Ti-Cr-Fe系合金の焼入状態の相構成と等時熱処理に及ぼすAl添加量の影響

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β titanium alloys such as Ti-22mass%V-4mass%Al, Ti-15mass%V-3mass%Cr-3mass%Sn-3mass%Al have high strength and excellent cold workability, so that the alloys have been used for the materials of golf club head, the frame of glasses, fasteners and so on. However it is necessary to lower the price of the alloys in order to accelerate the expansion of the application. It is the one of the effective way to substitute iron and chrominum for high-cost alloying elements like vanadium as β phase stabilization. So far we have found out that Ti-13 mass%Cr-1.2 mass%Fe-Al had the comparable tensile properties to the conventional alloys. In this study, the effect of aluminum content on the phase constitution of Ti-Cr-Fe alloys was investigated by measurements of electrical resistivity and Vickers hardness, X-ray diffraction and transmission electron microscope observation. The results obtained are as follows. In the solution treated and quenched state (STQ), resistivity(ρ) at liquid nitrogen(LN) and room temperatures(RT) increased monotonously with aluminium content. 0 %Al and 3.0 %Al alloys consisted of β phase and athermal ω. In the isochronal heat treatment, two minima of resistivity were observed at 623 K and 823 K. The former is due to the precipitation of isothermal ω phase and the latter is α precipitation. The temperature of resistivity minimum attributing to ω phase precipitation gradually increases with increasing of aluminium content. In 4.5 %Al and more, the minimum of resistivity by ω precipitation disappears and the minimum caused by ω precipitation remained. It is considered that aluminium content above 4.5 % was suppressed ω precipitation and enhanced α precipitation.

Ti-Cr-Fe系合金の焼入状態の相構成と等時熱処理に及ぼすAl添加量の影響

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