Nanostructured metals produced by physical vapour deposition or structural and gas-reactive applications

Abstract

This paper highlights some of the research being conducted at the Naval Research Laboratory on nanostructured materials synthesized by the inert-gas condensation method. This research effort was initially concentrated on the development of metal-based nanocomposites for high-temperature structural applications. The nanocomposite approach, used in this initial phase, was based on a strengthening concept that involved the use of nearly immiscible constituents: a ductile matrix and a particulate reinforcing phase. Following this approach, we produced copper-niobium, silver-nickel and copper-aluminium nanocomposites. The experimental results obtained on these nanocomposite systems were mixed. They did display some degree of strength enhancement and high-temperature strength retention. However, the results clearly pointed out certain processing challenges associated with the issues of oxide contamination and consolidation of nanostructured metals and alloys by conventional processing. In the course of this research, the recognition of the highly reactive nature of nanocrystalline metals, owing to their high specific surface areas, led us to consider the potential of nanostructured metals and alloys for gas-reactive applications. Accordingly, we have conducted initial studies on nanocrystalline palladium for hydrogen-sensing applications. The paper concludes by reconsidering the question of nanocomposites for structural applications within the context of some interesting and promising results of Valiev and of Inoue and Kimura who have produced metallic nanocomposites through two different routes that are both based on well established metallurgical practices.