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A D V A N C E D M A T E R I A L S & P R O C E S S E S | F E B R U A R Y / M A R C H 2 0 1 8 2 5 from tetrachloride, residual gases in the reactor, helium and argon impurities, and magnesium and sodium residues. SPONGE CONSOLIDATION The next step in the conventional ingot metallurgy approach is consolida- tion of the sponge into ingot. Crushed sponge is blended with alloying ele- ments and clean revert (scrap). Con- sumable electrodes are produced by welding 45 to 90-kg sponge compac- tions (electrode compacts) in an inert atmosphere, which are then double vacuum arc remelted (VAR). A portion of the elemental sponge compacts are often replaced with bulk (clean) scrap. Ingots are about 71-91 cm in diameter and weigh 4.5 to 9.0 t. Double melting, included in aerospace specifications, is required for thoroughmixing of alloying elements, scrap, and titanium sponge, and for improving yields, because va- porization of volatiles during the first melt leaves a rough, porous surface. Double melting removes residual vol- atiles such as Mg, MgCl 2 , Cl 2 , and H 2 . Triplemelting is specified for critical ap- plications such as rotating components in gas turbine engines. The third melt allows more time to dissolve high melt- ing-point inclusions that infrequently occur. This is often referred to as rotat- ing-quality titanium. A two-station VAR furnace for double melting (Fig. 5) features an annual production capacity of about 1400-3000 t, depending on the product mix; i.e., alloy and number of re- melts. The energy requirement is about 1.1 kWh/kg per single melt. Plas- ma cold hearth melting (PAM) and electron-beam cold hearth melting (EBM), shown in Fig. 6, are used for both consolidation and final melting. The hearth processes are well suited for us- ing scrap in various shapes and forms, and for avoiding costly electrode fab- rication inherent in consumable vac- uum arc melting. In addition, these processes can produce cast metal into shapes such as slabs. For many indus- trial applications, a single hearth melt is acceptable. Further, the low-cost hearth process can be designed to trap high-density inclusions such as carbide tool bits and oxynitride-rich (Type I) in- clusions in the hearth skull. ~AM&P Note: Look for Part 2 of this article se- ries in the April issue of AM&P cover- ing new production and processing technologies, economic aspects, spec- ifications and quality control, recy- cling and environmental concerns, and applications. For more information: Professor Sam Froes is a consultant to the additive manufacturing and titanium industries. He may be reached at 253.517.3034 or ssfroes@comcast.net. References 1. A.D. McQuillan and M.K. McQuillan, Metallurgy of the Rarer Metals, p 335, Academic Press: New York, 1956. 2. R.A. Wood, The Titanium Industry in the Mid-1970s, Battelle Report MCIC- 75-26, Battelle Memorial Institute, 1975. 3. H.B. Bomberger, et al., Titanium Technology: Present Status and Future Trends, Titanium Development Assoc., p 3-18, 1985. 4. S.S. Joseph and F.H. Froes, Light Metal Age, 4-6 (11-12), p 5-12, 1988. 5. S.R. Seagle and J.R. Wood, Synthe- sis, Processing and Modelling of Ad- vanced Materials, Vol 77-78, p 91-102, Trans. Tech. Pub., 1993. 6. F.H. Froes and I.L. Caplan, Ti 92 Sci. and Technol., TMS, 1993. 7. P.A. Blenkinsop, et al., Ti 95 Sci. and Technol., IMS, 1996. 8. F.H. Froes, Third ASM Int. Paris Conf. On Syn., Proc. and Model. of Adv. Matls., ASM Intl., p 3-38, 1997. 9. F.H. Froes, et al., Non-Aerospace Applications of Titanium, TMS, 1998. 10. K.L. Housley, Black Sand: The His- tory of Titanium, Metal Mgmt. Aero- space, 2007. 11. A. Imam, et al., Titanium and Tita- nium Alloys, Kirk Othmer Encyclopedia (online), p 1-41, 2010. 12. M. Molchanova, Phase Diagrams of Titanium Alloys, Israel Program for Scientific Translations, 1965. 13. F.H. Froes, et al., Titanium Tech- nology: Present Status and Future Trends, Titanium Development Assoc. (now Intl. Titanium Assoc.), 1985. 14. R. Boyer, et al., Materials Property Handbook: Titanium Alloys, ASM Intl., 1994. 15. M.J. Donachie, Titanium, A Tech- nical Guide, ASM Intl., 1988. 16. I.J. Polmear, Light Alloys, Metallurgy of the Light Metals, 3rd ed., Edward Arnold: London, 1996. 17. H.MargolinandH.Neilson,Titanium Metallurgy, Modern Materials, Advances in Development and Applications, Aca- demic Press, New York, Vol 2, p 225-325, 1960. 18. F.H. Froes, Titanium Powder Metal- lurgy: Developments and Opportunities in a Sector Poised for Growth, PM Rev., Vol 2, No. 4, p 29-43, 2013. 19. B. Dutta and F.H. Froes, Additive Manufacturing of Titanium Alloys, Else- vier/Butterworth-Heinemann, 2016. 20. N. Ohta, Chem. Eco. Eng. Rev., Vol 13, (22), 1981. 21. W.W. Minkler and E.F. Baroch, The Production of Titanium, Zirconium and Hafnium, 1981. 22. J.A. Slatnick, Availability of Tita- nium in Market Economy Countries, IC 9413, Bureau of Mines Information Circular, Washington, 1994. 23. R.C. Weast (Ed.), CRC Handbook of Chemistry, 62nd ed., CRC Press, 1982. 24. K.L. Housley, Kroll Process May Be on the Verge of Replacement or Modification, Titanium News, Metal Mgmt. Aerospace Inc., 2007. 25. Energy Use Patterns inMetallurgical and Nonmetallic Mineral Processing, Report No. PB-246 357, Battelle Co- lumbus Laboratories, U.S. DoC, Wash- ington, 1975. Vacuum-distilled titanium sponge produced by magnesium reduction. Courtesy of ATI Wah Chang.