过冷Ni-1at%Fe合金晶粒细化及再结晶机理分析

通过熔融玻璃净化与循环过热相结合的方法研究了过冷Ni-1at%Fe合金的微观组织演化及再结晶。通过再辉后快淬和空冷实验对比,证明大过冷下的细化组织是再结晶的产物。结合无量纲过热度的计算,系统考察了合金凝固组织随过冷度的演化规律。研究发现合金的凝固组织在所获得的过冷度范围内发生了两次晶粒细化,第一次细化归因于枝晶的熟化和重熔导致的高度发达树枝晶碎断,第二次细化归因于应力积累导致的再结晶。     

孪晶类型对AZ31镁合金静态再结晶的影响

对轧制下压方向平行和垂直晶粒c轴的两类板材进行150℃轧制(5%下压量)后,利用背散射电子衍射分析(EBSD)研究了轧制试样中不同类型的孪晶组织对静态再结晶的晶粒形核、微观组织及织构的演变的影响。结果表明:含有大量{1011-}-{1012-}双孪晶的样品中,二次孪生有效促进再结晶形核,显著细化晶粒。再结晶晶粒取向规律性不强,有效削弱基面织构。而含有大量{1012-}拉伸孪晶的样品,拉伸孪晶不能有效促进再结晶形核。退火过程中基体不断长大,当再结晶驱动力足够大时,基体会吞并周围拉伸孪晶,同时诱发织构改变,基体取向的织构逐渐增强,拉伸孪晶取向的织构逐步减弱。     

深过冷Cu_(98)Co_2合金的凝固组织演化

采用熔融玻璃净化配合循环过热的净化技术,对Cu98Co2合金进行了系统的深过冷实验。分别采用空冷与快淬两种冷却方法,在一定过冷度和冷却速率相结合下制备出单相固溶体探讨了过冷度及冷却速率对凝固组织的影响。实验结果表明,随过冷度提高凝固组织呈现粗大树枝晶→细小粒状晶→定向细枝晶→粗大粒状晶的演化趋势,基于枝晶生长模型,解释了上述凝固组织演化规律。在大过冷度下,由于该合金具有高层错能和高形核率,再结晶和晶粒长大迅速发生,凝固组织为晶界平直的粗大等轴晶。     

AZ31镁合金再结晶退火的准原位EBSD研究

对AZ31镁合金热挤压板进行室温轧制(形变量为8%)后,利用背散射衍射技术原位(in-situ EBSD)观测了轧制试样中不同类型的孪晶组织在再结晶退火过程中的取向演变。结果表明:退火过程中拉伸孪晶区域形成尺寸相对粗大的再结晶新晶粒,再结晶晶粒取向与拉伸孪晶的取向较为接近;压缩孪晶/双孪晶区域形成了细小的再结晶晶粒,再结晶晶粒偏离基面取向。孪晶再结晶显著影响镁合金在退火过程中的织构演变,轧制样品中,拉伸孪晶再结晶使得基面织构强度增强,压缩孪晶再结晶则可以在一定程度上弱化镁合金的基面织构。     

AZ31镁合金中拉伸孪晶静态再结晶的分析

基于前期工作对压缩孪晶静态再结晶的分析,主要利用XRD和EBSD技术进一步研究AZ31镁合金中拉伸孪晶静态再结晶过程中组织和织构的演变规律,以及再结晶初期新晶粒的取向特征,结果表明:拉伸孪晶不能有效地促进再结晶形核,其细化晶粒的效果不显著,其再结晶速率显著延迟于压缩孪晶;退火过程中并没有生成新的再结晶织构组分,表现为初始基面织构的减弱;新晶粒优先在拉伸孪晶的变体交叉处,或拉伸孪晶与压缩孪晶的交叉处形核,但其取向规律性不强,没有遵循初始拉伸或压缩孪晶内的取向规律,同时还对拉伸与压缩孪晶的再结晶行为进行了比较。     

不同轧制工艺对纯锡微观组织与性能的影响

本工作系统研究多晶纯锡(99.99%)在不同轧制工艺下的显微组织演变和力学行为,阐明纯锡在不同轧制状态下晶粒细化规律,以期为调控与优化纯锡的强韧化奠定理论基础。研究结果表明,不同轧制工艺对纯锡的微观组织和力学性能影响明显,其中轧制速度是影响纯锡的晶粒细化和力学性能提升的最主要因素,温度、速度和路径通过调控变形过程中的孪晶激发以及孪晶诱导再结晶的进程而实现不同工艺下的晶粒细化。轧制过程晶粒细化机制为：变形初期诱发60°<100>形变孪晶,在后续变形过程中孪晶逐渐演变为再结晶条带状组织,分割细化晶粒,且孪晶和再结晶组织的随机取向弱化原始粗晶产生的集中织构。轧制变形能明显提高纯锡的强度,且单向轧制工艺下的纯锡样品的TD方向的屈服强度和抗拉强度明显高于RD方向。     

大过冷度下Ni_(54.6)Pd_(45.4)合金的再结晶

通过将不同冷却阶段的试样淬火,研究了再结晶诱发的块状过冷Ni54.6Pd45.4合金的组织演化。结果表明,当过冷度大于临界过冷度时,由于再结晶引起的晶粒细化起始于快速凝固阶段结束之时,并在随后的冷却过程中发展。再结晶初始阶段由于晶核形成,导致晶粒尺寸降低。随后,由于晶粒的相互吞并长大占主导地位,晶粒尺寸增加。随着凝固前过冷度的增加,快速凝固的枝晶骨架间的变形程度增加,再辉温度在高温阶段停留的时间也降低。最终使得再结晶晶粒尺寸下降。     

Ni-B共晶合金非平衡凝固组织形态研究

采用熔融玻璃净化与循环过热相结合的深过冷技术,研究共晶合金Ni-3.6%B在不同的冷却速率和过冷度下凝固的室温组织变化规律。结果表明,过冷度和冷却速度都对凝固组织形态有重要影响,过冷度从16 K逐渐增加到301 K,熔断后的初生相-αNi由棒状晶转变为粒状晶,共晶组织从层片状转变为非规则点状组织;在大过冷条件下,改变冷却条件,冷却速率由真空炉中空冷、水淬、Ga-In合金淬冷和铜模激冷逐次增加,则所得室温共晶组织形态会由非规则点状转变为规则层片状。进一步理论分析表明,在小过冷条件下,共晶合金Ni-3.6%B的室温组织形态主要由过冷度决定,而在大过冷条件下,共晶组织形态则由冷却速率决定。     

利用道次间退火改善镁合金轧制成形性的研究

塑性较差的六方结构镁合金轧制时易出现裂纹,尤其是在1mm以下薄板带的终轧阶段。其原因是在较低温度下基面取向晶粒内形成的切变带不易扩展所致。研究了MB1,AZ31(MB2)镁合金在热模拟条件和实验室热轧过程中利用静态再结晶改善形变组织、细化晶粒、提高成形性的规律。实验表明,在选择的多道次轧制退火工艺下可顺利轧出0．3mm厚的薄板带,得到平均尺寸～7μm的等轴细晶。热模拟条件下得到的形变温度、形变量和形变组织的关系可帮助确定实际生产轧制过程中各道次轧制的温度。织构测定表明,各阶段退火前后都得到强的基面织构。终轧阶段无法利用{10^-12}拉伸孪晶的静态再结晶细化晶粒,而只能利用压缩孪晶／扩展的切变带的再结晶细化晶粒。本文对轧制时利用动、静态再结晶细化晶粒的潜力及工艺优化进行了讨论。     

退火处理对稀土镁合金组织和性能的影响

研究了退火制度对一种稀土镁合金微观组织演变和力学性能的影响。利用光学显微镜和扫描电镜观察显微组织，用XRD进行物相分析和织构分析，并在万能拉伸试验机上进行了力学性能测试。结果表明，随着退火温度的升高，形变孪晶逐渐消失，变形晶粒发生回复和再结晶，平均晶粒逐渐长大，由200℃时的6.35μm长大到350℃时的12.45μm,增大了96.1%。退火时间对稀土镁合金晶粒尺寸和织构构成的影响较小。稀土镁合金的基体晶内和晶界处分布着Al₂Y相，在液相中结晶，同时在固相中析出，凝固过程抑制α-Mg结晶晶粒的长大，细化凝固态初始晶粒尺寸；Al₂Y相在形变和热处理过程钉扎再结晶晶粒晶界，细化晶粒。随退火温度的升高，屈服强度和抗拉强度先降低后升高，伸长率先升高后降低。稀土镁合金试样经300℃保温60 min的退火处理后可获得最低的屈服强度和抗拉强度，分别为158 MPa和215 MPa,最高的伸长率16.0%。     

Large strain deformation of Ni3Al+B: Part II. Microstructure and texture evolution during recrystallization

The microstructure evolution and texture development of the intermetallic compound Ni₇₆Al₂₄, doped with minor additions of boron, was investigated during annealing subsequent to cold-rolling. Upon annealing of cold-rolled specimens, a hardness increase prior to recrystallization was observed. This is attributed to a relaxation process of the dislocation cores during annealing. Recrystallization proceeded with very different kinetics locally and a very small recrystallized grain size was obtained. From grain growth kinetics, the activation energy for grain boundary motion was found to be close to the activation energy for self-diffusion of Ni in Ni₃Al. The recrystallization texture was almost random. However, three texture components could be invariably recognized ({013}100, {012}021 and {112}294). They are related by special orientation relationships to the brass rolling orientation. A high frequency of annealing twins occurred in the recrystallized microstructure. The misorientation distribution function (MODF) shows a preference of certain low Σ boundaries, namely small-angle boundaries (Σ1) and twins (Σ3).     

Texture analysis of the transition from slip to grain boundary sliding in a discontinuously recrystallized superplastic aluminum alloy

Texture and microtexture measurements were correlated with mechanical property data for a superplastic 5083 aluminum alloy. Prior processing had included an overaging treatment followed by severe rolling deformation and the as-received material was annealed prior to mechanical testing. Discontinuous recrystallization by particle-stimulated nucleation during the annealing accounts for a predominantly random texture, although a weak {100}<0vw> component was present, as well as a random grain boundary disorientation angle distribution. During elevated temperature deformation under dislocation-creep-controlled conditions, a distinct <111> fiber component and a relatively weak {100}<001> cube orientation, which are mutually compatible during uniaxial tensile extension, became apparent in the texture. Also, low-angle boundaries became evident in the disorientation distribution. In contrast, the random texture component and the randomness of the disorientation distribution became more evident when the material was deformed under conditions of grain boundary sliding control of deformation. A transition from dislocation creep to grain boundary sliding observed in the microtexture measurements of this work may be predicted by treating constitutive equations for dislocation creep and grain boundary sliding in an additive manner.     

Recrystallization developed in the largely undercooled Ni54.6Pd45.4 alloy

The structure evolution driven by recrystallization in the bulk undercooled Ni_54.6Pd_45.4 alloy was investigated by quenching the sample at different cooling stages. It is found that recrystallization of the solid beyond the critical undercooling for grain refinement starts at the end of rapid solidification, and develops during the slow solidification and the subsequent cooling process. At the initial stage of recrystallization, nuclei successively form in the sample, leading to a decrease in grain size. At the later stage, annexation of grains dominates the recrystallization, due to which the grain size increases. As undercooling prior to solidification increases, the deformation degree in the rapidly solidified dendrite net rises, and the recalescence temperature as well as the duration at high temperature decreases. Consequently, the grain size of the recrystallization structure decreases.     

Development of novel grain morphology during hot extrusion of magnesium AZ21 alloy

Microstructure and microtexture evolution during static annealing of a hot-extruded AZ21 magnesium alloy was studied. Apart from fine recrystallized equiaxed grains and large elongated deformed grains, a new third kind of abnormal grains that are stacked one after the other in a row parallel to the extrusion direction were observed. The crystallographic misorientation inside these grains was similar to that of the fine recrystallized grains. The large elongated grains exhibited significant in-grain misorientation. A self-consistent mechanistic model was developed to describe the formation of these grain morphologies during dynamic recrystallization (DRX). The texture of pre-extruded material, although lost in DRX, leaves a unique signature which manifests itself in the form of these grain morphologies. The origin of abnormal stacked grains was associated with slow nucleation in pre-extruded grains of a certain orientation. Further annealing resulted in large secondary recrystallized grains with occasional extension twins.     

涂层导体用Ni9W合金基带再结晶及强立方织构的形成研究

采用X射线四环衍射技术对比分析了通过冷轧和轧制中间热处理制备的2种Ni-9.3at%W(Ni9W)合金基带的轧制织构和再结晶织构,研究了不同Ni9W合金基带在热处理过程中轧制织构向再结晶织构的演变。其次,采用背散射电子衍射(EBSD)技术对以上2种Ni9W合金基带的微观组织和立方织构进行了表征。结果表明,与传统冷轧Ni9W合金基带的轧制织构相比,经轧制中间热处理后其轧制织构中S取向和Copper取向的含量增加、Brass取向的含量减少,使其轧制织构的类型介于Brass型轧制织构与Copper型轧制织构之间。2种Ni9W合金基带经低温回复后,其轧制织构含量均有一定的增加;另外,再结晶过程中轧制织构的含量均迅速降低,但立方取向的含量并没有明显增加,而是出现大量的随机取向,Ni9W的再结晶具有了连续再结晶的特征,这也是导致Ni9W合金基带较难形成立方织构的一个主要原因。虽然经过轧制中间热处理后Ni9W合金基带在初始再结晶完成后并没有形成一定强度的立方织构,但其立方取向的含量仍然能在进一步热处理过程中通过立方取向晶粒的长大而得到加强。最后,采用轧制中间热处理制备的Ni9W合金基带经两步高温热处理后其立方织构的含量达到84.5%(15°)。     

Annealing behaviour of Mg-3Al-1Zn alloy sheet obtained by a combination of high-temperature rolling and subsequent warm rolling

The recrystallization and grain growth behaviour of Mg-3Al-1Zn alloy sheets with a deformation microstructure, obtained by a combination of high-temperature rolling and subsequent warm rolling, was investigated at different stages of annealing. The basal texture was significantly weakened as a result of the formation of new grains with a largely altered c-axis orientation relative to the initial basal orientation owing to discontinuous static recrystallization during primary recrystallization. The new grains nucleated mostly at the pre-existing grain boundaries rather than at the intersections of twins or within the twins. Subsequent grain growth led to further progression of the texture weakening accompanied by an enhancement in the basal pole inclination.     

Relating Initial Texture to Deformation Behavior During Cold Rolling and Static Recrystallization Upon Subsequent Annealing of an Extruded WE43 Alloy

Deformation behaviors during cold rolling and static recrystallization behaviors upon subsequent annealing of an extruded WE43 alloys with different initial textures were investigated in this study. Three types of differently textured WE43 initial alloys were labeled as samples I, II and III. The results showed that multiple twinning modes and basal slip dominated the deformation of samples during cold rolling. Cold-rolled sample I activated the larger number of double twins with high strain energy, accompanied by the more uniform strain distribution, than cold-rolled samples II and III. During subsequent annealing, recrystallized grains preferentially occurred in double twins, twin-twin intersections and grain boundaries, thereby making cold-rolled sample I have the more rapid recrystallization rate. Similar recrystallization textures formed in three types of cold-rolled samples at the recrystallization nucleation stage, and they never largely changed with the annealing time due to the uniform grain growth induced by the solute drag and the precipitation pinning at grain boundaries. After full recrystallization, the grain growth was controlled by the solute drag, instead of precipitates which were re-dissolved into the matrix. Finally, the nucleation and growth kinetics of static recrystallization were calculated, and the effects of initial texture on activation energies of recrystallization nucleation and growth were discussed.     

热轧Mg-1Zn和Mg-1Y合金退火组织演变及静态再结晶行为

对比研究了高温轧制制备的Mg-1.02Zn及Mg-0.76Y(质量分数,%)合金在不同温度退火条件下的组织演变及静态再结晶和晶粒长大动力学行为.结果表明,Mg-1Zn合金的轧制组织以剪切带和孪晶为主,在剪切带和孪晶内伴随着动态再结晶;而Mg-1Y合金的轧制组织中只有孪晶,未观察到剪切带和再结晶发生.退火过程中,Mg-1Zn合金静态再结晶过程主要受控于形核过程,而Mg-1Y合金则既受控于形核过程又受控于长大过程.利用经典的JMAK模型和长大模型分别描述了2种合金热轧制后的静态再结晶和晶粒长大动力学过程,结果表明,静态再结晶过程的Avrami因子n值与理想预测值偏离可能来自于再结晶的不均匀形核.固溶稀土Y原子比Zn原子对晶界移动的拖曳作用更强,导致Mg-1Y合金比Mg-1Zn合金晶粒长大因子n’更高.     

冷轧低压电子铝箔退火加热过程中的再结晶和晶粒长大

采用EBSD微取向分析、织构定量分析、晶粒尺寸分析等手段研究了低压电子铝箔不同退火加热过程对再结晶和晶粒长大行为的影响,并利用再结晶理论对相关过程进行了讨论.初次再结晶前的回复处理会明显降低冷轧铝箔的储存能及再结晶驱动力,并对再结晶晶粒尺寸和立方织构量产生规律性影响.特定的退火加热过程会诱发电子铝箔的晶粒异常长大,并导致立方织构量的明显下降.