Thermal Stability of Milled Nanocrystalline Tungsten Powders

Report No. ARL-TR-5541
Authors: Brady Butler, Eric Klier, Matt Kelly, and Micah Gallagher
Date/Pages: May 2011; 24 pages
Abstract: The development of nanocrystalline and ultrafine-grained bulk materials through powder metallurgy processes has long been constrained by the thermal stability of nanostructures. Many difficulties arise due to the fact that grain growth and densification occur within the same temperature regime. Additionally, the mechanisms supporting densification require some degree of grain coarsening in order to achieve full density. This study outlines the development of a thermally stable nanocrystalline tungsten powder and discusses the influence of grain size stability on the overall densification rate during pressureless sintering in hydrogen atmosphere. Furthermore, the activation energy of sintering is calculated to determine whether the mechanisms of grain growth and densification can be decoupled through the addition of thermal grain stabilizers.
Distribution: Approved for public release
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Last Update / Reviewed: May 1, 2011