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Title: Rafting and elastoplastic deformation of superalloys studied by neutron diffraction

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Publication Date:
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Scripta Materialia
Additional Journal Information:
Journal Volume: 134; Journal Issue: C; Related Information: CHORUS Timestamp: 2018-01-09 22:03:02; Journal ID: ISSN 1359-6462
Country of Publication:
United States

Citation Formats

Coakley, James, Lass, Eric A., Ma, Dong, Frost, Matthew, Seidman, David N., Dunand, David C., and Stone, Howard J.. Rafting and elastoplastic deformation of superalloys studied by neutron diffraction. United States: N. p., 2017. Web. doi:10.1016/j.scriptamat.2017.03.007.
Coakley, James, Lass, Eric A., Ma, Dong, Frost, Matthew, Seidman, David N., Dunand, David C., & Stone, Howard J.. Rafting and elastoplastic deformation of superalloys studied by neutron diffraction. United States. doi:10.1016/j.scriptamat.2017.03.007.
Coakley, James, Lass, Eric A., Ma, Dong, Frost, Matthew, Seidman, David N., Dunand, David C., and Stone, Howard J.. Thu . "Rafting and elastoplastic deformation of superalloys studied by neutron diffraction". United States. doi:10.1016/j.scriptamat.2017.03.007.
title = {Rafting and elastoplastic deformation of superalloys studied by neutron diffraction},
author = {Coakley, James and Lass, Eric A. and Ma, Dong and Frost, Matthew and Seidman, David N. and Dunand, David C. and Stone, Howard J.},
abstractNote = {},
doi = {10.1016/j.scriptamat.2017.03.007},
journal = {Scripta Materialia},
number = C,
volume = 134,
place = {United States},
year = {Thu Jun 01 00:00:00 EDT 2017},
month = {Thu Jun 01 00:00:00 EDT 2017}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1016/j.scriptamat.2017.03.007

Citation Metrics:
Cited by: 4works
Citation information provided by
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  • In situ compression tests combined with neutron diffraction were performed on Ti{sub 2}AlN MAX polycrystals with lamellar anisotropic microstructure: the diffraction peak evolution (position and profile) with applied stress reveals that lamellar grains parallel to compression axis remain elastic while lamellar grains perpendicular to compression plastify, both families being subjected to strong variations of heterogeneous strains (types II and III). We demonstrate that this behavior originates from the complex response of the very anisotropic lamellar microstructure and explains the observation of reversible hysteretic loops when cycling MAX polycrystals even in the elastic regime.
  • The rafting mechanism is one of the most important and interesting phenomena which appears in Ni base superalloys during high temperature creep tests. The precipitated {gamma}{prime} particles, which are arrayed periodically in the {gamma} matrix, coalesce and form rafting structures in the direction perpendicular to tensile stresses. To understand this phenomenon, element profiles and diffusion process have been investigated in the vicinity of the {gamma}/{gamma}{prime} interfaces. In this paper, the authors analyzed accurate element profiles, especially Al and Cr which are main alloying elements, in the most vicinity of {gamma}/{gamma}{prime} interface regions. The rafting mechanism is correlated with the diffusionmore » process on the basis of Al concentration profiles in a few nano meter distance from the {gamma}/{gamma}{prime} interfaces.« less
  • The effect that the morphological changes in {gamma}/{gamma}{prime} superalloys have on the mechanical properties of these materials is still an unresolved issue of the greatest interest. Experimental studies on [001] oriented single crystals have shown, for instance, that when a microstructure consisting of evenly spaced cuboids of {gamma}{prime} embedded in {gamma} was subjected to externally applied stresses at high temperature, then the coalescence occurred in an orientation-dependent way, and also that these rafting phenomenon can have a significant influence on the creep or fatigue life in load-bearing applications. In some alloys, the coalescence produced long rods or needles of {gamma}{prime}more » oriented parallel to the axis of stress, and others produced flat plates or rafts in an orientation perpendicular to the stress axis. In most alloys this orientation dependence was found to invert when a stress of opposite sign was applied. Recent attempts to predict the rafting behavior of these materials have suggested using a combined Monte Carlo/finite element approach which relies on the elastic strain energy and an isotropic interfacial energy term. While this approach succeeded in reproducing the map developed by Pineau and based on the elastic energy of inclusions, a large amount of computation was needed even for small lattices in simulations of the microstructural evolution. The present study, which is part of a wider research program on the mechanical performance of superalloys, is aimed at presenting a novel criterion providing an improved rafting prediction map and also a simpler way to model the energy anisotropy, so as to allow simulations of larger systems or for longer microstructural evolutions.« less
  • The phenomenon of rafting in superalloys is described, with particular reference to modern superalloys with a high volume fraction of the particulate {gamma}{prime} phase. It is shown that in the elastic regime, the thermodynamic driving force for rafting is proportional to the applied stress, to the difference between the lattice parameters of the {gamma} matrix and the {gamma}{prime} particles, and to the difference of their elastic constants. A qualitative argument gives the sign of this driving force, which agrees with that determined by Pineau for a single isolated particle. Drawing on the work of Pollock and Argon and of Socratemore » and Parks, it is shown that after a plastic strain of the sample of order 2 {times} 10{sup {minus}4}, the driving force is proportional to the product of the applied stress and the lattice misfit, in agreement with the results of the calculations of Socrate and Parks. The rate of rafting is controlled by the diffusion of alloying elements. Here, the tendency of large atoms to move from regions of high hydrostatic pressure to those of low may outweigh the influence of concentration gradients. The deformation of the sample directly produced by rafting is small, of order 4.5 {times} 10{sup {minus}4}. The rafted structure is resistant to creep under low stresses at high temperatures. Under most experimental conditions at relatively high stresses, rafting accelerates creep; this effect may be less pronounced at the small strains acceptable under operational conditions.« less
  • Eshelby`s energy-momentum tensor is used to provide an analytical expression for the driving force for rafting in the elastic regime in a superalloy with a high volume fraction of {gamma}{prime}. The structure is modelled as a simple cubic array of {gamma}{prime} cubes separated by thin sheets of {gamma}. During rafting, the {gamma}{prime} particles are constrained to remain tetragonal prisms. For tension along a cube axis, the driving force is proportional to the product of the tension {sigma}, the fractional difference {delta} of lattice parameters of {gamma}{prime} and {gamma} and the fractional difference m of their elastic constants c{sub 11} {minus}more » c{sub 12}. As in the calculation of Pineau for an isolated spheroid, needles are formed when this product {sigma}{delta}m is positive. Two- and three-dimensional systems behave similarly. The initial plastic strain in {gamma} is anelastic and in principle reversible. When the plastic strain exceeds m{delta}, platelets perpendicular to the stress axis are formed if the product {sigma}{delta} is negative.« less