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Atypical Defects in a B2 Fe-40A1–0.7C-0.5B Alloy

Published online by Cambridge University Press:  10 February 2011

L. Pang  and
K. S. Kumar
L. Pang
Affiliation:
Division of Engineering, Brown University, Providence, RI 02912
K. S. Kumar
Affiliation:
Division of Engineering, Brown University, Providence, RI 02912
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Abstract

The nature of defects in a quaternary Fe-40A1–0.7C-0.5B alloy was examined by transmissionelectron microscopy (TEM) techniques including weak beam microscopy and z-contrast imaging.Complex {001} stacking faults were observed in certain conditions in these alloys that were not previouslynoted in a ternary Fe-40A1–0.6C alloy. These faults exhibit a 1/2<001> displacement vectorthat lies in the plane of the fault and structurally misses an aluminum layer. Six variants of this faulttype are present. These faults are absent in brine-quenched and furnace-cooled alloys, but are readilyobserved in the air-cooled condition. In addition to the usual <111> superdislocations that are APBdissociatedinto 1/2<111> superpartials, dissociated <100> dislocations (into two 1/2< 100> partials)are also observed under certain conditions. Quenched and aged alloys show dissociated <001> loops.The absence of such defects in the B-free alloy and following certain heat treatments in the B-containingalloy, suggests that boron may be segregating to the cube planes and lowering the interfacialenergy on these planes. The presence of dissociated <001> loops in the quenched and aged alloy alsosuggests the formation of B-vacancy complexes that coalesce during aging, forming such dissociatedloops.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 552: Symposium KK – High-Temperature Ordered Intermetallic Alloys VIII , 1998 , KK4.5.1
Copyright
Copyright © Materials Research Society 1999

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