Developing Hardness and Microstructural Homogeneity in High-Pressure Torsion

Abstract

High-pressure torsion (HPT) is a processing technique in which samples, in the form of thin disks, are subjected to a high applied pressure and concurrent torsional straining. In principle, the strain introduced into the disk during the straining varies across the disk and there is a direct proportionality between the estimated strain and the radial position on the disk. This means that the strain is zero at the center of each HPT disk and it reaches a maximum value at the outer periphery. Contrary to these expectations, recent experiments show there is a gradual evolution with increasing numbers of revolutions such that the hardness of the disk gradually becomes reasonably homogeneous. This report examines the development of hardness and microstructural homogeneity with special emphasis on the evolution in hardness homogeneity along vertical sections of disks of high-purity aluminum processed by HPT. The results demonstrate that, at least for pure aluminum, the distributions in the hardness values are independent of the plane of sectioning.