Interdiffusion and Phase Relations in Ti-Aluminide/NB/Ti-Aluminide Composite Structures
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INTERDIFFUSION AND PHASE RELATIONS IN TI-ALUMINIDE/NBfTI-ALUMINIDE COMPOSITE STRUCTURES Z. Maa), M.A. Dayanandab), and L.H. Allena) a) Department of Materials Science and Engineering, University of Illinois, Urbana, IL 61801. b) School of Materials Engineering, Purdue University, West Lafayette, IN 47907. ABSTRACT We have studied interdiffusion and phase relations in two titanium aluminide/Nb/titanium aluminide composite structures at 1100 *C using solid state diffusion approach. The composite structures were prepared with two practical intermetallic alloys, y (Ti-48AI-2Nb-0.3Ta, in at.%) alloy and super-cc2 (Ti-25AI-10Nb-3V-1Mo, in at.%) alloy, and pure Nb sheet by diffusion bonding technique. The interfacial microstructures evolved during thermal diffusion annealing were characterized using optical microscopy, SEM, TEM and X-ray diffraction. The effect of Nb on the phase stabilities of two intermetallic alloys and the phase relations among different phases formed in the diffusion zone due to interdiffusion were analyzed in terms of rules of diffusion paths on the basis of the observed diffusion structures and experimental diffusion paths. INTRODUCTION Titanium aluminides with addition of a small amount of Nb have been of great technological interest for years due to their high temperature strength, low density, better creep and oxidation resistance relative to conventional titanium alloys[l]. The development of new titanium aluminide based intermetallic composites with optimum properties requires a full understanding of their interface structures and phase stabilities. On the other hand, synthesis of new titanium aluminide based intermetallic alloys needs a complete knowledge of Ti-Al-Nb ternary phase diagrams at temperatures where these materials undergo heat treatment. Although a number of systematic investigations have been carried out on the phase transitions[2] and phase relations[3] in this system, phase equilibria at some temperatures of interest are still not quite clear. Also, there is a lack of kinetics data in the literature concerning the interdiffusion of Ti, Al, and Nb in this system. For these reasons, we have investigated interdiffusion in titanium alurninide/Nb/titanium aluminide composite structures using solid state diffusion approach. The objectives of this work are two-fold: (1) to elucidate the evolution of interfacial structures in these composite materials during diffusion annealing at elevated temperatures and to establish their phase relationships based upon the observed diffusion structures and experimental diffusion paths; (2) to extract: useful interdiffusion data for Ti, Al, and Nb in some important intermetallics. In this paper, we only present the first part of this work. The theoretical background for diffusion analysis in multicomponent system and resultant interdiffusion data will appear elsewhere.
Mat. Res. Soc. Symp. Proc. Vol. 273. 91992 Materials Research Society
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EXPERIMENTAL PROCEDURE The materials used in this study were two commercially available intermetallic allo
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