ALLOY MORPHOLOGY UNDER SUPERHIGH SPEED DIRECTIONAL SOLIDIFICATION

This paper explains the principle of a newly developed ZMLMC directional solidification apparatus with a superhigh temperature gradient.With the help of the apparatus,research was done on the change of directional solidification structures of the cobalt based superalloy K10 at superhigh velocities.Relations between the primary and secondary dendrite arm spacings and the cooling rates Were investigated.Experimental results show that the primary and secondary dendrite arm spacings of directionally solidified cobalt based superalloys are respectively finer than one fifth and one eighth of those produced by conventional directional soli-dification processes.The primary and secondary dendrite arm spacing which can be decreased by increasing the cooling rate,and the relations between these spacings(λ1,λ2)and the temperature gradient(G)and solidfication rate(v)were as follows:λ1=1.428×10^(3)(G·v)^-1_(1)λ_(2)=0.132×10^(3)(G·v)^-1.