Production of Extra Low Oxide Beryllium Powder by the Rotating Electrode Process

Abstract

The Rotating Electrode Process (REP) is a method for producing high quality spherical metal powders. REP powder is made by melting the end of a cylindrical bar, which is rotated at high speed about its longitudinal axis, using an arc source for melting. As the end of the bar is melted, metal droplets are ejected by centrifugal force and solidify during flight through a helium atmosphere. The advantage of REP for producing powders of reactive metals is that molten metal is never in contact with other metals or refractories. This factor reduces the likelihood of contamination and makes possible the production of powder that is close to the input material in cleanliness and composition. The plasma rotating electrode process (PREP) is an extension of REP in which the tungsten cathode heat source is replaced by a plasma torch. Spherical Be powders can be produced using either REP or PREP, although extra low oxide powders having BeO contents less than 300 PPM are produced via PREP. Mechanical properties of low oxide PREP beryllium powder consolidated by hot isostatically pressing, while lower than those of commerical low oxide grades, still compare favorably. Yield strengths are in the range of 140 to 204 MPa (20 to 30 ksi) and tensile strengths 173 to 259 MPa (25 to 37 ksi) depending on HIP conditions. Microyield strength is between 34 and 40 MPa (5 to 6 ksi), which is exceptionally high considering the coarse grain si2e and low strength of the material.