803 金属間化合物 TiAl の環境助長き裂進展と昇温水素分析

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We investigated the environmental effects on fatigue crack growth rate in nearly lamellar, and duplex TiAl as well as single-phase γ-TiAl. The hydrogen evolution kinetics was analized by the thermal desorption spectroscopy (TDS). The fatigue crack growth rate was accelerated compared with those conducted in dry air, when cathodic charging was applied in a H_3BO_3+KCl solution. In the case of the lamellar and the duplex TiAl, this accelerates was high, in particular, at higher stress intensity factor range. In the case of the single-phase γ-TiAl, however, the threshold value becomes smaller in the cathodically charged condition, with higher crack growth rate. This indicates that the environmental influence is high, in partial, in γ-TiAl, compared with the lamellar and the duplex TiAl. Irrespective of the material tested, the hydrogen evolution rate was increased by cathodic charging, at lower temperature peaks and higher ones. The peaks at lower temperature are correlated with hydrides decomposition and detrapping of hydrogen from microstructual imperfections such as microvoides.
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