大晶粒Ni-42Al合金超塑变形中组织演变EBSD分析

采用电子背散射衍射(EBSD)技术,研究大晶粒Ni-42Al合金在1075℃、初始应变速率为1×10-3s-1条件下超塑变形中的组织演变.研究表明,变形前以大角度晶界为主,小角度晶界比例极低.在超塑变形中,持续有取向差5°以下的小角度晶界产生.随变形量的增大,新形成的小角度晶界取向差增加,转变为取向差较大的6°～15°小角度晶界,进而转变为15°以上的大角度晶界.小角度晶界的产生速率与小角度晶界转变为较大角度晶界的速率趋向一动态平衡.小角度晶界向较大角度晶界不断转变的结果使大角度晶界数量不断增加,最终导致晶粒显著细化.超塑变形使NiAl合金重合位置点阵(CSL)特征晶界发生改变,获得了有利于改善其室温塑性的CSL特征晶界结构.     

EBSD技术分析大晶粒NiAl合金高温塑性变形组织演变与CSL特征晶界分布

采用EBSD分析了1075℃和初始应变速率为8.75x10~(-4)S~(-1)条件下大晶粒NiAl合金高温塑性变形过程中的组织演变与重位点阵(CSL)特征晶界分布.变形前大晶粒NiAl合金以大角度晶界为主,小角度晶界比例极低.在高温塑性变形过程中,取向差5.以下的小角度晶界不断产生.随变形量的增大,新形成的小角度晶界取向差增加,转变为取向差较大的6.一15.小角度晶界,进而转变为15.以上的大角度晶界.小角度晶界的产生速率与转变为大角度晶界的速率趋向动态平衡.小角度晶界向较大角度晶界不断转变导致晶粒显著细化.CSL特征晶界分析表明,大晶粒NiAI合金高温塑性变形过程中,CSL晶界分布发生改变,将对合金室温力学性能产生影响.     

EBSD ANALYSES OF THE MICROSTRUCTURAL EVOLUTION AND CSL CHARACTERISTIC GRAIN BOUNDARY OF COARSE--GRAINED NiAl ALLOY DURING PLASTIC DEFORMATION

采用EBSD分析了1075℃和初始应变速率为8.75×10^-4 s^-1条件下大晶粒NiAl合金高温塑性变形过程中的组织演变 与重位点阵 (CSL) 特征晶界分布. 变形前大晶粒NiAl合金以大角度晶界为主, 小角度晶界比例极低. 在高温塑性变形过程中, 取向差5°以下的小角度晶界不断产生. 随变形量的增大, 新形成的小角度晶界取向差增加, 转变为取向差较大的6°---15°小角度晶界, 进而转变为15°以上的大角度晶界. 小角度晶界的产生速率与转变为大角度晶界的速率趋向动态平衡. 小角度晶界向较大角度晶界不断转变导致晶粒显著细化. CSL特征晶界分析表明, 大晶粒NiAl合金高温塑性变形过程中, CSL晶界分布发生改变, 将对合金室温力学性能产生影响.     

大晶粒单相Ni-50Al金属间化合物高温塑性

研究了原始晶粒尺寸为220 (m的正化学计量比单相Ni-50Al金属间化合物的高温变形行为及组织演变规律.结果表明,该合金在温度1000～1100 ℃,应变速率7.5×10~(-4)～1×10~(-3) s~(-1)范围内具有良好的高温塑性变形能力;在1075 ℃,应变速率为8.75×10~(-4) s~(-1)时,最大延伸率可达139%.金相显微分析表明,原始大晶粒组织经高温塑性变形后显著细化;EBSD与 TEM分析表明,变形过程中小角度晶界持续产生,较小角度晶界向较大角度晶界不断演变,最终导致晶粒显著细化.显微结构综合分析表明,大晶粒Ni-50Al合金的高温塑性变形是由位错的交滑移与攀移等交互作用产生的连续动态回复和再结晶导致的.     

大晶粒单相Ni-48Al金属间化合物超塑性变形过程中的组织演化

原始平均晶粒尺寸约为200μm的单相Ni-48Al金属间化合物在温度为1025—1100℃、应变速率为1.25×10~(-4)—2.00~10~(-3)s~(-1)范围内呈现超塑性。在1100℃、应变速率为1.125×10~(-3)s~(-1)时,最大延伸率可达188.2％。金相分析表明,超塑性变形过程中晶粒明显细化;电子背散射衍射分析(EBSD)和透射电子显微术(TEM)观察表明,超塑变形过程中形成了大量亚晶界网络,且随变形量增大,亚晶界及小角晶界比例不断增加。亚晶界由位错墙和位错网络构成,不稳定的亚晶界在超塑性变形过程中不断吸收晶内滑移和攀移位错,亚晶界位错密度不断增加,取向差不断增大。伴随亚晶界的滑移和迁移及亚晶的转动,部分亚晶界转变为小角度晶界,并进而转变为大角度晶界,即在超塑性变形过程中发生了连续动态回复与再结晶(CDRR)。     

取向与晶界对γ-TiAl双晶塑性行为影响的CPFEM模拟

基于晶体塑性理论和有限元方法,利用ABAQUS/UMAT二次开发接口,采用FORTRAN语言开发γ-Ti Al合金晶体塑性本构关系子程序,建立综合考虑位错滑移、形变孪晶和晶界效应的γ-Ti Al合金双晶体模型,模拟常温下不同晶粒取向差(2°、5°、8°、30°、45°和60°)与晶界效应对γ-Ti Al合金塑性变形的影响。结果显示:晶界的存在和晶粒取向差异会导致双晶体变形的不均匀性,在晶界处出现应力集中现象,且晶界区域表现出与晶粒内部区域不同的力学性质。晶界区域的受力状态受到相邻晶粒的影响,晶界角度较小时,两个晶粒滑移系的累积剪切变形较为协调,双晶体整体的塑性变形较为均匀。     

挤压态GH3625合金冷变形过程中的组织和织构演变

采用EBSD技术研究了挤压态GH3625合金冷变形过程中的组织演变、晶界特征分布、位错密度、应力分布及织构演变规律。结果表明,随着冷变形量的增加,晶粒变形程度加大,晶粒形貌由扁平状转变为细条状,晶体转动使得晶界与加载压力轴垂直分布;随着冷变形量的增加,大角度晶界逐渐向小角度晶界转变,孪晶界的比例逐渐增加。随着冷变形量的增加,局部取向差的平均值(■)升高,位错密度增加;同时,晶粒变形均匀性逐渐变好,应力集中分布逐渐向应力均匀分布转变。随着冷变形量的增加,其形变织构的类型基本保持不变,而具有稳定取向的Copper织构{112}111的强度略有降低;同时,由不均匀变形产生的Rotated-cube织构{001}110的强度降低;此外,形变孪晶的形成导致Goss织构{110}001和Brass-R织构{111}112的强度降低。     

γ-TiAl中<110>倾斜晶界断裂行为的分子动力学模拟(英文)

采用分子动力学(MD)方法研究γ-Ti Al合金中<110>对称倾斜界面的断裂行为,模拟在不同温度与应变速率下垂直界面方向的拉伸变形。结果表明:晶粒的相对取向及晶界特定的原子结构是影响位错形核临界应力的两个主要因素。取向差角度大于90°的Σ3(111)109.5°、Σ9(221)141.1°和Σ27(552)148.4°界面,位错在晶界处形核和扩展;取向差角度小于90°的Σ27(115)31.6°和Σ11(113)50.5°界面,无位错在晶界处形核,当应力达到峰值后界面直接断裂。γ-Ti Al双晶的断裂机制为微裂纹在界面处的形核及沿界面扩展;不同取向差界面的区别在于裂纹前端有无塑性区增韧。     

Si和Ti对高性能Cu-15Ni-8Sn合金在热变形过程中动态再结晶的作用（英文）

采用不同变形条件(变形温度750～950℃、应变速率0.001～10 s~(-1))的热压缩试验研究微量元素Si和Ti添加对Cu-15Ni-8Sn合金动态再结晶的作用。结果表明,添加Si和Ti对热变形过程中的动态再结晶具有显著的作用。添加的Si和Ti可以形成Ni_(16)Si_7Ti_6相,Ni_(16)Si_7Ti_6相促进低角度晶界向高角度晶界转变,因此,促进动态再结晶的形核过程;同时,Ni_(16)Si_7Ti_6相产生的钉扎作用抑制再结晶晶粒的长大。基于动态再结晶行为建立热加工图以优化合金的热变形工艺参数。在最优工艺参数下制备具有细小晶粒组织的热挤压态Cu-15Ni-8Sn合金,其伸长率达到30%,抗拉强度达到910 MPa。     

β相区加热TA15钛合金热变形显微组织演化

采用OM、XRD和EBSD研究经过β相区加热,在不同工艺参数下热变形水冷淬火后TA15钛合金的显微组织、相变和织构演化规律。结果表明:显微组织主要由被压扁、拉长的原始β晶粒转变的α′马氏体相及清晰β晶界组成,相变点以下温度变形的显微组织中出现沿原始β晶界分布的细小晶界α相晶粒;通过切变方式形成α′马氏体相固溶了Al和V元素,且晶格点阵收缩,衍射峰向高角度方向偏移;α′马氏体与原始β的晶体取向间满足Burgers位向关系,显微组织的晶粒取向分布也类似,且随着变形温度和应变速率的提高,材料的晶粒取向性增强;显微组织的晶粒尺寸均在7μm以内,α′晶粒继承母相β晶粒的取向差,在10°、60°和90°附近出现峰值。     

EBSD investigation on the evolution of microstructure and grain boundaries in coarse-grained Ni–48Al upon large deformation at elevated temperature

The evolution of microstructure and grain boundaries were investigated in coarse-grained Ni–48Al intermetallics during plastic deformation at 1075 °C with the initial strain rate of 1.5 × 10⁻³ s⁻¹ using electron backscatter diffraction (EBSD) technique. Before deformation, most grain boundaries were high-angled (HAGBs), with several particular angles being predominant. During initial deformation, low-angle grain boundaries (LAGBs) with misorientation less than 5° began to evolve. The misorientation of the newly-formed LAGBs increased with the increase of deformation, meanwhile, grain boundaries with misorientations between 6 and 15° were gradually observed, and finally transformed into HAGBs (misorientation angle > 15°). There appeared a steady state transition from the formation of new LAGBs to the transformation into high-angle grain boundaries. As a result, the grain size was refined continuously with the deformation strain.     

定向凝固Ni3Al合金高温变形后的显微组织特征

利用金相,扫描电镜和透射电子显微镜研究了定向凝固Ｎｉ３Ａｌ合金高温变形后的显微组织特征。研究结果表明,当变形速率较快时,原始柱状晶晶界无明显变化,晶内无明显结构存在;当变形速率较慢,合金呈现塑变形时,变形初期柱状晶晶界呈现“锯齿状”,后期原始柱状晶界消失,代之以晶粒尺度约为１５ｍｍ的晶粒带,晶粒带中既有小角度晶界,也有大角度晶界。     

Electron backscattered diffraction study on superplastic properties of coarse-grained Fe-27 at% Al

An electron backscattered diffraction technique has been used to investigate crystallographic features of a superplastic coarse-grained Fe-27 at% Al alloy. Alloy samples studied have been tensile tested in a temperature range between 600 and 800°C in air under an initial strain rate of 1×10⁻⁴ s⁻¹. As a result of dynamic recovery and recrystallization, the grain structure undergoes four major transitions: subgrain-boundary formation, grain-boundary migration, formation and growth of recrystallized grains. A model based on the microstructural evolution is described. Subgrains form during an initial stage of high-temperature deformation when deformation is conducted at low temperature (600°C). Upon further deformation at 700°C, grain boundaries migrate, resulting in the formation of new grains. When deformation is made further to a larger elongation or at even higher temperature (800°C), dynamic recovery and recrystallization occur significantly, resulting in grain refinement and hence superplasticity. Refined grains thus formed maintain crystallographic relationships with parent grains.     

Microstructure evolution in a large—grained TiAl alloy

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拉伸条件对Al—Li—Cu—Mg—Zr合金超塑变形行为的影响

研究了拉伸条件对温轧态Al-Li-Cu-Mg-Zr合金超塑变形行为的影响.结果表明:该合金在变形初期发生了界面取向差逐渐增大,从亚晶组织向再结晶组织变化的形变促使连续再结晶过程;应变速率越高,再结晶速度越快,再结晶晶粒越细;经高应变速率的第一阶段拉伸变形后,形成的细晶组织具有高的应变速率敏感性,同时在低应变速率的第二阶段拉伸变形中发生晶粒长大而具有高的应变硬化效果,两者的综合作用是两段速率拉伸获得高延伸率的根本原因。     

EFFECT OF TENSION CONDITIONS ON SUPERPLASTIC BEHAVIOUR OF AN Al-Li-Cu-Mg-Zr ALLOY

A much higher elongation of a warm rolled superplastic Al-Li-Cu-Mg-Zr alloy was madeunder two-stage strain rate tests comparing with the single ones.During initial stage ofdeformation a deformation-induced continuous recrystallization which converted a subgrainstructure into a recrystallized grain structure by a continuous increase in boundarymisorientations had occurred.The higher the strain rate,the faster the continuousrecrystallization and the finer the recrystallized grains.The fine recrystallized grain structureformed during the first stage deformation is the essential condition for the material to havehigh strain rate hardening and strain hardening during the low second stage superplasticdeformation.The combination of strain rate hardening and strain hardening is the reason whythe higher elongation may be obtained during two-stage superplastic deformation of the alloy.     

Phenomena and mechanism on superplasticity of duplex stainless steels

The superplasticity of Fe-24Cr-7Ni-3Mo-0.14N duplex stainless steel after being solution treated at 1350°C followed by 90% cold rolling was investigated at 850°C with a strain rate ranging from 10^-3-10^-1s^-1. The microstructure of duplex stainless steel consists of a matrix γ phase having low angle grain boundaries and a σ phase as second phase particles before the deformation at 850°C. It is well known that the constituent phases in duplex stainless steel is changed following α→α+γ→α+γ+σ→γ+σ through phase transformation during deformation at 850°C. The final microstructure of duplex stainless steel consisted of 70 vol.% of γ and 30 vol.% of the σ phase. A maximum elongation of 750% was obtained at 850°C with a strain rate of 3.16xl0^-3s^-1. The dislocation density within matrix γ grains was low and a significant strain-induced grain growth was observed during the deformation. The misorientation angles between the neighboring γ grains increased as the strain increased, thus the low angle grain boundaries were transformed into high angle grain boundaries suitable for sliding by dynamic recrystallization during the deformation at 850°C. The grain boundary sliding assisted by dynamic recrystallization is considered to be a controlling mechanism for superplastic deformation at 850°C.     

Electron backscattered diffraction study on superplastic coarse-grained Fe–27 at.%Al: processing effects

An electron backscattered diffraction technique has been used to investigate detailed crystallographic features of a superplastic coarse-grained Fe–27 at.%Al alloy. Alloy samples studied have been tensile tested to failure at 800°C in air under an initial strain rate of 1×10⁻⁴ s⁻¹. To examine processing effects, the hot isostatic pressing (HIP) has been applied prior to the superplastic deformation. The HIPed sample shows no observable pores in the fracture region while the sample without HIP reveals an elongated pore fracture structure. Nevertheless, HIP is shown to have no beneficial effects on the superplastic elongation, suggestive of the fact that the alleviation of cavity formation alone is insufficient in achieving better superplastic properties. After the superplastic deformation and the refined grains are formed, the presence of numerous small angle subboundaries in the large grain interior indicates the continuous event of recovery and recrystallization that occurs throughout the course of superplastic deformation. The post-deformation annealing yields a classic recrystallized large-grain structure, resulting from the surface-tension-induced boundary migration that reduces the grain surface-area. Conversely, the superplastic deformation of Fe–27 at.%Al involves a strain-induced boundary migration that causes the grain surface-area increase and results in a refined grain structure. The dynamic nature of recovery and recrystallization is therefore confirmed.     

双相NiAl金属间化合物超塑性

研究双相Ni-31Al金属间化合物的高温变形行为。结果表明,该合金在950~1075℃温度范围,1.25×10-4~8×10-3s-1应变速率范围内呈超塑性变形。在温度为1000℃、应变速率为5×10-4s-1时,最大延伸率可达281.3%。显微结构分析表明,超塑性变形过程中两相具有很好的协调变形能力,超塑性变形后原始组织拉长、细化。双相Ni-31Al金属间化合物超塑性变形机制可能为连续动态回复与再结晶。     

The annealing behaviour of deformed cube-oriented aluminium single crystals

Single crystals of the {001}〈100〉 cube orientation of a dilute single-phase Al–Si alloy have been deformed in plane strain compression at temperatures between 300 and 500°C at strain rates between 0.5 and 50/s. The stability of the cube orientation was found to be dependent on the deformation conditions, which is in agreement with previous work. The deformed crystals contained bands of subgrains of a range of sizes and misorientations. Detailed EBSD analysis of deformed and annealed crystals revealed a strong correlation between subgrain growth and misorientation, and analysis of the data enabled the mobility of low angle grain boundaries in the misorientation range 5–20° to be determined in the temperature range 300–450°C. It was found that the boundary mobility increased with increasing misorientation up to ∼15–20° and thereafter reached a plateau. The activation energies of migration were consistent with control by lattice diffusion of Si in Al and the activation energy was found to increase with increasing misorientation.