Low Temperature Deformation Kinetics of Ruthenium Aluminide Alloys
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Alloy A
Compositlon RuAI (GE)
77 K 470
298 K 400
B
RuAI + 0.5%8 (GE)
510
--
C
Ru51.5A148,5 (GE)
-
565
D
Ru54.5AI45.5 (GE)
515
540
E
Ru52AI43Sc5 (GE)
500
480
F
RuAI + 0.5%B (PM11)
712
570
G
Ru53AI47 + 0.5%B (PMTI)
782
730
H
Ru52AI48 (RHIP)
605
5'10
Table I. The 2% flow stress (MPa) for different compositions from compression tests at 77 K and room temperature.
by two orders of magnitude from approximately 104/s to 10-2/s after 2% plastic deformation with an Instron 5500R screw driven machine. Following deformation, TEM foils were cut from compressed samples at approximately 450 to the axis of the compression. Preparation of TEM foils consisted of mechanical grinding before electropolishing in an electrolyte of 10% lactic acid, 7% sulfuric acid, 3% nitric acid, 2% hydrofluoric and methanol. Samples were polished in the temperature range of -20 to -30'C, at 15 - 25 volts [8]. TEM analyses were performed in a Philips EM420T microscope at an operating voltage of 120 kV. Conventional tilting experiments were used to characterize Burgers vectors with seven to ten kinds of diffraction vectors (g) chosen for each analysis. RESULTS Table I lists the flow stress of RuAl-based alloys at a plastic compressive strain level of 2% for tests conducted in liquid nitrogen and at room temperature. For the alloys investigated, the flow stresses generally decreased by less than 25% between 77 K and room temperature, Table I. All RuAl-based alloys were subjected to a strain rate change during compression from approximately 10-4/s to 10-2/s. The change in flow stress for this variation in strain rate was typically only of the order of 10 to 20
Figure
1(a).
RuAI+0.5%B (b).
Ru 52AI43Sc 5 (f). Ru 52AI4 8 •
Ru 51.5 A148 5 (c). Ru 53 A147 +0.5%B (d). Ru 54 .5A145 .5
KK7.11.2
(e).
MPa over the range of temperatures investigated. The corresponding rate sensitivity, m' a-Inc
Mt
(1)
a lne
for each of the alloys was calculated and the results are listed in Table II. Alloy A B C D E
Composition RuAl (GE) RuAI + O.5%B (GE) Ru5l.SAI48.S (GE) Ru54.5AI45.5 (GE) RuM2AI43Sc5 (GE)
77 K .-0.0067 0.0097 0.0073 0.0066
298 K
F a H
RuAI + 0.5%B (PMTI) Ru53A147 + 0.5%B (PMln) Ru52A148 (RHIP)
0.0060 0.0082 0.0058
0.0062 0.0071 0.0040
0.0061 -
0.0072 0,0058 0.0059
Table II. Rate sensitivities for different compositions at 77 K and room temperature. Figures 2 (a)-(b) show the dislocation substructures of RuAl+0.5%B deformed at 77 K and room temperature after approximately 2% plastic strain. Both and dislocations are present with a significant density. Additionally dislocations are only occasionally observed. All dislocations lie on {1101 planes [4]. The and dislocations do not appear to result from any decomposition reaction and apparently both contribute to straining. Thus only a range for the magnitude of the activation volume can be determined, based on Burgers vectors for < 100> and < 110> dislocations, respectively. The activation volume V*, is defined as [9-11 ]: aAG
= kT(InY)T
a
kt
(2)
where AG is
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