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Experimental study of grain refinement mechanism in undercooled Ni–15at.%Cu alloy

Published online by Cambridge University Press:  31 January 2011

Gencang Yang
Affiliation:
State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an, Shaanxi 710072, People's Republic of China
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Abstract

Applying glass fluxing and cyclic superheating, rapid solidification of undercooled Ni–15at.%Cu alloy was performed by rapidly quenching the sample after recalescence. The evolution of microstructure and microtexture has been analyzed. At both low and high undercoolings, well-developed dendrites, within and around which are distributed by the fine equiaxed grains, are observed. At low undercooling, the completely grain-refined microstructure shows a highly oriented texture without annealing twins, whereas at high undercooling a fully random texture as well as a number of annealing twins is observed. On this basis, all the possible mechanisms for grain refinement, as well as their effects on the microstructure formation, were discussed. The grain refinement at both low and high undercoolings is concluded to originate from dendrite fragmentation. Particularly, at high undercooling, recrystallization, as a consequence of dendrite deformation (by fluid flow) and dendrite fragmentation (which provides grain boundary sites for recrystallization nucleation and for the “appearing” recrystallized grains), occurs and plays a role in the grain refinement and the formation of fully random texture.

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Articles
Copyright
Copyright © Materials Research Society 2010

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