Zr—4合金双轴疲劳行为及其微观变形机理Ⅱ.双轴循环变形亚结构及其？…

用透射电镜分别观察了Zr-4合金比例和非比例双轴疲劳变形亚结构.结果表明等效应变幅为0.8%,不同主应变比下,Zr-4合金比例双轴疲劳后典型的位错组态是{1010}柱面滑移产生的平行位错线.随着等效应变幅提高,从平面状向波纹状滑移转化,有形成位错胞的趋势.非比例加载过程中,随着相位角从30°增大到90°,位错组态从平行位错墙变化成位错胞.相位角为90°时,随着等效应变幅提高,位错保持位错胞结构,但位错密度增高.非比例变形前后织构分析表明随着相位角提高,{1010}极点密度减弱,{1011}锥面极点密度增强,表明合金塑性变形从以{1010}柱面滑移为主向柱面滑移加锥面滑移多系滑移转化.Zr-4合金非比例附加强化一方面是由于部分柱面滑移被锥面滑移取代后,滑移系本身临界分切应力提高;另一方面由于多滑移导致〈a/a〉和〈c+a〉/〈a〉位错与位错之间交互作用力提高.     

21-4N钢温变形拔制裂纹原因探讨

对２１－４Ｎ钢小规格材的生产采用温变形拔制的新工艺,对温变形拔制后材料出现表面裂纹的现象进行了观察和初步分析,结果表明,表面裂纹的产生与材料热处理工艺、温变形后微观组织的变化有关,经改进后,温变形拔制工艺不继优化和完善。     

塑性变形在氢致断裂中的作用

采用慢应变速率拉伸方法,研究了Ｆｅ－Ｓｉ试样在空气中拉伸、动态充氢拉伸及在空气中预应变一定量后动态充氢伸等实验条件下的断理解过程,结果表明,只有在充氢过程中进行塑性变形才能引起氢致开裂,即塑性变形提氢致开裂的必要条件,氢致开裂过程是氢与位错交互作用的过程。     

锥形图形衬底上氮化镓薄膜生长和表征

GaN films are grown on cone-shaped patterned sapphire substrates(CPSSs)by metal-organic chemical vapor deposition,and the influence of the temperature during the middle stage of GaN growth on the threading dislocation(TD)density of GaN is investigated.High-resolution X-ray diffraction(XRD)and cathodeluminescence(CL)wereusedtocharacterizetheGaNfilms.TheXRDresultsshowedthattheedge-typedislocation density of GaN grown on CPSS is remarkably reduced compared to that of GaN grown on conventional sapphire substrates(CSSs).Furthermore,whenthegrowthtemperatureinthemiddlestageofGaNgrownonCPSSdecreases,the full width at half maximum of the asymmetry(102)plane of GaN is reduced.This reduction is attributed to the enhancement of vertical growth in the middle stage with a more triangular-like shape and the bending of TDs.The CL intensity spatial mapping results also showed the superior optical properties of GaN grown on CPSS to those of GaN on CSS,and that the density of dark spots of GaN grown on CPSS induced by nonradiative recombination is reduced when the growth temperature in the middle stage decreases.     

多层HgCdTe异质外延材料的热退火应力分析

前期研究采用高温热处理方法,获得了抑制位错的最佳退火条件.通过比对实验,发现不同衬底上HgCdTe表面的CdTe钝化层在热处理过程中对位错的抑制作用各有不同.结合晶格失配应力和热应力对不同异质结构进行理论计算,借助X射线摇摆曲线的倒易空间分析,解释了CdTe钝化层对HgCdTe位错抑制的影响作用.     

The isolation and nucleation of misfit dislocations in strained epitaxial layers grown on patterned,ion-damaged GaAs

As shown previously, the misfit dislocation density of strained epitaxial III–V layers can be significantly reduced by isolating sections (via patterned etching) of a GaAs substrate before epitaxial growth. A disadvantage of this technique is that the wafer surface is no longer planar, which can complicate subsequent device fabrication. As an alternative, we have investigated growth of 350 nm of In_0.5Ga{0.95}As by molecular beam epitaxy at two temperatures on substrates which were patterned and selectively damaged by Xe ion implantation (300 keV, 10¹⁵ cm²). Selectively etched substrates were prepared as reference samples as well. The propagation of the misfit dislocations was stopped by the ion-implanted regions of the low growth temperature (400° C) material, but the damaged portions also acted as copious nucleation sources. The resulting dislocation structure was highly anisotropic, with dislocation lines occurring in virtually only one direction. At the higher growth temperature (500° C) the defect density fell, but the ion damaged sections no longer blocked dislocation glide. Images from cathodoluminescence and transmission electron microscopy show thatthe low growth temperature material has a dislocation density of 70,000 cm^-1 in the 110 direction and less than 10,000 cm^-1 in the 110 direction. Ion channeling and x-ray diffraction show that strain is relieved in only one direction. The strain relief is consistent with the relief derived from TEM dislocation counts and Burgers vector determination. However, even this high dislocation count is not sufficient to reach the expected equilibrium strain. Reasons for the anisotropy are discussed.     

共析钢中珠光体两相位错组态和界面结构的TEM研究

应用 TEM、SEM 等技术,对共析钢中珠光体的断裂途径、两相的位错结构和界面结构进行了研究。在铁素体中,除α/2〈111〉型位错占主导地位外,还观察到〈112〉型位错,对它的形成机理进行了讨论。在铁素体中的渗碳体片端部观察到〈100〉型位错,讨论了它和铁素体沿{100}平面解理开裂的联系。对两相界面的精细结构进行了衍衬观察和分析。     

Interaction of a transonic dislocation with subsonic dislocation and point defect clusters

The moving speeds of all observed dislocations in crystals are subsonic. There has been a view in the literature that the speed of subsonic dislocations can not be accelerated above the speed of sound because the energy required would be infinitely large. Recent molecular dynamics (MD) simulation had shown that it is possible to generate dislocations with an initial moving speed higher than the velocity of sound in solids. This raises a question: what will happen when a supersonic dislocation meets other defects along its moving path? This work reports the results of MD simulation on the interaction of a transonic dislocation with other subsonic dislocations as well as with point defect clusters. The results show that a vacancy cluster such as a void has an insignificant slow-down effect on the transonic dislocation, while a subsonic dislocation slows down the transonic dislocation to subsonic one. In some cases, the subsonic dislocation (or a subsonic part of a transonic dislocation) can overcome the traditional sound barrier.     

Fabrication of strained Si channel PMOSFET on thin relaxed Si1−xGex virtual substrate

A novel MBE-grown method using low-temperature Si technology is introduced into the fabrication of strained Si channel PMOSFETs. The thickness of relaxed Si_1−xGe_x epitaxy layer on bulk silicon is reduced to approximate 400 nm (x=0.2). The Ge fraction and relaxation of Si_1−xGe_x film are confirmed by DCXRD (double crystal X-ray diffraction) and the DC characteristics of strined Si channel PMOSFET measured by HP 4155B indicate that hole mobility μ_p has an maximum enhancement of 25% compared to similarly processed bulk Si PMOSFET.     

Dislocations by partition of unity

A new finite element method for accurately modelling the displacement and stress fields produced by a dislocation is proposed. The methodology is based on a local enrichment of the finite element space by closed form solutions for dislocations in infinite media via local partitions of unity. This allows the treatment of both arbitrary boundary conditions and interfaces between materials. The method can readily be extended to arrays of dislocations, 3D problems, large strains and non‐linear constitutive models. Results are given for an edge dislocation in a hollow cylinder and in an infinite medium, for the cases of a glide plane intersecting a rigid obstacle and an interface between two materials. Copyright © 2005 John Wiley & Sons, Ltd.