Effects of initial undercooling on microstructure formation and recrystallisation of undercooled melts

ABSTRACT

The critical undercoolings for the two grain refinement events and the onset of recrystallisation event are determined by detailed analysis of the microstructure evolution of bulk undercooled Ni–20 at.-%Cu alloy melts. The first grain refinement event occurred in the low undercooling range was explained by dendrite remelting. The second grain refinement event occurred in the high undercooling range was due to the combined effects of dendrite remelting stress-induced dendrite breakup during recalescence and recrystallisation during the near-equilibrium solidification stage after recalescence. The micro-stress induced by the solidification contraction during recalescence in the so called ‘first mushy zone’ would lead to distortion and breakup of primary dendrites. The stress-induced broken-up dendrites have sufficient driving force for recrystallisation.

KEYWORDS:

• Undercooling
• rapid solidification
• defects
• crystal growth

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors are grateful to the financial support of the National Natural Science Foundation of China (Nos. 51204147, 51274175) and International Cooperation Project supported by Ministry of Science and Technology of the People Republic of China (No. 2011 DFA 50520), Program for the Outstanding Innovative Teams of Higher Learning Institutions (OIT) of Shanxi and Project of Shanxi Scholarship Council of China (No. 2011 - key6).