Microstructure of Rapidly Solidified Ti 3 Al Alloys
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MICROSTRUCTURE OF RAPIDLY SOLIDIFIED Ti
A.
G.
JCSNa
K
R. TEAb
JACKSONa,
K.
R.
TEAL , D.
aSystems Research Laboratories,
H.
3 Al
ALLOYS
EYLON
, F.
Inc.,
2800 Indian Ripple Road,
45440 bAir Force Wright Aeronautical Laboratories,
FROES
, AND S.
J.
SAVAGE
Dayton,
OH
Materials Laboratory,
AFWAL/MLLS, Wright-Patterson Air Force Base, OH 45433 cMetcut-Materials Research Group, P.O. Box 33511, Wright-Patterson Air Force Base,
OH 45433
ABSTRACT The microstructures of ordered Ti 3 Al-lZr (alpha 2 +Zr) and Ti-Al-Nb alloys produced by ingot metallurgy (IM) and by rapid solidification (RS) are compared. The RS Ti 3 Al-iZr (alpha 2 structure) alloy displayed small antiphase domains (APD) of 10-20 nm in the as-produced condition, but large grain size. The latter observation is rationalized in terms of the cooling history used to produce the material. The RS Ti-Al-Nb alloy exhibited an equiaxed microstructure. The IM Ti-Al-Nb material displays a complete change in microstructure between 1010°C and 1035'C, indicating a narrow alpha+beta phase field.
INTRODUCTION Studies of cast and wrought ingot metallurgy (IM) Ti 3 Al show the alloy possesses high strength but low ductility at room temperature due to an ordered structure [1]. An investigation of rapidly solidified (RS) Ti 3 Al and Ti-Al-Nb alloys was initiated to determine the effects of RS on microstructure and properties, since RS allows both microstructural and constitutional benefits in a number of systems. The RS approach was investigated in this work in an effort to improve the room temperature ductility while maintaining the relatively high strength level. In this paper comparison of RS Ti 3 AI-lZr addition is made with IM material and some results for RS and IM alloys of a Ti-Al-Nb ternary are presented.
EXPERIMENTAL Ti 3 Al-lZr and Ti-Al-Nb billets were both extruded and swaged at 990'C to form bars. The alloys were heat treated at 990°C/2 hr/FC (furnace cool) to produce an equiaxed microstructure. Bars of the Ti 3 AI-lZr were converted to RS ribbon in vacuum by the pendant drop melt extraction (PDME) [2] process. Microstructures of each were examined by scanning and transmission electron microscopy on JEOL 1OOCX and 2000FX microscopes.
RESULTS Ti 3 Al-lZr IM and RS Figure 1 is a TEM micrograph of heat treated Ti 3 Al-lZr IM material, showing a lenticular grain morphology and contrast associated with antiphase domain boundaries (APD) [(1120) beam operative]. This structure is characteristic of Ti 3 AI which has been subjected to heat treatment at temperatures between 700°C and 1000%C [1]. APD size is .600-1500 nm, which is comparable to the size for Ti 3 AI annealed at 800%C for 20 minutes.
Mat. Res. Soc. Symp. Proc. Vol. 58. ' 1986 Materials Research Society
366
Figure 1.
(a) TEM micrograph of IN Ti 3 Al and (b) diffraction pattern from (a).
RS TisAl-lZr produced by the PDME process exhibits the microstructure shown in the optical micrograph in Figure 2. The microstructure consists of grains within which are the APDs. The APDs in thi
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