Research of reinforcement phase formation on the borders of sintered berillium grains

The paper presents the results of studying the effect of the state of grain boundaries (formed in the consolidation of beryllium powders by vacuum hot pressing on the strength properties of sintered beryllium. Scanning electron microscopy and X-ray spectral microanalysis were used to study the dependences of the morphology, elemental composition and structure of a dispersion hardening phase - beryllium oxide – on the content of low-melting impurities at the grain boundaries of sintered beryllium. A new hypothesis is proposed to explain the difference in the morphology and structure of reinforcing particles based on the transition features of amorphous beryllium oxide to a crystalline state (devitrification) at the grain boundaries of metallic beryllium. It is 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 leads to the formation of either finely dispersed high-strength reinforcing particles of beryllium oxide or large, lower-strength oxide clusters. Changes in the morphology and structure of reinforcing oxide particles at the metallic beryllium grain boundaries, in its turn, influence the dynamics of beryllium microstructure grain growth during vacuum hot forming and, ultimately, the effect of dispersed grain-boundary hardening of sintered n beryllium. The paper provides the statistically processed results of testing the mechanical properties of industrial hot-pressed blanks produced of less than 56 μm powders to determine the effect of various factors (the content of impurities, their ratio and particle size of the initial powders) on the strength properties of hot-pressed beryllium. The adequacy of the obtained regularities was evaluated using the approximation confidence coefficients and confirmed the conclusions made in the theoretical and experimental analysis of the research problem. The statistical studies substantiated a comprehensive quality indicator of initial powders in order to predict the strength properties of hot-pressed beryllium. The results obtained substantiate new possibilities for controlling the mechanical properties of sintered beryllium for various purposes.

A detailed description of the devitrification mechanism of d-mannitol

The transformation of undercooled d-mannitol into “phase X” previously interpreted as a second amorphous state is actually corresponding to a surface crystallization accompanied by a very slow bulk crystallization into α form.