Study of Reinforcing Phase Formation at the Grain Boundaries of Sintered Beryllium

Abstract

In this paper we present the results of studies of the effect the state of grain boundaries formed in consolidation of beryllium powders by vacuum hot pressing has on the strength properties of sintered beryllium. The dependences of the morphology, elemental composition, and structure of the dispersed strengthening phase, beryllium oxide, on the content of low-melting impurities at the grain boundaries of sintered beryllium were studied using scanning electron microscopy and X-ray microspectral analysis. A new hypothesis that explains the difference in the morphology and structure of reinforcing particles based on the features of the transition of amorphous beryllium oxide to the crystalline state (devitrification) at grain boundaries of metallic beryllium is proposed. It has been theoretically substantiated and experimentally confirmed that the devitrification mechanism can be homogeneous or heterogeneous, depending on the content and ratio of silicon and aluminum impurities. This difference determines the formation of either finely dispersed high-strength reinforcing particles of beryllium oxide or large and less strong oxide clusters. Changes in the morphology and structure of reinforcing oxide particles at the grain boundaries of metallic beryllium, in turn, affect the dynamics of grain growth in the beryllium microstructure during vacuum hot forming processes and, ultimately, the effect of grain-dispersed hardening of sintered beryllium. The results of testing the mechanical properties of industrial hot-pressed blanks of powders with fineness less than 56 μm to determine the effect of various factors (impurity content, their ratio, and particle size of the initial powders) on the strength properties of hot-pressed beryllium are statistically processed. The adequacy of the regularities is estimated using the coefficients of the approximation accuracy, which confirms the conclusions of the theoretical and experimental analyses of the studied problem. One complex indicator of the initial powder quality which makes it possible to predict the strength properties of hot-pressed beryllium is validated based on the statistical studies. The results substantiate new possibilities for controlling the mechanical properties of sintered beryllium for various purposes.