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Flow and Fracture Behavior of NiAl in Relation to the Brittle-Toductile Transition Temperature

Published online by Cambridge University Press:  26 February 2011

R.D. Noebe ,
R.R. Bowman ,
C.L. Cullers  and
S.V. Raj
R.D. Noebe
Affiliation:
NASA Lewis Research, MS 49–1, Cleveland, OH 44135.
R.R. Bowman
Affiliation:
NASA Lewis Research, MS 49–1, Cleveland, OH 44135.
C.L. Cullers
Affiliation:
NASA Lewis Research, MS 49–1, Cleveland, OH 44135.
S.V. Raj
Affiliation:
NASA Lewis Research, MS 49–1, Cleveland, OH 44135.
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Abstract

NiAl has only three independent slip systems operating at low and intermediate temperatures whereas five independent deformation mechanisms are required to satisfy the von Mises criterion for general plasticity in polycrystalline materials. Yet, it is generally recognized that polycrystalline NiAl can be deformed extensively in compression at room temperature and that limited tensile ductility can be obtained in extruded materials. In order to determine whether these results are in conflict with the von Mises criterion, tension and compression tests were conducted on powder-extruded, binary NiAl between 300 and 1300 K. The results indicate that below the brittle-to-ductile transition temperature (BDTT) the failure mechanism in NiAl involves the initiation and propagation of cracks at the grain boundaries which is consistent with the von Mises analysis. Furthermore, evaluation of the flow behavior of NiAl indicates that the transition from brittle to ductile behavior with increasing temperature coincides with the onset of recovery mechanisms such as dislocation climb. The increase in ductility above the BDTT is therefore attributed to the climb of <001> type dislocations which in combination with dislocation glide enable grain boundary compatibility to be maintained at the higher temperatures.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 213: Symposium Q – High-Temperature Ordered Intermetallic Alloys IV , 1990 , 589
Copyright
Copyright © Materials Research Society 1991

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References

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