Materials Week '97: Tuesday AM Session

Focusing on physical metallurgy and materials, Materials Week '97, which incorporates the TMS Fall Meeting, features a wide array of technical symposia sponsored by The Minerals, Metals & Materials Society (TMS) and ASM International. The meeting will be held September 14-18 in Indianapolis, Indiana. The following session will be held Tuesday morning, September 16.

TITANIUM EXTRACTION AND PROCESSING: Session III: Physical Metallurgy

Sponsored by: LMD Reactive Metals Committee

Program Organizers: B. Mishra, Dept. of Metall. & Matls. Engg., Colorado School of Mines, Golden, CO 80401; G.J. Kipouros, Dept. of Mining & Metall. Engg., Technical Univ. of Nova Scotia, Halifax, Nova Scotia, Canada B3J 2X4; J. Monsees, International Titanium Association, 1871 Folsom St., Suite #100, Boulder, CO 80302; S. Daniel, Oremet Titanium, 530 W. 34th Avenue, P.O. Box 580, Albany, OR 97321

Room: 203

Session Chair: Dr. G.J. Kipouros, Dept. of Mining & Metal. Engr., Technical Univ. of Nova Scotia, Halifax, Nova Scotia, Canada B3J 2X4; J. Monsees, International Titanium Association, 1871 Folsom St., Suite #100, Boulder, CO 80302

REACTION PATHWAYS DURING METALLOTHERMIC REDUCTION OF TiCl₄ BY UTILIZING CHEMICAL POTENTIAL DIAGRAMS: T.H. Okabe, T. Uda, E. Kasai and Y. Waseda, Research Center for Metallurgical Process Engineering, Institute of Advanced Materials Processing, Tohoku University, 2-1-1 Karahira, Aobaku, Sendai 980-77, Japan

Phase equilibria and reaction pathways during metallothermic reduction of TiCl₄ has been considered by utilizing isothermal chemical potential diagram for Ti-M-Cl (M = Mg, Na, Al) at 1073°K. Importance of electronically mediated reaction (EMR) is discussed for each metallothermic reduction by explaining mechanism of titanium deposition in the Kroll or Hunter process. In the Kroll process, long-range electronically mediated reaction (LR-EMR), in which titanium deposit and reaction container act as electron conductor, was found to be dominant, and this may result in formation of sponge titanium. Both electron and ion transfer in NaCl solutions are quite likely to occur in the reaction pathway during sodiothermic reduction of TiCl₄. The formation of titanium powder in the Hunter process may be attributed to short-range electronically mediated reaction (SR-EMR). The possibility of pure titanium production by an aluminothermic reduction are also discussed.

9:10 am

OXIDATION OF Ti₃Al AND Ti₃Al-Nb INTERMETALLICS: R.G. Reddy, X. Wen and Y. Li, Department of Metallurgical & Materials Engineering, University of Alabama, Tuscaloosa, AL 35487

The oxidation behavior of Ti-Al-Nb intermetallic compounds were investigated. The experiments were carried out using TGA in the temperatures between 750 to 1100°C in the oxygen atmosphere. The samples were analyzed using X-ray, SEM and EDS. From the experimental results, oxidation rate constants, and diffusion coefficients were calculated. The oxidation products formed were identified. The mechanism of oxidation of intermetallic compounds was discussed.

9:35 am

SURFACE HARDENING BEHAVIOR OF TITANIUM ALLOYS IN CARBURIZATION: A.S.M.A. Haseeb, M.F. Islam, O. Alam, S.A.M. Tofail, Department of Metallurgical Engineering, Bangladesh University of Engineering & Technology, Dhaka-1000, Bangladesh

Surface hardening of titanium alloys has been attracting a lot of interest in recent years because of their increasing use in machine components requiring improved tribological properties. The present papers describes a comparison of the surface hardening behaviour of different commercial titanium alloys in pack carburization. Carburization of Ti-3Al-2.5 V, Ti-6Al-4V, and Super Alpa-2 was carried out in a packed bed containing 50% Charcoal, 38% coke,10% Barium Carbonte, 2% Sodium Carbonate. Carburization was done in the temperature range of 850°C to 900°C, for 1 to 3 hour. The carburized samples were investigated by optical microscopy, microhardness measurements and X-ray diffraction (XRD) technique. Surface hardness as high as 800 VHN was achieved in the carburized samples. The hardness profile formed on each of the alloys are discussed in terms of phases formed and microstructure developed during the carburization process.

10:00 am BREAK

10:15 am

ISOSTATIC DIFFUSION WELDING OF DISSIMILAR TITANIUM ALLOYS: M.F. Islam, M.O. Alam, Department of Metallurgical Engineering, Bangladesh University of Engineering & Technology, Dhaka- 1000, Bangladesh: N. Ridley, Materials Science Centre, UMIST and University of Manchester, Grosvenor Street, Manchester, M1 7HS, UK

Microduplex Ti-3Al-2.5V (IMI-325), Ti-6Al-4V (IMI-318) and Ti-25Al-10Nb-3V-1Mo (Titanium Aluminide) sheet materials have a considerable potential for superplastic deformation at temperatures in the range of 850-870°C, 860-910°C and 940- 980°C, respectively. Isostatic diffusion welding of dissimilar couples of titanium alloys (Ti-3Al-2.5V to Ti-6Al-4V and Ti-6Al-4V to Ti-25Al-10Nb-3V-1Mo) was carried out at temperatures of 850 - 920°C and pressures of 2.1 MPa to 6 MPa in order to form a sound weld between dissimilar materials. An assessment of the quality of welds produced was made on the basis of metallographic examination, lap shear test and scanning electron microscopy of the lap shear fracture surfaces. EDAX (energy dispersive X-ray detector) microanalysis using a scanning electron microscope on metallographic samples across the weld line was also performed to characterize the diffusion affected interface region produced between the dissimilar alloys.

10:40 am

EFFECT OF THE TYPE OF CARBON ON CHLORINATION OF REFRACTORY OXIDES: Carbochlorination of Tantalum Oxide: J. Gonzalez, M.C. Ruiz, INTEQUI, Universidad Nacional de San Luis; A.E. Bohe, D.M. Pasquevich, Centro Atomico Bariloche, CNEA, CONICET, 8400 Rio Negro, Argentina

The effect of the type of carbon on the reaction of carbochlorination of a refractory oxide, such as tantalum oxide, was investigated by thermogravimetry. Reactants and residues were characterizad by XRD, SEM and BET. The carbons utilized were graphite, carbon black and carbon obtained from sucrose. In order to associate the reduction capacity of carbon with their reactivity in the carbochlorination, they were burning of with oxygen and a mixture of oxygen-chlorine. It was observed that due to the chlorine presence the oxidation rate is delayed and carbon black and sucrose carbon increment their mass due to the chemisorption of chlorine on the active sites. From experimental results it is viewed that the reduction capacity of carbons, is associated to the reactivation in the carbochlorination of tantalum oxide; this reactivity order is: carbon of sucrose > black carbon > graphite. The same order was observed for the mass increment in chlorine, reactivity with oxygen and mixture oxygen-chlorine.

11:05 am

PHASE EQUILIBRIA IN THE TITANIUM-IRON-OXYGEN SYSTEM: S. Itoh, A. Kikuchi, Department of Metallurgy, Tohoku University, Aza Aoba, Aramaki, Aoba-Ku, Sendai 980-77, Japan; T. Azakami, Department of Machinery, Saitama Institute of Technology, Saitama, Japan; K. Itagaki, Institute for Advanced Materials Processing, Tohoku University, Sendai, Japan

Phase relations and the equilibrium partial pressures of oxygen in the titanium-iron-oxygen ternary system have been studied at 1173-1373 K by means of a thermogravimetric method in a CO-CO₂ gas mixtures and X-ray diffraction technique for the quenched samples after the equilibrium experiments. The objective of this study is both to clarify the relation between the phase relations in the Ti-Fe-O ternary system and the equilibrium partial pressures of oxygen, and to discuss the possibility of upgrading natural ilmenite ore to a rutile substitute for extractive metallurgy of titanium. The results are summarized as follows: The phase diagram and isobars of oxygen in the titanium-iron-oxygen ternary system at 1173 to 1373 K have been determined. From the present results upgrading ilmenite (FeTiO₃) to a rutile (TiO₂) substitute is possible thermodynamically.