Achieving ultrafine-grained structure in a pure nickel by friction stir processing with additional cooling

Pure Ni was successfully friction stir processed (FSP) using a common heat-treated steel tool under additional water cooling. The FSP Ni exhibited a multi-modal grain size distribution, with some relatively coarse grains of about 3-5 lm distributed in the ultra-fine grained (UFG) matrix. Sound tensile properties with a high yield strength of similar to 500 MPa and a large uniform elongation of similar to 12% were achieved in the UFG FSP Ni, attributable to the enhanced strain hardening capacity. This study describes an effective low-cost method of processing high melting point metals, and also provides a methodology to produce UFG pure Ni by FSP. (C) 2013 Elsevier Ltd. All rights reserved.