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Mechanical Properties of Polycrystalline NiAl from Miniaturized Disk-Bend Tests

Published online by Cambridge University Press:  22 February 2011

S. J. Eck  and
A. J. Ardell
S. J. Eck
Affiliation:
Department of Materials Science and Engineering, University of California, Los Angeles, CA 90095–1595.
A. J. Ardell
Affiliation:
Department of Materials Science and Engineering, University of California, Los Angeles, CA 90095–1595.
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Abstract

Disk-shaped specimens of polycrystalline NiAl (grain size ∽25 μm), 3 mm in diameter and ranging in thickness from 165 to 370 μm, were indented in their centers to various indentation loads, F, using a Vickers indenter. The yield stress, σy, and apparent fracture stress, σfa, were measured as a function of F, with the indented side in tension, using a miniaturized disk-bend test (MDBT). Fracture does not originate at the indentation for F ≤ 39.2 N. Within this regime of behavior both σy and σfa are slightly larger than in unindented specimens, although σfa passes through a sharp minimum for F < 10 N. For F ≥ 39.2 N fracture originates at the indentations. In this regime σy is essentially constant, but significantly larger than σy at smaller values of F, while σfa decreases steadily with increasing F. We attribute the larger values of σy to strain hardening within the relatively large plastic zone surrounding the indentation. The reduction of σfa with increasing F in this regime occurs because the indentation serves as the point of failure. Fractography reveals NiAl fractures primarily in an intergranular manner. A preliminary estimate of the fracture toughness is 8.54 MPa·a.m1/2, which overestimates the true fracture toughness because σfa exceeds the true fracture stresses.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 364: Symposium L – High-Temperature Ordered Intermetallic Alloys–VI , 1994 , 285
Copyright
Copyright © Materials Research Society 1995

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