Enhancing electrochemical corrosion resistance in Al–6Ni alloys through trace Sc additions

Al–Ni-Sc alloys exhibit superior mechanical properties at both room and elevated temperatures, owing to the high thermal and chemical stability of Al3Ni microfibers, and Al3Sc nanoprecipitates. This study explores the impact of scandium additions (0.2 and 0.4 wt%) in eutectic Al–6Ni casting alloys and the influence of aging treatment on electrochemical corrosion behavior in a 0.05 M NaCl solution. Scandium addition did not alter the polarization curve direction but reduced the anodic current density, slowing corrosion. Scandium strengthened the passive film, evident in Electrochemical Impedance Spectroscopy (EIS) with higher Rp values. Sc addition influences the susceptibility to localized corrosion in Al–Ni alloys by promoting the coherence of passive films through the formation of Al3Sc nanoprecipitates and affecting the distribution of Al3Ni. XPS results show that as-aged Sc-containing increases the density of coherent Al3Sc nanoprecipitates, which could result in the formation of Sc2O3 film along with films like Ni2O3 and Al2O3. These synergistic effects contribute to improving the overall corrosion resistance with Sc additions subjected to aging treatment. The microgalvanic effects between the matrix and reinforcement phases, as a result of the formation of nobler Al3Ni and Al3Sc that serve as cathodes within anode Al matrix, cause severe pitting. Nevertheless, after aged treatment, the corrosion resistance dramatically drops for alloys with 0.2 wt% Sc and remains unchanged for 0.4 wt% Sc, due to higher density of nobler Al3Sc nanoprecipitates phase that can counteract the microgalvanic effects and lead to less extensive pitting than as-aged Al–6Ni-0.2Sc

A novel low-modulus titanium alloy for biomedical applications: A comparison between selective laser melting and metal injection moulding

The mechanical properties of new low-modulus beta titanium alloyed designed for biomedical applications are measured and compared when processed via the selective laser melting (SLM) and the metal injection moulding (MIM) processes. Mechanical tensile testing reveals important differences between them: (i) Under optimal laser settings, SLM produces strong, low-modulus and ductile properties. This is associated with the laser creating fully dense material with appropriate microstructure after solidification. (ii) MIM can produce materials with similar strength/stiffness ratios, but with reduced ductility. The differences between the processes are linked to changes in chemistry in the microstructure: carbon pickup from MIM binder and slow cooling rate is responsible for the appearance of Ti2C resulting in low ductility and very high strength together with a transition from intergranular to transgranular fracture