CuAlMn形状记忆合金的高阻尼特性

用悬臂梁弯曲共振法研究了新型CuAlMn系形状记忆合金在马氏体态和母相态的阻尼特性.研究结果表明:室温马氏体态Cu-10.5%Al-6%Mn(质量分数)和室温母相态Cu-11%Al-8%Mn形状记忆合金在表面应变振幅为4.05MPa时,都具有很高的阻尼性能,内耗Q-1接近0.1; 两种形态的CuAlMn形状记忆合金的阻尼性能都随应力振幅增加而下降,且母相态合金阻尼性能下降速度更快.     

从相变出发理解和计算变体间位向差

本文从相变出发,结合母相对称性建立相变与变体位向差之间的定量联系,详细介绍了如何计算相变矩阵和以之为基础的变体间位向差,并以fcc→bcc相变系统为例,运用相变矩阵和对称操作矩阵计算了N-W位向关系下变体间位向差,结果与前人从位向关系出发计算结果一致.本文方法有助于理解位向差的成因,特别有助于开展对无理位向关系引起的变体间位向差的分析.文中还进一步运用点群理论讨论了立方系N-W,K-S,Bain位向关系下独立存在的变体数目,并且推导了相变矩阵与位向关系矩阵之间的转换关系.     

铜基形状记忆合金时效过程中的原子有序态变化

高温Ｘ射线衍射及原位电阻测量等实验结果表明，淬火态Ｃｕ—Ａｌ—Ｎｉ—Ｍｎ—Ｔｉ形状记忆合金在母相和马氏体状态时效过程中，原子有序态的演变及时效机制是不同的．在母相态时效，先发生ＤＯ_３再有序化，随后发生原子短程无序或偏聚并进而析出贝氏体或平衡相．在马氏体状态时效，ＤＯ_３长程有序度无显著变化，没发生类似在母相态的再有序化，主要是原子短程无序化．     

INFLUENCE OF GRAIN SIZE AND ORDERING OF PARENT PHASE ON M_s IN A CuZnAl ALLOY CONTAINING BORON

The effect of grain size and ordering of the parent phase on the critical points of thermoelasticmartensitic transformation in Cu-25.62 Zn-3.97 Al-0.0018 B(wt-%)shape memory alloyhas been investigated.Based on the thermodynamics of phase transformation,a linear rela-tionship between the starting temperature of martensitic transformation and the reciprocal ofthe square root of grain size is obtained,i.e.M_s temperature rises with increasing grain size.It shows a good agreement with the results of electric resistance measurement.Applying theLandau's theory,a quantitative relationship between M_s and the ordering parameter of theparent phase is set up,which is well confirmed by the results of X-ray diffraction and electricresistance measurement.The activation energy of the ordering process in the parent phase ofthe alloy is calculated to be 46 kJ/mol.     

A synchrotron X-ray diffraction study on the phase transformation kinetics and texture evolution of a TRIP steel subjected to torsional loading

The martensitic phase transformation kinetics and the relation with texture evolution in the constituent phases were studied for a transformation-induced plasticity (TRIP) steel under a torsional loading condition at ambient temperature. Synchrotron X-ray diffraction was used to measure the evolution of phase fractions and texture in terms of pole figures and orientation distribution functions as a function of the applied shear strain. The effects of deformation texture development in the parent austenite phase on the observed phase transformation kinetics are discussed in terms of preferred transformation mechanisms. The texture evolution in the product martensite phase is also discussed in terms of possible texture inheritance from the parent austenite phase and its own deformation texture.     

Phase field microelasticity modeling of heterogeneous nucleation and growth in martensitic alloys

The phase field model is employed to study the structural mechanism of heterogeneous nucleation in the face-centered cubic to body-centered cubic martensitic transformation. The transformation is triggered in the undercooled parent phase by defects of varying potency, a dislocation loop or a group of loops. It is found that the metastable homogeneous state of the parent phase in this case is not necessarily stable even if the undercooling is small and the potency of defects is low – the parent phase transforms around the defects, forming a sessile metastable martensitic embryo. When the undercooling and the defect potency reach a critical value, the embryo loses its metastability with respect to the barrierless growth until the transformation is complete. This growth corresponds to an athermal martensitic transformation. It is shown that both sessile and growing martensitic embryos are not a single-domain particle as is usually assumed but rather an assemblage of twin-related domains. The modeling does not impose any a priori constraint on the possible microstructure of a martensitic nucleus.     

复合层对Al接触反应钎焊过程及接头性能的影响

研究了Cu ,Zn复合层对Al接触反应钎焊过程和接头质量的影响规律。Cu和Al形成共晶液相破坏了Al表面氧化膜 ,促使Cu Zn包晶液相和Al Zn Cu共晶液相在Al表面润湿。结果表明 ,采用复合层进行Al接触共晶反应钎焊时 ,Cu和Zn厚度比例合适 ,可提高钎焊接头的抗电化学腐蚀性能和接头强度     

Barrier-free heterogeneous grain nucleation in polycrystalline materials: The austenite to ferrite phase transformation in steel

The process of grain formation during structural solid-state phase transformations has commonly been analysed in terms of the classical nucleation theory. In polycrystalline materials a new phase generally forms at grain boundaries in the parent phase microstructure. Under certain conditions the net interfacial energy to form a new phase can be relatively small due to the release of grain boundary energy from the parent phase. The nucleation process is then governed by cluster dynamics. We propose a simple model to predict the cross-over between different heterogeneous nucleation regimes and apply it to recent synchrotron X-ray diffraction experiments on ferrite nucleation in steel.     

焊缝金属中针状铁素体晶粒长大行为

以针状铁素体(AF)组织为基体组织的大热输入焊缝金属作为研究对象,采用金相显微镜(OM)、扫描电子显微镜电子背散射衍射装置(EBSD)、全自动静态相变仪等手段表征了焊缝金属内细长状的针状铁素体(AF)组织晶粒的取向特征,分析不同焊接热输入对焊缝金属内AF晶粒形核以及长大行为的影响规律.?结果表明,在大热输入焊接条件下,...     

Elasticity-based model of the variant selection observed in the β to α phase transformation of a Zircalloy-4 sample

The β→α texture inheritance of a Zircalloy-4 sample has been investigated after an α→β→α transformation cycle. The final inherited α texture has been determined from a crystal orientation map determined by electron back-scattering diffraction, whereas the texture of the high temperature β phase has been reconstructed by a method analysing the orientations and misorientations of α variants. The comparison of the α texture calculated from the parent β texture without variant selection with the experimental sharp α texture shows differences due to a strong variant selection mechanism occurring during the phase transformation at cooling.A model of a variant selection mechanism based on the elastic anisotropy of the parent β phase leads to a simulated inherited α texture with the main characteristics of the experimental texture.     

Co影响Ni-Mn-Ga合金马氏体相变的第一性原理分析

采用基于密度泛函理论的第一原理平面波赝势法,研究了掺杂Co元素对Ni-Mn-Ga磁性形状记忆合金的能态密度分布的影响规律,阐明了Co对马氏体相变作用机理.研究表明,随Co含量增加,更多的Co3d-Mn3d杂化取代了Ni3d-Mn3d杂化,使母相稳定性提高,马氏体相变温度降低.Co的加入对Ni-Mn-Ga-Co母相的自旋向上能态密度几乎没有影响,但明显改变自旋向下能态密度.     

Bain对应和K-S模型的数学描述

利用Bain点阵对应对K－S模型的晶格改建过程进行了严密的数学描述，对于不同的马氏体正方度，提出了计算第一切变，第二切变及晶格调整的计算依据。并给出了普遍的计算公式。以Fe-1.4C和纯铁为例。计算了马氏体相变的点阵畸变。进一步分析表明。K－S模型实质是Bain模型的旋转。计算的结果与实测的取向关系相符合。     

THE LIMITATION OF MATANSITIC INVARIANT HABIT PLANE AND MARTENSITE MORPHOLOGY

ＴＨＥＬＩＭＩＴＡＴＩＯＮＯＦＭＡＴＡＮＳＩＴＩＣＩＮＶＡＲＩＡＮＴＨＡＢＩＴＰＬＡＮＥＡＮＤＭＡＲＴＥＮＳＩＴＥＭＯＲＰＨＯＬＯＧＹ￥Ｎ．Ｊ．Ｇｕ，Ｈ．Ｆ．Ｐｅｎｇ，Ｘ．ＹＳｏｎｇ，Ｆ．Ｘ．ＹｉｎａｎｄＥ．Ｘ．Ｗａｎｇ（ＤｅｐａｒｔｍｅｎｔｏｆＭａ...     

含硼的Cu—Zn—Al合金中母相晶粒度和有序度对Ms的影响

研究了母相平均晶粒尺寸和有序度对Cu-25.62Zn-3.97Al-0.0018B(wt-％)形状记忆合金热弹性马氏体相变点的影响。从相变热力学出发,得到马氏体相变点和晶粒尺寸的平方根的倒数成线性关系,并且随晶粒尺寸增大,马氏体相变点升高,与电阻法测得的结果符合很好。运用Landau理论,得到马氏体相变点和母相有序度的定量关系式,与X光衍射和电阻法试验的结果符合较好。求得试验用合金母相DO_3有序化的激活能约为46kJ/mol。     

On the ω phase formation in Cr–Al and Ti–Al–Cr alloys

The interaction between Al and the transition metals Ti and Cr on the stability of the ω phase in metastable β-based structures was studied. Alloys were quenched from the melt to retain at room temperature a metastable β phase (B2 structure), which is stable at high temperatures. The structural study of the ω phase was carried out by correlating the deviation of ω structure from the ideal ω phase to the compositions of the parent β phase. Deviation of ω structures from the ideal one was related to the electron concentration of the parent β phase. A diffuse ω structure is reported in the Cr₂Al phase (C11_b structure) for the first time. The results are consistent with our previous suggestions that Al stabilises the ω phase in transition metals by lowering the spatial conduction electron concentration in the parent β phase and by enhancing p–d hybridisation of valence electrons. In the ternary Ti–Al–Cr alloys, prolonged annealing of the Ti–30Al–10Cr and Ti–20Al–10Cr alloys at 450°C led to the formation of two types of ordered crystalline ω structure.     

Restitution of high temperature parent textures of bcc and hcp polycrystals by a non-linear positivity method

The evaluations of the parent texture from the inherited texture have been performed by different methods, in the case of an HSLA steel. Comparison of the results shows the great efficiency of the restitution of the parent texture by using a non-linear positivity method. The method has then been adapted to BCC to HCP transformation. An example of the restitution of the parent phase texture is proposed in the case of the transformation of a β metastable Ti based alloy.     

Preferred Orientations in a Meta-Stable Body-Centered-Cubic Zr-Cb Alloy

The deformation and annealing textures of a body-centered-cubic Zr-Cb alloy are similar to the textures of the more familiar body-centered-cubic metals. p]The preferred orientation of the newly transformed hexagonal-close-packed phase is related to the parent body-centered-cubic phase by the Burgers orientation relationship.     

Tb0.3Dy0.7Fe1.95-xNbx (x=0, 0.03, 0.06, 0.09) 合金的组织与磁致伸缩性能

采用高真空电弧炉制备了Tb0.3Dy0.7Fe1.95-xNbx(x=0,0.03,0.06,0.09)合金,研究了该系列合金的晶体结构、微观组织及磁致伸缩性能。结果表明:添加Nb元素后的Tb0.3Dy0.7Fe1.95-xNbx(x=0.03,0.06,0.09)合金基体相结构仍保持为MgCu2(C15型)立方Laves相,添加Nb后Tb0.3Dy0.7Fe1.95-xNbx合金基体相晶格常数几乎不变。Nb在基体相RFe2中和富Re相中都不溶,但在x=0.03时的RFe3相中微溶而形成Re(Nb,Fe)3相。初生相NbFe2(C14型)相的形成使凝固液体富稀土从而抑制了RFe3有害相形成。六方结构的NbFe2在与自身结构不同的RFe2(C15型)中不溶而单独成为一相存在于RFe2基体上。Nb的添加量x对磁致伸缩的影响很大,微量(x=0.03)Nb的添加有效抑制了RFe3有害相的生成而使得磁致伸缩性能提高最大,但当Nb含量继续增大时,由于顺磁相NbFe2和富Re相的析出影响了基体磁-弹性交互作用而使磁效伸缩性能下降。但相对于Tb0.3Dy0.7Fe1.95母合金都有少量提高。     

Energy landscape for martensitic phase transformation in shape memory NiTi

First-principles calculations are presented for parent B2 phase and martensitic B19 and B19′ phases in NiTi. The results indicate that both B19 and B19′ are energetically more stable than the parent B2 phase. By means of ab initio density functional theory, the complete distortion–shuffle energy landscape associated with B2 → B19 transformation in NiTi is then determined. In addition to accounting for the Bain-type deformation through the Cauchy–Born rule, the study explicitly accounts for the shuffle displacements experienced by the internal ions in NiTi. The energy landscape allows the energy barrier associated with the B2 → B19 transformation pathway to be identified. The results indicate that a barrier of 0.48 mRyd atom^?1 (relative to the B2 phase) must be overcome to transform the parent B2 NiTi to orthorhombic B19 martensite.     

MORPHOLOGY AND PHASE TRANSFORMATION OF GRANULAR BAINITE AND GRANULAR STRUCTURE

本文研究了低碳合金钢奥氏体在连续冷却或等温转变过程中形成的组织形态和转变机理。结果表明在中温贝氏体区得到“粒状贝氏体”组织,在先共析转变区得到“粒状组织”。两者都有“铁素体基体+小岛”形貌。但前者有表面浮凸现象,铁素体呈长条状,与母相维持K-S关系,惯习面为{111}_γ,小岛也多星长条状平行排列。后者无表面浮凸,铁素体呈无规则形状,与母相无严格位向关系,小岛亦呈无规则排列。然而这两种组织都是由扩散型相变机制形成的。最后,提出了形成这两种组织的相变模型。