Improved Microyield Strength in Beryllium Produced by Vapor Deposition

Abstract

Beryllium is a metal of major importance in the space and nuclear industries. It has a low density, high elastic modulus, elevated melting point, high heat capacity, and good nuclear hardness. However, Be also has some intrinsic problems such as low ductility and poor fabricability, which limits it from wider applications. Be has a hcp crystalline structure and is thus highly anisotropic. Several years ago, Nieh et al. used a physical vapor deposition technique to produce thick Be deposits and found that such deposits have unique grain and crystalline texture characteristics. Specifically, the deposit consisted of columnar grains with their major axis parallel to the direction of incident adatoms. The self-shadowing mechanism was not observed to have a prevalent contribution to the development of the microstructure during the growing process. The deposits were found also to be highly anisotropic with the major axis of their columnar grains corresponding to the [001] crystallographic direction and always pointing towards the evaporation source. In this paper, the authors describe these microstructural and crystallographic characteristics, and present a technique to improve the microyield strength of Be.