The re-examination on the process of the temper-hardening of Be-Cu alloys was performed by testing the hardness, microscopic structure and crystalline configuration of these alloys. Furthermore, the measurements of their thermal dilatation and electric resistance were also carried out, together with the thermal analysis.
As one of the consequences of these researches, it was found that the temper-hardening of Be-Cu alloys examined occurs in two steps. By the aids of normal and polarized microscopes, the second step of hardening was confirmed to be due to the formation of the typical γ-precipitation structure, as shown in Photo. 3: While, the first one was considered to be attributed to the dendritic or net-worked structures as reproduced in Photos. 1 and 18 respectively, at the inner portion of the grains, according to the specimens used were polycrystalline aggregates or single crystals crystallized directly from the melt. Here, it is to be noted that the diffraction patterns of X-rays taken with the specimens of the aforesaid two kinds of structures, were always found to consist mainly of a number of radiating bands, as shown in the Laue photographs, Photos. 26 and 37; this indicates without saying the presence of a fibrous-like configuration of micro-crystals. From the experimental results above mentioned, with regard to the first step of hardening, these two kinds of structures were inferred to be formed in consequence of the grain refinement attributable to the precipitation of the intermediate phase, β phase, which had been taken place before any γ-precipitates could be detected.
The foregoing consideration was confirmed again, by comparing it with the results of measurements on the differential dilatation and the electric resistance together with those of the differential thermal analysis. Thus, we may arrive at the following conclusions in connection with the mechanism of the temper-hardening of Be-Cu alloys: (1) Among the two steps of temper-hardening of these alloys, the first one is deemed to be given rise to by the grain refinement, the lattice distortion and the precipitation of the intermediate phase. (2) The second step of hardening is resulted from the precipitation of γ-crystallites and the decomposition of the intermediate phase. (3) The softening phenomenon existing between these two steps, can be attributed to the coagulation of the intermediate phase and the removal of the strain.
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