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.

Microstructures and tensile properties of a hot forged Ti−22Al−23Nb−3V−Y alloy were investigated systematically. Different heat treatments were performed to adjust the wrought microstructure to optimize tensile properties. It was found that features of O phase precipitates and its volume fraction was rather sensitive to the cooling rate after the solution. The volume fraction of primary lamellar O phase increased from 19.65% by solution treatment to 36.30% by annealing with furnace cooling and up to 100% by annealing with a controlled slow cooling rate of 1 ºC/min. Meanwhile, the width of the lamellar secondary O phase increased. Fine acicular second O phase contributed to strengthening, while the coarsen primary ones were favorable to the ductility. The solution & aging treated microstructure exhibited a good tensile strength of 1100 MPa and an acceptable ductility of 8% at room temperature, by contrast, annealing at 950 ºC with a controlled slow cooling rate gave rise to a higher elongation of 12%, but a relatively low strength of 960 MPa.

AlCoCuFeMnNi high-entropy alloy coating was prepared by plasma cladding method. The phase structure and microstructure of AlCoCuFeMnNi coating was investigated by XRD, SEM and EDS respectively. The results show that AlCoCuFeMnNi caotings have two BCC phase structure and typical dendrite structure and form good metallurgical bonding with substrate. The dendrite is the typical spinodal decomposition structure. After CeO2 doping, the change of peak intensity and FWHM is obvious due to the effect of Ce on the improvement of grain growth, microstructure and crystallinity. The addition of CeO2 is beneficial to reduce the cladding defect, make dendrite arm spacing enlarged and spinodal decomposition structure refined, and improve element segregation owing to the melioration effect in the temperature gradient, solidification rate, fluidity, wettability, and surface tension.

Two consolidated copper samples were prepared by consolidation of a gas atomized powder using two different routes of spark plasma sintering (SPS), respectively. The first route was direct SPS of copper powder at 800 °C for 10 minutes, and the second route was compacting copper powder by die-pressing to produce a powder compact followed by SPS of the powder compact at 800 °C for 10 minutes. The microstructures and tensile mechanical properties and the fracture surfaces of specimens have been studied. It was found that the level of consolidation of the sample made using Route 1 was higher than that of the sample made using Route 2, as reflected by the relatively higher strength and better ductility of the first sample than those of the second sample. The lower consolidation level of the second sample was depicted by the higher volume fraction of cavities in the fracture surfaces of specimens which were formed by separation of the powder particles at the weakly bonded interparticle boundaries. The grain sizes of the first sample were larger than those of the second sample. The reasons for the differences in the levels of consolidation and grain sizes associated with two SPS routes are discussed.

The microstructural evolution of Cu-10at%C nanocomposite powder during high energy mechanical milling (HEMM) of Cu/graphite powder mixture was studied. It was found that the efficiency of milling in refining the microstructure of the copper matrix was very high with the presence of graphite in the Cu/graphite powder mixture. The average grain size of the Cu matrix reaches its minimum value of about 30 nm just after milling for 6 h, and the graphite particles were refined down to about 10~20 nm after milling for 24 h. It envisaged that the refining of graphite particles down to 10 nm would be accompanied by formation of nanograins of copper matrix, and it appears that high energy mechanical milling can greatly enhance the solubility of carbon in copper though it is very hard to determine the exact solubility.