CW- Clockwise Rotations, CW-CCW – Clockwise followed by counter clockwise
The imposed load was fixed at 390KN (~5GPa) and a rotation speed of 1 rpm was used at quasi-constrained conditions. The processing of the disks was done at POSTECH, South Korea in the group of Prof. H.S. Kim. To measure the hardness variation across the disk, Vickers microhardness test (Make: EMCO-TEST, Austria; Model: Dura Scan-70) was conducted on the disks. The disks were mounted using Hot Mounting Equipment (Make: Struss Citupress-10) and then manually grinded and polished in order to obtain a mirror finish. To measure hardness variation precisely, microhardness indentation points were taken 0.5mm apart from each other on two mutually perpendicular diameters of the disk under conditions of applied load of 200g with a dwell time of 15sec. The microstructure of the processed HPT disks was characterized by Electron Back Scattered Diffraction (EBSD) attached to a FEG-SEM (Make: Carl Zeiss; Model Supra 40) using Channel 5™ Software (Oxford Instruments, UK). EBSD measurements were taken on the r-ѳ plane of disks at the centre, middle and edge region of the disks. For EBSD investigations, the samples were polished mechanically using SiC paper of grit size 2000, followed by electropolishing using a mixture of perchloric acid and ethanol as electrolyte (1:9) at 20V and -300C (using Liquid N2) for 20 sec.
Results