遠心噴霧法による超合金粉末の諸特性

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Many kinds of heat-resistant superalloys are widely used for the materials of engine parts of aircrafts, and the segregation and difficulty of forging are generally apt to occur in cast alloys because of bearing many alloying elements. Recently, the powder metallurgy and its superplastic formation technique have been available for the practical production of turbine disc etc.In order to sufficiently offer the improved properties of material, it is necessary to make microstructure of powder as fine as possible.The authors have developped liquefied helium cooling(LHC) centrifugal atomization technique and made a trial on a fine crystallization of particles by rapid solidfication of melt in the process of the atomization.An investigation was made about the relationship between powder characteristics of γ/γ precipitation strengthended Ni-base superalloy powders concering operating conditions for centrifugal atomization and characteristics of superplasticity of their HIPed (and extruded) compacts. The following results were obtained.(1) The microstructure of Ni-base superalloy powder (MERL76 and its modified alloy TMP-3) is fine and secondary dendrite arm spacing: SII is 1.5μm or less.(2) The superplasticity of sintered MERL76 powders are obtained: flow stress of 5kgf/mm2, m-value of 0.77 and ductile elongation of more than 700% at the strain rate of 7.7×10-4/sec (1050°C).(3) The influence of particle size on superplasticity behavior is comparatively a few at the present work. The modified alloy TMP-3 showed almost similar superplastic behavior to MERL76.(4) 50kg capacity centrifugal atomization equipment was newly designed and started being operated for practical uses of extensive super alloy powders.This induction furnace is designed to use bottom tapping instead of customary tilting to prevent intermix of non-metallic inclusion.(5) Highly rotating disk practically up to 25000rpm (diameter≤100mm) for finer powders.Consequently, the high-purity superalloy powder of mean diameter of 80μm is obtained at the atomization of the revolution speed of 24000rpm and the disc diameter of 90mm.
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遠心噴霧法による超合金粉末の諸特性

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