Rare Earth Oxide Dispersoid Stability and Microstructural Effects in Rapidly Solidified Ti 3 Al and Ti 3 Al-Nb
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RARE EARPTT
:'7lI-F DISPERSOID STABILITY AND MICROSTRUCTURAL
RAPIDLY SOLIDIFIED Ti 3 A1 AND Ti
EFFECTS IN
3 AI-Nb
J. A. Sutliff and R. G. Rowe General Electric Corporate Research and Development Schenectady, NY 12301
ABSTRACT The microstructures of titanium aluminide alloys containing a rare earth oxide dispersion have been characterized using analytical electron microscopy. The alloys, based on Ti 3 A1 (alpha-2), contained 0 to 10.7 atom% Nb and 0.5 atom% Er. Alloys were rapidly solidified by melt spinning and were subsequently consolidated by HIP and extrusion. The microstructure of each alloy was examined in the as-cast, as-HIP'ed, and as-extruded conditions. A fine dispersoid spaced less than 100 nm apart was observed in ribbon aged at 750aC. The effects of processing conditions on the dispersoid distribution as a function of matrix chemistry were studied. Hot deformation was also examined to investigate the nature of the interaction between the dispersoids and the matrix during deformation. Table I
Alloy Number 213 214 205 215 204
Alloy Compositions Ti Al Nb Bal. Bal. Bal. Bal. Bal.
24.8 25.4 24.6 24.8 25.3
4.9 6.0 7.5 10.7
(Atomic %) Er 0 0.6 0.6 0.5 0.6 0.5
0.2 0.3 0.4 0.4 0.3
W 0.08 0.18 0.04 0.10 0.06
INTRODUCTION Alloys of nominal composition Ti Al- 0, 5, 6, 7.5, or 10.7 atom% Nb with 0.5 atom% Er were rapidly solidified by melt spinning [1-3]. Ribbons were from 30 to 50 micrometers thick. The alloy compositions, as analyzed by the flame emission method, are tabulated in Table I. Tungsten contamination from the non-consumable arc melting electrode occurred in all alloys. Melt spun ribbons were consolidated by hot isostatic pressing (HIP) and extrusion. The ribbons were cold pressed into low carbon steel cans, and HIP'ed at 8500C, 30 isi, for three hours and extruded 7:1 at 870aC [4].
EXPERIMENTAL RESULTS As-Nelt-Spun and Aged Ribbon As-melt-spun ribbon had a columnar structure from the bottom of the ribbon to the top. Selected area electron diffraction (SAD) was used to analyze the crystal structure of the as-melt-spun ribbons. The Ti 3 A1 alloy with no Nb addition was analyzed as the ordered hcp DO1 9 structure, alpha-2 [5]. The alloys containing niobium were analyzed as the ordered bcc phase, beta-2 [6]. In addition to the ordered beta phase, diffraction patterns of as-melt-spun Ti Al-Nb alloys contained streaks and diffuse intensity maxima, indicative of the precipitation of omega phase. This structure has been
Mat. Res. Soc. Symp. Proc. Vol. 58. - 1986 Materials Research Society
372
observed previously' in solid state quenched Ti more atomic percent Nb [7].
3 Al-Nb
alloys containing 10 or
Figure 1 is a TEM micrograph of a Ti 3 Al ribbon viewed in the columnar All as-melt-spun ribbons contained a dispersion of fine growth direction. X-ray spectrometry confirmed that analyzed particles (10-50 nm) particles. Electron diffraction obtained from extracted particles contained erbium. indicated that the dispersoid was Er 03 [8,9]. The oxide dispersions in asThe average dimension of melt-
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