EFFECT OF SELF-ACCOMMODATION FOR TWINNED MARTENSITE AND INVARIANT HABIT PLANE

The shear components of strain tensors for matrix and twin crystal of (?)winned martensite wereroughly opposite after calculation,and the strain energy would be reduced.The growth ofmartensitic plates along the normal direction of the twin plane may depend upon the effect ofself-accommodation between the matrix and twin crystals.Based upon the analysis on thedisplacement vectors of the normals for different habit planes,the{10,3,15}_f plane could formthe macroscopic invariant habit plane;but the(5(?)5)_f,(2(?)2)_f,and(1(?)1)_f planes aredifficult to become the invariant planes.     

孪晶马氏体的自协作效应及不变惯习面SCIEI

本文计算了孪晶马氏体基体和孪生部份的应变张量,发现二者的切变分量大致相反,故应变能降低。马氏体片可依靠基体和孪晶间的自协作效应沿孪晶面的法问长大。根据对不同惯习面法线的位移矢量的分析,{10,3,15}f面可构成宏观的不变惯习面,而{575}f,{252}f和{111}f面则难以构成。     

中碳铁合金马氏体的一些特征

应用光学显微术及透射电子显微术和B-M表象晶体学理论对60和60Si2Mn钢中马氏体的形态、亚结构与晶体学特征进行了研究。中碳铁基马氏体的平均惯习面为{225}_f。铁基马氏体的微观惯习面为{111}_f。实测惯习面、取向关系及切变方向等与利用Bain应变及(100)[011]_f点阵不变切变系按B-M理论计算的结果一致。     

SUBSTRUCTURE AND CRYSTAL MORPHOLOGY OF MARTENSITE IN MEDIUM CARBON IRON ALLOYS

The morphologic,substructural and crystallographic characteristics of martensite in steels 60and 60Si2Mn have been investigated by means of optical and transmission electronmicroscopy combined with B-M phenomenological crystallographic theory.The average hab-it plane of martensite in medium carbon iron alloys is{225}_f.Experimental data on the habitplane and the orientation relationship between the austenite and martensite are in agreementwith the B-M theoretical calculation of using the Bain strain and lattice invariant shear on(100)[011]_f.     

Crystallographic analysis of the martensitic transformation in medium-carbon steel with packet martensite

Based on X-ray diffraction studies of the martensite texture in a single martensite packet, exact orientation relationships between the orientations of martensite crystallites and the original austenite single crystal in medium-carbon steel 37KhN3A have been determined to be as follows: (011)_α||(1; 0.990; 1.009)_γ to an accuracy of \( \pm 0.15^\circ ,{\left[ {01\overline 1 } \right]_\alpha }||{\left[ {1;1.163; - 2.133} \right]_\gamma }\) to an accuracy of ±0.15°. It has been shown that the orientation relationships proved to be almost the same as in the Fe–31% Ni alloy with a twinned martensite with close lattice parameters. Therefore, the conclusion has been drawn that the mechanism of the lattice deformation upon the martensitic transformation is the same in both alloys. It is described as follows. The lattice deformation occurs by shear on the (111) plane in the \({\left[ {11\overline 2 } \right]_{_\gamma }}\) direction and is accompanied by an additional change in the dimensions in the mutually perpendicular directions \({\left[ {11\overline 2 } \right]_{_\gamma }},\left[ {111} \right],\;and{\left[ {1\overline 1 0} \right]_{_\gamma }}\). The invariantlattice deformation is implemented by slip in martensite on the planes of the (112)_α type in the direction \({\left[ {\overline 1 \overline 1 1} \right]_\alpha }\). One of the 24 crystallographically equivalent variants of the transformation mechanism has been considered. Apart from this type of deformation, an additional deformation of martensite is possible that does not change its orientation. It has been shown that the orientation of the martensite crystallite calculated via the phenomenological theory of the martensitic transformations (PTMT) differs by approximately 1° from the experimentally determined orientation. This refers to both the lath and twinned martensite. In the twinned martensite, the invariant plane obtained in the PTMT calculations and the habit plane coincide. In lath martensite of 37KhN3A steel, the invariant plane of the martensite crystal obtained in PTMT calculations deviates by ~25° from the orientation of the surface of the martensite plate (habit plane), which is close to the (111)_γ plane. An explanation of this phenomenon is given.     

高碳铁合金马氏体的特征

应用透射电子显微术研究了1.03％C铁合金中片状马氏体的一些特征。此合金中片状马氏体的惯习面接近{224}_f。观察了马氏体片的形貌和分布,马氏体片的聚合和弯曲,马氏体的亚结构,以及残留的过冷奥氏体的亚结构。讨论了马氏体的形核与长大机制。     

CHARACTERISTICS OF MARTENSITE IN A HIGH CARBON FERROALLOY

Some characteristics of plate martensite in a 1.03% C ferroalloy have been studied by usingthe transmission electron microscopy.The habit plane of the plate martensite in this ferroalloywas found to be close to{224}_f.The morphology,distribution,coalescence and curving ofmartensite as well as the substructure in both martensite and austenite have been observed.The mechanism of both nucleation and growth of the martensite have been discussed.     

INFLUENCE OF MARTENSITE MORPHOLOGY AND CRYSTAL STRUCTURE ON THE PSEUDOELASTICITY IN A Cu-Al-Zn-Mn-Ni ALLOY

本文研究了Cu-Al-Zn-Mn-Ni合金的伪弹性变形行为,并用金相和X射线衍射法观察分析了变形及时效前后马氏体组织结构的变化。结果表明,合金在母相状态时的伪弹性与其原始马氏体组织结构密切相关;通过改善原始马氏体组织结构的自协作性和适当的时效处理可以显著提高合金的伪弹性。     

Phase and structural transformations in U and U-Nb alloy upon severe deformation and heat treatments

Transmission electron microscopy was used to analyze the twin and dislocation structure of samples of commercial uranium in the initial (undeformed) state and after severe deformation using explosive loading by plane and spherical waves of various intensity. It has been shown that an increase in the intensity of explosive loading by a plane wave leads, first, to an increase in the density of randomly distributed dislocations and twins and, then, to the development of polygonization processes with the formation of a subgrain structure of the α phase. Crystallographic analysis of the initial and deformation-induced twins in uranium has shown the presence of predominantly {130} twins of mixed type and, in singular cases, {172} and {176} twins of the second kind. It has been established that the retained spherical shells have a distinctly pronounced zonal structure, which contains information on the forward and reverse martensitic phase transformations of uranium (α ? β(γ) ? L, etc.) that occur under shock-wave loading by spherical waves. Conditions are determined for the manifestation of structural heredity in the U-6 wt % Nb alloy with recovery of the size and shape of grains of the initial high-temperature γ phase during the forward γ → α″ martensitic transformation upon cooling and during reverse α″ → γ transformation upon heating. Elimination of the structural heredity with significant grain refinement of the high-temperature γ phase occurs in the process of repeated quenching from 700°C after one type of preliminary treatments (cold deformation of α″ martensite, recrystallization of the deformed α″ phase, high-temperature aging of the initial α″ martensite, and eutectoid decomposition).     

A comparison of the phenomenological theory of martensitic transformations with a model based on interfacial defects

Structural models of martensitic interfaces are those where the habit plane (HP) is comprised of coherent terraces reticulated by arrays of interfacial defects. Such interfaces are shown explicitly to exhibit no long-range displacements and to move in a glissile manner by lateral motion of disconnections along the interface. We quantify predictions of HP and orientation relationship (OR) between the parent and product crystals for such models in terms of a reference lattice in an approach called a topological model (TM). These crystallographic quantities for the TM are compared with those of the phenomenological theory of martensite crystallography (PTMC). For the case of transformations resembling α to β in Ti, but where lattice invariant deformation is suppressed, the two models agree when the interplanar spacings of the terraces in the two crystals are the same. However, although the OR’s according to the two approaches are very similar, the predicted HP’s differ systematically when the terrace plane spacings are varied. The differences arise because the PTMC interfaces are unrelaxed configurations that are invariant planes of the geometrical shape transformation, whereas TM interfaces are physically invariant planes as a transformation progresses.     

Crystallographic analysis of the FCC → BCC martensitic transformation in high-carbon steel

Based on the phenomenological crystallographic theory of martensitic transformations, the following crystallographic characteristics of the tetragonal martensite in high-carbon steel have been calculated: orientation relationships between the crystal lattices of the bct martensite and fcc austenite; the magnitude and direction of the macroscopic shear; the habit plane; the angle and the axis of rotation of the crystal lattice of the martensite. The calculation was performed for three variants of lattice deformation: Bain deformation; two-shear Kurdjumov-Sachs deformation; and the deformation we suggested upon the analysis of the fcc-bcc transformation. In the last variant, a minimum rotation of the crystal lattice of martensite is required; consequently, this variant is closest to the real mechanism of the martensitic transformation. An expression has been derived that describes the interrelation between the degree of tetragonality of the crystal lattice of martensite and the magnitude of the shear deformation of the lattice. It has been shown that the 12 crystal-lographically equivalent variants of shear upon the formation of the lattice of the tetragonal martensite form three groups in each of which the martensite has the same tetragonality axis. For each variant of the shear, we have two equivalent variants of deformation of the martensite with invariant lattice. This results in 24 variants of orientation relationships.     

One-dimensional model of martensitic transformations

A modified Landau–Ginzburg theory for martensitic transformations is suggested. An accommodation strain energy in parent phase is added into the free energy of the system besides the Landau free energy and gradient energy which have been generally considered. Both the equilibrium state and the dynamic process of martensitic transformations are investigated by solving the equation of motion numerically. Two important features of martensitic transformations, i.e., transformational hysteresis and athermal transformation, can be displayed by the modified model. The results of numerical study of the model agree with experiments well, including surface martensite, thermoelastic and nonthermoelastic martensite formations, autocatalysis and burst transformation.     

300M超高强度钢板条马氏体的晶体学研究

电子衍射和晶体学测量证实,300M超高强度钢板条马氏体的惯习面为{335}_A型,与奥氏体的位向关系偏离K-S关系2.5°,为G—T关系,相邻板条间绕其公共面{110}_M法线相对旋转约60°,形成板条间不同的位向关系,包括近似{112}_M孪晶关系。     

Crystal-lattice distortions during mechanical twinning of the B2 phase of titanium nickelide via the mechanism of local reversible martensitic transformations

Tensor of distortions upon the formation of a {113} deformation twin by the mechanism of a combined (forward-plus-reverse) (occurring on an alternative transformation system) martensitic transformation in the B2 phase of titanium nickelide has been analyzed theoretically in the approximation of small deformations using the model of martensitic transformations based on the concept of “freezing” of cooperative thermal vibrations of atoms in close-packed atomic planes in metals. It is shown that this mechanism satisfactorily describes not only the reorientation angle but also the habit plane of the twin.     

Determination of the habit plane characteristics in the β–α′ phase transformation induced by stress in Ti–5Al–2Sn–4Zr–4Mo–2Cr–1Fe

The characteristics of the habit planes of the α″ orthorhombic martensite plates, induced by stress within a commercial sheet of Ti–5Al–2Sn–4Zr–4Mo–2Cr–1Fe have been investigated. First, the orientations of several grains in BCC phase which presented at least one α″ orthorhombic martensite plate, were determined by EBSD. The Miller indexes of habit planes within a parent grain were deduced from the intersection lines of the martensite plates on two perpendicular sides of the sample and from the orientation of the parent grain. These data are compared to the characteristics of the habit planes, calculated from the phenomenological theory of the martensitic transformation proposed by Wechsler, Liebermann and Read. The different results and their dispersions are analysed in this contribution.     

Martensite in a TiAl alloy quenched from beta phase field

Hexagonal martensite with well-developed midribs was obtained by iced-brine quenching of Ti44Al4Nb4Hf0.1Si from the beta phase field. Crystallographic characterisation shows great resemblances of the martensite in this alloy to the lenticular martensite in Fe–Ni alloys in the morphology and substructures of martensite plates. It also bears similarities with the martensite in titanium and its alloys in habit planes and orientation relationship with parent phase. Martensitic transformation under the conditions employed in this work was incomplete and the remaining beta phase after martensitic transformation, thus, underwent diffusional beta-to-alpha transformation or massive transformation, depending on the local circumstances.     

Effect of the elastic strain energy on the nucleation of Laves phases in α-iron base alloys

The elastic strain energy of coherent clusters in Fe-Mo, Fe-Ti, Fc-Nb and Fe-Ta systems has been calculated as a function of their shapes and orientations using the Eshelby’s method for anisotropic crystalline materials. The result is consistent with the formation of plate-shaped Laves phases in Fe-Nb, Fe-Ta and Fe-Ti systems and with that of spherical clusters, in Fe-Mo system, prior to the formation of plate-shaped Laves phase. The latter is believed to be formed due to the elastic interaction with the dislocations. The result also accurately predicts the {111}α habit plane of the Fe₂Nb and the {001}α of the Fe₂Ta Laves phases. The habit plane {011}α of the Fe₂Ti Laves phase is not consistent with the calculation result for pure β Ti clusters. However, a strong segregation of Fe atoms into β Ti clusters can favor the formation of {011}α instead of {001}α habit planes.     

马氏体相变的晶体学特征—不变平面应变

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。     

分子动力学模拟研究单个刃型位错对NiAl马氏体相变的影响

利用嵌入原子类型的势函数，通过分子动力学模拟方法研究了单个刃型位错对ＮｉＡｌ热诱发和应力诱发马氏体相变的影响，不受外力时，单个刃型位错的应变区不能诱发马氏体变核；位错在马氏体的长大过程中被继承，并可在相变的驱动下逐渐运动，拉应力作用下，３Ｒ结构的应力诱发马氏体首先在位错芯附近形核，长大过程中先形成蝶状马氏体，随后位氏多余半原子面的中部了发生了马氏体形核，刃型位错降低了应力诱发马氏体形核的激活能，并     

Prediction of crystallographic characteristics of martensitic transformation in a Ni–Mn–Ga based Heusler alloy

The energy minimization theory was applied to analyze the crystallographic features of the martensitic transformation in the alloy Ni_52.5Mn_23.5Ga₂₄ and the results obtained were compared with those determined by experiments. It is revealed that the index of the boundary between martensite variants belongs to the lattice plan family of {112}_M and the orientation relationship between the martensite variant 1 and 2 is characterized by a rotation of 82.1° about [1 0 0]_M1/[0 1 0]_M2. The orientation relationship between the parent phase and the martensite features a rotation of approximately 4° about the c axis of the parent lattice from the position of the conventional Bain relationship.