Nanostructured Cobalt Obtained by Combining Bottom-Up and Top-Down Approach

Abstract

Nanostructured metallic materials can be obtained by two major processing strategies: a bottom-up approach that starts with powdered metals to be mechanically and chemically compacted via different compaction methodologies, and a top-down approach that starts with bulk conventional metallic materials that are induced to a sometimes-extraordinary grain size reduction via different severe plastic deformation (SPD) methods. In the present study, a dual strategy was followed to obtain a sound and stable nanostructured commercially pure cobalt. Powdered cobalt of 2 μm was compacted by ball-milling (BM) followed by spark-plasma sintering (SPS) to obtain a bulk metallic material whose relative mass density reached a value of 95.8%. This process constituted a bottom-up strategy to obtain ultrafine submicrometer-grained bulk cobalt, and a top-down strategy of subjecting the BM + SPS submicrometer-grained cobalt to a specific SPD technique, namely equal-channel angular pressing (ECAP). The latter was carried out in one to four passes following so-called route BC, reaching 98.4% density and a nanometric-grained microstructure. The material was microstructurally and mechanically characterized by TEM (transmission electron microscope) and nanoindentation. The obtained results are a representative solid example for obtaining nanostructured metallic materials using both grain-refining strategies, bottom-up and top-down.

Spark Plasma Sintering of Cobalt Powders in Conjunction with High Energy Mechanical Treatment and Nanomodification

“…Results on untreated Co powders (set I) show that highest relative density of 99.3% was achieved at 800 • C. Fellah et al [37] achieved maximum relative density (94.5%) for cobalt nanopowders with SPS technique at 500 • C, 50 MPa pressure, 100 • C/min heating rate. Cabibbo (2018) used ball milling and SPS sintering on 2 µm cobalt powders to achieve a maximum relative density of 95.8% [38]. Lee et al [2] achieved a relative density of 81-95% for tungsten powders with SPS technique at 1600-1800 • C, 60-120 MPa pressure, 100 • C/min heating rate, holding times up to 60 min.…”

Numerical and Experimental Analyses of Equal Channel Angular Processing of Pure Aluminum

“…SPD is one of the most efficient top-down methods for the fabrication of UFG and NS materials [1][2]. In SPD processes, bulk billets are subjected to high plastic strains in order to obtain UFG materials [3].…”

Early Stages of Plastic Deformation in Low and High SFE Pure Metals

“…Several SPD techniques were successfully developed so far, these include high-pressure torsion (HPT), equal-channel angular pressing (ECAP), accumulative roll-bonding (ARB), accumulative press-bonding (APB), cyclic extrusion-compression (CEC), twist extrusion (TE), friction stir processing (FSP), repetitive corrugation and straightening (RCS), high-pressure sliding (HPS) ( [4][5][6][7] and references therein). A second approach start from powder metallic materials which are compacted to get UFG bulk alloys, and it is called bottom-up approach [11,12].…”