The effects of orientation and thickness on the notch-tensile creep strength of single crystals of a nickel-base superal
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INTRODUCTION
S I N G L E crystal blades of aircraft jet engines have been developed to improve creep strength, creep ductility, and thermal fatigue resistance compared with unidirectionally solidified and conventionally cast blades. ~According to previous studies,~-5 single crystals of the strongest nickel-base superalloys MAR-M200* and MAR-M247 had extensive *MAR-M is a trademark of Martin Marietta Company.
orientation dependence of creep properties, and were considerably more creep resistant in the [001] orientation1-5 and in the [111] orientation2,4,5 in uniaxial tensile creep. High temperature fatigue strength of single crystal MAR-M200 with the [001] orientation has also been reported to be superior compared with conventionally cast superalloys.l6 Mode of plastic deformation of single crystals is influenced by the crystallographic orientations not only in the tensile direction but also in the thickness direction. Thus, if a crack has been introduced, the creep properties will depend on the orientations in both directions. The authors have revealed that the notch-tensile strength of single crystals at room temperature was affected by the orientations in both directions and the thickness of specimen] In the present study, the influence of the crystallographic orientations in the tensile and the thickness directions and the thickness of specimen on the notch-tensile creep strength and the rupture ductility of single crystals of a nickel-base superalloy UDIMET 520 has been investigated.
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FOUR KINDS OF PLATES
Crystallographic orientations of four kinds of plates with different arrangement of slip systems are drawn in Figures l(a) through (d). The smooth and the notched speci-
*UDIMET is a trademark of Special Metals Corporation. K. SUGIMOTO, Research Assistant, T. SAKAKI, Associate Professor, and O. MIYAGAWA, Professor, are with the Department of Mechanical Engineering. Tokyo Metropolitan University, 2-1-1, Fukazawa, Setagayaku, Tokyo 158, Japan. T. HORIE, formerly Graduate Student. is now Engineer with Muroran Works, Nippon Steel Corporation, 12 Nakamachi. Muroran 050, Japan. K. KURAMOTO, formerly Graduate Student, Tokyo Metropolitan University, is now Engineer with Kobe Steel, Ltd. Manuscript submitted September 26. 1984. METALLURGICALTRANSACTIONS A
mens are specified in Figures 1(e) through (f), respectively. The Xt, X2, and X~ axes shown in Figure 1 are taken along the width, the tensile, and the thickness directions of the specimens, respectively. The slip systems shown in Figure 1 and Table I are the {111}(101) type slip systems on which the maximum resolved shear stress acts in every specimen, and named the principal slip systems (or more simply, the slip systems). In the following explanation, slip is assumed to occur on the principal slip systems. The resolved shear stress ~" acting on the principal slip systems is shown in Table I as a function of axial stresses o-~1, o-22, and o'33. On all the principal slip systems in the four kinds of plates, the same amount of resolved shear stress 0"22/~-6
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