Abstract.Research was conducted to investigate the potential for consolidating titanium powder using high-pressure torsion (HPT) at room temperature. The nanostructured samples processed by HPT were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM).The results show there is a significant refinement of the Ti powder and it consolidates into bulk nanostructured titanium with a mean grain size estimated by TEM as ~200-300 nm and a mean crystallite size measured by XRD as ~20-30 nm. Microhardness measurements and tensile testing show high strength and low ductility after consolidation under a pressure of 6.0 GPa for 5 revolutions. Additional short annealing at a temperature of 300°C for 10 minutes leads to a significant enhancement in ductility while maintaining the high strength.

Under operating conditions, alternated loading and fatigue are encountered, controlling the durability and safety of components and structures made of super duplex stainless steel (SDSS). In particular, the use of a cathodic protection (CP) system to protect the structure against corrosion can induce hydrogen charging of the SDSS. Thus, the aim of this study was to investigate the sensitivity of some industrial products made of SDSS 2507 (UNS S32750), without artificial thermal aging, under test conditions as close as possible to real environments. In situ fatigue tests under alternated 4-point bending conditions were conducted in natural seawater with and without CP. The fatigue behavior was evaluated as a function of environmental parameters, such as temperature, and material parameters, particularly the austenite spacing and microstructure around orbital welds by Tungsten Inert Gas (TIG) welding and stress concentrations, through the presence of surface defects. The fatigue life obtained in air or in seawater at the open circuit potential (OCP) was rather similar. Fatigue life enhancement was systematically observed under CP particularly in the range of low applied load, despite evidence of brittle failure on the fracture surfaces of samples tested under CP. The data suggest immunity of the SDSS to hydrogen embrittlement under the present experimental conditions of fatigue testing.