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JournalISSN: 0001-6160

Acta Metallurgica 

About: Acta Metallurgica is an academic journal. The journal publishes majorly in the area(s): Dislocation & Grain boundary. It has an ISSN identifier of 0001-6160. Over the lifetime, 7139 publication(s) have been published receiving 425883 citation(s).
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Journal Article
Abstract: Developments in deformation and recrystallization textures were studied in cold-rolled (50--90% reduction) ultra low carbon (ULC) steel using X-ray texture measurements and orientation imaging microscopy (OIM). During deformation, {gamma}-fiber (ND//{l_angle}111{r_angle}) increased between 0 and 50% reduction but then did not change significantly, while {alpha}-fiber (RD//{l_angle}110{r_angle}) increased progressively from 0 to 90% reduction. After complete recrystallization, however, a steady increase in {gamma} and almost no changes in {alpha} were observed with increasing strain. Developments in recrystallization textures were attributed to two parameters: (1) spacings ({lambda}{sub i}, as measured along the normal direction, ND, where i can be a specific component of {alpha}/{gamma}-fibers) of the {alpha}/{gamma} deformed bands; and (2) their relative ability to form recrystallized grains. While {lambda}{sub i} was determined by the deformation texture and the thicknesses of the deformed grains/bands and naturally decreased with increasing strain, estimations of parameter (2) were obtained from the so-called nucleation factors (N{sub i}, defined as the number of recrystallized i grains per i band--as measured/estimated along the ND). At higher strains, noticeable drops in the N{sub i}s of {alpha}-fiber were observed. Two plausible causes for such drops were increased stored energy advantages for {gamma} bands and orientation pinning in some of the {alpha}more » regions.« less

5 citations

Book ChapterDOI
Perry H. Leo1, R.F. Sekerka2Institutions (2)
Abstract: The effect of surface stress on the equilibrium conditions at crystal-melt, coherent crystal-crystal and greased crystal-crystal interfaces is investigated by using a variational method to test for equilibrium. In all three cases, the interface between the phases is modelled as a Gibbsian dividing surface, and the excess internal energy associated with the interface is allowed to depend on both the deformation of the interface and the crystallographic normal to the interface. The position of an interface can vary due to both deformation at the interface and transformation between the two phases at the interface (accretion), and so we define a special variation that accounts for both. Thus, surface stress appears explicitly in both the force and energy balances at crystal-melt and coherent crystal-crystal interfaces. In particular, an interfacial strain energy term appears in the energy balance at these interfaces; this term gives the energy of deforming the interface against the force associated with the surface stress, and is a new result from this analysis. Anisotropy also appears in this energy balance through a term that can be expressed by using Cahn and Hoffman’s ξ-vector. Finally, it is shown that a greased crystal-crystal system differs from crystal-melt and coherent crystal-crystal systems in that two independent deformations and crystallographic normals can be defined at a greased interface. However, by partitioning the excess energy associated with a greased interface between these deformations and normals, one can reduce the equilibrium conditions at a greased interface to those that obtain if the two crystals would interact only through a thin fluid layer at the interface.

81 citations

Journal Article
Abstract: Abstract A study has been made of the spontaneous growth of tin whiskers from tin electrodeposits on phosphor bronze sheet. The driving force for the evolution of tin whiskers is a biaxial compressive stress of about 8 MPa developed in tin deposits by the formation of an intermetallic compound of Cu 6 Sn 5 , especially in grain boundaries of tin films. The biaxial compressive stress gives rise to strains normal to the film plane, which are dependent on the tin grain orientations. The shear stresses due to differences between strains of different grains along the thickness direction make the tin surface oxide film sheared approximately along boundaries of grains with particular orientations which are different from the major texture of the film. Tin extrudes from the grains, whose surface oxide films are sheared. The extrusion takes place continuously by expansion of the dislocation loops by climb and their subsequent glide toward the surface in the slip direction to form whiskers.

425 citations

Journal Article
Abstract: Abstract A micromechanical model describing “quasi-ductile” Hertzian contacts in otherwise brittle ceramics is developed. The elemental basis of the model is a discrete “fault” along an internal weak interface, constrained at its ends by an elastic matrix and subject to frictional sliding, in the subsurface zone of high shear stress in the Hertzian field. By summation over a prescribed density of shear faults within the active plastic zone, the analysis leads to a constitutive identation stress-strain function, with special provision for the incorporation of microstructural variables. Experimental data from a series of mica-containing glass-ceramics with contiguous platelet microstructures are used to confirm the essential predictions of the model. It is demonstrated that plasticity increases with volume fraction and aspect ratio, but not size, of the platelets. Parametric evaluations by curve fitting the indentation stress-strain data allow for predictions of intrinsic stress-strain responses for the glass-ceramics in conventional uniform stressing states.

90 citations

Journal ArticleDOI
C. Marsh1, Haydn Chen1Institutions (1)
Abstract: An in situ X-ray diffraction study of the precipitation reaction of a supersaturated solid solution single crystal of Ni-12.5 at.% Al alloy was performed for moderately high temperatures. The diffusion-control coarsening model of Lifshitz and Slyozov is used to interpret the results of measuring the rate constants determined from the growth of the average particle size and volume fraction of the {gamma}{prime} phase precipitate as derived from the line width and integrated intensity of the superlattice reflection, respectively. Both the diffusion coefficient and the interfacial energy between the matrix and precipitates were experimentally determined for temperatures in the range of 550-700C. The interfacial energies are reasonable when compared with literature values and they seem to indicate a decrease with increasing temperature. The diffusion coefficients yield consistent yet lower values when compared to results for Ni-self diffusion in single crystals, and to polycrystalline measurements of Al diffusion in Ni at comparable temperatures. An enhanced diffusion is observed at 550C and possible explanations are offered. In addition, the coarsening rate was measured to be different for two crystallographic directions at the same temperature. This difference is suggested to be related to the precipitate morphology change from sphere to cuboid evidenced in manymore » Ni-base alloys.« less

30 citations

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