Thermoelectric assessment of laser peening induced effects on a metallic biomedical Ti6Al4V

Laser peening has recently emerged as a useful technique to overcome detrimental effects associated to another well-known surface modification processes such as shot peening or grit blasting used in the biomedical field. It is worth to notice that besides the primary residual stress effect, thermally induced effects might also cause subtle surface and subsurface microstructural changes that might influence corrosion resistance. Moreover, since maximum loads use to occur at the surface, they could also play a critical role in the fatigue strength. In this work, plates of Ti-6Al-4V alloy of 7 mm in thickness were modified by laser peening without using a sacrificial outer layer. Irradiation by a Q-switched Nd-YAG laser (9.4 ns pulse length) working in fundamental harmonic at 2.8 J/pulse and with water as confining medium was used. Laser pulses with a 1.5 mm diameter at an equivalent overlapping density (EOD) of 5000 cm-2 were applied. Attempts to analyze the global induced effects after laser peening were addressed by using the contacting and non-contacting thermoelectric power (TEP) techniques. It was demonstrated that the thermoelectric method is entirely insensitive to surface topography while it is uniquely sensitive to subtle variations in thermoelectric properties, which are associated with the different material effects induced by different surface modification treatments. These results indicate that the stress-dependence of the thermoelectric power in metals produces sufficient contrast to detect and quantitatively characterize regions under compressive residual stress based on their thermoelectric power contrast with respect to the surrounding intact material. However, further research is needed to better separate residual stress effects from secondary material effects, especially in the case of low-conductivity engineering materials like titanium alloys.

Concentrating solar power technologies. The DESERTEC megaproject

The European strategies on energy have been searching for years to reduce the dependency of Europe from fossil fuels. Underlying this effort, there exist geopolitical, economic, environmental reasons and the reality that oil reservoirs will dry out some day. Renewable energies have become a milestone of this strategy because their huge potential has emerged after years of uncertainty. One of the better developed renewable sources, which is nearer to commercial maturity is solar-thermal energy. In this paper, the current state of this technology will be described as well as the developments that may be expected in the short and mid terms, including the thermoelectric solar megaproject DESERTEC, a German proposal to ensure energy resources to the mayor areas of the EU-MENA countries. The reader will acquire a picture of the current state of the market, of the technical challenges already achieved and of the remaining ones.