水冷銅ハースによるプラセオジムおよびネオジムの電子ビーム溶解挙動

Abstract

Commercial-grade purity Pr and Nd metal rods were repeatedly melted in a 10kW EB-furnace to grasp the features of EB-melting of rare earth metals and the properties of the EB-melted rare earth metals. Initial amount of the melting samples was about 40g, and the beam current added was 0.22A and net melting time was 25X2min every double-melting for both metals.(1) The average weight-loss of Pr and Nd metals were respectively 7% and 25% every double-melting, suggesting about 350°C and 250°C higher temperatures of the melting pools than each melting point of Pr and Nd, respectively.(2) The significant decrease of the pressure inside the furnace after the melting of Nd rods reveals that the vapour of the metal can act as a strong getter of oxygen and nitrogen.(3) Among the gaseous impurity elements (C, H, O, N) with a total amount of 5000 wt.ppm and the metallic ones with each amount of several wt. ppm, only H in Pr was effectively removed from 76 to 4 wt. ppm. EPMA images showed the presence of a large amount of inclusion-like deposits for oxygen, but not for nigrogen.(4) Vickers hardness of Pr and Nd metals lowered from 58 to 32 and 50 to 36, respectively, while the grain size increased from 60 to 120μm in both metals.(5) Initiation temperature of oxidation detected by weight increase was 450°C for Pr metal and above 900°C for Nd metal. But the oxidation of the former before EB melting proceeded rapidly owing to the formation of cracks and the collapse of specimen.