Abstract
Molybdenum sheaths are critical for protecting thermocouple components in high-temperature furnace environments up to 2200°C, but traditional tungsten inert gas welding introduces significant material vulnerabilities. The welding process traditionally increases grain size through solidification and operational exposure while creating porosity that promotes brittle behavior. To address these limitations, a research program developed a molybdenum-lanthanum oxide (M-L) seamless tube as an alternative thermocouple sheath material. Characterization revealed that the M-L sheath demonstrates superior metallurgical properties, including smaller heat-affected zones, a refined fusion zone grain structure, and substantially reduced porosity. The study comprehensively compares unalloyed molybdenum and M-L materials, providing detailed insights into the mechanisms governing welding and performance of molybdenum alloys in extreme thermal environments.
