Effect of Milling Time on the Microstructure and Tensile Properties of Ultrafine Grained Ni–SiC Composites at Room Temperature

Abstract

Bulk metallic nickel-silicon carbide nano-particle (Ni-SiCNP) composites, with milling time ranged from 8 to 48 h, were prepared in a planetary ball mill and sintered using a spark plasma sintering (SPS) furnace. The microstructure of the Ni-SiCNP composites was characterized by transmission electron microscopy (TEM) and their mechanical properties were investigated by tensile measurements. The TEM results showed well-dispersed SiCNP particles, either within the matrix, between twins or along grain boundaries (GB), as well as the presence of stacking faults and twin structures, characteristics of materials with low stacking fault energy. Dislocation lines were also observed to interact with the SiCNP which were plastically nondeformable. A synergistic relationship existed between Hall-Petch strengthening and dispersion strengthening mechanisms, which was shown to greatly influence the mechanical properties of the Ni-SiCNP composites. Both the maximum yield and tensile strengths were found in the Ni-SiCNP composite with a milling time of 48 h, whereas the increased rate of strengths drastically decreased in material milled above 8 h due to the significant SiCNP agglomeration. The ball milling process resulted in the formation of nano-scale, ultra-fine grained (UFG) Ni-SiCNP composites when the milling time was extended for longer periods, greatly strengthening these materials. The sharp decrease in elongation percentages, however, should be comprehensively considered before irreversible inelastic deformation. Copyright (C) 2015, The editorial office of Journal of Materials Science & Technology. Published by Elsevier Limited. All rights reserved.