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As basic study to develop low cost b Ti alloys, changes in phase constitution, electrical resistivity and Vickers hardness with increase of Cr content were investigated in Ti-Cr binary alloys quenched from 1173 K. In solution treated and quenched state, hexagonal martensite, aЈ was identified at 3Cr and 5Cr alloys, whereas b phase was identified from 5Cr to 20Cr. In 7Cr and 10Cr alloys, athermal w was also identified. Resistivity increased with increase of Cr content up to 10 mass% Cr and then slightly decreased. Above 10 mass% Cr, resistivity at liquid nitrogen temperature was larger than that at room temperature. Maximum of HV appeared at 7 mass% Cr and then HV decreased with increase of Cr content up to 13 mass% Cr. Above 13 mass% Cr, HV slightly increased due to solution hardening by Cr addition. Temperature-resistivity curves of alloys from 10Cr to 20Cr were negative temperature dependence between 77 K and about 300 K. From change of the temperature-resistivity curves with Cr content, it is expected starting temperature of athermal w formation decreases with increase of Cr content. Trend of changes in HV of Ti-Cr, Ti-Fe and Ti-V alloys as a function of e/a was the almost same, though absolute these values of the three alloys are not same.

ABE , Shin-ya KOMATSU  Masahiko IKEDA and Takeo SAKURAI   Al 1Mg 2 Si 0,  0.17,  0.43,  0.72Cu alloys were solution treated for 3.6 ks at 848 K, water quenched and aged at 473 K. Behavior of added Cu during these heat treatments and eŠect of the Cu on age-hardening were investigated by resistometry and tensile test with assist of transmission electron microscopy. The resistivity in as water quenched state well coincides with the value calculated from 0.023 massFe, the equilibrium solubility at 848 K in Al Fe binary system, and all of other elements in solution. Moreover, the resistivity increases linearly with amount of the added Cu. Namely all of the added Cu is dissolved in the as quenched state. By Cu addition, the initial agehardening rate at 473 K aging is increased and the softening with over-aging is suppressed. Though the Cu addition increases proof stress at peak age-hardening, it also decreases the resistivity decrement from the as quenched state caused by the aging. This discrepancy, that the small total amount of precipitates, which is suggested from small decrement of resistivity by the peak aging, gives the larger age-hardening, can be explained by the decrease in average length with Cu addition which may be directly related to the increase in number of needle shaped precipitates per unit area.