Effects of Reinforced Particles on Dynamic Recrystallization of Mg Base Alloys during Hot Extrusion

主要研究了SiC颗粒增强镁基复合材料在不同挤压比、不同挤压温度下进行挤压后,SiC颗粒对镁合金基体中的动态再结晶现象影响。结果表明:挤压过程中颗粒周围产生了颗粒变形区(PDZ),并且颗粒变形区在低温挤压时以细小动态再结晶晶粒为主。颗粒促进动态再结晶晶粒形成的主要原因是颗粒周围较高的位错密度以及大的晶粒取向梯度。SiC颗粒对镁合金基体动态再结晶的影响主要有两方面:一方面,颗粒促进动态再结晶的形核以及生长,另一方面,当再结晶晶粒晶界碰到颗粒时,颗粒阻止了晶粒的继续长大。     

PARTICLE STIMULATED NUCLEATION AND THE FORMATION OF RSCRYSTALLIZATION TEXTURE IN Al-Mn ALLOY CONTAINING PARTICLES Ⅱ. Interaction Between Particles and Other Nucleation Sites and the Formation of Recrystallization Texture

本文报了Ａｌ－Ｍｎ合金形昧形变取向基体中粒子周围亚晶转动规律及对应的粒子促进形核晶粒的取向特征的基础上,进一步测定了处在晶界,立方带上的了周转新晶粒的取向分布。     

Al—Mn合金中粒子促进形核及初期再结晶织构 Ⅱ.粒子与其它形核位置的交互作用及初期再结晶织构

本文在分析了Al—Mn合金形变时不同形变取向基体中粒子周围亚晶转动规律及对应的粒子促进形核晶粒的取向特征的基础上,进一步测定了处在晶界,立方带上的粒子周围新晶粒的取向分布,最后分析了再结晶织构的形成．结果表明,处在这些位置上的粒子周围新晶粒一方面保留了晶内PSN晶粒的取向特征,另一方面也带有晶界及立方带形核的特点再结晶织构反映了不同类型形核位置形成的新晶粒的取向特征     

PARTICLE STIMULATED NUCLEATION AND THE FORMATION OF RECRYSTALLIZATION TEXTURE IN Al-Mn ALLOY CONTAINING PARTICLES Ⅰ. Deformation Zones Around Particles and Particle Stimulated Nucleation

利用ＳＥＭ中的和射电子衍射技术研究了Ａｌ－１．３Ｍｎ（质量分数,％）合金中没形变取向基体中粒子周围亚晶以及再结晶初期相应的粒子促进形核晶粒的取向分布,并将结果与单昌中的情形进行了比较。     

Al-Mn合金中粒子促进形核及初期再结晶织构 Ⅰ.粒子周围的形变区及粒子促进形核

利用SEM中的背散射电子衍射技术研究了Al—1．3Mn质量分数,％）合金中不同形变取向基体中粒子周围亚晶以及再结晶初期相应的粒子促进形核晶粒的取向分布,并将结果与单晶中的情形进行了比较结果表明,多晶中各形变取向基体中粒子周围亚晶转动的规律及粒子促进形核晶粒的取向与同取向单晶中的情况相同,并非是随机分布的．文章的第二部分将分析粒子与其它形核地点（晶界、立方带）的交互作用以及再结晶织构的形成     

Evolution of grain structure in AA2195 A1-Li alloy plate during recrystallization

The evolution of the grain structures in AA2195 Al-Li alloy plate warm-rolled by 80% reduction during recrystallization annealing at 500℃ was investigated by electron backscatter diffraction, scanning electron microscopy and transmission electron microscopy. It is found that the elongated grain structures are caused by the lamellar distribution of recrystaUization nucleation sites, being lack of large second phase particles （〉 1μm）, and dispersive coherent particles （such as δ′ and β′concentrated in planar bands. The recrystallization process may be separated into three stages： firstly, recrystallization nucleation occurs heterogeneously, and the nuclei are concentrated in some planar zones parallel to rolling plane. Secondly, the grain boundaries interacted with small particles concentrate in planar bands, which is able to result in the elongated grain structures. The rate of the grain growth is controlled by the dissolution of these small particles. Thirdly, after most of small particles are dissolved, their hindrance to migration of the grain boundaries fades away, and the unrecrystallized zones are consumed by adjacent recrystallized grains. The migration of high angle grain boundaries along normal direction leads a gradual transformation from the elongated grains to the nearly equiaxed, which is driven by the tension of the grain boundaries.     

Ti(C,N)对Ni基高温合金组织结构、力学性能和抗氧化性的影响

基于相场法,以第二相颗粒平衡体积分数不同的合金为对象,研究第二相颗粒的沿晶析出、长大及其对基体相晶界的钉扎作用.结果表明,第二相颗粒的平衡体积分数越大,其形核孕育期越短,形核与粗化的速度也越快;然而在第二相颗粒的长大阶段,平衡体积分数较大(15％～25％)时第二相颗粒长大速度较慢,而平衡体积分数较小(10％)时则长大速度较快.随着第二相颗粒平衡体积分数的增大,其对晶界的钉扎作用也逐渐增强,但平衡体积分数增大到一定程度,钉扎作用将趋于稳定.第二相颗粒对晶粒极限尺寸的影响遵循Zener关系.     

TiAl_3对TiC粒子在铝基体中分布及α(Al)晶粒形核的影响

研究TiC和TiAl_3细化工业纯铝时TiAl_3的存在对TiC在铝基体中分布及α(Al)晶粒形核的影响,分析Al-Ti-C晶粒细化机制.结果表明:TiC单独作为工业纯铝的晶粒细化剂时,大量TiC被α(Al)晶粒推向树枝晶的晶界处,从而限制了TiC的异质形核作用;当TiC和TiAl_3共同作为晶粒细化剂时,在α(Al)晶粒内部出现了大量TiC粒子,大量的TiC粒子成为了α(Al)的结晶核心,并且在TiC颗粒和铝基体的界面处存在"富Ti过渡区";TiAl_3在铝熔体中分解释放出Ti原子并向TiC粒子周围偏聚,形成的"TiC/铝熔体界面富Ti过渡区" 改善了TiC与α(Al)的结构适应性,降低了TiC粒子的表面张力,促进了TiC粒子在铝熔体中的均匀分布,提高了其形核能力.     

冷加工态Ti6Al4V合金的回复和再结晶行为研究

对冷拉拔变形量为60%的钛合金进行700～880℃,1～240min再结晶退火,利用金相显微镜、X射线衍射仪和透射电镜等手段分析不同状态下的组织演变、织构组成和位错组态。结果表明:冷变形后的Ti6Al4V合金经完全再结晶后α晶粒呈等轴状,β相在α相周围以条状沿α晶界析出或以小晶粒形式存在。计算表明,经60%冷变形量的钛合金再结晶激活能为107kJ/mol,较相同变形量的纯钛再结晶激活能高约50%。钛合金的再结晶分为回复、形核和晶核长大阶段,包括位错胞向亚晶转变、回复亚晶通过合并或长大形核、形核诱导高角度晶界形成而长大成新晶粒。经过冷拉拔后的丝材,存在着较强的100织构,而在再结晶过程中,沿100方向上产生的回复亚晶优先形核并长大形成新的晶粒。这导致在初始再结晶阶段,再结晶织构与冷变形织构取向一致,而在晶粒长大阶段,原先取向不利的晶粒吞并周围小晶粒长大,形成新的织构组元使原来的织构被弱化。     

Abnormal grain growth in Al–3.5Cu

Significant abnormal grain growth has been observed in an Al–3.5 wt.% Cu alloy at temperatures where the volume fraction of small CuAl₂ particles was less than about 0.01. The initial fine-grained material had a weak crystallographic texture and there was no indication that any special boundaries were involved in the abnormal growth. Island grains isolated within the abnormal grains also showed no indication of special orientation relationships with their surrounding grains. Measurements indicated that the island grains initially had a size advantage over other matrix grains. The fraction of pinning phase was much lower at abnormal grain boundaries than at boundaries in the fine-grained matrix into which they were growing. A variety of simulations were made, including attempts to model that difference in pinning phase distribution, but none of these were successful in predicting abnormal grain growth.     

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...     

Characterization of Multi-layer Weld Metal and Creep–Rupture Behavior of Modified 10Cr–1Mo Welded Joint

The rupture behavior of the modified 10Cr–1Mo steel multi-layer welded joint is determined by the fine-grain zones of the weld metal adjacent to the fusion line during the long-term creep test at 620 °C. The microstructures of multi-layer weld metal before and after the creep tests were characterized in detail, and its role in creep behavior was systematically investigated. Most grain boundaries of subgrains represented the low-angle boundaries in the weld metal adjacent to the fusion line both before and after the creep test. The widths of grains in the fine-grain zones were about 0.5–1 μm. The fracture morphology appeared as "wave" structure due to the cracking initiating from multi-layer grain boundaries in the fine-grain zones. Some W elements that melted into weld metal adjacent to the fusion line altered the thermodynamic and kinetic conditions of the Laves phase formation during long-term creep exposure. Laves phase particles mainly distributed along the grain boundaries due to the faster diffusion and segregation of Mo, W, and Si elements. Moreover, higher-density grain boundaries in the fine-grain zones led to easier nucleation and growth of Laves phase particles. Compared with other areas in the welded joint, the size of Laves phase particles in the fine-grain zones of the weld metal adjacent to the fusion line was the largest ones. The interface between Laves phase particles and the matrix acted as the nucleation site of creep micro-cavities. The creep micro-cavities grew up at the expense of fine-grain boundaries and even grew across the grain boundary deeply into adjacent grains, and then developed to cracks in the fine-grain zones.     

冷轧变形量对7A75铝合金组织性能的影响

研究了冷轧变形对7A75铝合金微观组织和力学性能的影响,并探讨了第二相粒子促进形核的机制。采用光学显微镜(OM)和透射电镜(TEM)观察了微观组织,采用万能拉伸试验机测试了力学性能,采用板材成形试验机测试了杯突值(IE)。结果表明:随冷变形量的增大,7A75铝合金的强度和伸长率均逐渐增大,且屈服强度的升高幅度大于抗拉强度。50%冷变形时屈服强度和抗拉强度分别达到435 MPa和460 MPa,与未经冷变形时相比分别提高了190 MPa和110 MPa,同时伸长率提高到14%。杯突IE值与伸长率的变化规律一致。30%、50%和70%的冷变形下,基体晶粒平均尺寸分别为31.5、13.5和13.0 μm,冷变形量越大,基体晶粒尺寸越细小越均匀。过时效处理后,7A75铝合金中的MgZn₂粒子尺寸大于0.5 μm时,在冷变形后的固溶处理过程中为再结晶提供形核位置;而50~100 nm之间的粒子钉扎在晶界处,有效地抑制了再结晶晶粒的长大。     

Coincidence Site Lattice (CSL) grain boundaries and Goss texture development in Fe-3% Si alloy

The role of CSL grain boundaries in Goss [(100)100] texture development Fe-3% Si has been investigated by direct crystallographic orientation measurement of (1) primary recrystallized specimens and (2) specimens following the early stages of secondary recrystallization. Goss oriented grains in the primary matrix were found to occur with a low frequency, and were not observed to have an initial size advantage or occur in clusters; however, these grains were determined to be frequently bounded by low Σ (i.e. Σ3-29) CSL interfaces. By calculating the possible orientation relationships between hypothetical grain orientations and the experimentally determined texture of the primary matrix, Goss oriented grains were determined to be statistically more likely to produce mobile low Σ CSL orientation relationships during random growth through the primary matrix than other major grain texture components. A deficit of these CSL interfaces, relative to the determined probability of occurrence during random grain growth, was experimentally determined for interfaces bounding Goss grains following secondary recrystallization treatments; this deficit was rationalized on the basis of preferential replacement by general (or higher Σ) interfaces due to enhanced mobility of these low Σ CSL grain boundaries.     

THE SUPERPLASTICITY AND DEFORMATION MECHANISM OF ULTRALIGHT BINARY Mg-8wt%Li ALLOY

1.IntroductionMagnesium--lithiumalloysarethelightestalloysamongthenonpoisonousmetalsandalloystll.Becauseoftheirlowdellsityandhighspecificstiffness,theyhavethepotentialforuseinaerospacesarmoredvehicle,automobileandelectricindustry.InordertoturnMg--Lialloysintospecificcomponentswithminimumamountofmachiningandjoining,itisdesirablethatMg-Lialloysexhibitsuperplasticity.UPtonow,superfinegraillscanbeobtainedinmagnesium-lithiumalloysbythefollowingways'(1)staticannealingafterthermomechanicaltreatment…     

Recrystallization of SRR99 single-crystal superalloy： Kinetics and microstructural evolution

As-cast SRR99 specimens were shot-peened and then annealed at 1250 and 1300°C for different times to investigate the kinetics of recrystallization.It was found that the relationship between annealing time and volume fraction of recrystallized grains could be described by the Johnson-Mehl-Avrami equation.Based on the kinetics analysis of the recrystallization process,the apparent activation energy for recrystallization was determined.In addition,the microstructural evolution during the recrystallization process at 1300°C was studied.Inwards,recrystallization first occurs in the dendritic core regions at the shot-peened surface.With the dissolution of coarse γ' particles in the interdendritic regions,the recrystallized grain boundaries move through the interdendritic regions.Finally,the fully developed grains nearly have a uniform depth.The recrystallization process at the shot-peened surface is similar to that of wrought materials,which includes nucleation of recrystallization,growth of recrystallized nuclei into the matrix,and growth of recrystallized grains by swallowing up each other.     

搅拌铸造SiCp/Al-7.0%Si复合材料的三维微观组织模拟

对搅拌铸造法制备SiC颗粒（SiCp）增强Al-7．0％Si（质量分数）复合材料的微观组织形成过程进行了模拟研究,建立了常规凝固条件下相应的宏观传热、等轴枝晶形核、生长以及颗粒推移的三维计算模型,采用一种改进的CA（cellular automaton）方法与有限差分法耦合进行数值计算,研究了不同颗粒体积分数对复合材料宏观传热、微观组织以及颗粒分布的影响．为了验证模拟结果,浇注了阶梯形金属型和砂型试样．结果表明,模拟得到的复合材料颗粒分布及微观组织与实验结果吻合良好．随着颗粒体积分数的增加,凝固时间逐渐缩短,基体晶粒逐渐细化,颗粒分布趋向均匀．     

Simulation of primary recrystallization using a modified three-dimensional cellular automaton

A modified three-dimensional cellular automaton algorithm has been developed to simulate primary static recrystallization of cold-worked metals. The driving force for the nucleation and growth of recrystallized grains is the volume free energy due to the stored dislocation density of the deformed matrix. Growth terminates upon impingement. The code allows the introduction of specific conditions for recovery, nucleation and grain boundary motion. The model is capable of simulating kinetics, microstructure and texture development during recrystallization. The modification of the cellular automaton approach allows for the simulation of an orientation dependent growth rate. A novel algorithm minimizes the computational load and computer memory requirement.     

TC17钛合金自表面纳米化机制及组织演化

采用二元合金晶体相场模型,耦合原子密度场和浓度场,在扩散时间尺度上模拟过冷熔体的形核,生长及粗化过程.研究表明:增加冷却速率,模拟区域内晶核富集,快速长大;一定范围内,随着冷却速率增大,晶粒尺寸减小,组织细化;晶粒长大过程中,晶界主要依靠位错的迁移或攀移进行运动.二元合金模拟还可以应用到枝晶凝固、外延生长,调幅分解中,前景广阔.     

DISTRIBUTION OF Nd-RICH PHASE PARTICLES IN AS-CAST Ti-5Al-4Sn-2Zr-lMo-0.25Si-1Nd ALLOY

For the as一cast Ti一55 alloy,the morphology of the alloy riser consists of coarse dendritezone and equiaxial grain zone the second phase particles are 2.0～25 μm in diameterSome particles appear at grain boundaries,the others precipitate within grains the shapesof the particles are mainly ellipsoids,and a few kinds of short needle-like and blockymorphologies The Nd-rich phase particles are enriched in the liquid be fore the interfaceand are engulfed along the solidification plane-front Finally bands of Nd-rich phase particles form parallel to the advancing solidification plane-front