Comparison of Rapidly Solidified Nickel Base Superalloys Prepared by Melt Spinning and Plasma Deposition
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COMPARISON OF RAPIDLY SOLIDIFIED NICKEL BASE SUPERALLOYS PREPARED BY MELT SPINNING AND PLASMA DEPOSITION
A.I. TAUB, M.R. JACKSON, S.C. HUANG AND E.L. HALL General Electric Corporate Research and Development PO Box 8, Schenectady, NY 12301
ABSTRACT The microstructure and yield strength of two nickel base superalloys prepared by melt spinning and plasma deposition are compared in the as-solidified condition and after annealing. The results support the interpretation of the yield strengths obtained by tensile testing melt spun ribbon as representative of the values obtained for bulk specimens with equivalent microstructures. The effectiveness of grain size strengthening in a nickel base superalloy is also examined. The Hall-Petch ry~tion appears to be obeyed, with a slope k = .77±.15 MPa-m
INTRODUCTION The rapid solidification of superalloys has attracted much attention over the past few years. Initially, attempts were made to process existing commercial alloys via the new rapid solidification techniques. It was generally found that those alloys whose chemistry had been tuned to produce optimal properties in the cast and wrought form exhibited only slight improvements when processed by rapid solidification. Present activities have therefore turned to developing new alloys designed specifically for rapid solidification processing. Within this new framework, melt spinning has been used as a screening process to select alloys with promise for good properties as processed by rapid solidification. Many investigators have examined the microstructure of alloys processed by melt spinning to determine the degree of homogeneity, structure refinement and phase stability of rapidly solidified alloys [1-31. This type of approach is justified because it has been shown that processes with equivalent cooling rates produce equivalent microstructures [1,4]. Several investigators have also used melt spun ribbons to determine the mechanical properties of rapidly solidified alloys. Microhardness and tensile test results on melt spun ribbons are reported routinely in the literature and in patent applications [5-71. However, there is little evidence to show that the mechanical properties of ribbons are similar to those of the same alloys processed by other rapid solidification techniques. It is essential to determine if the alloy properties are determined solely by the cooling rate or if the different processes affect the alloys in other ways. In this paper, we present preliminary data of a study of this question, comparing two nickel base superalloys prepared by melt spinning and low pressure plasma deposition (iSPD). The cooling rates attributed to these two processes are similar (-10 K/s), and they have been shown to produce alloys with similar microstructures [8,9]. The microstructure and tensile strength in as-solidified specimens will be examined, and the evolution of these properties with heat treatment will be discussed. Mat.
Res.
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28 (1984)D Elsevier Science Publishing Co.,
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390
EXPERIMENTAL The
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