单晶硅片中的位错在快速热处理过程中的滑移

研究了单晶硅片中维氏压痕诱生的位错在不同气氛下高温快速热处理中的滑移行为.研究表明: 在快速热处理时, 位错在压痕残余应力的弛豫过程中能发生快速滑移; 当快速热处理温度高于1100℃时, 在氮气氛下处理的硅片比在氩气氛下处理的硅片有更小的位错滑移距离. 我们认为这是由于氮气氛下的高温快速热处理在压痕处注入的氮原子钉扎了位错, 增加了位错的临界滑移应力, 从而在相当程度上抑制了位错的滑移. 可以推断氮气氛下的高温快速热处理注入的氮原子增强了硅片的机械强度. 关键词： 快速热处理 位错滑移 机械性能 单晶硅     

温度对大角度晶界变形过程影响的晶体相场法研究

应用晶体相场法研究大角度晶界在外加应力作用下温度对位错运动的影响。研究表明,大角度晶界在应力作用下会发生形状变化;当变形达到临界应变时,晶界褶皱处产生位错并发射进入晶粒内部;温度较低时,晶界处位错形核所需的临界应变更大。在应力作用下大角度晶界通过改变曲率和位错运动产生迁移,温度较高时有利于晶界迁移。     

不同加载条件下位错和溶质原子交互作用的数值模拟

动态应变时效,即位错和溶质原子的动态交互作用,对合金材料的力学性质产生重要影响. 本文基于蒙特卡罗方法,建立了“多位错-溶质原子” 二维动力学模型,分别模拟了单位错-恒定应力率、多位错-无应力、多位错-恒定应力和多位错-恒定应力率四种条件下位错和溶质原子的演化过程. 单位错-恒定应力率情况下,低应力率时位错被溶质原子钉扎而无法脱钉,高应力率时位错未被钉扎而一直运动,只有在适当应力率范围内,位错才呈现出反复的钉扎和脱钉;多位错-无应力时,溶质原子向正/负位错的下/上方偏聚;多位错-恒定应力时,位错运动受溶质原子钉扎的影响随应力增大而减小;多位错-恒定应力率时,集群化的钉扎和脱钉过程导致了位错总位移呈现阶梯状的演化. 模拟结果表明：“位错-溶质原子”尺度上呈现了动态应变时效微观过程,与其理论描述相一致. 关键词： 动态应变时效 动力学模型 位错运动     

有限温度下位错环的脱体现象

在FCC单晶铜中构造了滑移面为（111）,伯格矢量为b=［112］/6的圆形不完全位错环．采用分子动力学方法模拟了该位错环在0—350 K温度区间内的自收缩过程．模拟结果发现：零温度下,位错不能跨越Peierls-Nabarro势垒运动,迁移速度为0;50　K温度下,螺型和刃型位错具有基本相同的迁移速度;随温度增加,刃型位错具有较大迁移速度;温度较高时,位错核宽度进一步增加;小位错环周围的局部应力,引起4个脱体位错环;脱体位错环在原位错的应力作用下逐渐生长,原位错消失后,在自相 关键词： 单晶铜 位错环 分子动力学 位错源     

单晶铜纳米线屈服机理的原子模拟研究

采用分子静力学方法模拟了〈100〉单晶铜纳米线的拉伸变形过程,研究了纳米线屈服的机理. 结果表明：1） 纳米线初始屈服通过部分位错随机激活的{111}〈112〉孪生实现,后继屈服通过{111}〈112〉部分位错滑移实现;2） 纳米线变形初期不同滑移面上的部分位错在两面交线处相遇形成压杆位错,变形后期部分位错在刚性边界处塞积,两者都阻碍位错滑移,引起一定的强化作用. 关键词： 纳米线 屈服 位错 分子静力学     

存在异性夹杂的位错塞积

本文采用位错连续分布方法,导出了在外应力作用下异性夹杂和障碍之间相对障碍的单螺位错塞积和双螺位错塞积的分布函数的解析表达式D₁(η),D₂(η)。在靠近障碍一端,D₁(η)和D₂(η)具有-1/2次幂的奇异性,在靠近夹杂一端,D₂(η)具有-ω次幂的奇异性。并用双位错塞积的情况表示了与异性夹杂相接触的反平面剪切裂纹问题,导出了应力强度因子。这些表达式对于02/G₁<∞完全适用。对所得的结果进行了讨论。 关键词：     

硅中位错增殖的实验观察

用化学侵蚀法研究了在机械应力和热应力作用下硅中位错的增殖和非均匀成核。结果表明,在使位错增殖和成核作用上,热应力同机械应力是等效的。硅中小角晶界中的位错,原生孤立位错都能成为位错源;晶体内部的缺陷及表面蚀斑处的应力集中能够引起位错成核;硅中螺型位错能够通过交叉滑移机制发生增殖。对新生位错环空间分布的研究表明,Frank-Read机制可能是位错增殖的主要形式。位错能否发生增殖,主要决定于位错源所受分切应力的数值、晶体温度、位错本身的结构特点以及钉扎情况等。     

体心立方金属钽Ⅱ型裂纹尖端缺陷萌生的多尺度分析

本文采用多尺度准连续介质法(quasi-continuum method, QC)模拟体心立方(body-centered-cubic, bcc)金属钽(Ta)Ⅱ型裂纹尖端位错的形核与发射过程,获得位错发射位置与应力强度因子关系曲线,分析裂纹尖端缺陷萌生过程,研究全位错分解以及扩展位错形成机理. 位错活动在不同阶段表现出不一致的特征,新位错的发射对于位错运动具有促进作用. 研究表明,裂纹扩展初始阶段首先萌生点缺陷,点缺陷随着加载强度增加会萌生新的点缺陷,点缺陷最终运动到边界,导致Ⅱ型断裂破坏. 在全位错发射之前有不全位错的形核与发射表明全位错的分解分步进行,从势能曲线上来看,也就是两个极小值点的形成机理不同. 关键词： 多尺度 准连续介质法 Ⅱ型裂纹 扩展位错     

钛金属应力腐蚀机理电子理论研究

为从理论上揭示钛金属应力腐蚀行为的本质，建立了α钛晶粒及位错塞积形成的微裂纹原子 集团模型，利用递归法(recursion)计算了裂纹及晶粒内的电子结构参量(费米能级、结构能 、表面能、团簇能、环境敏感镶嵌能). 计算结果表明：氢在裂纹处的环境敏感镶嵌能较低 ，易于偏聚在裂纹处，且氢在钛金属裂纹处团簇能为正值不能形成团簇，具有有序化倾向， 趋于形成氢化物. 氢在裂纹处偏聚降低裂纹的表面能，使裂纹容易扩展. 裂纹尖端处费米能 级高于裂纹其他区域，使电子从裂纹尖端流向裂纹其他区域造成电位差，在电解质作用下裂 关键词： 递归法 电子结构 钛 应力腐蚀     

晶体缺陷规范场中的刃位错

本文用位错连续分布方法表出了刃位错所产生的应变和应力场,得到了刃位错芯区内、外的应力场,位错芯区的无限小位错分布用缺陷规范场表出,并在一定规范条件下求解了位错规范场,在刃位错芯区外,其应力场与Volterra位错的应力场完全一样,而在芯区内,当r趋于零,刃位错的应力场为有限,消除了应力的奇异性。 关键词：     

Changes of microstructure and magnetic properties of Nd-Fe-B sintered magnets by doping Al-Cu

The microstructural and magnetic properties of Al_100−xCu_x (15at%≤x≤45 at%) doped Nd-Fe-B magnets were studied. The distribution and alloying effects of Cu or Al on the intergranular microstructure were investigated by thermodynamic analysis, differential scanning calorimetery and microscopy techniques. It was observed that when the Cu content of Al_100xCu_x exceeds to 25 at%, the (Pr, Nd)Cu and CuAl₂ phases form in these magnets. The formation of (Pr, Nd)Cu phase depends on the negative formation enthalpy of (Pr, Nd)Cu and the exclusive distribution of Cu in the intergranular regions. The eutectic reaction between (Pr, Nd)Cu phase and (Pr, Nd) occurs at 480 °C, which forms the liquid phase that dissolves the (Pr, Nd)₂Fe₁₄B surface irregularities and thus increases the quantities of (Pr, Nd)-rich phase at the grain boundaries. These changes benefit the grain boundary microstructure, especially the distribution of (Pr, Nd)-rich phase, which effectively improves the intrinsic coercivity _iH_c due to the decreases of exchange coupling between the (Pr, Nd)₂Fe₁₄B grains.     

“绿色”液体激光介质的非线性光学特性研究

 利用氧化钕和盐酸为原料制得Nd(phen)2Cl3(三氯二邻菲罗啉合钕),测得其光谱特性并以稀土氧化钕、苯甲酸和邻菲罗啉为原料制得绿色液体激光介质钕离子的配合物——NdB3phen（三苯甲酸—邻菲罗啉合钕）.利用飞秒激光器,采用单光束Z-扫描法研究了NdB3phen的三阶非线性光学特性.结果表明:当入射飞秒激光脉冲波长为400 nm,峰值功率密度为2.94×1014 W/m2,脉宽为117 fs时,测得样品NdB3phen的非线性折射率为－2.84×10－18 cm2/W|NdB3phen在开孔条件下呈现反饱和吸收现象,测出双光子吸收系数的值为9.11×10－12 m/W.实验结果表明,NdB3phen的双光子吸收系数和非线性折射率随着光强的增强而增大.     

LiNbO3单晶体直拉法生长时组分过冷所形成的胞状界面和胞状组织

对于沿[0001]生长的LiNbO₃单晶体,组分过冷形成的胞状界面和胞状组织进行了形态学的研究(组分过冷是由于操作上的原因在熔体中掺入了Al₂O₃而引起的),确定了胞状界面和胞状组织的基本形态。胞状界面是由相毗邻的三角锥组成,三角锥的稜锥面为{0112}面组,毗邻的三角锥体间存在沟漕,其中的熔体中浓集溶质。在长成的晶体中的胞状组织或是由{1210}面构成的其母线平行于[0001]方向的稜柱体,或是由溶质浓集的三{1210}面相交而成的三叉。实验观测证实了白丝、白点、云层及溶质尾迹是胞状组织的某种表现,而温度起伏是形成间歇式胞状组织的原因。通过胞状界面的形态研究,确定了形态干扰的某些具体形式,并证实了破坏界面稳定性的形态干扰与界面邻近流体的动量边界层的稳定性有关。文章最后讨论了高熔点氧化物晶体与金属晶体的胞状组织在形态上的差异,认为是由于两类物质的不同熔化熵而产生的。 关键词：     

A study of the radiation of a Nd:YAG laser-MIG hybrid plasma

To study the coupling of a Nd:YAG laser beam and a MIG arc with the spectrum of the plasma, a new hollow probe method is used to collect radiation from specific points within the arc plasma. With the probe, the spatial distributions of the MIG arc radiation with and without the Nd:YAG laser hybrid plasma are collected and analyzed by a fiber spectrometer. Through analysis of the spectrum, radiation in the ultraviolet (Fe II dominated), visible (Fe I dominated) and infra (Ar I dominated) spectral zones are acquired for comparison of the difference between the MIG and Laser-MIG hybrid welding processes. The electronic temperature is calculated using the Boltzmann plot method and the electronic density is calculated using the Stark broadening method. The results show that the Laser-MIG hybrid welding processes cause the plasma energy to focus on the center of the welding arc and approach the welding pool. An ionizing duct abundant with Fe ions will be formed near the position of the impinging laser beam, which makes the welding arc stable. The electronic temperature of the Laser-MIG hybrid welding arc is a little higher than that of the MIG. The electronic density of Laser-MIG hybrid welding is higher than that of the MIG.     

放大自发辐射对激光冲击处理7050铝合金的影响

 利用高功率钕玻璃激光器对7050铝合金表面进行了冲击处理,保持泵浦功率不变,用压电传感器和示波器测试了激光冲击产生的压力波形,用X射线应力测量仪测量了激光冲击后铝合金表面的残余应力,并用非接触式光学轮廓仪分析了激光冲击后铝合金的表面形貌,研究了放大自发辐射强度对激光冲击处理7050铝合金冲击压力、残余应力和粗糙度影响的微观机理。研究结果表明:在泵浦功率不变前提下,放大自发辐射强度的增大降低了激光冲击波压力,铝合金表面残余压应力也随之降低,同时铝合金表面粗糙度增大。     

钕铁硼的冲击压缩特性

 利用二级轻气炮对恒磁体钕铁硼进行冲击压缩,采用阻抗匹配法进行测量,获得了平均初始密度为7.346 g/cm³的钕铁硼Hugoniot关系数据。实验结果表明,该种钕铁硼在19~78 GPa范围内,其D-u_p满足线性变化关系,即：C₀、λ分别为3.686 km/s、1.059,是一种稳定的压缩过程,其间没有相变产生。而较小的λ值表明该种钕铁硼材料偏向于疏松体结构,且容易被压缩。同时实验结果也为其状态方程和脉冲功率源等方面的研究工作提供了可资参考的实验参数。     

Effect of post-sintering annealing on microstructure and coercivity of Al85Cu15-added Nd-Fe-B sintered magnets

Effects of post-sintering annealing on the microstructure and coercivity have been investigated for the Al₈₅Cu₁₅-added (Pr, Nd)_14.8Fe_78.7B_6.5 sintered magnets. It is found that the optimum annealing temperature at which the coercivity _iH_c reaches a maximum decreases from 550 °C for the magnets added with 0.3% and 0.6% Al₈₅Cu₁₅ to 480 °C for the magnets added with 0.9% and 1.2% Al₈₅Cu₁₅. The decrease in optimum annealing temperature is related to the precipitation of Al-Cu or (Pr, Nd)−Cu liquid phase among (Pr, Nd)-rich phases during annealing. Existence of Al-Cu or (Pr, Nd)−Cu liquid phase is beneficial to dissolve the irregularities of (Pr, Nd)₂Fe₁₄B grain interface and increase the quantities of (Pr, Nd)-rich phases at the grain boundary, thus optimizing the grain boundary microstructure. The modifications of the microstructure are helpful to decouple the exchange interaction between (Pr, Nd)₂Fe₁₄B hard magnetic grains, thereby increasing the coercivity.     

Hardening nanostructures in an AlZnMg alloy

The formation of nanoscale and sub-nanoscale solute aggregates (clusters, Guinier–Preston zones and precipitates) in an AlZnMg alloy (Al–2.1 at.% Zn–1.5 at.% Mg) has been followed by a combination of experimental techniques with the aim of correlating the properties of the aggregates with their thermal history. The choice of thermal treatments was guided by the results of mechanical and calorimetric characterizations, supported by transmission electron microscopy for the identification of the morphology of the aggregates. Positron annihilation spectroscopy (using two variants of this technique, coincidence Doppler broadening and lifetime spectroscopy) was adopted for determining the local chemistry in the proximity of open volume defects. The geometrical parameters of the distribution (size, volume fraction, numerical density of the solute aggregates) were obtained by small-angle X-ray scattering. The results of the investigation provide new information regarding: two families of vacancy-rich clusters formed during or immediately after quenching; Guinier–Preston zones formed at 95°C after room-temperature pre-ageing; growth of η′ and?η?phases at 150°C; solute clusters formed at room-temperature in conditions of secondary ageing after preliminary heating at 150°C.     

Measurements of plasma temperature and electron density in laser-induced copper plasma by time-resolved spectroscopy of neutral atom and ion emissions

Plasma produced by a 355 nm pulsed Nd:YAG laser with a pulse duration of 6 ns focussed onto a copper solid sample in air at atmospheric pressure is studied spectroscopically. The temperature and electron density characterizing the plasma are measured by time-resolved spectroscopy of neutral atom and ion line emissions in the time window of 300–2000 ns. An echelle spectrograph coupled with a gated intensified charge coupled detector is used to record the plasma emissions. The temperature is obtained using the Boltzmann plot method and the electron density is determined using the Saha-Boltzmann equation method. Both parameters are studied as a function of delay time with respect to the onset of the laser pulse. The results are discussed. The time window where the plasma is optically thin and is also in local thermodynamic equilibrium (LTE), necessary for the laser-induced breakdown spectroscopy (LIBS) analysis of samples, is deduced from the temporal evolution of the intensity ratio of two Cu I lines. It is found to be 700–1000 ns.     

A direct mixed-body boundary element method for packed silencers

Bulk-reacting sound absorbing materials are often used in packed silencers to reduce broadband noise. A bulk-reacting material is characterized by a complex mean density and a complex speed of sound. These two material properties can be measured by the two-cavity method or calculated by empirical formulas. Modeling the entire silencer domain with a bulk-reacting lining will involve two different acoustic media, air and the bulk-reacting material. Traditionally, the interior silencer domain is divided into different zones and a multi-domain boundary element method (BEM) may be applied to solve the problem. However, defining different zones and matching the elements along each interface is tedious, especially when the zones are intricately connected. In this paper, a direct mixed-body boundary element method is used to model a packed silencer without subdividing it into different zones. This is achieved by summing up all the integral equations in different zones and then adding the hypersingular integral equations at interfaces. Several test cases, including a packed expansion chamber with and without an absorbing center bullet, and a parallel baffle silencer, are studied. Numerical results for the prediction of transmission loss (TL) are compared to experimental data.