共查询到19条相似文献,搜索用时 140 毫秒
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马氏体相变是无扩散的位移型相变,对于一个给定的材料,由切变产生的表面浮突是马氏体相变的主要特征之一,它对应唯一的切变角。因此,通过实验确定的切变角与马氏体晶体学表象理论(PTMC)预测的理论切变角进行对比,可以验证马氏体相变的切变机制。本文列举了几个例子来验证马氏体相变的切变机制。在这些例子中,首先原子力显微镜被用于精确测定马氏体相变的浮突角,然后基于表面浮突角计算出相变切变角,最后将计算的相变切变角与PTMC预测的理论切变角进行比较,由此验证马氏体相变切变机制的正确性。本文所举例子足以否定刘宗昌教授的马氏体相变切变机制缺乏实验依据的观点和马氏体相变非切变机制的结论。 相似文献
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研究马氏体相变中原子的位移方式具有重要理论意义。本文从理论上综合分析了奥氏体转变为马氏体过程中原子的移动方式。奥氏体转变为马氏体时,在相变驱动力作用下,原子主要是按照K-S位向关系从奥氏体晶格中直接转移到马氏体晶格上去的。当γ→α马氏体时,以晶体缺陷为起点出现涨落,原子无扩散的,集体协同位移,进行了晶格参数的调整,完成γfcc→αbcc-M的晶格重构。原子移动距离远远小于一个原子间距,比K-S切变位移小一个数量级,耗能小。奥氏体转变为马氏体将产生应变能,为了调整应变能和适应新旧相晶格匹配,而形成相变位错、层错或相变孪晶等晶体缺陷以调整应变能,从而完成马氏体晶格重构。切变位移"理论"是错误的。 相似文献
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贝氏体相变新机制的研究 总被引:1,自引:1,他引:0
21世纪以来,内蒙古科技大学在贝氏体相变理论研究方面取得了新成果。指出了过渡性是贝氏体相变的主要特征;提出了贝氏体的新定义和贝氏体相变的新机制;贝氏体相变在晶界形核,晶核是单相贝氏体铁素体(BF),不是BF共析分解;在贫碳区形核,是贫碳的γ→α理的无扩散相变,不是切变过程,而是以界面替换原子非协同热激活跃迁方式形核长大;钢中贝氏体碳化物(Bc)在γ/α相界面上形核,向BF中长大,最终被铁素体包围,也是以界面原子热激活跃迁方式进行的。 相似文献
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遴选了马氏体相变切变机制的现代试验结果,证明马氏体相变切变机制的正确性.在诸多有色合金中马氏体相变产生的切变能相对相变驱动力而言较大,但母相弹性常数的测定表明,马氏体相变时母相的弹性常数在特定方向将产生软化(对应切变方向),由此可有效地降低马氏体相变的切变能,从而得以使马氏体相变以切变形核.透射电镜的观察表明,层错迹线被单变体马氏体切过后将变成折线,并且试验测定的切变角与理论切变角很好地符合.透射电镜高分辨像揭示了马氏体/奥氏体界面处存在过渡区.这些区域的原子约从fcc奥氏体(111)面上的位置切变位移了50%,这是不同于扩散型相变的贝氏体/奥氏体界面.随后介绍了徐祖耀计算Fe-C合金马氏体相变切变能的方法.最后,指出了“马氏体相变非切变机制”理论提出者刘宗昌等由于对前人工作缺乏深入了解,在错误的物理概念基础上来计算马氏体相变切变能,导致错误结论. 相似文献
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钢的中温(贝氏体)等温处理获得的上、下贝氏体和粒状组织,都具有各自独立的c曲线;在转变初期均能获得单一的组织,而在转变的中、后期通常可获得相邻两组织的复合体.必须用单一组织和Arrhenius关系求相变产物的体激活能.将体激活能、组织形貌和体自由能曲线相结合可诠释下述论点:下或上贝氏体是碳原子扩散控制下在奥氏体中的贫碳或极贫碳区,进行“军队型”(队列式)原子无扩散马氏体样切变相变;而粒状组织是碳原子扩散控制下在奥氏体中的最贫碳区,发生“平民型”(非队列式)原子无扩散界面控制相变. 相似文献
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<正>5.3依据位向关系设计切变模型的误区随着温度的降低,母相中原子的扩散越来越困难,直到不能扩散位移,因此,在各种相变过程中,原子的位移方式不同是导致各类相变机制不同的根本原因。在较高的温度区间,过冷奥氏体发生共析分解,是原子进行以界面扩散为主的扩散型相变。过冷奥氏体在中温区,其碳原子可以长程扩散,但是铁原子和替换原子逐渐难以扩散,直至不能扩散。此时,为了完成过冷奥氏体转变为自由焓更低 相似文献
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论述了徐祖耀院士在马氏体相变、贝氏体相变及形状记忆材料方面的学术贡献。其中包括:揭示了无扩散马氏体相变中存在间隙原子(或离子)的扩散;完善了铁合金马氏体相变的热力学;解决了计算Fe-C合金相变开始温度(Ms)的难题;以孤立子理念演算和阐释了相变驱动力与马氏体长大速率之间的关系;以群论研究了形状记忆合金热弹性马氏体相变的对称性并建立了计算热弹性马氏体对称分布的数学模型;创建了铜基合金马氏体相变和贝氏体相变热力学;认证了陶瓷中存在贝氏体相变。 相似文献
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相变中的界面 总被引:2,自引:0,他引:2
J.W.Christian 《金属学报》1997,33(2):150-156
讨论了各类相变中的界面分类。重构型相变没有共格界面,相变产物形状也无系统性变化。位移型相变有完全共格或部分共格的界面,有可见的相变产物形状变化。完全共格界面出现在无成分变化的马氏体型相变以及有成分变化的扩散位移型相变中。这二种类型界面的迁移依靠台阶(马氏体相变中称之谓相变位错)的运动完成。部分共格界面也可能出现在马氏体型或较为少见的扩散型相变中。 相似文献
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The redistribution of C and N atoms during cryogenic treatment is crucial for the microstructure evolution and properties of high nitrogen martensitic steel. Here, the distinct redistribution behavior of C and N atoms in a martensitic stainless steel with 0.3 wt% C and 0.5 wt% N after cryogenic treatment were investigated by the atom probe tomography. Carbon clusters begin to form after cryogenic treatment at - 60 °C and gradually increase with the decrease of cryogenic treatment temperature. While Mo-N and Cr-N pairs are homogeneously distributed in the matrix even after cryogenic treatment at -120 °C, and then form enrichment phenomenon when the cryogenic temperature is deeply lowered to - 190 °C. It is found that the distinct redistributions of C and N atoms are associated with the different interaction energy between substitutional atoms and them. The stronger interaction between Cr, Mo atoms and N delays the segregation of N during the cryogenic treatment. Finally, the mechanical properties results confirmed that the deep lower cryogenic treatment is a promising method to improve the hardness and strength in the high nitrogen martensitic stainless steel. 相似文献
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E.C. Passamani V.P. NascimentoC. Larica A.Y. TakeuchiA.L. Alves J.R. ProvetiM.C. Pereira J.D. Fabris 《Journal of Alloys and Compounds》2011,509(30):7826-7832
The effect of chemical disorder over the martensitic phase transformation of the Ni50Mn36Sn14 Heusler-type alloy was systematically investigated by performing X-ray diffractometry (DRX), DC magnetization and 57Fe-doping and 119Sn-Mössbauer spectroscopy measurements. DRX patterns are characteristics of a L21-type chemically disordered structure, where the presence of this disorder was first evaluated by analyzing the relative intensity of the (1 1 1) DRX reflection, which varies in the case of Fe-doped and practically disappears for the milled samples. In consequence, the magnetic properties of Fe-doped well-milled samples related to the martensitic phase transformation change substantially. 300 K 57Fe-Mössbauer spectroscopy data suggest that the changes in the magnetic properties related to the martensitic transformation are intrinsically correlated to the ferromagnetic and paramagnetic fractions, which are respectively associated with Fe atoms replacing Mn- and Sn-sites. In the case of milled samples, the drastic reduction of alloy magnetization was explained by the increase of the number of Mn atoms in the shell regions, which have a reduced magnetic moment comparatively to those in the grain cores. The magnetization change and the temperature transition in the martensitic transformation are governed by the grain core. The initial magnetic properties and martensitic transformation can be recovered by a subsequent annealing on the milled sample. 相似文献
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V. V. Bliznuk V. G. Gavriljuk B. D. Shanina A. A. Konchits S. P. Kolesnik 《Acta Materialia》2003,51(20):6095-6103
The influence of carbon and nitrogen on the electronic properties and shape memory in Fe62Mn16Si10Cr9Ni4 (at.%) alloy was studied by means of conduction electron spin resonance (CESR) and dilatometry. It was shown that carbon causes localization of electrons at the atomic sites and clustering of substitutional atoms, whereas nitrogen leads to an increased concentration of free electrons at the Fermi surface and assists in a more homogeneous distribution of substitutional solutes. A larger recovered strain is found in the nitrogen-doped alloy in comparison with the carbon one. The role of carbon- and nitrogen-caused change in the electronic properties, short range atomic order and strengthening on the shape memory effect is discussed. 相似文献
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自20世纪20年代以来,基于马氏体相变产生的浮凸和在母相中预先刻制的直线变成在相界面上连续的折线,提出了以切变为基础的马氏体相变的晶体学特征—"不变平面应变"的概念。随后,以该概念为基础建立了马氏体相变晶体学表象理论(PTMC)。然而,刘宗昌等基于相同的实验,即马氏体相变后的直线刻痕仍为直线和浮凸形态为帐篷形,分别在2010年和2013年《热处理》杂志上发表文章,否定马氏体相变的"切变"机制进而否定马氏体相变的"不变平面应变"。如所周知,否定马氏体相变的"切变机制"就是否定"不变平面应变",因此刘宗昌等于2013年发表的文章彰显出他们的轻率。本文作者已在3篇文章中列举用原子力显微镜和透射电镜观察的结果驳斥了他们的错误观点,至少可以说,他们没有理解我们文章中的实验和理论。为此,本文再次引用Yang和Wayman的透射电镜实验结果,即单变体马氏体使预存在的层错迹线(直线)变成折线,而自协调的多个马氏体可使迹线仍为直线;单变体马氏体的浮凸为N形,但多变体马氏体的浮凸可以是帐篷形或更为复杂的形态,由此可以说明刘宗昌等错误观点的原因。最近,本文作者及其合作者基于PTMC计算了Mn80Fe15Cu5热弹性合金马氏体相变的惯习面,并与实验结果相符,由此确认了"不变平面应变"是马氏体相变晶体学特征的正确性。 相似文献
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概述对马氏体相变基本特征认识的进程,以及与马氏体相变密切相关的形状记忆材料的发展。对马氏体相变热力学、动力学、晶体学、形核-长大、非线性物理模型以及形状记忆效应、伪弹性和伪滞弹性研究进展作了总结。对马氏体相变的继续研究和应用作了展望。 相似文献
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Shape memory materials 总被引:3,自引:0,他引:3
徐祖耀 《中国有色金属学会会刊》2001,(1)
1 INTRODUCTIONShapememorymaterialsarerecognizedasquitefascinatingmaterialsandarenowbeing practicallyusedasfunctionalmaterialsforpipecouplings ,anten naeforcellularphones,variousactuatorsandmedicalimplantsandguidewires .They possesspotentialityforapplicat… 相似文献
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Y.Q. Ma C.B. Jiang H.B. XuDepartment of Materials Science Engineering Beijing University of Aeronautics Astronautics Beijing China 《金属学报(英文版)》2003,16(6):445-448
Cu-Al-Co and Cu-Al-Zr alloys were explored with Co or Zr additions in Cu-Al alloys for high temperature shape memory alloys. Samples were quenched after homogenized at 850℃ for 48h. It was found that both Cu-Al-Co and Cu-Al-Zr show AlCus martensitic phase at room temperature and exhibit martensitic transformation temperatures higher than 200℃, showing the potentials for developing as high temperature shape memory alloys. Thermal cycles were performed by DSC instrument on both Cu-Al-Co and Cu-Al-Zr alloys. The results show that Cu-Al-Co loses its martensitic transformation after five thermal cycles, and Cu-Al-Zr exhibits no martensitic transformation in the second thermal cycle. 相似文献