共查询到19条相似文献,搜索用时 156 毫秒
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相分析表明该合金由Al基固溶体和CuAl_2、ZrAl_3两种粒子所组成。合金超塑性变形后,利用标记线法测定了晶界滑移量对总变形量的贡献为60%左右。在δ≈30%的试样上观察到晶界变宽,在晶界上呈现折皱区,并在遇到第二相时改变方向。透射电镜分析表明,晶界滑移时出现晶界位错,在三晶交界处或晶界坎处向晶内激发位错,晶界是位错源与壑,激活的晶内位错通过滑移和攀移会形成位错亚晶界,晶内位错的激活与运动是晶界滑移的重要协调机制,晶界滑移与晶界位错运动有关。合金超塑性变形时,在晶界和CuAl_2相界处有空洞形成,研究了空洞面积分数与面缩率的关系。靠近断口处,空洞数和面积分数急剧增加,说明空洞的增殖、扩展和连接导致断裂。 相似文献
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通过形变热处理工艺制备2050铝锂合金细晶板材,采用光学显微镜、扫描电镜等研究预变形对第二相分布、晶粒组织及板材超塑性的影响。结果表明:采用预变形后,高温过时效过程中板材晶内形成大量亚晶,大量的亚晶界促进了T_B相的析出同时提高了粗化速率,显著增加了晶内T_B相的尺寸,使得有效激发再结晶形核第二相粒子体积分数由0.92%提高至3.28%。同时与未预变形板材相比,板材中心层平均晶粒尺寸由12.59μm降低至9.59μm,表层平均晶粒尺寸由10.79μm降低至8.60μm,晶粒细化效果得到明显改善,超塑性变形能力显著提升,在490℃,2×10~(-4)s~(-1)的变形条件下,伸长率由230%提高至470%。 相似文献
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用透射电镜详细观察了含微量稀土的 Al-Zn-Mg 合金在超塑变形过程中晶界位错的形态、运动及其与晶界第二相粒子的相互作用情况。发现晶界中的第二相粒子对位错沿晶界运动有明显的阻碍作用。实验还发现在含第二相粒子较多的晶界的超塑性合金中,晶界滑动是通过位错沿晶界运动和晶界的粘滞性流动两种机制同时发生作用进行的,它们相互促进并共同推动了晶界滑动的发展。首次在透射电镜下观察到超塑变形使晶界加宽的现象,在面缩率ψ=72.2%的样品中测得某晶界的宽度约为100nm,从而证实了超塑变形的晶界滑动和晶粒转动机制。 相似文献
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Fe-Mn-Si-Cr-Ni-C系形状记忆合金时效效果的研究 总被引:4,自引:1,他引:3
通过SEM分析,研究了时效后不同成分Fe-Mn-Si-Cr-Ni-C系形状记忆合金形状记忆效应和微观组织,在1123K时效时,超低碳合金1的形状回复率随时效时间的增加一直呈直线上升的趋势,含碳0.18%合金2的形状回复率随时效时间的增加而增加,在300min达到最大值后将随时间的进一步增加而缓慢下降,SEM分析发现在合金2的晶界和晶内析出富铬,富锰和富硅的合金碳化物,而合金1仅在晶界有第二相析出,且第二相成分不同于合金2中的,合金2中第二相粒子的长大速度显著高于合金1中第二相粒子的长大速度,且数量也多得多,通过时效强化奥氏体基体,可显著提高合金的形状记忆效应。 相似文献
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本文对铍青铜(QBe2)超塑变形中的空洞形成过程和晶粒重排进行了研究。结果表明,空洞的形成直接影响着晶粒重排过程。晶粒重排以多重方式进行,而不是单一方式,形成空洞是其中的一个步骤。对于含有第二相粒子的 QBe2合金,其超塑变形中所产生的位错与第二相粒子的交互作用是导致空洞形成的重要原因。空洞的形成并不直接导致材料的断裂,而断裂的真正原因是空洞的连结。文中给出了描述晶粒重排和空洞形成与连结的示意图。 相似文献
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本文研究了硬度相差较大的两相合金QA110-3-1.5铝青铜超塑变形机制。其中的α相较硬,晶粒不易变形,β相较软,晶粒易于塑性变形,且没有固定形状。晶界滑动是超塑变形的主要机制,晶内位错滑移和扩散蠕变则对晶界滑动起着协调作用。 相似文献
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Yu Zhang Shuai Chang Yuyong Chen Yuchao Bai Cuiling Zhao Xiaopeng Wang Jun Min Xue Hao Wang 《材料科学技术学报》2021,95(36):225-236
The superplasticity of Ti-43Al-9V-0.2Y alloy sheet hot-rolled at 1100 ℃ was systematically investigated in the temperature range of 750-900 ℃ under an initial strain rate of 10-4 s-1.A bimodal γ grain-distribution microstructure of TiA1 alloy sheet,with abundant nano-scale or sub-micron γ laths embed-ded inside β matrix,exhibits an impressive superplastic behaviour.This inhomogeneous microstructure shows low-temperature superplasticity with a strain-rate sensitivity exponent of m =0.27 at 800 ℃,which is the lowest temperature of superplastic deformation for TiAl alloys attained so far.The maximum elongation reaches ~360% at 900 ℃ with an initial strain rate of 2.0 × 10-4 s-1.To elucidate the softening mechanism of the disordered β phase during superplastic deformation,the changes of phase composi-tion were investigated up to 1000 ℃ using in situ high-temperature X-ray diffraction (XRD) in this study.The results indicate that β phase does not undergo the transformation from an ordered L20 structure to a disordered A2 structure and cannot coordinate superplastic deformation as a lubricant.Based on the microstructural evolution and occurrence of both y and β dynamic recrystallization (DR) after tensile tests as characterized with electron backscatter diffraction (EBSD),the superplastic deformation mecha-nism can be explained by the combination of DR and grain boundary slipping (GBS).In the early stage of superplastic deformation,DR is an important coordination mechanism as associated with the reduced cavitation and dislocation density with increasing tensile temperature.Sufficient DR can relieve stress concentration arising from dislocation piling-up at grain boundaries through the fragmentation from the original coarse structures into the fine equiaxed ones due to recrystallization,which further effectively suppresses apparent grain growth during superplastic deformation.At the late stage of superplastic de-formation,these equiaxed grains make GBS prevalent,which can effectively avoid intergranular cracking and is conducive to the further improvement in elongation.This study advances the understanding of the superplastic deformation mechanism of intermetallic TiAl alloy. 相似文献
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Influence of the Al2Cu‐phase on the superplasticity of AlCuMn alloy High‐temperature creep‐resistant AlCuMn wrought alloy has been investigated and optimised with respect to their superplastic deformability; a maximal elongation ε of 850 per cent was thus attained at a deformation temperature of 530°C. Prerequisites for superplastic deformation behaviour and for the associated high elongation values of these aluminium alloys are an especially fine‐grained structure as well as a decrease in the amount of Al2Cu phase and a uniform distribution of this phase in the structure. Superplastic deformation (SPD) results in a pronounced change in the shape of the large particles of the θ‐phase; the particles of this phase thereby form veins along the boundaries of adjacent grains. During deformation, the grains lose their equiaxial shape and elongate in the direction of tension as a result of pronounced intragranular sliding dislocation in the microstructure. Transmission electron micrographs of the deformed structure have revealed a pile‐up of dislocations in the grains of the aluminium alloy. The grain size of commercially available sheets of AlCuMn wrought alloys with a thickness of 1 mm is approximately 30 μm. After optimising, the grain size of the sheets produced by the new method was on 12 μm until 5 μm. The new technique differs only slightly from industrial manufacture. 相似文献
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K. N. Melton 《Journal of Materials Science》1975,10(10):1651-1654
The effect of annealing at 400? C on the microstructure of a cold-worked Al-0.8 wt % Zr alloy is reported. It is shown that the initially high dislocation density in the cold-rolled material is progressively reduced, although the grains and subgrains were exceptionally resistant to coarsening. Precipitation of the metastable cubic Al3Zr phase occurred, both discontinuously in the form of fan shaped precipitates and also on the grain boundaries and within the grains as small, nearly spherical particles. The mechanical properties of the alloy at 400? C are consistent with a major dislocation contribution to the overall deformation process, in contrast with most other fine grained materials which are superplastic. 相似文献
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通过高温拉伸实验研究TC18钛合金在温度为720~950℃,初始应变速率为6.7×10~(-5)~3.3×10~(-1)s~(-1)时的超塑性拉伸行为和变形机制。结果表明:TC18钛合金在最佳超塑性变形条件下(890℃,3.3×10~(-4)s~(-1)),最大伸长率为470%,峰值应力为17.93MPa,晶粒大小均匀。在相变点Tβ(872℃)以下拉伸,伸长率先升高后下降,在温度为830℃,初始应变速率为3.3×10~(-4)s~(-1)时取得极大值373%,峰值应力为31.45MPa。TC18钛合金在两相区的超塑性变形机制为晶粒转动与晶界滑移,变形协调机制为晶内位错滑移与攀移;在单相区的超塑性变形机制为晶内位错运动,变形协调机制为动态回复和动态再结晶。 相似文献
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The second phase particles were observed during the whole manufacturing process of conventional grain oriented electrical steels, exhibiting that the areal density of particles in the center was obviously higher than that on the surface at each manufacturing stage. After hot rolling, the approximately equiaxed grains formed upon recrystallization were present on the sheet surface while the deformation structures were retained in the central part. Thus, the dislocation density on the surface was evidently lower than that in the center and this trend became more noticeable after the first cold rolling. Since new precipitates were mainly nucleated at dislocations during both hot rolling and annealing following cold deformation, the difference in dislocation density resulted in the inhomogeneous distribution of particles through the thickness of sheet. According to this, Goss grains, which were usually found near the surface, tended to grow up more easily during the secondary recrystallization treatment. 相似文献
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Askar Sheikh-Ali 《Journal of Materials Science》2007,42(10):3621-3626
The anisotropy of flow stress in a cold rolled sheet of Ti-6Al-4V alloy has been observed during superplastic deformation
at 850 °C. At this temperature, the alloy has duplex microstructure with almost equiaxed grains of the alpha and beta phases.
The maximum value of flow stress has been established for the rolling direction and minimum—for the transverse one. Also,
the anisotropy of crystallographic texture weakening in the alpha phase has been observed. However, it has been demonstrated
that texture in the alpha phase cannot be responsible for the observed anisotropic behavior. Texture in the beta phase is
the suggested reason for the flow-stress anisotropy during superplastic deformation. 相似文献
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Zhiyi LIU Jianzhong CUI Guangrun BAI Metal Forming Department Northeastern University Shenyang China 《材料科学技术学报》1993,9(4):301-303
The effects of concurrent pulses in holding duration on superplasticity of 2091 Al-Li alloy have beeninvestigated in this paper.The results of superplastic deformation showed that concurrent pulses inholding duration decreased the optimum holding time for superplastic deformation(ε=3.33×10~(-2) s~,T=500℃)from 15 to 5 min and increased elongation(δ)from 530 to 550%.Themetallographic observations showed that the specimens appliedly by concurrent pulse were com-pletely recrystallized after holding 5 min at 500℃,and grains refined to about 2μm,and those spec-imens unapplied current pulses were partly recrystallized even after holding 15 min at 500℃.theelectron probe analyses indicated that concurrent pulses promoted atomic diffusion.It is pointed outthat concurrent pulses accelerate atom diffusion and dislocation motion.increase nucleation rate ofrecrystallization and decrease the optimum holding time for superplastic deformation and increasesuperplastic properties. 相似文献
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Grain boundary sliding and accommodation mechanisms during superplastic deformation of ZK40 alloy processed by ECAP 总被引:1,自引:0,他引:1
Controlling mechanism during superplastic deformation of ZK40 alloy processed by ECAP was identified. Effects of twinning
and dynamic strain ageing (DSA) on superplasticity were analyzed. Amplitude in stress oscillation was correlated with solute
atom concentration theoretically. Twinning can be an enhancing factor in grain boundary sliding and DSA had apparent influence
on stress fluctuation; they were accommodation mechanisms for superplastic deformation through grain reorientation and interaction
between solute atoms and dislocations, respectively. The interaction between mobile and forest dislocations played a dominant
role for the occurrence of DSA, when dislocation density was relatively low in large grains. The effect of DSA became more
active with increasing temperature, although grain boundary sliding (GBS) was the controlling mechanism throughout the whole
process of superplastic deformation under elevated temperatures. 相似文献