Abstract: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比ange of directional solidification structures of the cobalt based superalloy K 10 at superhigh velocities. Relations between the primary and secondary dendrite arm spacings and the cooling rates Were investigated. Ezperimental 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 proceases. The primary and secondary dendrite arm spacing which can be decreased by increasing the cooling rate,and the relations between these spacings (λ_{1 ,} λ₂) and the temperature gradient (G) and solidfication rate(v)were as follows: λ₁= 1.428 ×10³(G·v)^-1, λ₂=0.132× 10³(G·v)^-1.

Key words: superhigh speed directional solidification  superalloy  dendrite arm spacing