Phase and Microstructure of Fe Modified A1 3 Ti
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PHASE AND MICROSTRUCTURE OF Fe MODIFIED A13 Ti W. D. PORTER*, K. HISATSUNE**, C. J. SPARKS*, W. C. OLIVER*, AND A. DHERE*** * Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6117 •* School of Dentistry, Nagasaki University, Nagasaki 852, Japan • ** E. I. du Pont, Chattanooga, TN 37415
ABSTRACT Alloys of A175_xFexTi25, where x = 0 to 12 at. % Fe, were fabricated by splat cooling and examined primarily with X-ray diffraction to determine the crystallographic phases present, their composition, volume fraction, lattice parameters, and sublattice occupation. The tetragonal DO2 2 structure of A13Ti dissolved 0.8 ± 0.4 at. % Fe, with additional iron partitioned to the L12 structure containing 6.2 ± 0.4 at. % Fe, and completed the transformation to the L12 structure with the addition of about 6 at. % Fe. The lattice parameters of both phases were independent of iron concentration up to about 6 at. %. At 8 at. % Fe, the iron was found to be predominantly distributed on the nominal aluminum sublattice which also contained about 5 at. % Ti. The AI3 Ti composition was similarly found to contain about 5 at. % Ti on the aluminum sublattice. All compositions, including a single crystal of A16 7 Fe8 Ti 2 5 , were found to be brittle. INTRODUCTION The tetragonal DO 2 2 compound AI3 Ti has recently received attention as a possible structural material because of its low density, 3.4 g/cm 3 , and its good oxidation resistance [1-2]. A13 Ti has the disadvantages, however, that it is a line compound and is extremely brittle at room temperature, presumably due to the lack of slip systems associated with the crystal symmetry [2]. It is known that stable cubic L1 2 ternary compounds having the stoichiometry A175_xZxTi25 exist, where Z is Cu, Ni, or Fe and x = 8 to 12.5 [3,4]. Cubic alloys based on these compounds have several attractive features and may be more easily made ductile as the L12 structure provides more slip systems for plastic deformation. At -1350 'C, the melting point of these alloys is much higher than other aluminum-based alloys. The densities of the alloys, 3.8-4.0 g/cm 3 , are 8-15% lower than those of titanium alloys [5]. Preliminary studies have indicated the alloys are alumina formers having good oxidation resistance and retain their strength, as indicated by hot hardness, much better than Ti-6A1-4V, a widely used titanium alloy [6]. Since an understanding of the factors influencing the stability of the DO 2 2 and L12 structures is desirable, the current study was initiated to determine the effect of iron additions on the c/a ratio of the 1D022 structure. It had been suggested that iron additions may stabilize the L1 2 structure by reducing the c/a ratio of the tetragonal D022 structure to the point where it is no longer stable [7,8]. X-ray diffraction and electron microprobe results will be presented for alloys having the composition A17 5 _xFexTi25, where x = 0 to 12. Site occupation and the long-range order present in the alloys will also be discussed. EXPERIMENTAL PROCEDURE Sample
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