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Title: Triple junction drag effects during topological changes in the evolution of polycrystalline microstructures

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Journal Article: Publisher's Accepted Manuscript
Journal Name:
Acta Materialia
Additional Journal Information:
Journal Volume: 128; Journal Issue: C; Related Information: CHORUS Timestamp: 2017-10-04 22:23:25; Journal ID: ISSN 1359-6454
Country of Publication:
United States

Citation Formats

Zhao, Quan, Jiang, Wei, Srolovitz, David J., and Bao, Weizhu. Triple junction drag effects during topological changes in the evolution of polycrystalline microstructures. United States: N. p., 2017. Web. doi:10.1016/j.actamat.2017.02.010.
Zhao, Quan, Jiang, Wei, Srolovitz, David J., & Bao, Weizhu. Triple junction drag effects during topological changes in the evolution of polycrystalline microstructures. United States. doi:10.1016/j.actamat.2017.02.010.
Zhao, Quan, Jiang, Wei, Srolovitz, David J., and Bao, Weizhu. Sat . "Triple junction drag effects during topological changes in the evolution of polycrystalline microstructures". United States. doi:10.1016/j.actamat.2017.02.010.
title = {Triple junction drag effects during topological changes in the evolution of polycrystalline microstructures},
author = {Zhao, Quan and Jiang, Wei and Srolovitz, David J. and Bao, Weizhu},
abstractNote = {},
doi = {10.1016/j.actamat.2017.02.010},
journal = {Acta Materialia},
number = C,
volume = 128,
place = {United States},
year = {Sat Apr 01 00:00:00 EDT 2017},
month = {Sat Apr 01 00:00:00 EDT 2017}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1016/j.actamat.2017.02.010

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  • Current theories of grain growth presume that grain boundary migration is the rate-limiting step, and either explicitly or implicitly assume that triple junctions can always move with sufficient speed to accommodate the changing positions of the grain boundaries. Following from some recent observations of triple-junction drag effects in tricrystals of zinc and in molecular dynamics models, an analytical theory is developed to explore the effects of triple-junction drag upon grain growth, for a two-dimensional solid. The theory is developed in the framework of the Von Neumann-Mullins formulation, and demonstrates that drag effects operating exclusively at the triple junctions result inmore » a retardation of grain growth. The stability of six-sided grains in the isotropic, drag-free case of the Von Neumann-Mullins analysis is successively extended to grains of 6 {+-} N sides, where N increases with the strength of the triple-junction drag.« less
  • Short interruptions of the growth of polycrystalline films often lead to stress evolution that is reversed when growth is resumed. Correlated in situ stress measurements and ex situ transmission electron microscopy and atomic force microscopy characterizations of grain boundary surface grooves as a function of the interruption time are reported for films deposited at different temperatures and held for different times before quenching to room temperature. These studies suggest that during film deposition surface grooves at grain boundaries are kinetically constrained to be shallow, while during a growth interruption surface diffusion allows grain boundary grooves to deepen and approach theirmore » equilibrium depth. The latter relieves a component of the compressive stress associated with trapped atoms in the grain boundaries. When growth is resumed, the non-equilibrium surface morphology is reestablished and the compressive stress increases to its pre-interruption value.« less
  • Microstructures formed as a result of multiple twinning have been simulated by means of computer modeling. Grain boundary misorientation (character) and triple junction distributions have been studied with the emphasis on the effect of initial texture and multiple twinning process. Although grain boundary distributions are similar in all the microstructures modeled, sharp initial texture leads to a somewhat enhanced amount of {Sigma}3 boundaries and to a considerable increase in the number of triple junctions containing two {Sigma}3 boundaries. The impact of these parameters on the material susceptibility to intergranular crack propagation has been analyzed and implications for grain boundary engineeringmore » has been discussed.« less
  • The grain boundary and triple junction hardenings in molybdenum with different carbon content were studied in connection with the character and the connectivity of grain boundaries at triple junctions by the micro-indentation test. The triple junction hardening is smaller at the junctions composed of low-angle and {sigma} boundaries than at the junctions composed of random boundaries. This difference in the hardening depending on the grain boundary connectivity becomes more significant with a decrease in carbon content in molybdenum.
  • The classical concepts of grain growth in polycrystals are based on the dominant role of grain boundaries. This is reflected by the well known von Neumann-Mullins relation. According to this approach triple junctions do not affect grain boundary motion, and their role in grain growth is reduced to maintaining the thermodynamically prescribed equilibrium angles at the lines where boundaries meet. In the current study the experimental data of triple junction mobility are considered with respect to the process of grain growth in 2D systems, in particular with regard to the controlling kinetics. When boundary kinetics prevails grain growth in amore » polycrystal complies with the von Neumann-Mullins relation. When grain growth is governed by the mobility of triple junctions the kinetics change, and the von Neumann-Mullins relation does not hold anymore. This is the more pronounced the smaller the triple junction mobility. We present a generalized theory of 2D grain growth including a limited triple junction mobility. In this concept the criterion {lambda} plays a central role. It reflects the ratio of boundary to triple junction mobility but is proportional to the grain size as well. The generalized von Neumann-Mullins relation can be expressed in terms of {lambda}. For small values of {lambda}, conspicuous changes of microstructure evolution during grain growth and of microstructural stability are predicted. The theoretical predictions are compared to results of computer simulations by a virtual vertex model.« less