Materials Education: Front Page
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Video Microscopy of Solidification: A Teaching Supplement to the August 2007 JOM
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By Cathy Rohrer and Todd Osman, Materials Technology@TMS Moderators
Posted on:
8/2/2007...
In the August 2007 issue of JOM, Lars Arnberg and Ragnvald H. Mathiesen present in-situ video observations of solidification in Al-Cu alloys under various conditions. "The Real-Time, High-Resolution X-Ray Video Microscopy of Solidification in Aluminum Alloys"1 demonstrates the use of high-brilliance synchrotron x-radiation (SR) to examine solidification in metals. This approach is a step beyond the use of transmission microscopy to examine solidification of transparent organic compounds with phase diagram characteristics comparable to metal alloys. Observations using this latter technique have been utilized in classroom texts such as Porter and Easterling's Phase Transformations in Metals and Alloys2 as model systems representative of metal solidification. But as Arnberg and Mathiesen point out, the SR technique provides new opportunities for demonstrating solidification in actual metals for traditional MSE teaching purposes, as well as providing "quantitative data on solidification morphologies, solute distributions, and kinetics that will serve as benchmark data for modeling."
The animated videos can be viewed in the web-enhanced Page-Turning JOM version of Arnberg's and Mathiesen's article. They have also been made available on MaterialsTechnology@TMS's Education Community Digital Resource Center (DRC), together with three PDF presentations giving details of the experimental procedure and mathematical models explaining some of the observations. Each video clip within the article demonstrates a different set of thermal conditions. Equiaxed solidification is shown in "an Al-20wt.%Cu alloy that has been inoculated by the addition of a grain-refining Al-Ti-B master alloy." The in-situ video shows continuous nucleation both within the melt and on the walls of the sample. In contrast, columnar dendritic growth can be observed in another Al-20wt.%Cu alloy at the beginning of the fragmentation—solute pile-up video. (Click here to view this video.) In this experiment, the influence of solute pile-up, together with the solidification direction opposing the downward gravitational direction, resulted in fragmentation of the dendrites. Subsequent lateral growth of the fragments ultimately blocks the growth of the original columnar front. The PDF presentation, "In-situ Studies of Dendrite Fragmentation in Al-Cu," describes the mathematical models for the concentration and thermal distributions resulting in the fragmentation and subsequent columnar-to-equiaxed transition. Color-enhanced time snapshots of the copper distribution ahead of the dendrites are also presented.
In addition to Arnberg's and Mathiesen's work, the Education community DRC provides an evolving set of resources to supplement the teaching of introductory MSE courses. A compilation of some of the available solidification/casting related educational resources available to TMS members follows:
Casting and Solidification: Examples of Resources Available on the Education Community Digital Resource Center for an Introduction to Materials Science Engineering Course
Casting Videos
Click here for videos on aluminum processing, including casting
Click here for videos on steel processing, including casting
Casting Simulations
Click here for a suite of JOM-e articles with animations including the effect of inoculation on as-cast microstructures, mold filling, and complex foundry castings
Solidification Videos
Click here for videos of Al-Cu solidification
Click here for confocal microscopy videos of solidification
Click here for laser-engineered net shaping videos of solidification
Casting/Solidification Online Tutorials and Example Problem Sets
Click here for "Practical Examples in Metalcasting Design"
Click here for online tutorials on solidification
Click here for problem sets and solutions on metal processing, including casting and solidification
Click here for lecture notes and problem sets on solidification
Files were last updated July 17, 2007.
References
1. L. Arnberg and R.H. Mathiesen, "The Real-Time, High-Resolution X-Ray Video Microscopy of Solidification in Aluminum Alloys," JOM, 59 (8) (2007), pp. 20–26.
2. D.A. Porter and K.E. Easterling, Phase Transformations in Metals and Alloys (Berkshire, England: Van Nostrand Reinhold (UK) Co. Ltd., 1981), pp. 220–221. Figures taken from L.R. Morris and W.C. Winegard, Journal of Crystal Growth 6 (1969), p. 61 (Cellular dendrites in carbon tetrabromide) and K.A. Jackson, Solidification, American Society for Metals, 1971, p. 121 (Columnar dendrites in a transparent organic alloy).
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