工业纯钛板材的轧制织构及微观组织对其孪晶和再结晶行为的依赖性

将工业纯钛（CP-Ti）板轧制至不同程度,随后进行退火以及进行20%的再轧制。通过电子背散射衍射（EBSD）对合金微观组织的变化进行表征。重新轧制后,｛112｝<23>压缩孪晶和｛102｝<101>拉伸孪晶产生。可以观察到孪晶的层状结构,这是由变形孪晶的缠结以及二次和三次孪晶的产生引起的。平均晶粒尺寸和孪晶量之间没有简单的关联。0.5 h退火样品中的晶粒尺寸随其预变形程度的增加而显著减小。重新轧制倾向于使晶格的重新取向更接近法线方向。虽然织构变化和孪晶体积分数很小,但平行于RD方向的｛100｝纤维织构仍然保留。     

基于VPSC仿真的ZK60镁合金拉伸变形行为

通过实验和粘塑性自洽（VPSC）模型,研究了在室温下挤压态ZK60镁合金沿不同方向拉伸时的变形机制开动情况,及其与流动曲线、织构演变和显微组织的对应关系。通过调节VPSC模型的参数,建立了滑移和孪生耦合的晶体塑性力学模型。比较了不同方向拉伸过程中织构演变的差异,分析了变形机制对屈服不对称性的影响。实验和模拟结果表明：当沿垂直于挤压方向（PED）拉伸时,由于｛102｝孪晶开动,大部分晶粒发生大角度旋转（约90°）。柱面<a>滑移是导致ZK60合金沿不同方向拉伸时出现明显屈服不对称的主要变形机理。当ZK60合金沿挤压方向（ED）拉伸时,由于晶粒的择优取向分布,｛101｝孪晶难以开动,导致ZK60挤压态镁合金拉伸屈服强度较高。ZK60镁合金沿着与ED成45°的方向拉伸时,屈服应力高于沿PED拉伸,但随着拉应力逐渐增大,由于沿PED拉伸时柱面<a>滑移逐渐开动,沿PED应变后期的应力曲线逐渐高于沿与ED成45°方向应变的应力曲线。     

初始织构对差厚板非均匀塑性变形的影响

CR340轧制差厚板（TRB）在轧制过程中,其不同的厚度区形成了不同的织构,分别是薄区的{111}<01>和{141}<22>织构,过渡区的{225}<10>和{211}<01>织构,厚区的{876}<5>和{411}<01>织构。根据EBSD测试结果,建立了各厚度区的多晶体塑性有限元模型,研究了单向拉伸时各厚度区的晶粒织构对滑移系开动情况和应力应变分布的影响规律。结果表明,薄区的{111}<01>织构和厚区的{876}<5>织构有利于滑移系的开动,开动的数量分别为9和8组,这使得等厚区在变形中的应力集中弱化,具有良好的塑性变形行为。而过渡区的{225}<10>、{211}<01>织构的晶粒滑移系开动较少,开动的数量分别为6和7组,导致应力集中,其塑性变形行为较差。差厚板各厚度区织构的差异导致其塑性变形呈现明显的不均匀性,其断裂位置发生在单轴拉伸时塑性变形较差的过渡区。     

大晶粒纯镁疲劳变形过程中交叉滑移迹线的分析

在室温条件下研究了大晶粒纯镁疲劳变形过程中有可能激活的滑移系统及滑移迹线。结果表明,经过疲劳变形后大量的纵横交叉滑移迹线在样品表面产生,基于晶粒取向与滑移迹线方向的综合判定,这种纵横交叉滑移迹线是由反复疲劳变形过程中基体的基面滑移与同一区域内｛102｝孪生过程中所再次产生的基面滑移而形成。通过实验观察到最有可能发生的锥面滑移系统为在｛101｝面上所产生的<113>锥面滑移,但总体上来说,基面的滑移迹线比锥面的滑移迹线更密集,这说明锥面滑移在整个疲劳变形过程中被抑制。     

镍基高温合金在变形热处理过程中的组织和织构演变

采用电子背向散射衍射技术研究了镍基高温合金冷变形和再结晶退火过程中的组织演变、晶界特征分布、应变分布及织构演变规律。结果表明,当冷变形量较小（ε≤45%）时,晶粒沿着轧制方向被拉长,呈扁平状于基体中均匀分布,应力主要集中在晶界和孪晶界（TB）附近,大角度晶界（HAGBs）和TBs逐渐向亚晶界（Sub-GBs）和小角度晶界（LAGBs）转变。同时,出现Goss织构 {110}<001>、Brass-R织构{111}<112>、Twinned-Copper织构{552}<115>和Copper织构{112}<111>。当轧制压下量超过70%时,晶粒形状逐渐从扁平变为纤维状,晶粒的变形均匀性逐渐变好,应变分布变得均匀,LAGBs开始占主导地位。同时,织构类型保持不变,但织构强度增加。在1120 ℃退火15 min后,孪晶的长度分数随着轧制压下量的增加而增加。同时,变形织构转变为再结晶织构,织构类型增加,但织构强度减弱。此外,当退火孪晶的比例增加时,Copper织构{112}<111>不断向Twinned-Copper织构{552}<115>转变,并且经过30%~80%轧制变形的试样产生织构{124}<211>。     

室温变形γ—TiAl基合金中形变孪晶与α2片的交截机制

利用透射电镜在室温变形的γ-TiAl基合金中研究了一种新的形变孪晶与α2片的交截机制.选区电子衍射和矩阵分析结果表明γ基体中的形变孪晶切过α2片时,如果形变孪晶的宽度与α2片宽度相当,则α2片可以通过K1={3031},η1=1/18<10 16>的孪生机制来协调形变孪晶产生的切变.由于α2片与γ基体之间存在(0001)α2∥{111}γ,<1120>α2∥<011>γ的晶体位向关系,α2片的1/18<10 16>{3031}切变矢量等价于形变孪晶的切变矢量1/6<112]{111},因此形变孪晶产生的切变可完整地切过α2片而不需要交截区附近γ基体中其它滑移系或孪晶系开动来辅助协调变形.     

Ti-6Al-3Nb-2Zr-1Mo钛合金在低温高应变速率下的变形行为

在变形温度为193~298 K、应变速率为2000~3000 s^-1的范围内,对Ti6321钛合金进行动态压缩试验,研究温度和应变速率对材料力学性能和变形行为的影响。采用光学显微镜（OM）、透射电子显微镜（TEM）和电子背散射衍射（EBSD）表征和分析了合金的微观结构演变。结果表明,随着温度的降低和应变速率的增加,Ti6321钛合金的动态屈服强度和平均流动应力均增大,而断裂应变明显降低。采用Johnson-Cook本构方程预测了Ti6321钛合金在低温高应变速率下的力学行为,拟合结果与实验结果吻合较好。微观结构分析表明,随着变形温度的降低,｛112｝和｛101｝2种孪晶的含量明显增加,即变形机制逐渐由孪晶的辅助作用转变为孪晶占主导地位。     

大型TC18钛合金棒材多火次锻造过程的织构演变模拟

使用了一种多尺度耦合的方法来预测织构。首先采用宏观有限元方法,模拟了TC18钛合金棒材在接近实际工艺条件下的多火次锻造过程,并得出了在锻造过程中棒材芯部与边部的等效应变及剪切应力σ_XY分布不均匀的特征。然后,通过宏观有限元模型与介观粘塑性自洽模型（VPSC）多尺度耦合的方法模拟得到了锻造过程中棒材芯部和边部织构的演变情况。结果表明,六方锻造方式使棒材芯部由｛110｝<112>织构过渡到｛111｝<110>织构,并由｛110｝<110>织构过渡到｛111｝<110>织构。整个锻造过程中即是｛111｝型织构与｛110｝型织构相互转变的过程。这种过渡织构在极图中呈现出类似于剪切织构的特点,经分析：这种织构并非是剪切织构,而是锻造过程中由六方锻造方式和｛110｝、｛111｝型2类织构间的相互转变共同作用下形成的。经过棒材的形变过程,边部形成了｛100｝和｛111｝型2种织构。通过对比发现,六方锻造方式不仅不易生成｛100｝型织构,而且有利于｛100｝型织构的减弱和消除。拉伸试验结果表明,六方锻造样品的力学性能均达到标准要求。     

冷却介质对商业纯钛 β→α 相转变组织及织构的影响

利用OM、ECC、EBSD、TEM等表征技术和显微硬度实验研究了经β固溶处理的商业纯钛板材在β→α相变过程中不同冷却介质对其组织演变、变体选择、织构遗传及力学性能的影响。结果表明：随着冷却速率的降低,相变组织依次呈细针状α′马氏体（水冷和液氮冷）、Widmanst?tten组织（空冷）及粗大晶粒（炉冷）,且冷却速率越快,则转变组织越细,进而其硬度值越高。在β→α冷却过程中,只有炉冷条件下由于出现了部分不满足Burgers关系的取向,导致其并不严格遵循Burgers取向关系。与原始组织相比,水冷和液氮冷条件下由于出现新的织构成分（<0001>//TD、<110>//ND）,导致其织构分布更分散;炉冷条件下由于发生了强烈变体选择而出现织构遗传现象,导致更强的相变织构。因此可以通过提高冷却速率来抑制变体选择,进而弱化相变织构。     

TB17钛合金在等温时效过程中的相析出行为

采用X射线衍射、扫描电子显微镜、透射电子显微镜和硬度测试分析了新型超高强韧钛合金TB17在等温时效过程中析出相的演变及时效响应。结果表明：该合金在350 ℃时主要发生β→β+ω相变,ω相为细小的颗粒。在450 ℃下进行时效处理时,α相通过ω相辅助形核的方式形核长大。在550和650 ℃时主要发生β→β+α相变,α相为片层状。在该温度范围内长时间进行时效处理的TB17合金存在2种类型α相,满足Burgers关系的1α相和不满足Burgers关系的2α相。其中2α相为孪晶α相,在1α相内部｛102｝孪晶面形核,并不断消耗1α相而长大。TB17钛合金的时效特征与其他β型钛合金相似。TB17钛合金的时效响应快,显微硬度随着时效温度升高呈现出先增加后降低的趋势,在450 ℃时效处理下硬度达到最大。     

Effect of deformation texture on the anisotropy of elasticity and damage of two-phase steel sheets

The effect of small tensile deformation (3, 6, and 10%) on the texture of preliminary annealed sheets of two-phase DP600 steel (0.10 C, 0.15 Si, 1.4 Mn, 0.007 P, 0.008 S, 0,009 N, 0.02–0,06 Al, 1 Cr–Mo–Ni (wt %)) is studied. Against the background of the annealing texture in the sheets, the {001} <110>, {111} <110>, {111} <112>, {111} <312> components of the slip texture and {115} <110>, {115} <552>, {221} <110>, {221} <114> orientations are developed, which can be associated with the twinning processes. The anisotropy pattern of the Young’s modulus (E) in the sheet plane remains the same after tensile deformation of the annealed sheets. After tension, the values of E decrease in all directions as a result of the onset and development of microdamages. The anisotropy of damage (D) in the plane of the steel sheets after tension is characterized by a maximum in the transverse direction (TD) and a minimum in the rolling direction (RD).     

Crystal plasticity finite element simulation of NiTi shape memory alloy based on representative volume element

Crystal plasticity finite element method based on a representative volume element model, which includes the effect of grain shape and size, is combined with electron backscattered diffraction experiment in order to investigate plastic deformation of NiTi shape memory alloy during uniaxial compression at 400 °C. Simulation results indicate that the constructed representation of the polycrystal microstructure is able to effectively simulate macroscopically global stress-strain response and microscopically inhomogeneous microstructure evolution in the case of various loading directions. According to slip activity and Schmid factor in {110}<100>, {010}<100> and {110}<111> slip modes, <100> slip modes are found to play a dominant role in plastic deformation, while <111> slip mode is found to be a secondary slip mode. In addition, the simulation results are supported well by the experimental ones. With the progression of plastic deformation, the (001) [\(0\bar 10\)] texture component gradually disappears, while the γ-fiber (<111>) texture is increasingly enhanced.     

Effect of crystallographic anisotropy of β-tin grains on thermal fatigue properties of Sn–1Ag–0˙5Cu and Sn–3Ag–0˙5Cu lead free solder interconnects

Abstract

An effect of the crystallographic anisotropy of β-tin grains on thermal fatigue properties of Sn–1Ag– 0˙5Cu and Sn–3Ag–0˙5Cu lead free solder interconnects were discussed. From an orientation imaging microscopic observation, three types of microstructures (single crystal-like, fine grain type and large grain type) were observed in both solders. The single crystal-like microstructure disappeared and the large grain type occurred by further fatigue due to recrystallisation. Because single crystal-like microstructure had the {100} plane approximately parallel to strain concentrated areas, recrystallisation could be retarded if the slip systems of {100}<011> or {100}<010> operate and an amount of thermal strain decreases because these slip systems have the larger critical resolved shear stress due to an anisotropic nature of β-tin. One of the reasons Sn–3Ag–0˙5Cu had longer thermal fatigue life than Sn–1Ag–0˙5Cu can be the number of the single crystal-like or the fine grain type microstructures in Sn–3Ag–0˙5Cu were larger.     

Study on the cold rolling deformation behavior of polycrystalline tungsten

Tungsten is paid special attention due to its superior properties, especially in nuclear field. Meanwhile it is suitable for texture simulation investigation of BCC metals and alloys as it's near elastically isotropic. This study investigates the cold rolling deformation texture of polycrystalline tungsten using RS model, in which the stress and strain consistence is realized simultaneously. The texture evolution and effects of deformation parameters, including external as well as internal reaction stress, strain and activation of different slip, on texture during rolling are discussed by comparing the simulated results and reported experimental results in literatures. The results show that, the cold rolling deformation texture could be simulated statistically based on RS model. The accumulation of each reaction stress is different. The up-limit of reaction stress σ'₁₂ is found to be medium, meaning that σ'₁₂ exerts important effect on texture evolution. Much lower accumulation level of σ'₁₃ as well σ'₂₃ is displayed, each of which within certain range contributes to the increase of different γ-fiber texture components. The effect of σ'₂₂ can't be ignored during rolling, especially in the case of obtaining {111}<110> texture. Regarding the deformation textures of tungsten rolled to true strains of −1.7 and −2.91, {001}<110> texture is strengthened with the increasing strain and becomes dominant, implying the easier activation of {112}<111> slip systems; γ-fiber texture is weakened at higher strain, and the formation of {111}<112> texture shows significant effect of surface shear stress σ₁₃, which is due to the nonnegligible surface friction when rolling at high temperature.     

Dislocation core structures and yield stress anomalies in molybdenum disilicide

Stacking fault energies in MoSi₂ due to shear along <331> have been calculated by modified embedded atom method (MEAM) calculations. Preliminary calculations have also been made of dislocation core structures and their response to applied stress. The results are used to investigate the configuration and mobility of 1/2<331> dislocations. Shear of 1/6<331> in the {103} plane of MoSi₂ produces an anti-phase boundary (APB) whose geometry, called APB(1), is different from that produced by 1/6<331> in the opposite direction, APB(2). Calculations show that APB(1) is stable and APB(2) is unstable. MEAM calculations show that there is a stable fault close to APB(2) with a displacement of ∼1/8<331> in the same direction. The {103} planes have an unusual five layer stacking sequence with successive planes offset by 1/5<301>. Shear of 1/10<351> in the correct direction gives a low energy intrinsic fault. This vector is close to the 1/8<331> shear that produces a stable fault. Various dissociated configurations of 1/2<331> dislocations are considered based on these partials. All can have asymmetrical arrangements which will respond differently to the direction of the applied stress, explaining the yield stress asymmetry in MoSi₂. All of the slip systems (<100>{0kl} and <111>{110} as well as <331>{103}) exhibit yield stress anomalies at different temperatures. Different core configurations at high and low temperatures are used to explain the phenomena.     

Mechanical Properties and Deformation Mechanisms of Mg-Gd-Y-Zr Alloy at Cryogenic and Elevated Temperatures

In this study, mechanical properties and deformation mechanisms of Mg-Gd-Y-Zr alloy at temperatures ranging from 77 K to 523 K have been investigated. The effects of temperature on the mechanical properties, deformation mechanism, and fracture mechanism are discussed. The results show that the strengths of alloy decrease gradually while the elongations increase progressively with increasing temperature. The maximum ultimate tensile strength of the alloy as high as 442 MPa is obtained at 77 K. As the temperature increases from 77 K to 523 K, the ultimate tensile strength of the alloy decreases from 442 MPa to 254 MPa and the elongations increase from 6.3% to 28.9% gradually. The study verifies that the deformation at 77 K is predominated by basal slip and \({{\left\{ {10\bar{1}2} \right\}} \mathord{\left/ {\vphantom {{\left\{ {10\bar{1}2} \right\}} {\left\langle {10\bar{1}1} \right\rangle }}} \right. \kern-0pt} {\left\langle {10\bar{1}1} \right\rangle }}\) deformation twinning system. At 223 K, lots of twins emerge primarily at grain boundaries. At 373 K, all dislocations are proved to be 〈a〉 dislocations. At 523 K, although basal slip is still the dominant deformation mechanism, non-basal slip systems also become activate.