기계적 합금화된 산화물 분산강화 니켈기 초내열 합금에서 초기 결정립 크기가 결정립 형상비에 미치는 영향

Abstract

Mechanically alloyed(MA) oxide dispersion strengtthened(ODS) Ni-based superalloy attract great attention as advanced high temperature materials, because they can retain useful strength up to a relatively high gractions of their melting points. Production of a coarse elongated grain structure is very important in MA ODS alloys, since the creep rupture strength is usually increasing with the increasing grain aspect ratio(GAR). The formation of coarse elongated grains is possible during seceondary recrystallization by a process of directional zone annealing. The effects of the primary grain sizes on the GAR values of a newly developed MA ODS Ni Based superalloy alloy 99. were investigated. The grain structure after zone annealing was strongly depended on primary grain sized of as extraded this alloy. The optimum grain sizes for production a coarse elongated structure ranged from 0.45um to 0.55um in this alloy system. Where the primary grain size was less than 0.45um, preannealing heat treatment prior to zone annealing brought into the optimum grain size, therby producing a coarse elongated structure.