Mechanical properties of nanocrystalline materials

Principles of equal-channel angular pressing as a processing tool for grain refinement

Using high-pressure torsion for metal processing: Fundamentals and applications

Hall-Petch relation and boundary strengthening

Dynamic and post-dynamic recrystallization under hot, cold and severe plastic deformation conditions

Using equal-channel angular (ECA) pressing at room temperature, the grain sizes of six different commercial aluminum-based alloys (1100, 2024, 3004, 5083, 6061, and 7075) were reduced to within the submicrometer range. These grains were reasonably stable up to annealing temperatures of ∼200 °C and the submicrometer grains were retained in the 2024 and 7075 alloys to annealing temperatures of 300 °C. Tensile testing after ECA pressing through a single pass, equivalent to the introduction of a strain of ∼1, showed there is a significant increase in the values of the 0.2 pct proof stress and the ultimate tensile stress (UTS) for each alloy with a corresponding reduction in the elongations to failure. It is demonstrated that the magnitudes of these stresses scale with the square root of the Mg content in each alloy. Similar values for the proof stresses and the UTS were attained at the same equivalent strains in samples subjected to cold rolling, but the elongations to failure were higher after ECA pressing to equivalent strains >1 because of the introduction of a very small grain size. Detailed results for the 1100 and 3004 alloys show good agreement with the standard Hall-Petch relationship.

Equal-channel angular pressing of commercial aluminum alloys: Grain refinement, thermal stability and tensile properties

Improvement of mechanical properties for Al alloys using equal-channel angular pressing

The potential for scaling equal-channel angular pressing (ECAP) for use with large samples was investigated by conducting tests on an aluminum alloy using cylinders having diameters from 6–40 mm. The results show the refinement of the microstructure and the subsequent mechanical properties after pressing are independent of the initial size of the sample and, for the largest sample with a diameter of 40 mm, independent of the location within the sample at least to a distance of ∼5 mm from the sample edge. By making direct measurements of the imposed load during ECAP, it is shown that the applied load is determined by the sample strength rather than frictional effects between the sample and the die walls. The results demonstrate the feasibility of scaling ECAP to large sizes for use in industrial applications.

The potential for scaling ECAP: effect of sample size on grain refinement and mechanical properties

http://www.dunand.northwestern.edu/refs/files/AkamatsuEtal.pdf

Influence of rolling on the superplastic behavior of an Al-Mg-Sc alloy after ECAP

Experiments were conducted to evaluate the influence of equal-channel angular pressing (ECAP) on the magnetic properties of a Cu-1.8 wt.% Co alloy containing 0.2 wt.% Cr which forms ferromagnetic Co-rich precipitates in the Cu matrix after aging treatment. Coherent face-centered-cubic precipitates were formed by isothermal aging at 873 and 1073 K for 259 ks. The two different aging temperatures gave precipitates of different sizes, which were expected to show either single-domain or multidomain structure. In the case of small precipitates, one pass of ECAP was effective to improve coercivity, but further pressings tended to decrease coercivity and saturation magnetization due to random orientation and dissolution of the precipitates. In the case of large precipitates, shape change to increase coercivity is difficult. Saturation magnetization was increased by the demagnetizing effect of the precipitates. Electron holography provided the quantitative magnetization measurements for rounded cubic and elongated Co precipitates, indicating the increased in-plane magnetization of the elongated precipitate due to the demagnetizing effect as a result of deformation.

Takayoshi Fujinami

Papers

Equal-channel angular pressing of commercial aluminum alloys: Grain refinement, thermal stability and tensile properties

Improvement of mechanical properties for Al alloys using equal-channel angular pressing

The potential for scaling ECAP: effect of sample size on grain refinement and mechanical properties

Influence of rolling on the superplastic behavior of an Al-Mg-Sc alloy after ECAP

Application of equal-channel angular pressing to Cu–Co alloy with ferromagnetic precipitates