Improved product quality and resource efficiency in porous tungsten machining for dispenser cathode application by elimination of the infiltration process

Abstract

Porous tungsten is a difficult-to-machine material commonly used in the manufacture of high-performance dispenser cathodes [1]. The functional performance of such cathodes is directly linked to the surface porosity of the machined porous tungsten workpiece. Conventional machining leads to smearing of surface pores [1]. Current industry practice involves the use of a plastic infiltrant that stabilizes the pores during machining [2]. In order to increase the sustainability of the dispenser cathode manufacturing process, we propose a materials-science driven approach to machining porous tungsten. Heated and cryogenic machining are compared to determine an effective method to increase surface porosity. The ductile/brittle transition of the body-centered-cubic (BCC) refractory metal tungsten is exploited to alter the cutting mode between shear cutting (heated machining) and controlled brittle fracture (cryogenic machining). We conclude that cryogenic machining via controlled brittle fracture using a fine-grained PCD tool is the most effective approach to infiltrantfree machining of porous tungsten for dispenser cathode applications.