C、N元素对Fe—Mn—Si合金层错能的影响

通过X射线实验测出Fe-Mn-Si-N-C形状记忆合金中的层错几率，并讨论了N、C元素的添加对层错几率和层错能的影响。通过电子衍射斑点位移的方法测得Fe-29．9Mn-6.0Si形状记忆合金局部区域的层错几率，发现比X射线衍射测得的层错几率大两个数量级，分析差异来自于电子衍射测量的是局部的高密度层错区域。     

基于热力学理论的Fe-Mn-Al-C系低密度钢层错能计算模型

本研究详细分析了基于热力学相关理论建立的层错能(SFE)计算模型和测定层错能的实验方法,将基于Olson-Cohen热力学理论模型计算的Fe-Mn-Al-C低密度高强钢的层错能结果与若干文献中的实测值进行了比较,验证了Olson-Cohen热力学理论模型的可靠性,并回溯和修正了模型中各主要参数。使用层错能模型对Fe-(10~30)Mn-(0~12)Al-(0~1.2)C(质量分数/%)系低密度钢进行计算,结果表明,Mn、Al、C含量的增加均会使低密度钢的层错能增加,但层错能对Al元素最敏感,各元素对层错能的影响能力为γSFE,AlγSFE,MnγSFE,C。此外,温度升高会使层错能增加,且高温区间(300~1 000K)相比低温区间(0~300K)层错能增加更快。     

合金元素对铁锰硅系形状记忆合金层错能的影响

根据规则固溶体的热力学模型,分别计算铁锰硅、铁锰硅铬、铁锰硅铬镍形状记忆合金的层错能,研究硅、锰、铬、镍合金元素对铁基形状记忆合金层错能的影响。结果表明,锰、铬、镍元素均提高铁锰硅系合金层错能,而硅则降低合金的层错能,其中每１％（原子分数）元素变化对合金层错能影响比例,硅∶锰∶铬∶镍为：－０．２７∶１∶１．１∶１．７。为了获得较佳的形状记忆效应,加入铬、镍元素的同时,降低锰含量以使合金具有低的层错能     

Si 含量对 Fe-Mn-Si 合金层错能的影响

根据层错能的热力学模型,计算了三种 Fe-Mn-Si 合金的内禀层错能。计算结果表明,随着 Si 含量增加 Fe-Mn-Si 合金的层错能降低。在此基础上讨论了 Si 含量对 Fe-Mn-Si 合金形状记忆效应的影响。     

X射线衍射法测定Fe-Mn-Si形状记忆合金层错几率的研究

Ｆｅ－Ｍｎ－Ｓｉ合金的形状记忆效应来源于马氏体相变,而马氏体相变则通过奥氏体内形成每隔一层｛１１１｝面上的堆垛层错来完成。与层错能相关的层错几率可能控制马氏体的相变机制。本文根据Ｗａｒｅｎ的衍射理论,用Ｘ射线衍射峰位移和峰宽化两种方法测定了Ｆｅ－Ｍｎ－Ｓｉ合金的层错几率,其结果表明随锰含量增加,层错几率降低。本文着重对提高衍射峰位移和峰宽化两种测定方法的精度及其影响因素进行详细的研究,并认为峰位移法更简便     

硅外延片晶体缺陷的研究

本文采用金相显微镜和X射线形貌术研究硅外延层晶体缺陷的问题。实验结果表明:外延层中存在有层错,其分布不均匀,并从X射线形貌相中分析出层错的形式。     

锰元素对TWIP钢层错能和变形机制的影响

根据层错能的热力学模型,计算了Fe-XMn-3Si-3Al 系高强度高塑性TWIP钢的层错能.计算结果表明,随锰含量增加Fe-XMn-3Si-3Al系 TWIP钢层错能增加,在此基础上讨论了锰含量对Fe-XMn-3Si-3Al 系TWIP钢变形机制、力学性能和微观组织的影响.在合金中Mn含量的提高使层错能增加,而层错能的增加使Fe-XMn-3Si-3Al系钢表现出不同的变形机制,即逐渐由TRIP效应变为TWIP效应;同时随着Mn含量的提高,合金的抗拉强度降低,而塑性提高.     

衍射线宽化的线形分析和微结构表征

引起衍射线条宽化的不仅是微晶和第Ⅱ类(微观)应力,还有层错/孪生和位错。围绕着如何分离这种多(二、三乃至四)重宽化效应和如何求解微晶尺度、微观应变(力)、层错几率、层错密度和位错分布参数等,发展了一系列线形分析方法。从线形卷积关系、微晶-微应变宽化线形分析、微晶-微应力-层错宽化线形分析和微晶-层错-位错宽化线形分析共4个部分介绍了线形分析技术的发展和应用,以及笔者近十年进行的某些研究工作。     

CuZnAl形状记忆合金马氏体相中非基面层错的研究

利用透射电子显微镜精确地测定了ＣｕＺｎＡｌ形状记忆合金马氏体相中（１２８）１８Ｒ非基面层错的层错面为（１３７）。一种新的非基面层错被确定为（１３１）１８Ｒ，其位移矢量为１／２（１０１）。     

密堆六方纳米材料微结构的X射线衍射表征

提出分离密堆六方结构的纳米材料X射线衍射花样中微晶-微应变、微晶-层错、微应变-层错二重和微晶-微应变-层错三重宽化效应的一般理论、处理数据的最小二乘方法和计算程序。并用于镍-氢电正极材料原始β—Ni（OH）2和电池经活化、循环后的微结构的表征和研究。结果表明,原始β—Ni（OH）2仅存在微晶-层错二重宽化效应,活化和循环后存在微晶-应变-层错三重宽化效应,并存在明显的选择宽化。把活化和循环后和原始β—Ni（OH）2相比较可知,晶粒形状、大小、微应变和层错几率都发生重大的和不可逆的变化。     

Thermodynamic calculation of stacking fault energy in Fe–Mn–Si shape memory alloys

Based on thermodynamic considerations together with measurement of the stacking fault probability (Psf) by X-ray diffraction profile analysis, the stacking fault energy (SFE, γ) of austenite in Fe–Mn–Si shaped memory alloys can be estimated. For instance, the stacking fault energy of an fcc(γ) phase in an Fe–30.3Mn–6.06Si was calculated as 7.8 mJ/m². Compositional dependence of stacking fault energy in these alloys with certain composition range has also been derived as SFE(γ)=180.54+7.923 wt.% Mn–46.38 wt.% Si (J/mol), showing that the stacking fault energy increases with the addition of Mn and decreases with the addition of Si.     

Stress transmission through three-dimensional granular crystals with stacking faults

We explore the effect of stacking fault defects on the transmission of forces in three-dimensional face-centered-cubic granular crystals. An external force is applied to a small area at the top surface of a crystalline packing of granular beads containing one or two stacking faults at various depths. The response forces at the bottom surface are measured and found to correspond to predictions based on vector force balance within the geometry of the defects. We identify the elementary stacking fault as a boundary between two pure face-centered-cubic crystals with different stacking orders. Other stacking faults produce response force patterns that can be viewed as resulting from repetitions of this basic defect. As the number of stacking faults increases, the intensity pattern evolves toward that of an hexagonal-close-packed crystal. This leads to the conclusion that the force pattern of that crystal structure can be viewed as the extreme limit of a face-centered-cubic crystal with a stacking fault at every layer.This work was supported by NSF-CTS 0090490 and by the NSF MRSEC Program under DMR-0213745. MJS acknowledges support by the University of Chicago MRSEC Summer 2002 REU program.     

4H-SiC晶体中的层错研究

采用物理气相传输法(PVT法)在4英寸(1英寸=25.4 mm)偏<11¯20>方向4°的4H-SiC籽晶的C面生长4H-SiC晶体。用熔融氢氧化钾腐蚀4H-SiC晶体, 并利用光学显微镜研究了晶体中的堆垛层错缺陷的形貌特征和生长过程中氮掺杂对4H-SiC晶体中堆垛层错缺陷的影响。结果显示, 4H-SiC晶片表面的基平面位错缺陷的连线对应于晶体中的堆垛层错, 并且该连线的方向平行于<1¯100>方向。相对于非故意氮掺杂生长的4H-SiC晶体, 氮掺杂生长的4H-SiC晶体中堆垛层错显著偏多。然而, 在氮掺杂生长的4H-SiC晶体的小面区域, 虽然氮浓度高于其他非小面区域, 但是该小面区域并没有堆垛层错缺陷存在, 推测这主要是由于4H-SiC晶体小面区域特有的晶体生长习性导致的。     

The influence of aluminium content to the stacking fault energy in Fe-Mn-Al-C alloy system

Four Fe-30Mn-0.9C-XAl alloys are employed to investigate the influence of aluminium content to the stacking fault energy in Fe-Mn-Al-C alloy system. The range of aluminium content is zero to 8.47 wt%. Based on the thermodynamic model, the stacking fault energy can be obtained through calculation. Increasing the aluminium content will make the stacking fault energy of Fe-30Mn-0.9C based alloys increase at 300 K.     

X-ray diffraction studies of GdFe2 Mössbauer samples

X-ray diffraction techniques have been used to determine the lattice parameters and stacking fault probabilities of specimens of the cubic Laves phase compound GdFe₂ used in Mössbauer experiments. The lattice parameter for most samples was 7.400±0.005 Å. All the samples exhibited high stacking fault probabilities. The sta-cking fault probabilities lay in the range 0.12 to 0.35.     

Temperature Dependent Work-hardening Behaviour in an Fe-Mn-Si-Cr-Ni Shape Memory Alloy

The work-hardening behaviour in an Fe-Mn-Si-Cr-Ni alloy has been investigated using tensile test at different temperatures and TEM observation. It was found that besides the intersection of εmartensite, the intersections of ε martensite with stacking fault and the cross-slip of dislocation which is difficult to occur in the alloy with low stacking fault energy are also important factors to the temperature dependent work-hardening behaviour.     

Deformation induced Nanostructure and texture in MP35N alloys

The macro-texture was related to the nano-platelets formed during the rolling deformation of a Co-Ni-Cr-Mo alloy (MP35N) with low stacking fault energy. The deformed materials showed {011}(533) texture but also had {011}(211) and {011}(100) texture components. The {011}(533) component reached the maximum at 74% reduction-in-area. Further deformation of the material to 80% decreased the intensity of the {011}(533) component. The cold deformation introduced platelets of a few atomic layer in thickness and less than 100 nm in diameters. The habit planes of the platelets were identified to be {111}, which were perpendicular to both the rolling and {011} crystallographic plane. Therefore, the tensile strain in the rolling direction assisted formation of the platelets, which were identified as stacking faults. A high density of nano-platelets and dislocations strengthened materials and influenced the plastic deformation behaviors and texture evolution. Thus, the MP35N developed slightly different textures from other low stacking fault energy materials. The maximum at {011}(533) was related the nanoplatelets and stacking fault energy. The {011}(112) and {110}(001)components could be linked to the low stacking fault energy.