NiAl热诱发马氏体相变的分子动力学模拟

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．     

Ti36Ni49Hf15高温形状记忆合金的显微组织与界面结构

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     

Cu—Zn—Al双程记忆合金中Ⅱ类孪晶的界面观察

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”．     

铜基形状记忆合金马氏体变体之间关系的表象理论计算与群论分析

运用马氏体相变的表象理论计算了铜基形状记忆合金中马氏体变体的惯习面,利用群论原理分析了变体之间可能存在的界面类型.将表象理论计算结果与群论分析结合起来,得出马氏体24个变体之间存在着反映孪晶、180°旋转孪晶、120°旋转孪晶和90°旋转孪晶等4类孪晶关系以及23种界面类型．     

形状记忆合金中的马氏体变体在外场下的再取向和再分布机制

利用相场方法研究了马氏体变体在循环应力作用下再取向和再分布的微观机制。模拟结果表明,随着外应力的增加,在孪晶界面会出现母相的形核和长大,以此实现变体间的转化,这是3种变体转化为2种变体的主要再取向机制;卸载后消失的变体在孪晶界面重新形核并长大以完成系统内微观组织的再分布。在Mn-Cu合金中这种机制是控制循环载荷下形状记忆效应产生的主要机制。     

Ni9钢微观结构的TEM研究

利用ＴＥＭ研究了Ｎｉ９钢中马氏体与奥氏体的微观结构，结果表明，多数回火奥氏体不是严格地按Ｋ－Ｓ或Ｎ－Ｗ关系析出，而是在这两种取向附近变化；在同一马氏体束内，奥氏体可按上述近似关系的不同变化析出；回火奥氏体主药第马氏体晶界析出，呈板条状，惯习面为（３３５）／／（３４１），奥氏体向马氏体转变时易形成马氏体孪晶，这是孪晶在随后的回火过程中消失。     

硅钢中的贝氏体及其转变模型

含硅钢在贝氏体温区短时等温获得了准贝氏体组织：贝氏体铁素体（ＢＦ）＋残余奥氏体（ＡＲ）．ＢＦ中具有Ｓｐｉｎｏｄａｌ分解现象，类似于马氏体时效的早期现象，结合Ｘ射线衍射法定量测定结果，证明ＢＦ过饱和碳。ＢＦ／ＡＲ相界面位错是以混合位错为主的位错圈。ＢＦ中含有高密度位错和孪晶，而ＡＲ中缺陷主要为层错和孪晶，层错面或孪晶面与界面台阶有对应关系，表明阶面不会沿界面宽面侧向移动。根据实验结果提出了贝氏体铁素     

CuAlMnZnZr合金拉伸变形及其宽滞后效应

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。     

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     

马氏体相变和形变孪晶对Fe—Mn—Si—Al钢机械性能的影响

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。     

相变中的界面

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。     

Synthesis of nanocrystalline NiAl by mechanical alloying

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.     

NiAl—TiC内生复合材料的高温拉伸行为

研究了ＨＰＥＳ法制备的ＮｉＡｌ－ＴｉＣ内生复合材料的高温拉伸行为及ＮｉＡｌ／ＴｉＣ的界面特点，结果表明，内生ＴｉＣ颗粒可大幅度提高ＮｉＡｌ的高温拉伸强度，在ＮｉＡｌ与ＴｉＣ之间存在着一种相互交错的界面，它对提高复合材料的高温拉伸强度具有重要贡献。     

NiAl－TiC内生复合材料的高温拉伸行为

研究了ＨＰＥＳ法制备的ＮｉＡｌ－ＴｉＣ内生复合材料的高温拉伸行为及ＮｉＡｌ／ＴｉＣ的界面特点．结果表明，内生ＴｉＣ颗粒可大幅度提高ＮｉＡｌ的高温拉伸强度．在ＮｉＡｌ与ＴｉＣ之间存在着一种相互交错的界面，它对提高复合材料的高温拉伸强度具有重要贡献．     

Indentation-induced localized deformation and elastic strain partitioning in composites at submicron length scale

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.     

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.     

Interphase boundary fracture and grain boundary precipitation of Ni3Al(γ′) phase in β-NiAl bicrystals

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.     

MORPHOLOGY OF MELT SPINNING SUPERSATURATED B2 NiAl

ＭＯＲＰＨＯＬＯＧＹＯＦＭＥＬＴＳＰＩＮＮＩＮＧＳＵＰＥＲＳＡＴＵＲＡＴＥＤＢ２ＮｉＡｌ￥ＳＵＮＢａｏｄｅ;ＣＨＥＸｉａｏｚｈｏｕ;ＬＩＮＤｏｎｇｌｉａｎｇ;ＺＨＯＵＹａｏｈｅ（ＤｅｐａｒｔｍｅｎｔｏｆＭａｔｅｒｉａｌｓＥｎｇｉｎｅｅｒｉｎｇ,Ｓｈａ...     

PAS consolidating behavior of mechanically alloyed nanocrystalline NiAl intermetallic compound

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.