观察法,利用熔融的KOH对泡生法、提拉法、温度梯度法生长的蓝宝石晶体进行了位错腐蚀形貌分析。结果表明:与提拉法生长出的蓝宝石相比,泡生法和温度梯度法生长出来的蓝宝石的位错密度较低,同时位错分布形态比较均匀,双晶摇摆曲线半高宽越窄位错密度越低。因此,在测试蓝宝石晶体时可以通过测试半高宽来间接说明蓝宝石晶体的位错密度情况,并探讨晶体位错缺陷密度、分布与晶体生长工艺之间的关系,对相关机制进行了阐述。     

立方准晶中螺型位错的弹性场

本文发展了立方准晶的位错弹性理论 ,通过立方准晶的反平面弹性问题的控制方程 ,得到了其含有螺型位错时的位移场与应力场的解析表达式。为研究此固体材料的塑性变形提供了重要信息。     

基于两态稳定性原子级存储方式的分子动力学模拟

采用Morse型势函数对体心立方晶体表面层及近表面层原子的行为进行了分子动力学模拟．模拟结果表明，在体心（次表层）原子操纵前后，体心立方晶体的顶角原子位置只有微小变化，其晶格结构基本保持不变且处于稳定平衡状态，即体心立方晶体具有两态稳定性，该特性为实现原子级的数据存储提供了可行性．同时，对数据存储时可能出现的多原子双稳态组合问题进行了分子动力学模拟，发现在多原子双稳态组合情况下，晶体的结构在操纵其相邻晶格的体心原子时仍保持稳定．提出了一种实现原子级存储的新方式，只需在两个稳定平衡态间激发用于存储数据的体心原子，可以提高数据存储的成功率，保证可重复性和稳定性．     

立方准晶中螺型位错的弹性场

本文发展了立方准晶的位错弹性理论,通过立方准晶的反平面弹性问题的控制方程,得到了其含有螺型位错时的位移场与应力场的解析表达式。为研究此固体材料的塑性变形提供了重要信息。     

Electronic structures and properties of V, Nb and Ta metals

0　ＩｎｔｒｏｄｕｃｔｉｏｎＴｏｄｅｓｉｇｎａｌｌｏｙｓｓｃｉｅｎｔｉｆｉｃａｌｌｙ ,ｓｙｓｔｅｍａｔｉｃｓｃｉｅｎｃｅｆｒａｍｅｏｆｍｅｔａｌｓａｎｄａｌｌｏｙｓｉｎｃｌｕｄｉｎｇｔｈｅｓｙｓｔｅｍａｔｉｃｓｃｉｅｎｃｅｏｆｐｕｒｅｍｅｔａｌｓ (ｏｎｅ ａｔｏｍ (ＯＡ)ｔｈｅｏｒｙ) [1,2 ]ａｎｄｔｈｅｓｙｓ ｔｅｍａｔｉｃｓｃｉｅｎｃｅｏｆａｌｌｏｙｓ (ｃｈａｒａｃｔｅｒｉｓｔｉｃｃｒｙｓｔａｌ(ＣＣ)ｔｈｅ ｏｒｙ) [3～ 6 ]ａｒｅｅｓｔａｂｌｉｓｈｅｄ ,ｗｈｉｃｈｃａｎｇｉｖｅｄｉａｇｒａｍｓｏｆ…     

Electronic structures and properties of Ti, Zr and Hf metals

Ａｔｒｏｏｍｔｅｍｐｅｒａｔｕｒｅａｎｄａｍｂｉｅｎｔｐｒｅｓｓｕｒｅ ,ｔｈｅｓｔａｂｌｅｃｒｙｓｔａｌｌｉｎｅｓｔａｔｅｏｆｔｈｅｅａｒｌｙｔｒａｎｓｉｔｉｏｎｍｅｔａｌｓＴｉ,ＺｒａｎｄＨｆｉｓａｈｅｘａｇｏｎａｌｃｌｏｓｅ ｐａｃｋｅｄ(ｈｃｐ)ｓｔｒｕｃｔｕｒｅ (αｐｈａｓｅ) .Ａｔｈｉｇｈｔｅｍｐｅｒａｔｕｒｅ ,ａｌｌｔｈｅｓｅｔｈｒｅｅｍｅｔａｌｓｕｎｄｅｒｇｏａｐｈａｓｅｔｒａｎｓｆｏｒｍａ ｔｉｏｎｉｎｔｏａｂｏｄｙ ｃｅｎｔｅｒｅｄｃｕｂｉｃ (ｂｃｃ)ｓｔｒｕｃｔｕｒｅ (βｐｈａｓｅ) …     

氦在bcc和fcc过渡金属中稳定性的理论研究

采用基于密度泛函理论的从头算对bcc和fcc过渡金属中氦原子的稳定性进行了研究。计算结果表明,除了V和Nb外,不管是bcc还是fcc,氦都是在替换位置最稳定。对于间隙位置,在bcc过渡金属中,氦在四面体位置比八面体位置更稳定,而在fcc过渡金属中,间隙氦的稳定位置没有规律可循。对有磁性的bcc Fe和fcc Ni进行自旋和非自旋极化研究,发现金属的磁性对间隙氦的稳定位置没有直接的影响。     

高能球磨Fe70Ni30纳米晶的XRD和HRTEM研究

用XRD（X射线衍射）和HRTEM（高分辨透射电镜）研究了高能球磨Fe70Ni30二元金属合金的微结构随球磨时间（t）的变化情况。结果表明：以羰基铁和羰基镍为原料，通过高能球磨得到了bcc结构FeNi纳米晶合金。球磨10h时，羰基铁和羰基镍开始形成合金，但大部分R、Ni原子仍分别以bcc结构和fcc结构存在。球磨100h时，样品以bcc结构的FeNi合金为主，球磨200h后，样品中fcc结构Ni特征峰几乎消失，FeNi纳米晶达到最小粒径的平衡值。～8nm。高能球磨过程中，晶界区域的层错缺陷是合金化和纳米晶形成的重要因素．     

Atomic states and properties of Pt-electrocatalyst

Proton exchange membrane fuel cell (PEMFC) has the characteristics of high power, low temperature operation, simple system structure, no-noise, no pollution and high effi- ciency and so on so that many researchers focused their attention on it among fuel cell. Therefore it is called as the fourth generation electricity technology and generally recog- nized the best hopeful candidate for combustion engine of automobile in the twenty-first century[1―3]. But there are a lot of problems such as…     

铁锰铝铬合金局域结构的近边X射线吸收精细结构研究

利用同步辐射Ｘ光测量了Ｆｅ－Ｍｎ－Ａｌ－Ｃｒ合金的ＭｎｌｓＮＥＸＡＦＳ谱,多重散射团簇（ＭＳＣ）理论分析显示合金基体中的Ｍｎ和Ｆｅ分别以体心立方和面心立方微晶的形态存在,它们之间的耦合保证了合金是一种稳定的奥氏体钢。     

Characterization of 17-4PH stainless steel powders produced by supersonic gas atomization

17-4PH stainless steel powders were prepared using a supersonic nozzle in a close-coupled gas atomization system. The characteristics of powder particles were carried out by means of a laser particle size analyzer, scanning electron microscopy (SEM), and the X-ray diffraction (XRD) technique. The results show that the mass median particle diameter is about 19.15 μm. Three main types of surface microstructures are observed in the powders: well-developed dendrite, cellular, and cellular dendrite structure. The XRD measurements show that, as the particle size decreases, the amount of fcc phase gradually decreases and that of bcc phase increases. The cooling rate is inversely related to the particle size, i.e., it decreases with an increase in particle size.     

Cold-temperature deformation of nano-sized tungsten and niobium as revealed by in-situ nano-mechanical experiments

We constructed and developed an in-situ cryogenic nanomechanical system to study small-scale mechanical behavior of materials at low temperatures.Uniaxial compression of two body-centered-cubic(bcc)metals,Nb and W,with diameters between400 and 1300 nm,was studied at room temperature and at 165 K.Experiments were conducted inside of a Scanning Electron Microscope(SEM)equipped with a nanomechanical module,with simultaneous cooling of sample and diamond tip.Stress-strain data at 165 K exhibited higher yield strengths and more extensive strain bursts on average,as compared to those at 298 K.We discuss these differences in the framework of nano-sized plasticity and intrinsic lattice resistance.Dislocation dynamics simulations with surface-controlled dislocation multiplication were used to gain insight into size and temperature effects on deformation of nano-sized bcc metals.     

Nucleation barrier of fcc(γ)→hcp(ε) martensitic transformation in Fe-based alloys

Based on the dislocation theory and Olson's stacking fault model, a model describing the nucleation of an hcp(ε) martensite embryo at low-angle grain boundary is proposed with the influence of external stress field taken into account. The dependences of temperature (T), shear stress (τ) and dislocation density at grain boundary on the martensite nucleation in FeMnSi based alloy, as an example, are numerically simulated. It has been shown that there exist the subcritical and critical embryos during the course of ε-phase nucleation. The free energy difference between them is just the energy barrier of embryo growth. Depending on T and τ, the characteristic embryo sizes may vary in wide ranges and decrease with increasing a and decreasing T. The energy condition of martensitic transformation at Ms and critical shear stress (τc) is discussed from the viewpoint of kinetics and thus the TEM observed result that stacking fault energy is not zero at Ms temperature is reasonably explained. Besides, it is pr