Experimental and finite element analysis of Cu and Nb severely deformed by 3-axis forging

Abstract

The evolution of microstructure during 3-Axis Forging (3AF) of OFHC Copper and RRR Niobium has been investigated using both experimental and numerical simulation techniques. The finite element analysis (FEA) aspect was carried out using DEFORM, a commercial software. The 3AF process was conducted at 25° C with a cross-head speed of 0.015 mm s−1 and a strain per pass of 0.2. Vickers hardness testing and orientation imaging microscopy (OIM) showed that the evolution of microstructure during 3AF can be classified into three regions: At low strain, region I, in which the high angle grain boundary percentage (HAGB%) declines due to the increase in low angle grain boundary (LAGB) resulting from dynamic recovery. At intermediate strain, region II, there is a progressive increase in HAGB%, due to the conversion of most of the LAGB to high angle grain boundaries (HAGB). This is followed by region III, in which the HAGB% remains relatively unchanged due to a stable microstructure formed by continuous recrystallization. Assessment of the grain size revealed that refinement occurred in regions I and II, resulting in a final grain size of about 2.0 μm and 1.4 μm in Cu and Nb, respectively. Flownet analysis of the first two cycles showed that four deformation zones similar to the hardness pattern were developed in both materials during the 3AF. These zones correlated well with the effective strain and hardness distributions. The highest effective strain and hardness were found in the core of the material (zone A), while the least hardness developed at the edges (zones C and D).