Low-Temperature Superplastic Deformation of Cold-Rolled Fe–5.6Mn–1.1Al–0.2C Steel

Metallurgical and Materials Transactions A - A cold-rolled low Al-added medium Mn steel was employed to investigate the low-temperature superplastic deformation at a relatively high initial strain...     

Lattice Effects in La-Sm-Ca-Mn-O

The doping effects of Sm in La0.67Ca0.33MnO3 oxide were studied. The results show that with increasing the doping amount of Sm the phase transition temperature of metal-insulator for the materials decreases monotonically, the cor-responding peak resistance increases rapidly, the Curie temperature decreases monotonically, and the magneto-resistance ratio increases quickly. The effects of Sm doping can be explained in terms of lattice effects.     

Role of Nb Addition on Microstructural Stability and Deformation Behaviors of FeMnAlC Lightweight Steels at 400 °C

Metallurgical and Materials Transactions A - As part of efforts to fabricate FeMnAlC lightweight steels suitable for high-temperature applications, the influence of Nb addition on the...     

Deformation Modes in the Single-Crystal Nickel-Based Superalloy CMSX-4 During Compressive Deformation at 1000 °C

Metallurgical and Materials Transactions A - After compressive deformation at 1000 °C and a strain rate of 2.5 × 10−4 s−1, deformation mechanisms in the [001]-oriented...     

Microstructural and Orientation Dependence of the Plastic Deformation Behavior in β-type Ti-15Mo-5Zr-3Al Alloy Single Crystals

The plastic deformation behavior of a β-type Ti-15Mo-5Zr-3Al alloy with a body-centered cubic (bcc) structure, which is a promising material for biomedical applications, was investigated. The orientation dependence of the plastic deformation behavior was examined by using a single crystal. In addition, changes in the mechanical properties depending on the microstructure were examined. The β single phase was maintained even after short-time annealing below 673 K (400 °C). Thus, the variations in the mechanical properties were small. However, an ellipsoidal ω phase and a lath-like α phase were precipitated in long-time annealing at 573 K (300 °C) and 673 K (400 °C), leading to large increases in the yield stress. For the deformation behavior, a dislocation with a Burgers vector parallel to á 111 ñ \left\langle {111} \right\rangle was observed irrespective of the heat-treatment conditions and loading orientations. However, the observed slip plane changed considerably depending on the loading axis, and the yield stress exhibited a strong orientation dependence because of the dislocation core structure effect in the bcc-structured crystals. The physical properties of Mo, which is the main constituent atom in the current alloy, may strongly affect the dislocation core structure and induce the characteristic orientation dependence of the plastic behavior.     

Microstructural Engineering in Eutectoid Steel: A Technological Possibility?

Eutectoid wire rods were subjected to controlled thermo-mechanical processing (TMP). Both increased cooling rate and applied stress during the austenite-to-pearlite decomposition produced significant changes in the microstructure: major increases in the pearlite’s axial alignment and minor decreases in the interlamellar spacing. The pearlite alignment was correlated with changes in the ferrite crystallographic texture and the state of residual stress. Microstructural engineering, improved axial alignment of pearlite, through controlled TMP gave a fourfold increase in torsional ductility. TMP of eutectoid steel thus appears to have interesting technological possibilities.     

Deformation processes in hot worked copper and α brass

The generation of the fine grained, dynamically recrystallized microstructure has been studied in hot rolled copper and α brasses and in 70:30 brass deformed by hot torsion. The new grains, which developed preferentially at grain boundaries and inhomogeneities of deformation, contained none of the deformation features present in unrecrystallized parts of the microstructure. This observation is contrary to theories of dynamic recrystallization which imply that the microstructure contains a spectrum of grains ranging from just recrystallized to severely deformed. Texture studies showed cold rolled textures at low rolling temperatures but in the case of copper the texture became quite flat after rolling at 350 and 425 °C. Flat textures were associated with a minimum grain size. At higher rolling temperatures the textures were again typical of cold rolled material. It is suggested that while normal slip processes are operating at all temperatures there is an additional contribution from grain boundary deformation processes associated with fine grained microstructures. Such processes would account for the absence of normal deformation features from dynamically recrystallized microstructures.     

Microstructural aspects of strain localization in AlMg alloys

The literature contains a number of continuum plasticity models describing the onset of strain localization but little definitive work which describes the microstructural transitions which accompany localization. In the present study a range of metallographic methods have been used in order to observe the progression of localization from events within single grains to the spatial organization of these events across the entire sample. The deformation mode used was cold rolling and observations were made using a variety of orientations relative to the rolling direction. It is concluded that in the AlMg system, localization begins by a structural instability in the accumulated dislocation substructure and later becomes organized into macroscopic bands due to local stress concentrations. The structure of the macroscopic bands is complex. They contain some high angle boundaries suggesting that they form due to the rapid and cooperative action of a number of slip systems over distances of the order of 0.2 μm. The bands cross grain boundaries and are organized in a cooperative sense because they represent local softening events. Thus, the shear bands in AlMg appear to form without texture softening or the need for the precursor of a lamellar structure. They involve a dramatic local change in the process of dislocation accumulation which is essentially a form a local dynamic recovery. The events become spatially organized to form macroscopic bands inclined at approx. 35° to the rolling plane as required by continuum plasticity.     

TiAl基合金超塑性变形中的位错运动

研究了结晶Ｔｉ－３３Ａｌ－３Ｃｒ－０．５Ｍｏ合金在超塑性变形过程中的位错运动。透射电镜分析结果表明，超塑性变形时，合金中存在大量位错运动，在晶界附近和晶粒内形成了位错网，并在晶界上出现位错塞积。大多数位错是从晶界及α２相粒子处发射出来的。     

超塑性变形的高温金相研究

应用高温金相显微术研究了晶粒平均直径为6.8μm的LC4铝合金在505℃超塑性变形过程中的显微组织变化.所获得的主要结果如下:(1)超塑性变形过程中存在广泛的晶界滑动和晶粒转动。(2)超塑性变形过程中原有晶粒的等轴形状及其尺寸基本上保持不变,而且变形前原来位于材料表面的晶粒,在超塑性拉伸变形后仍然位于材料表面,但部分原来的相邻晶粒会发生分离,它们之间由表面下移来的晶粒形成新的表面,导致试样表面积的增加。(3)超塑性变形的主要机制为晶界滑动所导致的三维的晶粒重排。     

含Sc铝镁合金的超塑变形机制

采用透射电镜研究了含微量Ｓｃ元素的ＡｌＭｇ合金在超塑变形过程中的显微组织和位错行为。结果表明：合金在超塑变形过程中发生了四个连续过程：①动态再结晶；②晶界向晶内激发位错；③位错在晶内密集并且受到第二相Ａｌ３Ｓｃ质点的阻碍作用，同时通过攀移越过晶内弥散分布的Ａｌ３Ｓｃ粒子；④位错向晶界运动并在晶界处消失。动态再结晶是合金在超塑变形中存在的组织效应，起到了细化晶粒，诱发微细晶超塑性的作用。该合金超塑变形的主要机制为晶界滑动伴随晶内位错运动     

晶界在超塑性变形中的作用

超塑性材料所具有的微细晶粒组织,意味着材料的单位体积内存在着大量的晶界。本文结合作者及其合作者近几年来所进行的研究工作,详细地论述了晶界在超塑性变形中所起的重要作用。     

金属超塑状态下正挤压变形力的工程计算

利用主应力法,结合金属超塑性力学方程,推出了金属超塑性正挤压变形力的计算式;对TangS提出的金属超塑性挤压模型进行了订正和改进。采用锌铝共析合金对理论计算公式进行了实验验证。     

TWIP钢室温静态拉伸下的组织形态和变形机制

在室温下对退火Fe-24Mn-1Si-1.5Al-0.045CTWIP钢进行了不同程度的拉伸变形,采用JEM-2100透射电子显微镜对变形后的组织形貌进行表征和分析。研究结果表明:在变形初期,晶粒内存在着大量位错,它们相互缠结,呈胞状结构。在此阶段,位错滑移为主要变形机制。随着变形量的增加,形变孪晶在晶界等处形成,孪生机制被激活,孪生和滑移机制相互竞争。双孪生系统在大多数晶粒内先后被激活,孪生和滑移机制相互交割,起到动态细化晶粒的作用,使强度显著提高。在变形后期,试验钢的变形机制主要是TRIP效应,以及孪生与滑移的相互作用而诱发了去孪生机制,层状组织出现,孪晶特征减弱,从而导致样品的局部变形和失效。     

硅片塑性形变与位错

通过１２００℃、１５ｈ急冷热处理实验，研究了硅中位错对高温塑性形变的影响及热处理过程中位错密度的变化。实验结果表明，硅中原有位错密度越大或热处理急冷温度越高，均使塑性形变更加严重。位错密度为０４～２×１０３ｃｍ－２的硅片的弯曲度变化是无位错硅片的３倍多，１２００℃急冷产生的形变量是７７０℃急冷的４倍。无位错硅片在高温热处理中会产生大量位错，且急冷温度越高，产生的位错越多。热处理中区熔硅片容易在边缘产生位错星形结构。     

形变诱导析出在SAF2205超塑组织细化中的作用

运用变形能、相变温度、原始晶粒尺寸与金属组织细化之间的关系,提出了控制σ相析出的新方法.在此基础上,用分段恒温拉伸的方法,对SAF2205钢恒温热拉伸后的性能和微观组织进行了实验研究.研究结果表明:采用变温的恒温热拉伸方法,通过快速冷却,使σ相的析出发生在变形过程中,细小、弥散分布的σ相可以抑制晶粒的长大;为了保证σ相的形变诱导析出,实现双相不锈钢的低温超塑性变形,需要采用较快的冷却速度.     

WSTi3515S阻燃钛合金超塑性变形行为及本构关系研究

通过电子万能试验机对具有粗大晶粒的β型WSTi3515S阻燃钛合金进行了超塑性拉伸试验,分析了热力学参数对超塑性能及力学行为的影响,建立了该合金超塑性本构关系。结果表明:WSTi3515S阻燃钛合金可在较宽的温度范围及应变速率区间内(800～920℃,0. 000 5～0. 01 s~(-1))实现超塑性;且在高温低应变速率条件下超塑性能良好,最大延伸率可达556%。与细晶超塑性不同,WSTi3515S合金在超塑性拉伸过程中,稳态变形阶段很短甚至不出现,变形主要集中在准稳态变形阶段,且准稳态变形阶段越长,获得延伸率越大。基于Arrhenius方程建立的本构方程精度不高,而由逐步回归法构建的本构方程误差值基本在5%以内。     

Ti-12Co-5Al合金高速低温超塑变形

采用合适的冶炼及形变热处理工艺获得了具有x-Ti+Ti₂Co金属间化合物双相超细组织的Ti-12Co-5Al合金板材。该合金呈现出优异的高速低温超塑性,在700℃的较低温度和3×10^-2s^-1的高应变速率条件下获得了延伸率为1550%的超塑性。微观组织研究表明,超塑变形促进了Ti₂Co粒子的长大和形状变化,且在延伸率达500%时试样中仍无孔洞产生。