Fabrication of porous tungsten with tunable pore structures via low-temperature pressureless sintering: Processing and mechanisms

Abstract

Porous tungsten plays a critical role in field emission electric propulsion (FEEP) thrusters by synergistically combining sharp emitter tips with efficient internal propellant transport. The emission performance of FEEP thrusters exhibits strong dependence on the emitter's porosity and pore density. Nevertheless, conventional fabrication methods for porous tungsten face challenges in achieving porosity levels of 20–40 % concurrently with precise pore density control. This study proposes a fabrication strategy that integrates wet ball milling with powder metallurgy, enabling pressureless sintering at low temperatures (1200–1500 °C). The developed method allows for the synthesis of porous tungsten featuring uniform pore size and homogeneous pore distribution. Through precise regulation of sintering temperature and holding time, we achieved porous tungsten with controlled porosity (21.98–38.16 %), pore density (2.2–16.32 pores/10μm²), peak compressive strength of 987.2 MPa, and Vickers hardness ranging from 107.77 to 204.85 HV. The growth kinetics of sintering necks were analyzed based on the Kuczynski model, yielding a scaling exponent n = 4.50 and activation energy Q. Fitting of necks in porous tungsten prepared with varied ball-milling durations revealed the mechanistic influence of milling on powder sintering activity. These results underscore bulk diffusion as the predominant mass transport mechanism, with the reduced activation energy attributed to enhanced sintering kinetics from ultrafine powders and optimized milling processes. This work provides a theoretical framework for successful low-temperature sintering of porous tungsten.