Original Date: 11/03/1996
Revision Date: 01/18/2007
Best Practice : Super Laminate for Active Metals Vacuum Induction Melting
The Oak Ridge Y-12 Plant Materials Engineering Department was requested by Department of Energy (DOE) divisions to assist and evaluate disposal alternatives for over 235 tons of submarine reactor core hardware. The material consisted of Zircaloy 4 which had classified shapes and possible stray radioactive elements. The options included burial, determined an unacceptable option; electric arc melting which, although effective, was very costly; and the less expensive Vacuum Induction Melting (VIM) process which could yield recyclable material if proven successful.
Traditional crucibles used in the VIM process are constructed of graphite which can withstand 2000°C. However, graphite causes detrimental material problems due to the carbon reaction with this reactive alloy while in the molten state. The objective then was to develop a crucible coating which would prevent the carbon reaction from occurring. Experimental development began with seven choices of refractory material, four metal coatings and six various crucible base materials. Within 18 months of the first meeting, Y-12 had successfully developed an effective crucible coating that would inhibit the carbon reaction and maintain functional rigidity throughout the process.
By meeting this challenge, Y-12 introduced a new world class technology. Melting reactive metals in a graphite system is now possible with the Super Laminate for Active Metals VIM process. To date, 500 pound ingots have been cast with a cost savings of three to ten times the magnitude of traditional electric arc melting. Y-12 has refined the process to include enhanced plasma spray capabilities for small crucibles and molds.
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