Analysis of solidification microstructures during wedge-casting

Abstract

Solidification microstructure evolution is a function of both alloy composition and thermal history. With a wedge-shaped mold, castings can be subjected to a range of cooling rates differing by orders of magnitude, typically 10¹–10³ K/s, in a single run. Combining microstructure analysis, temperature measurements of the quenching melt and heat transfer analysis, wedge casting is an effective and flexible technique to explore the spectrum of alloy solidification microstructures. The utility of the wedge-casting technique is, in the current study, developed to examine bulk glass-forming alloys by combining multiple thermal probes with a measurement-based kinetics analysis of the phase selection competition and critical cooling rate conditions. Based upon direct thermal measurements, microstructural analysis and kinetics modelling, it is evident that the usual report of a single critical cooling rate for bulk glass formation should be modified to include a critical cooling rate range in order to account for nucleation controlled behavior. Furthermore, in comparing glass-forming alloys in terms of relative ease of glass formation, it is necessary to consider the relative heat flow characteristics as well as the relative nucleation kinetics.

Acknowledgements

The support of DARPA/DOE through the Lawrence Livermore National Laboratory (subcontract B529197), as well as the valuable assistance from Dr L. Kaufman and the other members of the HPCRM team, are gratefully acknowledged.