Developing high-pressure torsion for use with bulk samples

Experiments were conducted to examine the feasibility of extending conventional processing with high-pressure torsion (HPT) from use with thin disks with thickness of ∼1 mm to bulk cylindrical samples with height of ∼8 mm. Two cylindrical samples of an Al-Mg-Sc alloy were processed through 1/4 and 1 turn and then examined on different planes of sectioning. The results confirm the potential for using HPT with small cylinders but they show there are significant and systematic variations in the values of the Vickers microhardness throughout the samples after processing. After one turn in HPT, the highest values of the microhardness were achieved in the central plane around the outer edge of the sample where the hardness increased by a factor of >2 compared with the solution-treated condition. Microstructural examination revealed an array of equiaxed grains in this region with an average grain size of ∼200 nm.