Title: Correlations between the crystallographic texture and grain boundary character in polycrystalline materials

Authors: R. Edwin García, and Mark D. Vaudin

Source: Acta Materialia, Article in Press, Corrected Proof

Abstract:

A method is presented to determine the misorientation probability distribution function in polycrystalline materials based on a known, analytical or numerical, representation of the associated orientation probability distribution function, i.e., texture. The proposed formulation incorporates the local grain-to-grain orientation correlations by combining local or macroscopic statistical information, and finds a natural interpretation through the well-known stereographic projection (pole-figure) representation. The proposed formulation distinguishes between antiparallel crystallographic orientations, as well as cone-angle and polar angle misorientations. For fiber-textured samples, it is quantitatively shown that highly oriented samples are equivalent to polycrystals with a high density of low-angle misorientations, while completely random (untextured) materials are equivalent to microstructures with a high probability of large-angle misorientations.

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Title: A generalized field method for multiphase transformations using interface fields

Authors: I Steinbach and F Pezzolla

Source: Physica D: Nonlinear Phenomena, Volume 134, Issue 4, 10 December 1999, Pages 385-393

Abstract: The recently developed multiphase field method, describing the interaction between an arbitrary number of individual phase fields with individual characteristics, is reformulated by the use of interface fields. This reformulation allows for the decomposition of the nonlinear multiphase field interactions into pairwise interaction of interface fields. This removes some difficulties in the treatment of triple points or higher order interactions that occurred in the original model. The interface fields being defined in a (2Ñ) dimensional space, where Ñ is the order of the multiple point, can be interpreted being the generalized coordinates for this variational problem. The considered example of a multiphase change problem indicates clearly that a relaxation ansatz for the evolution of the field variables towards the minimum of the free energy is warranted only for generalized coordinates, while a relaxation ansatz using functionally dependent variables and the Lagrange formalism in general mixes time and energy scales.

Note: Hat Tip: Deep.

Title: Modeling the formation and dynamics of polycrystals in 3D

Authors: Ryo Kobayashi and James A. Warren

Source
: Physica A: Statistical Mechanics and its Applications, Volume 356, Issue 1, 1 October 2005, Pages 127-132

Abstract
:
Phase field models of solidification have been extended to include grain boundaries, using a variety of techniques. A model developed by Kobayashi et al. [Physica D 140 (2000) 141] has been used to model a host of physical phenomena, but has so far been confined to two dimensions. In this letter we describe how to extend this model of polycrystalline solidification to three dimensions (3D).

In Nature this week

August 16, 2007

  1. Formation of metallic glass in a pure metal:

    In order to form a glass by cooling a liquid, the normal process of solid crystallization must be bypassed. Achieving that for a pure metal had seemed impossible — until pressure was applied to liquid germanium.

  2. Ageing and cancer:

    At first glance, cancer and ageing would seem to be unlikely bedfellows. Yet the origins for this improbable union can actually be traced back to a sequence of tragic—and some say unethical—events that unfolded more than half a century ago. Here we review the series of key observations that has led to a complex but growing convergence between our understanding of the biology of ageing and the mechanisms that underlie cancer.

Update: Abi on a news report in the Telegraph about the Germanium metallic glass work (and also on “probably the only instance in science in which confusion itself is elevated to the level of a principle” 🙂

In Nature this week

August 10, 2007

Break-down of Hall-Petch

August 8, 2007

Title: The strongest size

Authors: A. S. Argon; S. Yip

Source: Philosophical Magazine Letters, Volume 86, Issue 11 November 2006 , pages 713 – 720

Abstract:
The well known break-down of the Hall-Petch effect of the rise of the plastic resistance with decreasing grain size in polycrystalline metals, when the grain size drops into the nanometre range resulting in a peak plastic resistance at a grain size of about 12-15 nm, is explained by considering two alternative and complementary rate mechanisms of plasticity, grain boundary shear and dislocation plasticity, each contributing to the overall strain rate in proportion to the volume fraction of the material in which they operate. In the model for a given applied strain rate it is shown that the plastic resistance reaches a maximum at a grain size of about 12.2 nm in Cu when the two mechanisms contribute to the overall strain rate equally, defining the so-called strongest size.

Title: Grain growth as a stochastic and curvature-driven process

Authors: Y. G. Zheng; C. Lu; Y. -W. Mai; H. W. Zhang; Z. Chen

Source: Philosophical Magazine Letters, Volume 86, Issue 12 December 2006 , pages 787 – 794

Abstract:

Grain growth subjected to the interplay of stochastic and curvature-driven mechanisms in a single-phase system has been investigated. Numerical results have shown that when the grains are smaller than several tens of nanometres the dominating mechanism is stochastic diffusion control of boundaries. As the grains grow the influence of the deterministic curvature-driven mechanism increases and finally controls the process. In terms of finite-difference solutions to the Fokker-Planck continuity equation, the predicted grain size approaches a log-normal distribution, which agrees well with experimental observations.