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1.
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. 相似文献
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Thomas R. Bieler Scott C. Sutton Bret E. Dunlap Zackery A. Keith Philip Eisenlohr Martin A. Crimp Brad L. Boyce 《JOM Journal of the Minerals, Metals and Materials Society》2014,66(1):121-128
The evolution of heterogeneous deformation in a tantalum polycrystal was examined during a three-point bending experiment using electron backscatter pattern mapping. Slip bands formed at strains as low as 1%, and they became more intense with strain. Heterogeneous deformation was evident as intragranular orientation gradients as large as 30° were observed after a strain of about 8%. Nonmonotonic changes in the local average misorientation distribution were observed, implying that dislocation substructure developed in a complex manner. Slip bands were analyzed using plane traces computed from local orientation information. With the assumption of uniaxial stress, Schmid factors for favorable slip systems were identified for each grain and compared with observations, showing evidence for macroscopic activity on both {110} and {112} slip systems. Reconstructed boundary data were used to estimate the geometric potential for slip transfer at grain boundaries. The correlations indicated that when active slip systems were favorably oriented for slip transfer across the boundary, it was often observed in the form of continuous slip bands aligned across the boundary. In boundaries where geometrical alignment and Schmid factors were not favorable for slip transfer, there was a higher likelihood to form ledges (topographic discontinuities) along the grain boundaries. Dislocation pileups at grain boundaries were also correlated with a low potential for slip transfer. 相似文献
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Ya Liu Sai Liu Xuping Su Haoping Peng Jianhua Wang Hao Tu 《Journal of Phase Equilibria and Diffusion》2013,34(2):82-88
The aim of this paper is to identify selective oxidation of high strength steels under different conditions. FISHER model is introduced to simulate diffusion and precipitation of chemical elements in metallic matrices and grain boundary, a scheme of its analytical solution is given. Effects of grain size, dew point and annealing temperature related to concentration of oxygen during annealing treatment are presented. The results are consistent well with literatures. The calculation shows that the selective oxidation of CMnSi TRIP steel at ferritic annealing in a low dew point N2-10%H2 atmosphere of ?30 °C result in the formation of internal MnO in the matrix and SiO2 particles in the subsurface. The calculations agree well with the experimental results. 相似文献
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本研究在550℃下对纯钨分别进行了1、2、5和10圈的高压扭转变形,并对变形前后的微观组织进行了EBSD和TEM表征。结果显示,纯钨经过大塑性变形后,晶粒得到细化,大角度晶界比例上升,同时晶内位错逐渐向晶界处移动并产生有序化排列。采用修正位错模型对变形前后的晶界能量进行了计算,计算结果表明纯钨在经过大塑性变形后,晶界上的能量升高并且能量主要来自于变形过程中在晶界处积累的额外位错。同时在变形后的试样中观察到了一种特殊的非平衡晶界,分析可知非平衡晶界的形成条件是材料晶粒尺寸在位错平均自由程以下,并且是在大塑性变形材料中形成的。其在TEM高分辨下的形貌特征表现为较宽的晶界厚度和晶面干涉形成的莫尔条纹。 相似文献
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S. K. Lawrence B. P. Somerday R. A. Karnesky 《JOM Journal of the Minerals, Metals and Materials Society》2017,69(1):45-50
Enhanced dislocation processes can accompany decohesion mechanisms during hydrogen degradation of ductile structural metals. However, hydrogen–deformation interactions and the role of defects in degradation processes remain poorly understood. In the current study, nanoindentation within specifically oriented grains in as-received, hydrogen-charged, aged, and hydrogen re-charged conditions revealed a “hysteresis” of indentation modulus, while the indentation hardness varied minimally. Thermal pre-charging with approximately 2000 appm hydrogen decreases the indentation modulus by ~20%, aging leads to a slight recovery, but re-charging drives the modulus back down to values similar to those measured in the hydrogen-charged condition. This “hysteresis” indicates that dissolved interstitial hydrogen is not solely responsible for mechanical property alterations; hydrogen trapped at defects also contributes to elastic property variation. 相似文献
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通过扫描电子显微镜(SEM)、电子背散射衍射(EBSD)、取向成像显微技术(OIM)研究了在不同冷轧及退火工艺下 Ni-Cr-W 系高温合金晶界特征分布的规律。结果表明,70%变形量下再结晶完成所需时间较短,特殊晶界比例随着退火时间延长先增加后减少;10%变形量下再结晶驱动力较小,再结晶所需时间较长,特殊晶界比例在长时间退火后达到最大值。在晶粒团簇内部,晶粒之间有Σ3n的取向关系,而不同的晶粒团簇间,晶粒则没有这种特殊的取向关系。 相似文献
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The mechanical response of a bi-crystal model with a 90° grain boundary under external compressive and tensile loading parallel to the boundary plane normal was investigated with molecular dynamics simulations.The grain boundary was found to migrate along two opposite directions upon compressive and tensile straining,with the formation of inter-connected coherent twin boundary and basal/prismatic boundary.The atomic details of such grain boundary migration were unraveled,which indicated the role of interface dislocations.The temperature effect was also discussed. 相似文献
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A broken-bond type computational method has been developed for the calculation of the five-dimensional grain boundary energy. The model allows quick quantification of the unrelaxed five-dimensionally specified grain boundary energy in arbitrary orientations. It has been validated on some face-centred cubic metals. The stereo projections of grain boundary energy of ∑3,∑5,∑7,∑9,∑11,∑17 b and ∑31a have been studied. The results of Ni closely resemble experimentally determined grain boundary energy distribution figures, suggesting that the overall anisotropy of grain boundary energy can be reasonably approximated by the present simple model. Owing to the overlooking of relaxation matter, the absolute values of energy calculated in present model are found to be higher than molecular dynamic-based results by a consistent magnitude, which is 1 J/m2 for Ni. The coverage of present method forms a bridge between atomistic and meso-scale simulations regarding polycrystalline microstructure. 相似文献
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利用背散射电子衍射花样(EBSD),分析了冷轧变形量、退火温度和保温时间对高纯铝晶界特征分布的影响,并探讨了纯铝的变形再结晶行为与低∑重位点阵晶界(Coincidence Site Lattice,简称CSL)大量形成之间的内在联系.结果表明,变形量20%的试样在360 ℃退火时低∑-CSL晶界比例达到了44.2%,与低层错能金属相比,铝的∑3^n晶界比例较低,其他低∑-CSL晶界比例较高.不同变形量试样的∑3^n晶界比例在再结晶温度退火取得最大值,升高退火温度或延长保温时间,晶粒都将发生长大,一般大角度晶界的迁移会吞并已有的低∑-CSL晶界,造成∑3^n晶界和低∑-CSL晶界比例都有所下降. 相似文献
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A. J. Levinson D. J. Rowenhorst A. C. Lewis 《JOM Journal of the Minerals, Metals and Materials Society》2014,66(5):774-779
In this work, the effect of grain boundary engineering (GBE) on the structure and connectivity of networks of two types of boundaries was quantified. General high angle boundaries and “special” Σ = 3 and Σ = 9 coincident site lattice boundaries were considered. The effect of GBE processing was to increase the population and length of special boundaries and to disrupt the network of high-angle grain boundaries (HAGBs) in the microstructure. The GBE processing resulted in an increase in the population of special boundaries as determined by line length fraction from approximately 37% to approximately 57%. The connectivity of the special boundaries, as determined by topological analysis, increased by a factor of 4, while the connectivity of HAGBs decreased by an order of magnitude. Cluster sizes in the special boundary network increased across the range of sizes, and the maximum cluster size of HAGBs decreased significantly. The metrics reported here allow for a quantitative analysis of grain boundary connectivity in microstructures, as well as for a quantitative means of comparison of microstructures. These metrics will be used in simulations of diffusional creep, with the aim of quantifying structure–property relationships in grain boundary engineered systems. 相似文献
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Yongli Wang Liangyin Xiong Shi Liu 《金属学报(英文版)》2014,27(4):615-620
The permeability and diffusivity of hydrogen in directionally solidified polycrystalline and single crystal nickel foils were measured by gas permeation method.The results showed that both hydrogen diffusivity and permeability were higher in directionally solidified nickel specimen than those in single crystal one at the temperature ranging from 300 to480 °C,and confirmed the existence of short-circuit diffusion along the grain boundaries(GBs) in the directionally solidified nickel.The results suggested that the rapid diffusion along GBs was more obviously characterized in terms of higher permeability rather than higher diffusivity.The contribution of grain boundary to hydrogen transportation was represented by the differences of diffusivity(and permeability) in single crystal nickel and directionally solidified nickel.By modifying the Fick's first diffusion law and counting the grain boundary density,the hydrogen diffusivity and permeability of rapid diffusion along GBs were calculated.The results suggested both the diffusivity and permeability fit the Arrhenius relationship well at different temperature. 相似文献
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S. Yukawa M. J. Sinnott 《JOM Journal of the Minerals, Metals and Materials Society》1955,7(9):996-1002
A high resolution autoradiographic study of the diffusion of a nickel isotope (Ni63) into copper in the temperature range of 650° to 925°C, with particular emphasis on grain boundary diffusion, has been made. The extent of grain boundary diffusion is a function of the grain boundary angle and the diffusion temperature. The ratios of the grain boundary diffusion coefficient to the lattice diffusion coefficient ranges from 104 to 105. The activation energy for grain boundary diffusion decreases with increasing grain boundary angle. 相似文献
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钢中奥氏体晶界遗传性再探讨 总被引:2,自引:0,他引:2
作者用20Cr2Ni4A钢研究了晶界遗传现象和本质、再次处理前的热变形对晶界遗传的影响以及晶界传对力学性能的影响。研究表明,该钢存在典型的晶界遗传现象,其本质在于加热过程中于原晶界处形核的新相奥氏体分属于两个原奥氏体晶粒,并且不能跨越原晶界合并或长大。高温大变形能够彻底消除晶界遗传现象。遗传下来的粗大原晶界对材料的力学性能无特殊影响。 相似文献
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S. J. Fensin C. Brandl E. K. Cerreta G. T. Gray T. C. Germann S. M. Valone 《JOM Journal of the Minerals, Metals and Materials Society》2013,65(3):410-418
We investigate the responses of four representative grain boundaries in face-centered cubic Cu bicrystals to shock compression as a function of the loading direction. Two loading directions are considered, either parallel or perpendicular to the grain boundary plane, representing the extremes that a polycrystalline sample will ordinarily experience under the uniaxial strain conditions of planar shock loading. Using molecular dynamics simulations, we demonstrate that the deformation processes during shock compression of the same boundary are altered measurably by changing the loading direction. The Majority of the differences in the nanoscale deformation processes were related to the activation of varying slip systems in the same boundary under the two loading conditions. This change in deformation processes, and hence the plastic response, might eventually affect the failure stress for a grain boundary. 相似文献
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晶界作为微观结构的重要组成部分,对材料的性能起着关键性的影响.晶界相变是准确阐述众多材料现象的重要信息.然而,由于晶界结构复杂、晶界相变观测困难等原因,迄今为止仍缺乏对这些材料现象的直接证据和机理解释.随着先进表征设备特别是球差校正透射电镜的发展,再加上功能强大的计算机模拟,建立界面热力学模型并构建不同类型的晶界相图,为晶界结构及晶界相变的研究提供了广阔的前景.本文从晶界与晶界相变的分类、表征、界面热力学模型、晶界相图的构建等方面,综述了界面热力学与晶界相图的研究进展,展望了该研究领域未来发展的重点及趋势. 相似文献
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利用形变及热处理工艺提高了690合金的低Σ重位点阵(Coincidence Site Lattice, CSL)晶界比例,通过电子背散射衍射(EBSD)技术表征了由不同类型晶界构成的网络特征,结果表明通过晶界工程处理,能够形成以大尺寸“互有Σ3n取向关系晶粒的团簇”显微组织为特征的晶界网络分布,这种显微组织是再结晶过程中多重孪晶充分发展的结果。通过晶间腐蚀浸泡实验表明通过晶界工程处理的样品抗晶间腐蚀性能较未经过晶界工程处理的样品明显提高。腐蚀后样品的显微形貌表明大尺寸“互有Σ3 n 取向关系晶粒的团簇”能够阻止晶间腐蚀向样品内部扩展,并且能够保护下层的显微组织。 相似文献