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Abstract Samples of fine structured Cu were fabricated by spark plasma sintering (SPS) of compacts of Cu nanopowder/micron-sized powder blend with a ratio of 3:7 by weight, and one of the SPSed samples was further processed by hot extrusion. The microstructures of the as-SPSed and the as-extruded samples and the tensile properties and fracture behavior of the as-extruded sample were studied. It was found that the microstructures of the samples consist of a concoction of ultrafine and coarse grains with high dislocation densities ( ~1015 m-2) as a result of microstructural evolution during material processing. Some nanograins were oxidized to form Cu2O particles residing around the coarse grains. Extrusion of the SPSed sample increases its microhardness from 70 HV to 90 HV. The electrical conductivity of the as-extruded sample reaches 87% international annealed copper standard (IACS), and its tensile properties are 200 MPa for yield strength, 218 MPa for ultimate tensile strength and 9% for elongation to fracture. The tensile test specimens from the as-extruded sample exhibit nearly ideal plastic deformation and undergo ductile fracture, suggesting that the fine-grained copper is a highly desirable material for high strength electrical conductors.

In this work, we characterize the hollow hematite (α-Fe2O3) micro spheres obtained by two non-template techniques: i) sol gel and ii) spray roasting process. Both techniques allow the production of high yield hollow hematite spheres up to 100 g for the case of sol gel and up to 500 kg for the case of spray roaster process. The samples were characterized by X-ray diffraction, scanning electron microscopy and Mössbauer spectroscopy. The results indicate nearly uniform hollow spheres with diameters of around 1–1.5 μm and consisting of polycrystalline hematite. The Mӧssbauer spectroscopy reveals the signal change of quadrupole shift values evidencing the occurrence of the Morin transition and that the samples show an antiferromagnetic order at 77 K as in bulk hematite. The Morin temperature (TM) for both samples was obtained from the measurements of the magnetic moments as a function of the temperature in zero field cooling (ZFC) and field cooling (FC) modes. The values of TM for both samples are lower than that reported for bulk hematite (TM(bulk) = 263 K). Remarkably, the ZFC and FC loops do not overlap in both samples, revealing irreversible Morin transition. However, the sample obtained by sol gel presents thermal hysteresis with TM values of 260 K (in ZFC) and 248 K (FC). Whereas, the sample obtained by spray roaster process presents complete irreversibility and TM values of 252 K (in ZFC) and 242 K (in FC). Keywords: Hollow spheres, Hematite, Morin transition, Thermal hysteresis

4Cr5MoSiV (H11) steel machining chips were crushed to a powder and then consolidated into discs by hot pressing under various consolidation parameters. The discs were subjected to modified spheroidizing annealing treatment, and their evolved microstructure, tensile mechanical properties and fracture behavior were studied. The microstructure consisted of α−Fe as a matrix, together with heterogeneously distributed non metallic inclusions from the chip-crushing step and precipitated secondary phases. The yield strength, fracture strength and elongation to fracture of the consolidated discs were determined to be in the range of 215∼264 ​MPa, 344∼415 ​MPa and 1.2∼2.6%, respectively. The strength of the recycled H11 steel was comparable with that of the ingot metallurgy (IM) H11 steel, but the tensile ductility of the former was significantly lower than that of the latter, being mainly caused by the fracture of the non-metallic inclusions along with the hard secondary phase particles in the IM H11 steel which leads to premature fracture of the samples. The Vickers hardness of the samples were in the range of 144∼194 HV being comparable to that of the IM counterpart. Factographs of the fracture surface demonstrated that the tensile test specimens fractured in a brittle fracture mode.