Evaluating a New Core‐Sheath Procedure for Processing Hard Metals by Equal‐Channel Angular Pressing

A new design of billet, based on a core–sheath configuration, was used for the processing of Ni, Fe, and a NiTi alloy by equal‐channel angular pressing (ECAP) at room temperature. This configuration involves inserting metal cores within Fe sheaths prior to processing and it is designed especially for use with hard‐to‐deform materials. Billets were processed through one or two ECAP passes at room temperature and the microhardness values were recorded across the transverse directions within the cores to evaluate the flow process. As in conventional ECAP, the hardness increased significantly after the first pass and there were regions of lower hardness along the bottom surfaces of each core. The gradient of hardness decreased with increasing core diameter but the average microhardness values remained unchanged. Three‐dimensional finite element simulations were used to evaluate the flow behavior after one pass of ECAP using different core metals. These simulations show the lower areas of the cores undergo less deformation than the upper areas and the homogeneity increases with increasing levels of friction at the core–sheath interface.