共查询到19条相似文献,搜索用时 156 毫秒
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NiAl热诱发马氏体相变的分子动力学模拟 总被引:6,自引:0,他引:6
运用NiAl合金的镶嵌原子势,进行了B2结构NiAl中热诱发马氏体相变的分子动力学模拟,从而研究马氏体形核和长大的微观机理.首先进行了0K等体积条件下NiAl的相稳定性分析,发现0K时点阵参数c与a之比约为1.31的bct结构是稳定结构,B2结构只是一种亚稳结构.在热诱发马氏体相变的模拟过程中,由于NiAl中Ni原子和Al原子的振动性质存在着差异,造成了马氏体的不均匀形核.对另两种不同初始构型的系统进行的模拟进一步证实了不均匀形核的存在,并通过计算B2结构NiAl中Ni原子和Al原子的热运动均方位移解释了其原因.模拟中,B2结构奥氏体经热诱发马氏体相变转变为fctL1_0结构的马氏体.马氏体在长大过程中内部形成了若干转变孪晶. 相似文献
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利用透射电镜和高分辨电镜系统地研究了Ti36Ni49Hf15合金的显微组织与相结构、热致马氏体形貌、亚结构、马氏体变体间的组织结构和界面结构结果表明,固溶处理Ti(36)Ni(49)Hf(15)合金的室温组织由马氏体基体和呈球状与多边形状的(TixHf(1-x))2Ni第二相粒子组成.马氏体相为单斜B19’结构,点阵常数为:α=0.2454nm,b=04087nm,c=0.4791nm;)β=99.32°.Ti(36)Ni(49)Hf(15)合金的热形成马氏体变体间构成典型的自协作组态观察到的有矛头状、嵌镶块状和楔状三种形态马氏体变体其亚结构为(001)复合李晶.矛头状和嵌镶块状马氏体变体之间互成(011)Ⅰ型、<011>Ⅱ型孪晶关系,在这些变体内部还存在与其呈(111)Ⅰ型孪晶关系的楔状小变体.(011)Ⅰ型孪品界面比较平直、共格性好、界面两侧原子相对(011)面呈镜面对称;<011>Ⅱ型孪晶界面呈现缓慢弯曲的特征;(111)Ⅰ型孪晶界面呈波浪形结构 相似文献
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用高分辨电镜观察了Cu-Zn-Al双程记忆合金中9R型热弹性马氏体内A:B型变体对及其界面结构变体A和B以[011]β(即[591]9R)为轴旋转了180°,呈Ⅱ类孪晶取向关系A:B型变体对还具有(114)[110]9R,A//(114)[192]9R,B取向关系,在这一取向下,观察发现堆垛缺陷仅存在于变体A中,变体A与B以共格界面相匹配,界面为无理指数界面,即K1(10.8429 2.5859).界面在原子尺度上大量存在着1—2个原子高度的结构台阶,偶尔存在7—8个原子高度的生长台阶.结构台阶面为(114)9R,台阶梯度方向为[201]9R台阶面与K1面边线夹角的测量值约为7.3°;接近理论计算值7.45”. 相似文献
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利用拉伸试验、电阻—温度曲线测量、光镜、X射线衍射及透射电镜分析方法研究了Cu-Al10.2-Mn4.9-Zn4.6-Zr0.3合金的宽滞后效应。结果表明,随着应变的增大,该合金相变滞后增宽,马氏体可逆转变量减少。在应力下合金组织变化如β→2H转变、18R→2H转变、某些变体择尤长大,变体间的合并是主要变形机制。这些运动导致了交叉组织、带状组织、锯齿状边界、孪晶碎片及位错缠结的产生,破坏了变体间界面共格关系,使得其在热激活作用下难以运动。这可能是产生宽滞后效应和使可逆马氏体量减少的主要原因。 相似文献
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研究了加有Al和Si的奥氏体Fe(15-30wt%)Mn合金的形变孪晶,马氏体相变和机械性能,做了不同形变速率和不同温度的拉伸试验。用光镜,X射线衍射和扫描电镜观察了塑性形变过程中在γ基体中形成的孪晶,α‘(体心立方)和ε(密集六方)马氏体。 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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M.H. Enayati F. Karimzadeh S.Z. Anvari 《Journal of Materials Processing Technology》2008,200(1-3):312-315
The nanocrystalline NiAl intermetallic compound was synthesized by mechanical alloying of the elemental powders. The structural changes of powder particles during mechanical alloying were studied by X-ray diffractometery, scanning electron microscopy and microhardness measurements. The mechanical alloying resulted in the gradual formation of nanocrystalline NiAl with a grain size of 20 nm. It was found that NiAl phase develops by continuous diffusive reaction at Ni/Al layers interfaces. The NiAl compound exhibited high microhardness value of about 1035 Hv. 相似文献
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Three-dimensional spatially resolved strains were mapped in a model NiAl/Mo composite after nanoindentation. The depth-dependent strain distributed in the two phases and partitioned across the composite interfaces is directly measured at submicron length scale using X-ray microdiffraction and compared with a detailed micromechanical stress analysis. It is shown that indentation-induced deformation in the composite material is distinct from deformation expected in a single-phase material. This difference arises in part from residual thermal strains in both phases of the composite in the as-grown state. Interplay between residual thermal strains and external mechanical strain results in a complex distribution of dilatational strain in the Mo fibers and NiAl matrix and is distinct in different locations within the indented area. Reversal of the strain sign (e.g., alternating tensile/compressive/tensile strain distribution) is observed in the NiAl matrix. Bending of the Mo fibers during indentation creates relatively large ~1.5° misorientations between the different fibers and NiAl matrix. Compressive strain along the 〈0 0 1〉 direction reached ?0.017 in the Mo fibers and ?0.007 in the NiAl matrix. 相似文献
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《Acta Materialia》2003,51(18):5385-5398
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. 相似文献
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《Acta Materialia》2003,51(6):1561-1572
The effect of the crystallography of film-like Ni3Al(γ′) precipitates along grain boundaries of NiAl(β) on the fracture stress at room temperature was examined using β bicrystals with controlled orientations. The selected variant of γ′-film satisfied the Kurdjumov–Sachs (K–S) relation with a neighbouring β crystal, and deviated from the relation with an adjacent β crystal. In the course of tensile deformation at ambient temperature, fracture occurred preferentially at the (β/γ′) interphase boundary deviating from the K–S relation, which showed no plastic flow, and the fracture stress decreased with increasing deviation angle. In contrast, slip transfer from γ′-film to β crystal across coherent (β/γ′) interface was observed, when the variant of γ′-film satisfied the K–S relation with both neighbouring β crystals. To clarify the relation between the interphase boundary fracture and the deviation angle from the K–S relation, the boundary structure of incoherent (β/γ′) interfaces was discussed using O-lattice theory and transmission electron microscopic observations. 相似文献
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MORPHOLOGYOFMELTSPINNINGSUPERSATURATEDB2NiAl¥SUNBaode;CHEXiaozhou;LINDongliang;ZHOUYaohe(DepartmentofMaterialsEngineering,Sha... 相似文献
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In this study, nanocrystalline NiAl intermetallic compound was obtained by mechanical alloying and PAS (plasma activated sintering
method). Nanocrystalline NiAl powder was fabricated after 30 hr of milling with 2 wt.% stearic acid added as a PCA (process
control agent) to the Ni-50at%Al composition. The grain size of the nanocrystalline NiAl powder was about 10 nm. Nanocrystalline
NiAl powder was consolidated at 1000°C, 1100°C, 1200°C and 1300°C for 2 min with 30 MPa compressive force. The surface morphology
of the NiAl consolidated at 1300°C was very regular and dense, above 96% of theoretical density (5.9 g/cm3). Al4C3 was observed in the NiAl consolidated at 1300°C by TEM analysis. It is thought that the carbons came from the stearic acid
during the MA process and the graphite mold during the PAS process. The grain size of the NiAl consolidated at 1300°C did
not increase but the grain shape became flat due to compressive force. 相似文献