Enhancing copper infiltration into alumina using spark plasma sintering to achieve high performance Al2O3/Cu composites

Al2O3/Cu (with 30 wt% of Cu) composites were prepared using a combined liquid infiltration and spark plasma sintering (SPS) method using pre-processed composite powders. Crystalline structures, morphology and physical/mechanical properties of the sintered composites were studied and compared with those obtained from similar composites prepared using a standard liquid infiltration process without any external pressure. Results showed that densities of the Al2O3/Cu composites prepared without applying pressure were quite low. Whereas the composites sintered using the SPS (with a high pressure during sintering in 10 minutes) showed dense structures, and Cu phases were homogenously infiltrated and dispersed with a network from inside the Al2O3 skeleton structures. Fracture toughness of Al2O3/Cu composites prepared without using external pressure (with a sintering time of 1.5 hours) was 4.2 MPa·m1/2, whereas that using the SPS process was 6.5 MPa·m1/2. These toughness readings were increased by 18% and 82%, respectively, compared with that of pure alumina. Hardness, density and electrical resistivity of the samples prepared without pressure were 693 HV, 82.5% and 0.01Ω•m, whereas those using the SPS process were 842 HV, 99.1%, 0.002Ω•m, respectively. The enhancement in these properties using the SPS process are mainly due to the efficient pressurized infiltration of Cu phases into the network of Al2O3 skeleton structures, and also due to high intensity discharge plasma which produces fully densified composites in a short time

Drilling for fissures and exploiting common ground in the discourse of oil production: An enhanced eco-discourse analysis, Part 2

This is the second part of a two-part article which proposes an enhanced approach to eco-discourses after weighing the (dis)advantages of mainstream Critical Discourse Analysis (CDA) and Positive Discourse Analysis (PDA). Part I explored the theoretical grounding for an enhanced PDA, introduced the research method and then, based on the adapted analytic framework of Stibbe (2016), undertook a critical analysis of the discourses of Shell Oil Company (SOC). Part II uses the same analytic framework to analyse Greenpeace USA’s (GPU) discourse and compare it to the SOC discourse. The emphasis in Part II is on the exploration of potential fissures in the discourses across difference, and the possible common grounds upon which to design alternative discourses that are empathetic, comprehensible and legitimate to a coalition of social forces. Practically, Part II finds that the two groups use similar discourse strategies, such as salience and framing, but with different orientations. Methodologically, Part II argues that corpus-aided comparative discourse analysis, with a focus on discourse semantics, will facilitate the identification of ‘greenwashing’ strategies that strengthen and stabilize current hegemonic social order; this part also points to avenues of alternative discourses which exploit the inherent contradictions or fissures within that hegemonic order. Theoretically, the paper suggests that within an enhanced Positive Discourse Analysis approach, it is also important to seek out points of convergence between progressive positions and to articulate these within a hybrid, counter-hegemonic discourse that maximizes its potential for uptake, while it destabilizes the prevailing discourses at precisely the fissure points identified

Experimental and theoretical analysis of microstructural evolution and deformation behaviors of CuW composites during equal channel angular pressing

CuW composites were synthesized using an equal channel angular pressing (ECAP) technique. Microstructural evolution during sintering process was investigated using both optical microscopy and transmission electron microscopy (TEM), and their deformation mechanisms were studied using finite element analysis (FEA). Results showed severe plastic deformation of the CuW composites and effective refinement of W grains after the ECAP process. TEM observation revealed that the ECAP process resulted in lamellar bands with high densities dislocations inside the composites. Effects of extrusion temperature and extrusion angles on stress-strain relationship and sizes of deformation zones after the ECAP process were investigated both theoretically and experimentally. When the extrusion angle was 90°, a maximum equivalent stress of ~1001 MPa was obtained when the extrusion test was done at room temperature of 22 °C, and this value was lower than compression strength of the CuW composites (1105.43 MPa). The maximum equivalent strains were varied between 0.5 and 0.7. However, when the extrusion temperature was increased to 550 °C and further to 900 °C, the maximum equivalent stresses were decreased sharply, with readings of 311 MPa and 68 MPa, respectively. When the extrusion angle was increased to 135°, the maximum equivalent stresses were found to be 716.9 MPa, 208 MPa, and 32 MPa for the samples extruded at temperatures of 22 °C, 550 °C and 900 °C, respectively. Simultaneously, the maximum equivalent strains were decreased to 0.2–0.4. Furthermore, results showed that the maximum equivalent stress was located on the sample's external surface and the stress values were gradually decreased from the surface to the center of samples, and the magnitudes of plastic deformation zones at the surface were much larger than those at the central part of the sintered samples. FEA simulation results were in good agreements with experimentally measured ones

Effect of reduced graphene oxides decorated by Ag and Ce on mechanical properties and electrical conductivity of copper matrix composites

This work investigated the influence of reduced graphene oxide (rGO) modified with silver (Ag) and cerium (Ce) on mechanical and electrical properties of copper matrix composites. Powders of Ce doped rGO and Ag doped rGO were synthesized using a hydrothermal reduction and an electroless plating (glucose chemical reduction) method, respectively. Then, copper matrix composites with the doped rGO content of 0.25wt% were synthesized using ball milling and spark plasma sintering (SPS). The dispersion of the modified rGO and its bonding with the copper matrix have been signficantly improved. Hardness values of Ce-rGO/Cu and Ag-rGO/Cu composites were 26.3% and 16.4% higher than those of the sintered copper, and 19.4% and 10% higher than that of unmodified rGO/Cu composite. At the same time, the Ce-rGO/Cu and Ag-rGO/Cu composites maintained good conductivity and high ductility (with elongations of 26.3% and 25.2%, respectively). Compared with the sintered copper, the tensile strengths of these two types of copper matrix composites were 7.5% and 12% lower, respectively. The increase in hardness by using the the modified rGOs is mainly due to the grain refinement of the matrix, and the lower value of the tensile strength is due to the defects of the modified rGOs and their poor bonding with the copper matrix