钢中贝氏体相变理论研究的新进展

总结了近年来内蒙古科技大学在贝氏体相变领域的主要研究成果.指出过渡性是贝氏体相变的主要特征;提出了贝氏体和贝氏体相变的新定义;认为以往的热力学计算不准.贝氏体铁索体的相变驱动力约为905 J/tool;提出了切变一扩散整合机制,贝氏体相变的晶核是单相BF,不是共析分解,贝氏体铁索体(BF)在贫碳区形核,是贫碳的Pa的无扩散相变,不是切变过程,而是以界面替换原子热激活跃迁方式形核长大;钢中贝氏体碳化物(Bc)在γ/a相界面上形核,向奥氏体和铁索体中长大,最终被铁索体包围,是以原子热激活跃迁方式进行的扩散型相变.     

贝氏体相变理论研究新进展

贝氏体相变理论研究具有重要理论意义和应用价值.综合阐述了贝氏体相变学术论争的焦点问题.通过大量试验事实和深入的理论分析,批驳了两派的错误观点.指出了贝氏体的正确的定义;贝氏体相变的过渡性特征,贝氏体相变与共析分解和马氏体相变存在原则区别.贝氏体浮凸为帐篷形,非N型,不具备切变特征.从热力学、动力学、晶体学角度阐述了贝氏体相变非切变,也非扩散过程.提出了贝氏体铁素体(BF)、贝氏体碳化物(BC)形核长大新机制.贝氏体相变过程中原子移动的特点是界面控制,原子非协同热激活跃迁机制,并且与实际相符合.     

块状转变与钢中贝氏体相变的亲缘关系——再论贝氏体相变的切变扩散整合机制

应用JEM-2010高分辨电镜和Quanta-400型环境扫描电镜,运用试验与综合分析的方法,研究了纯铁的块状转变和钢中的贝氏体相变,通过对相变的形核、长大,贝氏体亚单元和组织的形成的综合研究和分析,认为贝氏体相变与块状转变存在亲缘关系.依靠随机涨落,形成贫碳区,贝氏体铁素体在贫碳的奥氏体中形核.Fe原子和替换原子通过热激活跃迁、界面扩散或切变等方式,重复产生亚单元.在亚单元边界处,富碳奥氏体析出碳化物或成为残留奥氏体.贝氏体相变机制具有过渡性,即切变扩散整合机制.     

贝氏体相变机制的探讨

贝氏体相变理论争论多年.研究贝氏体相变机制具有理论意义.运用理论的综合分析的方法,从贝氏体相变的过渡性入手,讨论了贝氏体铁素体的形核、热力学、动力学以及组织形貌、亚结构等与相变机制的联系,认为贝氏体相变具有明显的过渡特征,提出贝氏体相变机制是过渡性质的扩散切变整合机制.     

贝氏体铁素体形成的热激活跃迁机制

贝氏体形核机理尚有争议.应用QUANTA-400型环扫电镜研究了20CrMo钢贝氏体铁素体的形核-长大,提出了原子热激活跃迁的形核机制.认为过冷奥氏体在孕育期中,依靠成分涨落,形成贫碳区,由于三种涨落的非线性正反馈作用使奥氏体晶格瓦解,建构α核坯,铁原子和替换原子以热激活跃迁方式转入α核坯中,以界面过程控制方式形成贝氏体铁素体晶核,并且迅速长大.     

34CrNi3MoV钢贝氏体的形貌及孪晶亚结构

用SEM,TEM的方法对34CrNi3MoV钢贝氏体的形核长大和亚结构进行了研究,结果表明,上贝氏体在晶界处形核,向晶内生长,在形核初期,首先形成一个贝氏体铁素体基元,随后沿不同方向析出碳化物,导致形成上下贝氏体不同的组织形貌;同时经选区衍射及标定与组织图相结合,确定在34CrNi3MoV钢的上下贝氏中存在孪晶亚结构.     

珠光体到贝氏体的演化

综合以往的科学研究结果,论述了从珠光体分解到贝氏体相变是1个逐渐演化的过程.批驳了扩散学派所说的贝氏体是共析分解产物,所谓贝氏体是珠光体转变的延续的观点.指出了珠光体与贝氏体在扩散、形核、动力学、组织形貌、亚结构等方面的区别.     

Mechanical properties of fine-grained dual phase low-carbon steels based on dynamic transformation

The fine grained dual phase (FG-DP) steel with ferrite grains of 2-4.5 μm and martensite islands smaller than 3 μm was obtained through the mechanism of deformation-enhanced ferrite transformation (DEFT). Mechanical properties of the steel were tested at room temperature. The results indicated that with a similar volume fraction of martensite (about 20vol%),FG-DP steel ex-hibited a superior combination of higher strength and more rapid strain hardening at low strains compared with the coarse-grained dual ph...     

氧化镁部分稳定氧化锆的相变与抗热震性能研究

应用TEM，XRD和TMA研究氧化镁部分稳定氧化锆(MgO-PSZ)的相变、微观组织和结构、热膨胀特性。发现四方相到单斜相的相变分两步完成，相变发生的温度范围分别是1150～1180和460～830℃．通过特殊的热处理可以改变MgO-PSZ中的相结构和比例，其中细小的四方相颗粒的存在对抗热震性有明显影响，TMA下的动态拉伸实验观察裂纹扩展发现，在裂纹尖端存在马氏体单斜相的富集区，表明细小的四方相对裂纹扩展有阻止作用。     

TEM study of transformation units and the growth mechanism of bainite

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Phase transformation behaviors and shape memory effects of TiNiFeAl shape memory alloys

Measurements of electrical resistivity, X-ray diffraction, and tensile test at room temperature and ?196°C were performed to investigate the effects of Al addition substituting Ni on the phase transformation behaviors, the mechanical properties, and the shape memory effects of Ti50Ni47Fe2Al1 and Ti50Ni46.5Fe2.5Al1 alloys. It is found that 1at% Al addition dramatically decreases the martensitic start transformation temperature and expands the transformation temperature range of R-phase for TiNiFeAl alloys. The results of tensile test indicate that 1at% Al improves the yield strength of Ti50Ni47Fe2Al1 and Ti50Ni46.5Fe2.5Al1 alloys by 40% and 64%, but de- creases the plasticity to 11% and 12% from 26% and 27% respectively. Moreover, excellent shape memory effect of 6.6% and 7.5% were found in Ti50Ni47Fe2Al1 and Ti50Ni46.5Fe2.5Al1 alloys, which results from the stress-induced martensite transformation from the R-phase.     

Martensite transformation induced by deformation and its phase electrochemical behavior for stainless steels AISI 304 and 316L

The martensite transformation induced by tensile elongation and its effect on the behavior or phase electrochemistry of AISI 304 and 316L in 3.5% NaCl solution were studied.The results show that the content of α′-martensite in stainless steel 304 increases with the true strain,As α′-martensite content increased.freee corrosion potential and pitting potential of stainless steel 304 in 3.5% NaCl solution appeared the change trend of a minimum.It was also found that pitting nucleated preferentially at the phase interfaces between martensite and austenits,There exsted apparent differnece between electrochemical properties of austenite and of martensite for stainless steel 304 and 316L in 3.5% NaCl solution.     

β' Cu-Zn-Al 合金中温区等温转变的研究

利用光学显微镜及透射电镜考察了β′Ｃｕ－Ｚｎ－Ａｌ合金中温区等温转变，发现其初期形成的α１内部具有完整的层错亚结构，其体转变激活能约为Ｚｎ扩散激活能的１／３．