Abstract The effect of temperature was investigated on the consolidation of blended elemental powders of aluminum and copper by equal channel angular pressing (ECAP). Aluminum and Copper powders (1:1% vol.) were blended and consolidated in a 90° ECAP die at room (RT) and cryogenic temperatures (CT - ~77 K). ECAP samples were pressed until 4 passes at room temperature in route Bc. As a reference, a sample was obtained by conventional uniaxial pressing. The obtained results indicated a much denser (>99.5%) and harder structure by cryogenic ECAP. The hardness after one pass at CT was comparable with 4 passes at room temperature. Tensile tests performed at CT for materials with similar chemical composition showed a simultaneous increase in strength and ductility at CT, corroborating the results obtained by ECAP. The partial suppression of dynamic recovery and the activation and the transition between deformation mechanisms at CT, as well as stacking fault energies (SFE) of such metals, played an important role in these results. Copper presented a much higher capability of strain hardening than aluminum, due to its lower SFE and much lower homologous temperature. X-ray diffraction indicated a strong correlation between the variation of average microstrain and the variation of hardness on both metals. The results of this study demonstrated the great potential of the application of very low temperatures for the obtaining of deformation metal-metal composites.

Equal channel angular pressing (ECAP) is one of the severe plastic deformation processes that can also be used for metallic powder consolidation. Consolidation of blended elemental powders of iron, chromium, nickel, and manganese (Fe-25Cr-20Ni-2Mn wt. %) was performed at room temperature in a Φ = 120° die by 1 and 2 passes. SEM micrographs indicated that single pass ECAP consolidated sample presented close to full densification. Additional pass of ECAP led to hardness increase and to an apparent better mixing between the different particles. SEM/EDX analysis made before and after heat treatment of the samples showed that effective diffusion only took place after heat treatment and especially in the sample subjected to 2 ECAP passes. Results indicate that alloying by ECAP consolidation and posterior heat treatment is feasible, especially for systems that cannot be processed by conventional means, as well as mechanical alloying.

Tantalum has been cited to have many biomaterial applications, exhibiting biocompatibility and outstanding corrosion resistance. Tantalum may be covered with tantalum oxide using the electrochemical process of anodic oxidation. The oxide surface is known to be bioactive and more corrosion resistant. In this research, compact tantalum oxide films were obtained by potentiostatic and potentiodynamic methods in H2SO4 and H3PO4 (1 mol.L-1) electrolytes. By XPS analysis the stoichiometry Ta2O5 was detected. The thermodynamic stability of those oxides was compared and the results indicated that Ta2O5 obtained in H2SO4 has higher thermodynamic stability than Ta2O5 obtained in H3PO4. The incorporation of (PO4)3- ions and the formation of a bilayer oxide are responsible for the reduced stability. Also, the better control of chemical kinetic of oxide formation allows potentiodynamic oxides to be more stable. Ta2O5 shows spontaneous dissolution in artificial blood, nevertheless, it remains stable even after 60 days of immersion. By scratching tests was possible to notice that Ta2O5 is highly adherent to the tantalum metallic substrate and by mechanical indentation was possible to measure a lower elastic modulus for the Ta2O5 than the metallic substrate, what can be considered as distinguished properties for biomedical applications.