Abstract
Allvac 718Plus alloy is a compromising Ni-based superalloy at elevated-temperature of 704℃,due to its combination of good mechanical properties and excellent structure stability.The precipitation behaviors during heat treatment in Allvac 718Plus alloy processed by rapid solidification technique were systemat-ically investigated in this work.The evolution of secondary phases in rapidly solidified(RS)718Plus alloy during annealing at 960℃is:η+MC in 1 h,η+MC+Laves(C14)in 6 h,and MC+Laves(C14)in longer duration.The growth and dissolution behaviors of η phase are evidenced in RS samples and differ-ent types of dislocations at the η/γ interface are characterized.Based on these experimental observations,we examine the transformation mechanisms of γ→η and η→γ,which are related to the formation of stacking faults(SFs)with a 1/6[211]γ Shockley partial dislocation and the climbing of 1/4[00001]η edge dis-locations at the η/γ interface,respectively.Both MC and Laves(C14)phases are enriched in Nb and Mo,with a higher level of Ti in MC carbides and Cr in the Laves(C14)phase.The precipitation of MC carbides is driven by the high concentration of C atoms in γ-matrix,while the Cr segregation promotes the later nucleation of Laves(C14)phase in γ-matrix around MC carbides,which is due to the Cr atoms rejection from MC carbides into the matrix.
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