Mechanical and oxidation properties of AlRu-based high-temperature alloys
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METALLURGICAL TRANSACTIONS A
below that expected at 7.0 pet strain in room-temperature deformation. The AI4sRu51Ce sample fractured at 200 °C. Elastic constants were measured using the techniques described in a prior reportjj2j for binary AI-Ru alloys and three ternary alloys w i t h Cr or Si. As Figure 4 shows, Cr and Si b o t h raise the shear moduli and Si has about double the effect of Cr. Quantitatively, the effects in terms of the modulus G and the concentration c are given by
120
q
115
g
110
5%Cr -
o9 i
•
5% S i
.3%Cr 105-
w T 100
9.=
9O47
I
50
I
55 ATOMIC %RU
60
Fig. 4 - - Shear m o d u l i for binary AI-Ru alloys and ternary alloys with C r or Si.
VOLUME 24A, MARCH 1993--761
values o f e~ (= 1/G dG/dc) o f 0.7 for Cr and 1.4 for Si. Such values are typical for substitutional solutes. For example, in Cu eG values range from 0.3 for Pd to 2.9 for Sn. t]3J Fractography was done on sample 90X2--one of the more promising alloys (A14sRus~Y). In spite o f the fact that it is also one o f the tougher alloys, the fracture surface showed some areas o f intergranular parting, as in the l o w e r portion o f Figure 5. More typical is the fibrous surface shown earlier. Oxidation tests in flowing air, as described in our earlier work,(8] were done at 1100 °C and a few tests at 1350 °C. After an initial parabolic weight g a i n , many o f the alloys lost weight, either through volatilization o r spalling o f the oxide. Here we report the initial parabolic data. Figure 6 includes the data at 1100 °C, and Table II presents those at 1350 °C. Values o f the rate constant k o f about 10-1° gm2-cm4/s correspond to an oxidation depth o f less than 25/~m/100 h. Values at or b e l o w this value identify potentially useful alloys. The figure includes results from our previous study,ts~ as well as those listed in Table I. Among these data, only four alloys qualify, and these only at 1100 °C. Of the four, the least rapid oxidation
AI Ru
Al~eRusl Y
AI47Ru ~I~ ~
AI46Ru~,Cr3 • AI45.sRuso.sSc2B~ 5 • Ai47Ru51Cr 2 AI~ 3Ruso 2CrsBo ~ •AI4~Ru51Ce
o~
•
~'
AI47 ~Rus2 5Cro.3 (Lost Weight)
AI44.sRUso.sSi5
• Ales 5Ruso.sCr 5
0
10 12
I
10-~1
I
I
10 10 10-9 parabolic Rate Constant at 1100°C (g2/crn4-s)
I
10-8
,10-~
Fig. 6--Parabolic r a t e constants (k) at 1100 °C for initial oxidation of various a l l o y s vs the chisel toughness (CT). Desirable C T ' s are > 2 ; desirable k ' s are ~10 -~° gmZ-cm4/s.
is f o r the lowest toughness alloy--A14~.sRus05Crs. The best combinations o f low oxidation and high toughness are seen to be A147Ru53 and A148Rus~Y, with a slight preference f o r the binary composition. At 1350 °C, the lowest oxidation rate is for A143Ru52Sc5 (Table II), with a good chisel toughness[71 o f 2+. The AI-Ru and A1-Ru-Y alloys have promising combinations o f oxidation rates at 1100 °C and mechanical properties at room temperature, where most intermetallics are brittle. One alloy with good high-temperature mechanical properties, 17~ A143RuszScs, has only marginally unacceptable oxidation
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