ODS-Legierungen : abnormales Kornwachstum im Temperaturgradienten

Abstract

Abnormal grain growth in ODS superalloys, which leads to the desired coarse grain structures, was examined. A heat treatment in a temperature gradient (i.e. zone annealing) causes directional grain growth producing very elongated grain structures. Two temperature limits were determined which control the abnormal grain growth process: an "initiation temperature" (T(aKw)) which must be reached to initiate the process, and a "minimum temperature" (T(w)) required to maintain abnormal growth. T(w) is always lower than T(aKw) both of which define the temperature range in which abnormal grain growth occurs continuously during zone annealing without the "nucleation" of new coarse grains. The physical explanation of these two temperatures is associated with the mechanisms of the onset and the propagation of abnormal grain growth. These mechanisms can be best understood by the influence of foreign atoms on grain boundary motion (impurity-drag theory).