| To understand the dependency of microstructures on non-sag property and ductility in molybdenum wire, five different specimens were prepared through sintering, swaging and drawing processes. Each specimen was doped with K₂O and SiO₂ in various amounts, i.e., 0, 0.028, 0.14, 0.28 and 0.49(K+Si) by weight percents, and isochronally annealed at various temperatures for 30 minutes. The microvickers hardness was measured as a function of annealing temperature and then optical micrographs were taken with each specimen annealed at 1400℃ and 2000℃. Each specimen annealed at 1000℃ and 2000℃ underwent. 90˚ repetition bending until crack occurred to evaluate its ductility. Non-Sag values were measured in temperature range from 1000℃ to 2340℃(0.9Tm) under load of 250g, and then some fractured surfaces were observed by scanning electron microscopy. The specimen doped with 0.28(K+Si) weight percent was completely recrystallized at a temperature between 1800℃ and 2000℃ and its grain structure consisted of elongated and interwoven shape grains, including many small bubbles at grain boundary, of which aspect ratio(length/width) was about 30. This grain structure showed a good ductility after recrystallization and an excellent non-sag property over 0.5T_m. When the microstructures were not fully recrystallized, however, the sagging-resistance was increased with the doping amount of K₂O and SiO₃, and the ductility was inversely decreased. Especially, when the bubbles grew, the fracture occurred easily due to a sagging phenomenon assisted by the reduction of effective area supporting the load. |
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