High temperature elastic properties of polycrystalline mar-m200 (a nickel base superalloy)
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THE
present investigation was undertaken to facilitate an experimental study of the shock response of MAR-M200 at elevated temperatures. In the literature only the values of Young's modulus of MAR-M200 have been reported to 1255 K. l The present investigation provides the values of shear modulus and Young's modulus to 1125 K. The elastic constants of M A R M200 were determined by a sonic resonance method. 2 MATERIAL AND EXPERIMENTAL TECHNIQUE MAR-M200 is a vacuum induction melted and vacuum cast nickel base precipitation hardening alloy. A relatively large a m o u n t of tungsten (12.5 pct by weight) is added to enhance solid solution strengthening and carbide formation. The presence of cobalt (10 pct by weight) increases the solubility temperature, i.e., the solvus temperature of the g a m m a prime hardening phase Ni 3 (A1,Ti). The addition of c h r o m i u m increases the oxidation resistance of the nickel matrix (austenite-gamma phase) while simultaneously improving the high temperature properties of the alloy. The elemental composition of MAR-M200 is given in Table I. The material used in the present investigation was obtained f r o m Hitchner Manufacturing C o m p a n y , Milford, N H , in the f o r m of rectangular plates roughly 30 cm x 15 cm • 0.4 cm in dimensions. The rectangular specimen of MAR-M200 used in the present work had dimensions of 10.173 cm x 1.347 cm x 0.249 cm. The deviation of the dimensions f r o m the true rectangular form of the specimen was less than 0.001 cm. Elastic moduli were determined by using a sonic resonance technique? The measurements were performed by suspending the specimen of MAR-M200 with two carbon fibers in a nichrome wire furnace. Measurements were carried out both in open atmosphere and under vacuum. Temperature was measured with a chromel-alumel thermocouple with its hot junction located 1 m m away from the middle of the specimen or spot-welded at one of the two nodal points
from which the specimen was suspended. The resonant frequencies measured under the various conditions at a given temperature were found to be not significantly different f r o m one another. A schematic of the system used to p e r f o r m the experiments is shown in Fig. 1. The values of Young's modulus E(T) and shear modulus G(T) at a temperature T o f a rectangular solid determined f r o m its flexural FE(T) and torsional Fa(T) resonant frequencies are given, respectively, by the following relations?
E(T) = 0.94642 p(T) L4(T) F2(T) C/t2(T) and
G(T) = 4 L2(T) p(T) FZ(T) R
METALLURGICAL TRANSACTIONS A
[2]
whe~:e p(T) is the density at temperature T; L(T) and t(T) are the length and cross-sectional dimension in the direction of flexural vibration of the rectangular specimen; and C and R are correction factors for determining Y o u n g ' s modulus and shear modulus from the flexural and torsional resonances, respectively, of a rectangular bar. 3,4 The magnitude of C depends on L, t, and Poisson's ratio (/~). For the MAR-M200 specimen with L = 10.173 cm, and t = 0.249 cm, the magnitude of C va
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