Columnar to equiaxed transition in solidification processing

TLDR

The columnar to equiaxed transition (CET) is a microstructural transition that must be controlled during certain solidification processes. The authors describe CET models and microstructure selection maps based on nucleation and dendritic growth, and show how processing maps can be generated by coupling these models with numerical solidification calculations, exemplified by epitaxial laser metal forming and aluminum alloy arc welding. Such processing maps aid in controlling solidification microstructure.

Abstract

The columnar to equiaxed transition (CET) is a microstructural transition that has to be controlled during certain solidification processes. CET models and microstructure selection maps, based on nucleation and dendritic growth models, are briefly described. Processing maps can be established by combining a CET model with numerical calculations of local solidification conditions. Such processing maps are helpful for the control of the solidification microstructure. As examples, two processes are discussed: the epitaxial laser metal forming (E-LMF) process where a single crystalline superalloy part is repaired in single crystal form and equiaxed grains have to be avoided; and the arc welding of aluminium alloys where equiaxed grains are the preferred solidification structure.