Mechanical Properties of Rapidly Solidified Nickel-Base Superalloys and Intermetallics
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MECHANICAL PROPERTIES OF RAPIDLY SOLIDIFIED NICKEL-BASE SUPERALLOYS AND INTERMETALLICS
A. I. TAUB AND M. R. JACKSON General Electric Corporate Research and Development, Schenectady, New York 12301
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ABSTRACT The improvements in the mechanical properties of nickel-base alloys that have been made possible by rapid solidification processing are The results of processing by powder metallurgy, laser melting, reviewed. In general, low pressure plasma deposition and spray forming are examined. the increased homogeneity obtained by rapid solidification allows for increased alloying and improved hot workability. The refined grain size improves the low and intermediate temperature strength, but leads to lower strengths at high temperature. For the high temperature applications, post solidification grain growth is required, as for example the directional recrystallization of powder metallurgy preforms. The development of a novel means of producing a fine dispersion from amorphous alloy precursors and the recent work attempting to improve the ductility of the intermetallic phases NiAl and Ni3A1 are also described.
INTRODUCTION Over the past three decades nickel-base alloys have been continuously improved in their high temperature strength and creep and fatigue resistance by advances in chemistry and processing. This paper will review those advances which have been made possible by rapid solidification processing. Before proceeding with that discussion however, it is necessary to clarify which processes should in our opinion be classified as rapid solidification. The problem arises because the definition of rapid solidiWe choose to follow the suggesfication processing is somewhat arbitrary. tion of Cohen, et.al. [11 that the transition from conventional to rapid solidification occurs at cooling rates of about 100 K/s. More precisely, rapid solidification processing encompasses those techniques which produce microstructures that are either more refined, more homogeneous or completely novel when compared to the structures obtained by solidifying at rates below 100 K/s. It is convenient to group the advances obtained in nickel-base alloys through rapid solidification processing into two categories. The first category consists of those developments which take advantage primarily of the increased homogeneity provided by rapid solidification and thereby allow for increased alloying to obtain improved mechanical properties [25]. Much of the early work in rapid solidification of nickel-base alloys falls into this category which can be described more in terms of process development than alloy development. The most prominent advances have been made in powder metallurgy (P/M) processing. We also include in this category the development of low pressure plasma deposition, layer glazing and spray forming. The second category of interest consists of alloy development studies which have been tailored to take advantage of rapid solidification processing, as for example the introduction of a fine dispersoid into superalloys. More rec
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