Koji Tanoue and Hiroyuki Ogata
Department of Materials Science and Engineering, Faculty of Engineering, Kyushu Institute of Technology, Kitakyushu 804-8550It is investigated how the morphological change of secondary recrystallized grains grown in powder metallurgy tungsten fine wires has an effect on creep at high temperatures after it is quantitatively estimated. The quantitative treatment of the grain morphology is possible by using f1 as the representative one of the grain shape parameters. The optimum interlocked grain structure is defined as the grain morphology in which the grain aspect ratio is minimized under the condition that the area of grain boundaries does not increase drastically. The high-temperature creep can then be characterized by the index ΔI(=f1−f01) which indicates the degree of deviation from the optimum interlocking of grains which is designated by f01. The region of power law creep in the deformation mechanism maps is minimized at ΔI=0 at which the grains are most favourably interlocked, being extended as ΔI deviates from ΔI=0. It is considered that the deformation in the region is strongly influenced by grain boundary sliding, being further done by grain boundary cavitation with an increase in ΔI at ΔI>0.
bubble, interlocking, non-sag grain structure, deformation mechanism map, activation energy for steady state creep, grain boundary sliding, grain boundary cavitation, doped wire