Effect of Hydrogen on the Behavior of Y-TiAl Atomized Powders
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EFFECT OF HYDROGEN ON THE BEHAVIOR OF y-TiAl ATOMIZED POWDERS D. S.
SHONGa,
Y-W. KIMa,
C.
F. YOLTONb,
AND F. H. FROESc
aMetcut-Materials Research Group, P.O. Box 33511, Wright-Patterson Air Force Base, OH 45433-0511 bCrucible Materials Corporation, Crucible Research Center, P.O. Box 88, Pittsburgh, PA 15230-0088 CU.S. Air Force Wright Aeronautical Laboratories, AFWAL/MLLS,
Wright-Patterson Air Force Base,
Materials Laboratory,
OH 45433-6533
ABSTRACT The effect of hydrogen on the phase stability of y-TiAl and a 2 -Ti3Al phases was studied, with emphasis on the investigation of decomposition of a metastable a 2 phase to a stable y phase in gamma alloy powders. In this work, progressive decomposition of a 2 + y was observed to occur during aging with increasing temperatures or time under vacuum and under H2 . The microstructural analysis indicated that hydrogen may facilitate such decomposition to occur at lower temperatures and shorter aging time.
INTRODUCTION The effect of hydrogen on the physical and mechanical properties in a-Ti and $-TI alloys has received a considerable amount of attention in the last few decades [1-3]. The central focus has been on the hydrogen embrittlement caused by the formation of titanium hydride precipitates in the a-Ti lattice r3], or microstructural modification through temporary hydrogen alloying processes [4]. However, little information about the hydrogen effect has been reported on high temperature a 2 -Ti 3 Al and y-TiAl titanium aluminides which are being considered for applications in hypersonic, hydrogen-fueled aerospace vehicles such as the National Aerospace Plane (NASP) [51. In this paper, the effect of hydrogen on decomposition of metastable a2 phase, retained in atomized powders with a gamma alloy composition produced by rapid solidification, to stable y phase during aging is reported.
EXPERIMENTAL The as-received TiAl and Ti-34A1-1.3V-0.52C (wt%) alloy powders were produced by plasma rotating electrode atomization techniques. The hydrogenation experiments on atomized powders were undertaken at 427°C, 482°C, and 538*C, respectively, for 20 hr in a vacuum chamber back filled with 0.02MPa pressure of hydrogen. The hydrogen concentrations for both alloy powders are listed in Table I and illustrated in Fig. 1. TABLE I.
CHEMICAL ANALYSIS OF HYDROGEN CONTENTS (ppm by weight) IN ALLOY POWDERS
Condition Alloy TiAl Ti-34AI-1.3V-0.52C
As-Atomized 5.3 13.43
Mat. Res. Soc. Symp. Proc. Vol. 133. ' 1989 Materials Research Society
427
Hydrogenation Temperature, *C 482 538
10.5 36.32
26.9 281.0
300.9 541.45
712
600 (1) TW 500
(2) Ti-34A1-1.3V-.52C (wt%) (2)
C
0
400
S (1
200
~10004 0 Fig.
100
500 400 300 200 Hydrogenation Temperature ("C)
600
1. Plot of hydrogen content vs. hydrogenation temperature.
RESULTS Fig. 1, hydrogen content increased as hydrogenation As shown in However, hydrogen absorption temperature increased for both alloy powders. all conditions, In powders. alloy in both different were rates There was a sharp Ti-34AI-1.3V-0.52C contained mo
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