STRUCTURE AND INITIAL PRECIPITATION IN A RAPIDLY SOLIDIFIED NICKEL SUPER-ALLOY

A nickel base superalloy (Nimonic 80A) has been rapidly solidified at cooling rates of between 105 to 106 K.S-1 by pendant drop melt extraction and by chill block melt spinning in an evacuated chamber backfilled with helium or argon. The internal structure is described in terms of process variables pertaining to rotating chill block quenching techniques. Both transmission electron microscopy and atom-probe field-ion microscopy have been employed to give structural and constitutional data on quenched and aged specimens. The as-quenched structure is homogeneous apart from fluctuations in titanium concentration which upon aging undergoes a spinodal phase decomposition to form disordered Ni3(Ti,Al,Cr) precipitates in the matrix, which after prolonged aging produces ordered γ (Ni3(Ti,Al)). inin6 particles form readily on grain boundaries and also appear in conjunction with ordered γ, via a discontinuous reaction, after short aging times. © 1979 American Society for Metals and the Metallurgical Society of AIME.