, Volume 35, Issue 12, pp 3855-3861

Microstructure characterization and creep deformation of an Al-10 Wt Pct Ti-2 Wt Pct Cu nanocomposite

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Abstract

The creep behavior of a cryomilled Al-10Ti-2Cu nanocomposite has been studied at temperatures of 533, 588, and 644 K at initial applied stresses ranging from 55 to 117 MPa. Although the strain rates fall within the 10−10 to 10−9 S−1 regime, we observe no evidence of threshold-type creep behavior in this material. We attribute this to the unique microstructure of the present material combined with the mechanism of dislocation slip in ultrafine grain size materials. In particular, the very fine AIN precipitates present within the microstructure are ineffective as obstacles to dislocations during high-temperature deformation. The coherent nature of these fine particles along with their extremely small size prevents a strong dislocation-particle attraction. The inability of the activation energy for self-diffusion in Al to successfully collapse the present creep data onto a single slope combined with the fact that the true activation energy for creep exceeds the value for lattice self-diffusion are both features found in materials containing second-phase particles, which deform simultaneously with the matrix during high-temperature deformation. In the present case, these particles are likely to be Al3Ti.