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Deformation Band Velocities and Local Strain Rates in a Ni-Cr-Fe Alloy (Inconel)

Published online by Cambridge University Press:  14 March 2011

Harry N. Jones  and
C. R. Feng
Harry N. Jones
Affiliation:
Materials Science and Technology Division, Naval Research Laboratory Washington, DC 20375, U.S.A.
C. R. Feng
Affiliation:
Materials Science and Technology Division, Naval Research Laboratory Washington, DC 20375, U.S.A.
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Abstract

Nickel based alloys with nominal compositions similar to 78Ni -15Cr -7Fe, commonly referred to as “Inconel”, exhibit serrated flow (Portevin-LeChatelier effect) in the temperature interval of 230-730°C. Within this temperature range a series of thermally activated processes can also be observed when a wire sample of the alloy is heated with the direct resistance method under dead-weight loading while stressed above the room temperature yield. These processes include the expected initial period of plastic deformation at the start of heating followed by its complete arrest at a higher temperature, a behavior that is completely at odds with models for the thermal activation of plastic flow in metals. As the temperature is increased after this first arrest a cascade of two or three large plastic instabilities involving the high velocity propagation of narrow deformation bands is observed. Measurements of the band velocities using the time of flight within a 50.8 mm gage length extensometer indicate that they can exceed 2 m/s in some cases. Estimates of the maximum local strain rate attained within the deformation bands, obtained with a diametral extensometer, approach 15-18 s−1. The localization of plastic flow into narrow, high velocity bands in this material is the result of the collective behavior of dislocations interacting at a high density. As demonstrated by TEM examination of the complex dislocation structures associated with these various events, however, it is difficult to rationalize a specific mechanism for these effects. If one assumes that both serrated flow and the thermally activated strain bursts are manifestations of the same basic mechanism these observations pose a challenging problem for interpretation with models for the Portevin-LeChatelier effect in this material.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 683: Symposium BB – Materials Instabilities and Patterning in Metals , 2001 , BB4.5.1
Copyright
Copyright © Materials Research Society 2001

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References

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