Nesse trabalho, apresentamos a caracterização estrutural de regiões soldadas em aço austenítico AISI-304, que foram submetidas a processo de nitretação a plasma (20%N2 + 80%H2). Posteriormente as amostras foram hidrogenadas catodicamente. As temperaturas de nitretação foram de 400, 500 e 550°C. As regiões da solda e fora da solda hidrogenadas após a nitretação foram comparadas por DRX, microscopia ótica e microscopia eletrônica de varredura (MEV). As fases austenita-γ, martensita-α', martensita-ε, ferrita-α e os nitretos CrN, γ'-Fe4N e e-Fe2+xN foram identificados. As microestruturas de ambas as regiões e da zona termicamente ativada (ZTA) foram similares. Para 400°C, a estequiometria das fases formadas foi diferente das observadas em 500°C e 550°C. Os efeitos provocados pela hidrogenação foram mais acentuados em 550°C, com o arrancamento da camada nitretada.

Structural characterization of weld and outside weld regions of AISI-304 nitrided (20%N + 80%H) and cathodically hydrogenated is presented. Nitriding temperatures were 400, 500 e 550°C. The weld and outside weld regions were compared by XRD, optical microscopy and SEM. The phases γ-austenite, α'-martensite, ε-martensita and α-ferrite and the nitrides: CrN, γ'-Fe4N e e-Fe2+xN were identified. Microstructures of both regions and the thermal active zone were similar. For 400°C the stoichiometry of the formed phases was different from that formed at 500°C and 550°C. Hydrogen effects were more intense for 550°C, due to chipping occurrence.

The effects of Ag addition on some physical properties of YBa2Cu3O7-δ superconductor has been studied. The samples were produced by different routes and characterized by scanning electron microscopy, differential thermal analysis, thermogravimetric analysis, X-ray diffraction and nanoindentation. The superconducting properties were studied by dc magnetization and electrical resistivity measurements. The X-ray patterns revealed that all samples were polycrystalline and corresponded to the orthorhombic YBa2Cu3O7-δ phase. However, for some samples, silver appears to be present within the grains. The superconducting properties were not significantly influenced by Ag addition. Hardness and elastic modulus were also obtained by instrumented indentation. Ag addition was found to be effective in improving the mechanical properties, probably by filling the pores in the grain boundaries. Hardness profiles indicated values between 3.1 and 3.4 GPa at deep tip penetration depths. The highest elastic modulus of 146 GPa was attained for samples prepared using Y2O3, BaCO3, CuO and Ag2O as precursors, while the lowest modulus (125 GPa) was obtained for the pure YBa2Cu3O7-δ sample.

Mechanical and tribological properties os AISI 304 and AISI 316 stainless steels submited to glow discharge ion nitriding are reported.The atmosphere was 20:80 - N2:H2 with substrate temperatures ranging from 300 to 500 °C. Treatment at 300 °C produced expanded austenite (γN) in both steels. Increasing the temperature, the phases γ´-Fe4N and - Fe2+xN were present and the latter is the major phase for AISI 304. At 500 °C, the CrN phase was also identified in both steels. Hardnesses of about 13-14 GPa at near surface regions were obtained in both steels. Moreover, AISI 316 nitrided at 500 °C has the deepest hard layer. Tribological tests showed that wear can be reduced by up to a factor of six after the nitriding processes, even for a working temperature of 300 °C. The profiles during and after nanoscratch tests did not reveal significant differences after nitriding processes in both steels.

The nanoindentation technique allows the determination of mechanical properties at nanometric scale. Hardness (H) and elastic modulus (E) profiles are usually determined by using the Oliver-Pharr method from the load/unload curves. This approach is valid only for flat surfaces, or at least, when a very low degree of asperity is present (lower than 30 nm). The basic statement is the determination of the zero tip-surface contact point. If a rough surface is present, errors can occur in determining this contact point and, as a consequence, the surface hardness and elastic modulus profiles are drastically altered resulting in under evaluated values. Surfaces with different roughness were produced by controlled nitrogen glow discharge process on titanium. The changed nitriding parameters were different N2/H2 atmospheres and temperatures (600 °C-900 °C). The most correct H and E profiles were obtained by using the contact stiffness analysis method, proposed here, that overcomes the surface roughness. The obtained results were compared with available literature data.