To improve the balance of the electrical conductivity and mechanical strength for dilute Cu-Ti alloys by aging in a hydrogen atmosphere, the influence of aging temperature ranging from 673 K to 773 K (400°C to 500°C) on the properties of Cu-3 at. pct Ti alloy was studied. The Vickers hardness increases steadily with aging time and starts to fall at 3 hours at 773 K (500°C), 10 hours at 723 K (450°C), or over 620 hours at 673 K (400°C), which is the same as the case of conventional aging in vacuum. The maximum hardness increases from 220 to 236 with the decrease of aging temperature, which is slightly lower than aging at the same temperature in vacuum. The electrical conductivity at the maximum hardness also increases from 18 to 32 pct of pure copper with the decrease of the temperature, which is enhanced by a factor of 1.3 to 1.5 in comparison to aging in vacuum. Thus, aging at 673 K (400°C) in a hydrogen atmosphere renders fairly good balance of strength and conductivity, although it takes nearly a month to achieve. The microstructural changes during aging were examined by transmission electron microscopy (TEM) and atom-probe tomography (APT), and it was confirmed that precipitation of the Cu 4 Ti phase occurs first and then particles of TiH 2 form as the third phase, thereby efficiently removing the Ti solutes in the matrix.
The influence of hydrogen pressure during isothermal aging on the mechanical strength, electrical conductivity, and microstructure of Cu-3 at% Ti alloys was investigated under various hydrogen pressures from 0 to 0.8 MPa. The variation of hardness with aging time was not significantly different among all specimens aged under the hydrogen pressures. This is because the hardness is improved primarily by the precipitation strengthening of Cu 4 Ti particles, which is less affected by hydrogen pressure. The electrical conductivity increased more significantly for specimens aged under higher hydrogen pressure, due to a rapid reduction in the concentration of Ti dissolved in the matrix, which is attributed to the accelerated formation of TiH 2 . The conductivity at peak-hardness was improved by a factor of approximately 1.4 in the specimens aged at both 773 and 723 K under the highest hydrogen pressure, compared to that for the specimen aged in vacuum. Therefore, aging under high hydrogen pressure assisted in the significant improvement of both strength and electrical conductivity.
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