耐熱合金A286の時効組織と高温強度について

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Many researches on the high temperature strength of heat resisting alloys related to the microstructures have been presented in recent years. As a matter of fact, the correspondence of high temperature strength to the microstructures is very significant for precipitation type alloys. The heat resisting alloy A 286 reported in the present paper is one of the precipitation hardening alloy. As the first part of the studies on the alloy A 286, the aging structures are hereby presented. As the results of phase identification by means of X-ray and electron diffraction, γ' phase, η phase, G phase, Laves phase, and TiC were identified. Nucleation and growth of these precipitates at a series of aging temperatures were observed. The results are as follows : G phase with the cubic type lattice was observed at the grain boundary, which did not significantly grow at 650℃, but remarkable growth occurred at temperatures above 760℃. η phase with the hexagonal type lattice nucleated at the grain boundary and grew into the grain with Widmannstatten appearance, which was not observed at 650℃ aging, although appreciable η phase precipitation was observed at 718℃ for 50 hrs and at 800℃ for 2 hrs, respectively. γ' phase with the f.c.c. type lattice was observed within the grain with the spherical shape, of which many of small precipitates were nucleated at 650℃, although its rate of growth was remarkably increased as the temperature become higher. It might be considered that the hardness was mainly determined by the precipitates of γ' phase. Laves phase with the hexagonal type lattice was observed at the grain boundary and within the grain, which precipitated at the stage of over aging. TiC was stabilized at the solution treatment, and subsequently it was not essentially changed during the aging treatment. Effect of the melting processes on the precipitation process was significant. Especially, the effect was very remarkable at the time of precipitation of G and η phase at the grain boundary in the first stage of the aging, that is, the rate of precipitation in vacuum melted alloy was smaller than that in the air melted one. As for the intragranullar precipitates such as γ' phase and Laves phase, the same effect was also recognized, although the order of magnitude was relatively smaller. It is supposed that the phenomena as mentioned above is due to the existence of boron atoms which came into the solution from the crucible during the melting process.
社団法人日本材料学会の論文
1961-03-15

耐熱合金A286の時効組織と高温強度について

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