Effect of zero, normal and hyper-gravity on columnar dendritic solidification and the columnar-to-equiaxed transition in Neopentylglycol-(D)Camphor alloy

• Published in: Journal of crystal growth 2019-04, Vol.512, p.47-60
• Main Authors: Zimmermann, G., Hamacher, M., Sturz, L.
• Format: Article
• Language: English
• Subjects: A1. Convection; A1. Dendrites; A1. Directional solidification; A2. Growth from melt; A2. Microgravity condition; B1. Alloys; Camphor; Casting alloys; Centrifugal casting; Cooling rate; Crystal growth; Equiaxed structure; Laminar flow; Liquid-solid interfaces; Material properties; Microgravity; Nucleation; Solidification; Temperature gradients; Three dimensional flow
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2019.01.043

[Display omitted] •Transparent model alloy allows for in-situ observation of the solidification.•Solidification experiments performed in g-levels ranging from zero-g up to 10g0.•Growth of columnar dendrites nearly independent of the g-level.•High g-levels result in a cascade-like settling of growing equiaxed dendrites.•The columnar to equiaxed transition is accelerated in hyper-g environment. Centrifugal casting is an important method to produce superior-quality cast parts. The microstructure and therefore materials properties strongly depend on the hyper-gravity level. To investigate the effect of gravity level on the solidification behavior, the transparent model alloy Neopentylglycol-(D)Camphor is used, which solidifies like metals. Its optical transparency allows for in-situ observation of columnar and equiaxed crystal growth. The experiments were carried out in a constant temperature gradient with two different cooling rates, and for g-levels ranging from zero-g in microgravity environment up to 10g0 on a centrifuge. It is found that the overall temperature and solutal fields close to the solidification front are not significantly altered by the laminar 3D melt flow in hyper-g environment. As a consequence, the growth velocity and primary spacing of columnar dendrites is nearly independent of the g-level. Increasing the cooling rate allows for nucleation and growth of equiaxed dendrites in the undercooled region ahead of the columnar solid-liquid interface. Here, at high g-levels the nucleation rate increases significantly and an accelerated, cascade-like settling of the growing equiaxed dendrites is observed. As a result, an earlier transition from columnar to equiaxed dendritic growth is detected in hyper-g environment.