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Fracture Strengths of Individual Grain Boundaries in Ni3Ai Using a Miniaturized Disk Bend Test

Published online by Cambridge University Press:  25 February 2011

Douglas E. Meyers  and
Alan J. Ardell
Douglas E. Meyers
Affiliation:
Department of Materials Science and Engineering, University of California, Los Angeles. CA 90024–1595
Alan J. Ardell
Affiliation:
Department of Materials Science and Engineering, University of California, Los Angeles. CA 90024–1595
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Abstract

The results of our initial efforts at measuring the fracture strengths of grain boundaries In Ni3Al using a miniaturized disk-bend test are presented. The samples tested were 3 mm in diameter and between 150 and 300 μm thick. An Ingot of directlonally-solidlfled, boron-free Ni3Al containing 24% Al was annealed between 1300 and 1350 °C to induce grain growth, producing many grain boundaries In excess of 1.5 mm in length. Specimens were cut from these In such a way that one long grain boundary was located near a diameter of the specimen. The relative orientations of the grains on either side of the boundary were determined from electron channeling patterns. Low-angle boundaries are so strong they do not fracture; Instead the samples deform In a completely ductile manner. High-angle boundaries always fracture, but only after considerable plastic deformation of the two grains flanking them. Fracture is Indicated by a load drop in the load vs. displacement curves. A method involving extrapolation of the elastic portion of these curves to the displacement at fracture is used to estimate the fracture stresses. This procedure yields consistent values of the fracture strengths of high-angle boundaries. The measured stresses are large (∼2 to 3 GPa), but considerably smaller than those required for the fracture of special boundaries, as predicted by computer simulations. No correlation was found between the fracture stresses or loads and the geometry of the high-angle boundaries, many of which are close to, but deviate from, coincident site lattice orientations.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 238: Symposium Cb – Structure and Properties of Interfaces in Materials , 1991 , 375
Copyright
Copyright © Materials Research Society 1992

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