Abstract
A solidification experiment “TRACE” of the transparent alloy Neopentylglycol (NPG)-37.5wt.% D-Camphor (DC) was conducted on-board the sounding rocket TEXUS-47 in low-gravity environment to investigate the columnar growth and the columnar-to-equiaxed transition (CET). To improve the fundamental understanding of solidification and CET in microgravity, the current laboratory scale experiment was tried to be numerically reproduced by a recently developed 5-phase volume averaging model. The temperature gradient in the solidification cell is applied to the simulation. In absence of melt flow, the calculated cooling curves, columnar tip position, tip undercooling and velocity, and number density of equiaxed crystals were compared to the results of in-situ real-time observations of the experiment. The CET could be predicted at position close to that of experiment. Simulation reveals the competitive growth between the columnar and equiaxed crystals before CET. Modelling parameters of equiaxed nucleation and columnar tip growth are the key to regulate this competition and to locate the CET. Experimental verification of modelling parameters considering melt flow is intended in the future work.
Highlights
Mechanical properties of alloys are directly related to their as-cast structure
Equiaxed grain structure exhibits more isotropic properties and are formed upon nucleation that can be provoked by several mechanisms: (1) heterogeneous nucleation [3]; (2) the ‘big band’ theory [4]; (3) partial remelting of columnar dendrites [5]; and (4) the showering down of dendrite crystals formed from the casting top surface [6]
columnar-equiaxed structure with a transition zone (CET) occurs if the volume faction of equiaxed grains ahead of the columnar tip front is high enough to block the advancement of the columnar tip front [7]
Summary
Mechanical properties of alloys are directly related to their as-cast structure. Columnar growth is favoured for example in single crystal growth [1] or in some turbine blades [2]. High thermal gradient at solid/liquid interface promotes the columnar growth. CET occurs if the volume faction of equiaxed grains ahead of the columnar tip front is high enough to block the advancement of the columnar tip front (hard blocking) [7]. The columnar growth is initiated by applying a cooling rate of 1/300 K/s at heater and cooler at a roughly constant gradient.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: IOP Conference Series: Materials Science and Engineering
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
