共查询到17条相似文献,搜索用时 147 毫秒
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用实验方法研究了奥氏体不锈钢在等径角挤压冷变形(路径RC)过程中组织变化。实验结果表明:当剪切方向与孪晶带方向成一定角度时,在剪切力的作用下,孪晶逐渐由大块孪晶→由剪切带分割的孪晶(楼梯状)→小块状→奥氏体亚晶或马氏体晶粒;部分孪晶在剪切力作用下,剪切带可直接碎化成具有大角度位向差的细小晶粒(奥氏体亚晶+马氏体晶粒),可发生马氏体相变;当剪切方向与孪晶带方向相同时,孪晶带区域也可发生马氏体转变;3道次变形后,具有明显特征的孪晶已很少,此后继续进行剪切变形,孪晶碎化组织(含马氏体)和奥氏体剪切滑移带(含碎化晶粒)的变形以剪切滑移方式进行,当奥氏体的滑移遇到阻力时,可局部形成局部形变孪晶来协调变形;随变形道次的增加,马氏体转变也越多,在多次剪切以及道次中的交叉滑移作用下,马氏体板条逐渐被高密度位错墙分割而碎化成细小的晶粒;8道次变形后,可获得60~230 nm的等轴晶粒。 相似文献
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室温下对纯钛进行多道次等径弯曲通道变形(ECAP),分别采用光学显微镜(OM)、透射电镜(TEM)、电子背散射衍射仪(EBSD)、室温拉伸和显微硬度观察,测试纯钛变形过程组织演变和力学性能变化规律,探讨纯钛室温变形机制和孪生行为。结果表明,纯钛ECAP变形过程中出现■拉伸孪晶和■压缩孪晶,随着挤压道次的增大,孪晶数量先增大后减小。孪晶的出现有效改变晶格取向,激发进一步位错滑移,辅助塑性变形过程,使纯钛显微组织有效细化,经过4道次ECAP变形,平均晶粒尺寸由约63.79μm细化至约2.81μm。1道次变形后晶粒细化效果最显著,平均晶粒尺寸比变形前减小约94%;随着变形道次的增加,晶粒细化效果减弱,4道次变形后平均晶粒尺寸累积减小约95.6%。同时,大量位错、孪晶和亚晶的形成,使得位错、孪晶以及亚晶之间的相互作用加强,显著提高了纯钛的屈服强度和显微硬度,4道次变形后,屈服强度从215 MPa增加到600 MPa,增幅为179%;显微硬度从HV 129增加到HV 200。由于1道次变形后晶粒细化效果最显著,并且出现大量孪晶和位错,屈服强度与硬度的增幅也最大。 相似文献
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综述了金属结构材料和功能材料基体相晶体结构、层错能、Hollomon参数lnZ对等通道转角挤压ECAP变形组织演变规律影响的研究进展,试样基体相的晶体结构对变形组织的演变起重要的影响作用。随着应变量的增大,密排六方结构金属先形成形变孪晶、再启动优先存在的但被阻塞的滑移系统;面心立方结构金属的位错滑移主导着组织演变与晶粒细化过程,先形成亚晶界,再增大组织取向差,最终形成大角度晶界。在高层错能材料中,随着Hollomon参数lnZ增大,位错运动受到抑制,驱使变形机制从位错滑移逐渐转变成形变孪晶;当Z参数减小时,在ECAP高层错能材料中会形成微尺度的剪切带。在低层错能材料中形成丰富的孪晶,极低层错能的材料形成宏观剪切带。而中等层错能材料的变形机制则取决于Z值的高低。分析了ECAP过程动态再结晶的影响因素,认为γm·ln2Z30不宜作为ECAP过程是否发生动态再结晶的判据,ECAP过程动态再结晶的影响因素还有待进一步研究,如弄清ECAP过程温升规律、分析淬火保存ECAP变形组织将有助于研究ECAP动态再结晶。 相似文献
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45钢等径弯曲通道变形及组织细化研究 总被引:2,自引:0,他引:2
研究了等径弯曲通道(ECAP)变形后45钢中先共析铁素体及珠光体组织的演变特征.结果表明,ECAP变形4道次后,片层状的珠光体组织演变成了超细的渗碳体颗粒均匀分布于亚微晶铁素体基体的组织.先共析铁素体由原始的平均晶粒尺寸约为30 μm演变为大角度晶界分离的、平均晶粒尺寸约为0.4μm的超细晶组织.ECAP变形后,先共析铁素体首先在其内部会形成具有薄片层界面(LBs)的板条位错胞甚至亚晶组织.进一步变形时位错胞或亚晶可继续细化.再进一步变形时通过晶界滑移和晶粒旋转的方式可以获得具有大角度晶界分离的、等轴的超细晶组织. 相似文献
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热加工对铸造AM50镁合金显微结构和力学性能的影响 总被引:4,自引:0,他引:4
采用锻造和等通道转角挤压(ECAP)等技术研究了热加工对铸造AM50镁合金显微结构和力学性能的影响, 以改善该合金的力学性能.结果发现, ECAP对铸造AM50镁合金和锻造AM50镁合金两种显微结构的影响不同, 这是由于两种状态初始晶粒尺寸不同引起的.铸态AM50镁合金晶粒尺寸粗大, 经过ECAP工艺后, 晶界上出现大量平直滑移线;而锻态AM50镁合金经过ECAP工艺后, 晶粒进一步细化, 滑移线痕迹不明显.铸态AM50镁合金经过ECAP工艺后显微硬度从54.5提高到72.3, 锻造AM50镁合金经过ECAP工艺后显微硬度从60.3提高到81.9.铸造AM50镁合金经过锻造及ECAP工艺热加工后力学性能抗拉强度提高到320 Mpa, 同时延伸率保持在35%以上. 相似文献
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Grain structures in gas tungsten-arc welds of austenitic stainless steels with ferrite primary phase
The grain structures were investigated in full penetration gas tungsten-arc (GTA) welds in sheets of 304 and 321 austenitic
stainless steels for a range of welding conditions. In type 321 steel welds, fine equiaxed ferrite dendrites were observed
in the ferrite phase. The equiaxed structure was ascribed to heterogeneous nucleation of ferrite on Ti-rich cuboidal inclusions
present in this steel, since these inclusions were observed at the origin of equiaxed dendrites. In type 304 welds, the ferrite
grains were columnar, except in less complete penetration specimens, where a few coarse equiaxed dendrites appeared to originate
from the weld surface. The secondary austenitic grain structure was columnar in both steels. In type 304 steel, the columnar
austenitic grain structure did not necessarily correspond to the primary ferrite grains. In type 321 steel, the secondary
austenite was columnar despite the equiaxed structure of the primary ferrite. Factors which affect the columnar-to-equiaxed
transition (CET) are discussed. The failure to form equiaxed austenitic grains in type 321 steel is ascribed to austenite
growing across the space between ferrite grains instead of renucleating on the primary equiaxed ferrite. 相似文献
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Kyung-Tae Park Yong-Seog Kim Dong Hyuk Shin 《Metallurgical and Materials Transactions A》2001,32(9):2373-2381
Two grades of low-carbon steel, one containing vanadium and the other without vanadium, were subjected to equal channel angular
pressing (ECAP) at 623 K up to an effective strain of ∼4. After equal channel angular pressing, a static annealing treatment
for 1 hour was undertaken on both pressed steels in the temperature range of 693 to 873 K. By comparing the microstructural
evolution during annealing and the tensile properties of the two steels, the effect of the addition of vanadium on the thermal
stability of ultrafine-grained (UFG) low-carbon steel fabricated by intense plastic straining was examined. For the steel
without vanadium, coarse recrystallized ferrite grains appeared at annealing temperatures above 753 K, and a resultant degradation
of the strength was observed. For the steel containing vanadium, submicrometer-order ferrite grain size and ultrahigh strength
were preserved up to 813 K. The enhanced thermal and mechanical stabilities of the steel containing vanadium were attributed
to its peculiar microstructure, which consisted of ill-defined pearlite colonies and ultrafine ferrite grains with uniformly
distributed nanometer-sized cementite particles. This microstructure resulted from the combined effects of (a) the preservation
of high dislocation density providing an effective diffusion path, due to the effect of vanadium on increasing the recrystallization
temperature of the steel; and (b) precipitation of fine cementite particles at ferrite grain boundaries through the enhanced
diffusion of carbon atoms (which were dissolved from pearlitic cementite by severe plastic straining) along ferrite grain
boundaries and dislocation cores. 相似文献
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摘要:对粗晶201LN奥氏体不锈钢采用60%冷变形结合700℃退火120s工艺制备超细晶奥氏体不锈钢,研究晶粒细化对奥氏体不锈钢高温力学性能的影响。利用光学显微镜、扫描电子显微镜、透射电子显微镜、电子背散射衍射技术对粗晶和超细晶奥氏体钢进行了组织表征,并使用万能试验机测试20和650℃环境下力学性能。结果显示粗晶奥氏体不锈钢经过冷变形结合退火工艺处理,平均晶粒尺寸由18μm细化为0.9μm,屈服强度由383MPa提高到704MPa,而伸长率由63.8%下降到46.3%,表明晶粒细化能有效提高奥氏体不锈钢屈服强度的同时较小损害塑性,TEM证实其形变机制均为形变诱导马氏体和孪生协同作用。当温度由20℃提高到650℃时,粗晶奥氏体不锈钢屈服强度和伸长率分别下降到180MPa和28.1%,超细晶奥氏体不锈钢屈服强度和伸长率分别为384MPa和24.2%。这表明在650℃高温环境下细晶强化作用仍然有效,粗晶和超细晶奥氏体不锈钢也有较好的塑性,其形变机制分别变为位错滑移和位错滑移+层错+孪生。 相似文献
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等径弯曲通道变形对超低碳钢组织及性能的影响 总被引:1,自引:0,他引:1
研究了室温下C方式等径弯曲通道变形(ECAP)对超低碳钢组织及性能的影响。结果表明:第1道次ECAP变形后,组织细化效果最显著;随变形道次的增加,组织由取向差小的板条状亚晶演变成取向差大的等轴晶;第4道次ECAP变形后,晶粒平均尺寸约03 μm;变形道次继续增加,晶粒尺寸变化不显著,而晶粒取向差不断增大。这表明第4道次ECAP变形为超低碳钢细化极限;ECAP变形可大幅度提高超低碳钢的强度,并保持较高的塑性。 相似文献
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C. X. Huang G. Yang C. Wang Z. F. Zhang S. D. Wu 《Metallurgical and Materials Transactions A》2011,42(7):2061-2071
The technique of equal-channel angular pressing (ECAP) was used to refine the microstructure of an AISI 301 austenitic stainless
steel (SS). An ultrafine-grained (UFG) microstructure consisting mainly of austenite and a few martensite was achieved in
301 steel after ECAP processing for four passes at 523 K (250 °C). By submitting the as-ECAP rods to annealing treatment in
the temperature range from 853 K to 893 K (580 °C to 620 °C) for 60 minutes, fully austenitic microstructures with grain sizes
of 210 to 310 nm were obtained. The uniaxial tensile tests indicated that UFG 301 austenitic SS had an excellent combination
of high yield strength (>1.0 GPa) and high elongation-to-fracture (>30 pct). The tensile stress–strain curves exhibited distinct
yielding peak followed by obvious Lüders deformation. Measurements showed that Lüders elongation increased with an increase
in strength as well as a decrease in grain size. The microstructural changes in ultrafine austenite grains during tensile
deformation were tracked by X-ray diffraction and transmission electron microscope. It was found that the strain-induced phase
transformation from austenite to martensite took place soon after plastic deformation. The transformation rate with strain
and the maximum strain-induced martensite were promoted significantly by ultrafine austenite grains. The enhanced martensitic
transformation provided extra strain-hardening ability to sustain the propagation of Lüders bands and large uniform plastic
deformation. During tensile deformation, the Lüders bands and martensitic transformation interacted with each other and made
great contribution to the excellent mechanical properties in UFG austenitic SS. 相似文献