纵向磁场对不同尺寸定向凝固高温合金DZ417G组织的影响

进行了外加纵向静磁场下高温合金DZ417G的定向凝固实验,考察了纵向磁场对不同尺寸试样凝固组织形貌的影响.结果显示,在温度悌度为70℃/cm,抽拉速率为5μm/s时,施加磁场后一次枝晶间距减小,并在试样边缘出现等轴晶组织;随着试样尺寸的增大,在试样边缘和中心的柱状枝晶组织遭到破坏,形成等轴晶组织,且出现"斑状"偏析.这些现象可归结为磁场在固/液界面前沿合金熔体中诱发的热电磁对流(TEMC)所致.     

TB9钛合金棒材组织遗传效应与性能

以TB9钛合金为研究对象，对比分析了TB9铸锭不同部位在热加工过程中的组织差异，揭示了TB9钛合金棒材的组织遗传效应及其对性能的影响。结果表明，TB9钛合金铸锭可以分为底部沿轴向的柱状晶区，芯部的等轴晶区，边部与轴向呈45°的柱状晶区。其中铸锭底部的柱状晶具有较强的<100>织构，在随后的锻造和热轧过程中，<100>织构的柱状晶难以破碎，具有很强的遗传性，致使最终棒材尾部残留粗大的柱状晶结构，时效后抗拉强度仅为987 MPa。铸锭芯部等轴晶区没有明显的择优取向，最终制备的棒材晶粒细小，组织均匀，棒材的性能优良，抗拉强度可达1290 MPa。     

A Successful Synthesis of the CoCrFeNiAl0.3 Single-Crystal, High-Entropy Alloy by Bridgman Solidification

For the first time, a face-centered-cubic, single-crystal CoCrFeNiAl_0.3 (designated as Al0.3), high-entropy alloy (HEA) was successfully synthesized by the Bridgman solidification (BS) method, at an extremely low withdrawal velocity through a constant temperature gradient, for which it underwent two BS steps. Specially, at the first BS step, the alloy sample underwent several morphological transitions accompanying the crystal growth from the melt. This microstructure evolves from as-cast dendrites, to equiaxed grains, and then to columnar crystals, and last to the single crystal. In particular, at the equiaxed-grain region, some visible annealing twins were observed, which indicates a low stacking fault energy of the Al0.3 alloy. Although a body-centered-cubic CoCrFeNiAl (Al1) HEA was also prepared under the same conditions, only a single columnar-crystal structure with instinctively preferential crystallographic orientations was obtained by the same procedure. A similar morphological transition from dendrites to equiaxed grains occurred at the equiaxed-grain region in Al1 alloy, but the annealing twins were not observed probably because a higher Al addition leads to a higher stacking fault energy for this alloy.     

柱状晶Cu-Al-Be形状记忆合金低温压缩性能研究

利用竖直下拉式热型连铸技术制备柱状晶Cu-Al-Be形状记忆合金,其马氏体相变结束温度(Mf)在-50℃以下,柱状晶生长方向为轴向。在温度低于Mf时,对普通多晶、平行于柱状晶方向和垂直于柱状晶方向的试样分别进行单向压缩试验,并进行金相组织观察与断口形貌分析。结果发现,柱状晶Cu-Al-Be合金杆件组织结构为类似于贝壳的仿生结构且断裂形式相似,垂直于柱状晶方向的试样塑性最好,断裂前吸收能量最高,综合性能最好。     

Microstructure and crystal growth direction of Al-Mg alloy

The microstructures and crystal growth directions of permanent mould casting and directionally solidified Al-Mg alloys with different Mg contents have been investigated. The results indicate that the effect of Mg content on microstructure is basically same for the alloys prepared by these two methods. The primary grains change from cellular crystals to developed columnar dendrites, and then to equiaxed dendrites as the Mg content is increased. Simultaneously, both the cellular or columnar grain region and the primary trunk spacing decrease. All of these changes are mainly attributed to the constitutional supercooling resulting from Mg element. Comparatively, the cellular or columnar crystals of the directionally solidified alloys are straighter and more parallel than those of the permanent mould casting alloys. These have straight or wavy grain boundaries, one of the most important microstructure characteristics of feathery grains. However, the transverse microstructure and growth direction reveal that they do not belong to feathery grains. The Mg seemingly can affect the crystal growth direction, but does not result in the formation of feathery grains under the conditions employed in the study.     

Dendrite fragmentation and columnar-to-equiaxed transition during directional solidification at lower growth speed under a strong magnetic field

The effects of strong magnetic fields on the columnar-to-equiaxed transition (CET) have been investigated experimentally. Six alloys have been directionally solidified at low growth speeds (1–10 μm s^?1) under magnetic fields up to 10 T. Experimental results show that the application of a strong magnetic field causes a dendrite fragmentation and then the CET. The thermoelectric magnetic force acting on cells/dendrites and equiaxed grains in the mushy zone has been studied numerically. Numerical results reveal that the value of the thermoelectric magnetic force increases as the magnetic field intensity and the temperature gradient increase. A torque is created on cells/dendrites and equiaxed grains. This torque breaks cells/dendrites and drives the rotation of equiaxed grains. The rotation of equiaxed grains in the mushy zone will further destroy cells/dendrites. Thus, with the increase of the magnetic field intensity and the temperature gradient, the volume fraction of equiaxed grains in front of columnar dendrites increases. When the magnetic field intensity and the temperature gradient reach a critical value, the growth of columnar dendrites is blocked and the CET then occurs. The present work may initiate a new method of inducing the CET via an applied strong magnetic field during directional solidification.     

EFFECTS OF WITHDRAWAL RATE ON MICROSTRUCTURE AND STRESS RUPTURE PROPERTIES OF A Ni3Al–BASED SINGLE CRYSTAL SUPERALLOY IC6SX

采用螺旋选晶法制备Ni₃Al基单晶合金IC6SX试棒, 研究了不同拉晶速率对凝固组织和高温持久性能的影响. 结果表明, Ni₃Al基单晶合金IC6SX凝固组织为树枝状, 随着拉晶速率从1.5 mm/min增加到6 mm/min, 一次枝晶间距逐渐减小. 与普通镍基高温合金不同, 位于枝晶干处的次生γ'相尺寸比枝晶间处的大. 随着拉晶速率的增加, 枝晶干和枝晶间处的γ'相尺寸都逐渐减小, 由不规则形状逐渐立方化, 枝晶间处的初生γ'相的数量逐渐增多. 一次枝晶间距和γ'相尺寸对高温持久性能影响显著, 随着拉晶速率的增加, 组织细化, 铸态IC6SX单晶合金的高温持久寿命增加.     

Microstructure and properties evaluations of spot-welded ferritic steel sheets via static magnetic field

Ferritic steel spot nuggets were produced with or without a static magnetic field. The microstructures and properties evaluations of the nuggets with or without a static magnetic field were investigated. Disordered columnar grains and some equiaxed grains among the columnar grains with a static magnetic field were discovered in this study. Based on the evaluations of the microstructure and properties, the nugget mechanisms, strengthening mechanisms, and infrared behavior of the joint were discovered. The diameter and strength of each nugget were improved with the application of a static magnetic field. The welding time and the welding force can both influence the nugget characteristics via a static magnetic field. The tensile strength of the spot joint regularly varied with magnetic field; the maximum value was 245 MPa, 11%, which was approximately 30% higher than that of the nugget without magnetic field (187 MPa, 3.8%). The magnetization force applied on the dendrite at the same time can cause the columnar dendrite to deform, break and deflect from the direction of solidification.     

连续铸造Ag-28Cu合金的组织形貌表征

采用连续铸造技术制备了Ag-28Cu合金棒材,用金相显微镜(OM)与扫描电镜(SEM)对其组织形貌进行了分析表征。结果表明,Ag-28Cu连铸合金的组织均为典型的三区结构:细等轴晶区、柱状晶区和中心的等轴晶区,在铸锭中还散落着形貌清晰、形态规整的白色枝晶。     

IN718合金增材制造温度场仿真及微观组织分析

针对微观组织的调控相关问题,构建了IN718材料激光选区熔化(selective laser melting,SLM)温度场仿真的三维有限元模型,研究了激光功率和扫描速度对熔池温度场和凝固机理的影响,进而预测增材制造材料的微观组织,为微观组织的调控提供理论依据.首先分析了激光功率和扫描速度对熔池尺寸的影响,分析了不同工...     

连铸空心管坯内置行波磁场对凝固组织的影响

利用低熔点Sn-3．5％Pb合金进行了空心管坯内置行波磁场的静态模拟实验研究。结果表明：管坯内置行波磁场可以引起金属熔体内部纵截面上的大环流，减小了熔体凝固前沿的温度梯度，降低了金属熔体的冷却速率，抑制了熔体的枝晶生长，从而促进了晶粒的球化，改善了管坯的凝固组织。     

退火处理及沉积方向对激光沉积TA15钛合金性能和组织的影响

以TA15钛合金粉末为原料,利用激光沉积制造方法制备TA15钛合金拉伸试样厚壁件。通过光学显微镜(OM)、扫描电子显微镜(SEM)和X射线衍射(XRD)等方法研究退火温度及沉积方向对TA15钛合金组织、拉伸性能的影响,以及α相变形机制。结果表明：随着退火温度升高,显微组织中α相长宽比呈上升趋势;激光沉积成形TA15钛合金厚壁件在沉积和垂直沉积方向上的力学性能存在差异,沉积方向上的抗拉强度明显均低于垂直沉积方向上的抗拉强度;柱状晶晶界对α片层的受力变形有一定的阻碍作用;α片层通过挤压变形和滑移变形两种机制发生变形或断裂;两种方向上拉伸断裂方式不同,沿沉积方向上断裂为韧性断裂,沿垂直沉积方向上断裂为半解理半韧性断裂。     

Zn—Al合金热型连铸定向凝固的晶体生长机理

对热型连铸条件下Zn-Al系列合金引锭时的晶体形核和随后的本的竞争生长过程进行了探讨,组织观察表明,单向热流条件下引锭端部生核的晶粒当其枝晶择优生长方向与热流方向一致时才能生长,其它取向的晶粒逐渐被淘汰,合金的凝固特性对选晶过程有极大的影响,ZA5和ZA8合金由于凝固范围窄,晶体直接由引锭端部的晶粒通过竞争生长获得柱状晶组织,ZA12,ZA22和ZA27含Al量高,凝固范围宽,其平行柱状晶组织是从引锭端部的等轴晶区发展而来的。     

脉冲电场对Al-5.6%Cu合金柱状晶间距的影响

运用定向凝固方法,在凝固过程中将脉冲电场平行地作用于Al-5.6%Cu合金柱状晶的生长方向上,考察了不同脉冲电场电压及冷却速度对柱状晶间距的影响.试验结果表明:随着脉冲电场电压的升高,柱状晶间距呈直线上升的趋势;冷速越大,不同脉冲电场时的柱状晶间距与原始状态下柱状晶间距差值的变化幅度越大,即脉冲电场作用效果对冷速的响应越明显.     

ULCB钢焊接熔池凝固过程数值模拟

采用元胞自动机法建立ULCB钢焊接熔池凝固过程的宏微观耦合模型,模拟非均匀温度场下焊接熔池凝固过程的组织形貌演变和溶质场分布,分析不同形核参数和合金成分对焊接熔池枝晶形貌的影响。结果表明,熔池边缘形成柱状晶,熔池中心形成等轴晶,柱状晶和等轴晶相互抑制长大;枝晶生长过程中始终存在着枝晶偏析现象;形核密度和合金成分影响枝晶的形核和生长,随着形核密度和合金成分的增加,焊缝中等轴晶区域增加,晶粒细化。     

STRUCTURE OF Al-Cu EUTECTIC ALLOY SOLIDIFIED IN COMPLEX FIELD OF CENTRIFUGAL AND ELECTROMAGNETIC FORCES

1.IntroductionMuchattentionhasbeenpaidtothefluidnowinsolidification,whichdramaticallyinfluencesthestructureandsegregationinalloysandfinallydeterminesthepropertiesofcastingsl'].Onewaytoproducemeltflowisbytheapplicationofmagneticfield,andthismethodhasbeenwidelyusedincontinuouscastingandothelmetallurgicalprocesses[2,31.Electromagneticcelltrifugalcastingisanovelandpromisingtechniqueofmaterialpro-cessing,andlittleknowledgeonsolidificationinthisprooes3restraillsitsapplicationinindustry.InEMCCproce…     

Giant magnetocaloric effect in a Heusler Mn50Ni40In10 unidirectional crystal

A modified high-pressure optical zone-melting technique was used to grow a Mn-rich Heusler Mn₅₀Ni₄₀In₁₀ unidirectional crystal. Experimental results showed that the produced unidirectional crystal underwent a magnetic transition in austenite, followed with a martensitic transformation from a ferromagnetic austenite to a ferromagnetic martensite upon cooling. Under a magnetic field change of 30 kOe, the total effective refrigeration capacities (RC_total) reached as high as 231.58 J/kg when the magnetic field was applied along parallel to the crystal growth direction, or 246.79 J/kg when the magnetic field was applied along perpendicular to the crystal growth direction. It was suggested that this unidirectional crystal growing technique may provide an effective approach to enhance the magnetocaloric effect of Mn-rich Heusler materials.     

磁场和NiCl2联合作用下镁合金焊接接头的显微组织和力学性能

为了分析磁场和活性剂联合作用下镁合金焊接接头的显微组织和力学性能变化规律，采用A-TIG焊接AZ91镁合金，并在试验过程中引入纵向交流磁场，实现磁场和活性剂联合作用下镁合金的TIG焊接. 对不同活性剂涂覆量下焊接接头的成形性、物相组成、显微组织、力学性能进行检测，分析磁场和活性剂联合作用下电弧形态和熔池金属结晶形核特点，探讨其中的机理. 试验结果表明，磁场的引入对增加熔深、提高焊接效率产生负面影响，但是对提高焊接接头力学性能作用效果十分明显，在所选磁场参数下，活性剂涂覆量为3 mg/cm2时，焊接接头的成形状态和组织性能达到了最佳匹配，此时成形系数为2.38，焊缝抗拉强度和断后伸长率分别为338 MPa和13.3%；磁场和活性剂的联合作用下，电弧呈螺旋下沉旋转运动，并带动熔池运动，改变晶体结晶条件，促进细小等轴晶形成和孪晶的出现，使得焊接接头的力学性能得到提升；同时，磁场的引入可以改变晶体的生长模式，晶体沿(0001)晶面出现择优生长现象.     

激光表面熔覆制备ODS Ni基高温合金涂层的凝固组织

采用横流CO2激光，在Ni基高温合金表面制备了纳米Al2O3弥散强化(ODS)Ni基合金熔覆层。利用光学显微镜、扫描电镜及EDS附件分析了熔覆层的组织结构。结果表明：界面晶粒的生长方向为垂直于界面的“外延式”生长；加入纳米Al2O3，界面的生长形态发生变化，由细长的柱状树枝晶转变为较短的树枝晶；纳米Al2O3含量增大至1％时整个断面获得等轴枝晶组织；纳米Al2O3作为异质形核的核心，细化了组织。     

一种镍基单晶叶片叶身-缘板转接区铸造缺陷的形成机理

某种铸态镍基单晶叶片腐蚀后,观察到叶身-缘板转接区存在一种形状规则的条带状杂晶缺陷,且具有方向性,其长度方向平行(或垂直)于叶身和缘板的枝晶生长方向。采用光镜法(OM)、电子探针(EPMA)和电子背散射衍射技术(EBSD),分别研究了缺陷的组织、成分、取向,采用ProCAST模拟研究了缘板区域的温度场和过冷度分布。研究结果表明,叶身-缘板转接区杂晶缺陷由多个柱状晶粒构成;柱状晶粒的组织和成分与缘板基体一致,与基体的取向差形成小角度和大角度晶界;叶身-缘板转接区的过冷度比缘板边缘小,为缘板上的最后凝固区域。在此基础上,提出叶身-缘板转接区杂晶缺陷的形成机理,为消除该缺陷提供了理论基础。