Dispersoid Modification of Ti 3 Al-Nb Alloys
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DISPERSOID MODIFICATION OF Ti
3 Al-Nb
ALLOYS
R. G. Rowe, J. A. Sutliff, and E. F. Koch General Electric Corporate Research and Development Schenectady, NY 12301
ABSTRACT Titanium aluminide alloys with matrix compositions of essentially Ti 3 Al plus 0, 5, 7.5, and 10 a/o Nb and with and without rare earth elements for The alloys were rapidly solidified by dispersoid formation were prepared. Ribbon was consolidated by HIP and extrusion at temperatures melt spinning. The effects of processbelow the beta transus temperatures of the alloys. ing conditions and dispersoid additions on room temperature ductility and fracture toughness were studied.
INTRODUCTION The ordered compound Ti3 Al has good strength and creep resistance at Ti 3 Al-Nb alloys at high temperatures, but nil ductility below 600 C [1-3]. niobium levels of 5 atomic percent and above exhibit some ductility at low Refinement of slip length has been thought to be a means temperatures [4]. Reduction of grain size of modifying the deformability of Ti3 Al [5-7]. The introduction of a reduces slip localization, improving ductility [7]. dispersed phase may also refine the slip length [2], and has been shown to We improve post-creep ductility in alpha + alpha-2 titanium alloys [8]. have evaluated the effect of rapid solidification and the introduction of rare earth dispersoids on the microstructure and properties of Ti 3 Al-Nb alloys. Alloys based upon Ti 3 Al with 0, 5, and 7.5a/o niobium were rapidly solidified
[9,10],
as base alloys and with
alloy additions
to form either
or cerium sulfide and oxysulfide dispersoids
Er
2
03
[11].
EXPERIMENTAL The alloy compositions tabulated in Table I were rapidly solidified by Melt spun ribbon was from 30 to 50 micrometers arc melt spinning [12,13]. First, some of thick. Two major compositional variations were observed. the alloys had significant aluminum losses during arc melting of elemental constituents. In addition, all alloys also exhibited some tungsten contamiThis may have contrination from the non-consumable arc melting electrode. buted to variability in the mechanical property data, but not to the trends which we observed. Ribbon was consolidated by cold compaction, hot isostatic pressing 0 Alloys were HIP'ped at a temperature of 900 C and (HIP) and extrusion. Extrusion billets of all Ti Al-Nb alloys pressure of 30 ksi for 3 hours. were heated to 9250C and extruded at a reduction ratio of from 6 to 7:1. 0 Alloys without Nb were extruded at a temperature of 1108 C. 0
change in the size or density of Er2 0 or HIP at 900 C produced little 0 Extrusion Ce-S dispersoids which were formed in ribbon aged at 750 C [14]. 0 at 925 C resulted in refinement of the grain size of dispersoid-bearing The grain alloys and grain coarsening of alloys without dispersoids [14]. Extrusion also produced size of extruded alloys is shown in Table 11.
severe coarsening of the Er
2
0 3 dispersoid to particle diameters from 0.1
Mat. Res. Soc. Symp. Proc. Vol. 58. 1 1986 Materials Research Society
360
to 1.0 micrometers. The
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