Mechanical properties of polycrystalline NiAl from miniaturized disk-bend tests
- Univ. of California, Los Angeles, CA (United States). Dept. of Materials Science and Engineering
Disk-shaped specimens of polycrystalline NiAl (grain size {approximately}25 {mu}m), 3 mm in diameter and ranging in thickness from 165 to 370 {mu}m, were indented in their centers to various indentation loads, F, using a Vickers indenter. The yield stress, {sigma}{sub y}, and apparent fracture stress, {sigma}{sub fa}, 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 {sigma}{sub y} and {sigma}{sub fa} are slightly larger than in unindented specimens, although {sigma}{sub fa} passes through a sharp minimum for F < 10 N. For F {>=} 39.2 N fracture originates at the indentations. In this regime {sigma}{sub y} is essentially constant, but significantly larger than {sigma}{sub y} at smaller values of F, while {sigma}{sub y} decreases steadily with increasing F. The authors attribute the larger values of {sigma}{sub y} to strain hardening within the relatively large plastic zone surrounding the indentation. The reduction of {sigma}{sub fa} 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{center_dot}m{sup 1/2}, which overestimates the true fracture toughness because {sigma}{sub fa} exceeds the true fracture stresses.
- DOE Contract Number:
- FG03-86ER45264
- OSTI ID:
- 78334
- Report Number(s):
- CONF-941144--; ISBN 1-55899-265-0
- Country of Publication:
- United States
- Language:
- English
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