Spark Plasma Sintering of Nanocrystalline Cu and Cu-10?Wt?Pct Pb Alloy

For the first time, we report here that high purity nanocrystalline Cu and Cu-10 wt pct Pb alloys can be densified with more than 90 pct theoretical density at a low temperature of 623 K (350 °C) using spark plasma sintering (SPS) in argon atmosphere at a pressure of 100 MPa. Scanning electron microscopy (SEM) analysis indicates that molten Pb particles travel through Cu grain boundaries, delineating a “flowlike” pattern in the microstructure. An extensive transmission electron microscopy (TEM) analysis of the ultrafine scale microstructure reveals partial wetting of Cu by liquid Pb as well as entrapment of Pb particles within the Cu matrix. The sintering kinetics and microstructural evolution are discussed in reference to the intrinsic characteristics of SPS as well as phase equilibria in the Cu-Pb system. An important result is that high hardness of around 2 GPa is measured in the Cu-10 wt pct Pb nanostructured alloy, SPS at 573 K to 623 K (300 °C to 350 °C).     

Electropulsing Induced Texture Evolution in the Recrystallization of Fe-3 Pct Si Alloy Strip

Electropulsing induced texture evolution in the primary recrystallization of a Fe-3 pct Si alloy strip was studied using the electron backscattered diffraction technique. The results revealed that the electropulsing strengthened considerably the recrystallization of a cold-rolled Fe-3Si alloy strip. Various textures with high-energy storages, such as α (100)〈110〉, γ (111)〈110〉, γ (111)〈112〉, and G-texture (110)〈001〉, formed after several seconds of electropulsing treatment (EPT), depending on the intensity of electropulsing. The athermal effect of electropulsing is 319 times stronger than the thermal effect of electropulsing for the formation of the G texture. The mechanism of electopulsing induced texture evolution is discussed from the point of view of Gibbs free energy and dislocation dynamics.     

Effects of Route on Microstructural Evolution and Mechanical Properties of Cu-8 Wt Pct Ag Alloy Processed by Equal Channel Angular Pressing

Equal channel angular pressing (ECAP) is applied to investigate the microstructural evolution and mechanical properties of Cu-8 wt pct Ag alloy subjected to one to four passes via four different routes (A, B_A, B_C, and C). It is demonstrated that better mechanical properties, a higher fraction of high-angle boundaries, and a smaller grain size can be obtained most rapidly with route A, whereas the specimen processed by route B_C contains relatively inhomogeneous microstructure and has poor mechanical properties. The ultimate tensile stress (UTS) of the Cu-Ag alloy processed by route B_C saturates after four passes; in contrast, the UTS of the Cu-Ag alloy processed by route A increases continuously in relation to the number of ECAP passes. Based on the experimental results, the strengthening mechanisms of the Cu-8 wt pct Ag alloy processed by different routes as well as the efficiency of different routes in refining the binary alloy are discussed.     

Corrosion Behavior of Alloy 625 in PbSO4-Pb3O4-PbCl2-ZnO-10?Wt?Pct CdO Molten Salt Medium

Corrosion behavior and degradation mechanisms of alloy 625 under a 47.288 PbSO₄-12.776 Pb₃O₄-6.844PbCl₂-23.108ZnO-10CdO (wt pct) molten salt mixture under air atmosphere were studied at 873?K, 973?K, and 1073?K (600?°C, 700?°C, and 800?°C). Electrochemical impedance spectroscopy (EIS), open circuit potential (OCP) measurements, and potentiodynamic polarization techniques were used to evaluate the degradation mechanisms and characterize the corrosion behavior of the alloy. Morphology, chemical composition, and phase structure of the corrosion products and surface layers of the corroded specimens were studied by scanning electron microscopy/energy-dispersive X-ray (SEM/EDX) and X-ray map analyses. Results confirmed that during the exposure of alloy 625 to the molten salt, chromium was mainly dissolved through an active oxidation process as CrO₃, Cr₂O₃, and CrNbO₄, while nickel dissolved only as NiO in the system. Formation of a porous and nonprotective oxide layer with low resistance is responsible for the weak protective properties of the barrier layer at high temperatures of 973?K and 1073?K (700?°C and 800?°C). There were two kinds of attack for INCONEL 625, including general surface corrosion and pitting. Pitting corrosion occurred due to the breakdown of the initial oxide layer by molten salt dissolution of the oxide or oxide cracking.