3D x-ray microprobe investigation of local dislocation densities and elastic strain gradients in a NiAl-Mo composite and
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3D x-ray microprobe investigation of local dislocation densities and elastic strain gradients in a NiAl-Mo composite and exposed Mo micropillars as a function of prestrain Rozaliya I. Barabasha) Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831; and Materials Science and Engineering Department, University of Tennessee, Knoxville, Tennessee 37996
Hongbin Beib) Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831
Yanfei Gao Materials Science and Engineering Department, University of Tennessee, Knoxville, Tennessee 37996; and Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831
Gene E. Ice Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831
Easo P. George Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831; and Materials Science and Engineering Department, University of Tennessee, Knoxville, Tennessee 37996 (Received 12 August 2009; accepted 6 November 2009)
3D spatially-resolved polychromatic microdiffraction was used to nondestructively obtain depth-dependent elastic strain gradients and dislocation densities in the constituent phases of a directionally solidified NiAl–Mo eutectic composite consisting of 500–800 nm Mo fibers in a NiAl matrix. Measurements were made before and after the composite was compressed by 5% and 11%. The Mo fibers were analyzed both in their embedded state and after the matrix was etched to expose them as pillars. In the as-grown composite, due to differential thermal contraction during cooldown, the Mo phase is under compression and the NiAl phase is in tension. After the prestrains, the situation is reversed with the Mo phase in tension and NiAl matrix in compression. This result can be explained by taking into account the mismatch in yield strains of the constituent phases and the elastic constraints during unloading. The dislocation density in both the Mo and NiAl phases is found to increase after prestraining. Within experimental uncertainty there is little discernible difference in the total dislocation densities in the Mo phase of the 5% and 11% prestrained specimens. However, the density of the geometrically necessary dislocations and the deviatoric strain gradients increase with increasing prestrain in both the Mo and NiAl phases.
Address all correspondence to these authors: a) e-mail: [email protected] b) e-mail: [email protected] This paper was selected as an Outstanding Symposium Paper for the 2008 MRS Fall Meeting, Symposium EE Proceedings, Vol. 1137E. To maintain JMR’s rigorous, unbiased peer review standards, the JMR Principal Editor and reviewers were not made aware of the paper’s designation as Outstanding Symposium Paper. DOI: 10.1557/JMR.2010.0043 J. Mater. Res., Vol. 25, No. 2, Feb 2010
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I. INTRODUCTION
Micropillar compression testing has become a popular way to character
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