Anisotropic grain boundary area and energy distributions in tungsten

Cyclic stress–strain response of an equal channel angularly pressed Sn-3.8Ag-0.7Cu alloy was investigated to seek a mechanistic understanding of cyclic softening in Sn-rich alloys. The equal channel angular pressing (ECAP) was applied to modify the microstructure of the solder alloy by breaking up the needlelike Ag3Sn intermetallic phase into fine granules and by reducing the large β-Sn dendrites into smaller and equiaxed grains. The extruded alloys were subjected to strain-controlled fatigue test at various strain amplitudes. It was found that the extruded alloy exhibited a sharp decrease of the stress amplitude within the initial few cycles compared with the as-cast alloy. After only a few cycles, the alloy suffered from noticeable surface damage. In situ scanning electron microscopy observations of the cyclic bending specimens revealed an approximately logarithmic relationship between crack density and the number of cycles. A theoretical model of microcrack accumulation was constructed to explain the rapid cyclic softening behavior. The predicted results, based on the model, agreed well with the experimental data and indicated that the rapid softening had resulted from an increased tendency for grain boundary cracking in the ECAPed microstructure due to the increase in the grain boundary area per unit volume and the reduced resistance of Ag3Sn to grain boundary sliding.

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Influence of Inter-Pass Cooling on Microstructural Evolution and Plastic Deformation of Heavy EH47 Plates

Materials ◽

10.3390/ma12101686 ◽

2019 ◽

Vol 12 (10) ◽

pp. 1686

Author(s):

Junyu Wu ◽

Bin Wang ◽

Bingxing Wang ◽

R. D. K. Misra ◽

Zhaodong Wang

Keyword(s):

Plastic Deformation ◽

Grain Boundary ◽

Microstructural Evolution ◽

Volume Fraction ◽

Uniform Elongation ◽

Hexagonal Structure ◽

Tensile Fracture ◽

Boundary Area ◽

Plastic Deformation Behavior ◽

Deformation Pass

Herein, the influence of inter-pass cooling (IC) and conventional two-stage rolling (CTR), on microstructural evolution and plastic deformation behavior of ultra-heavy EH47 plates, is demonstrated. It is reported that the deformation amount and deformation rate, in every deformation pass during rough rolling, at 1/4- and 1/2-thickness of IC steel were higher than the CTR steel. The volume fraction of ferrite and acicular ferrite was 45% and 18%, at 1/4-thickness, and 35% and 50% at 1/2-thickness of IC steel, respectively, whereas the sum of both ferrite phases was smaller than 25% in the CTR steel. The austenite grain boundary area and high-angle grain boundary fraction in the IC steel were higher than the CTR steel. The high density of fine and shapeless pearlite has been observed in IC steel, whereas large-size carbides, with hexagonal structure, have been observed in CTR steel. Compared to the CTR steel, the density of precipitates was apparently lower in IC steel. Two kinds of Nb containing precipitates, such as (Ti, Nb)(C, N) and (Nb, Ti)C, were observed in the tested steels. Total ductility and uniform elongation of the IC steel were higher than the CTR steel. During the tensile process, the crack initiation energy and crack propagation energy of the IC steel were higher than the CTR steel. Moreover, the volume fraction of retained austenite (FCC) was reduced from 7.71% to 0.42% near the tensile fracture in IC steel at 1/4-thickness. In additon, the strain of synergetic plastic deformation of the IC steel was higher than the CTR steel. Meanwhile, compared to the CTR steel, the synergetic plastic deformation of the IC steel occurred at low stress after the yield point, which can be ascribed to the presence of fewer microcracks in the IC steel. Hence, a delayed fracture has been observed in the IC steel plate.

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Grain Size and Chemical Composition Effects on the Grain Boundary Resistance of Ceria

MRS Proceedings ◽

10.1557/proc-730-v4.4 ◽

2002 ◽

Vol 730 ◽

Author(s):

Xiao-Dong Zhou ◽

Harlan U. Anderson ◽

Wayne Huebner

Keyword(s):

Electrical Conductivity ◽

Grain Size ◽

Grain Boundary ◽

Boundary Resistance ◽

Impedance Spectra ◽

Total Resistance ◽

Boundary Area ◽

Oxygen Ions ◽

Composition Effects ◽

Increasing Temperature

AbstractStudies related to the effects of grain size (30nm – 5.0μm) on the electrical conductivity of undoped CeO2 and Ce0.90Gd0.10O1.95 were performed. A series of impedance spectra as a function of temperature and grain size were analyzed. It was found that the ratio of the grain boundary resistance to the total resistance became lower with decreasing grain size, increasing temperature or increasing Gd content. For the case of Gd doped CeO2, the source of the grain boundary resistance may be due to the trapping of oxygen ions in the grain boundary area.

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Simulation of the Kinetics of Grain-Boundary Nucleated Phase Transformations

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.172-174.1128 ◽

2011 ◽

Vol 172-174 ◽

pp. 1128-1133 ◽

Cited By ~ 3

Author(s):

Eric A. Jägle ◽

Eric J. Mittemeijer

Keyword(s):

Grain Size ◽

Grain Boundary ◽

Phase Transformations ◽

Size Distribution ◽

Grain Size Distribution ◽

Kinetic Models ◽

Micro Structure ◽

Boundary Area ◽

Random Nucleation ◽

Kinetics Of

The kinetics of phase transformations for which nucleation occurs on parent-micro-structure grain boundaries, and the resulting microstructures, were investigated by means ofgeometric simulations. The inﬂuences of parent microstructure grain-boundary area density,parent grain-size distribution and parent→product kinetics were analysed. Additionally, thesimulated kinetics were compared with predictions from two kinetic models, namely a modelproposed for spatially random nucleation and a model proposed for grain-boundary nucleation.It was found that the simulated transformed fraction as function of time lies in between the twomodel predictions for all investigated parent microstructures and parent→product kinetics.

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