| To identify bubble formation substance in molybdenum doped with K₂O and SiO₂ two kinds of specimens were prepared; first, solid potassium disilicate was intentionally implanted in molybdenum powder followed by compacting at 300MPa. Then the compact was sintered at 2200℃. Secondly, molybdenum powder doped with potassium disilicate was produced from the hydrogen reduction of molybdenum trioxide, MoO₃, doped with potassium disilicate in acqueous solution. The doped powder was compacted and sintered at the same conditions as the former specimen. The sintered ingot was swaged and drawn to 1mm diameter wire. To analyze the bubble formation substance during sintering, hot isostatic pressing (HIPing) at 1900℃ under 190MPa was applied to transform bubbles into solid particles and to collapse pores induced by sintering. And to analyze the entrapped substance in the bubble of molybdenum wire, HIPing was performed at 2000℃ under 190MPa after annealing at 2000℃ for 30minutes. Scanning electron micrographs were taken and bubble formation substance was analyzed by using EDX (energy dispersive X-ray spectroscopy) and WDX(wave dispersive X-ray spectroscopy). It was analyzed that the evolution of bubble was due to the vaporization of K-Si oxide during sintering and Al-K-Si complex oxide during annealing of wire. Al-oxide participated in bubble formation for wire was exidsted as separate one from K-Si oxide in sintered ingot. The substructure of as-drawn state was observed by using TEM(transmission electron microscopy) to understand the reaction of Al-oxide with K-Si oxide during wire making process. It was cautiously concluded that the participation of Al in bubble formation should be assisted by the deformation processes such as swaging and drawing inducing the distribution of bubble formation substance along the tangled dislocation cell boundaries. |
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