Investigation of TiCr Hydrogen Storage Alloy

A new reversible hydrogen storage material, based on TiCr metal alloy, is proposed. Cr and Ti were mixed and melted in a final atomic ratio of 1,78. Chemical-physical characterisations, in terms of XRD and SEM-EDX, were performed. The quantification of Laves phases was performed through Rietveld refinements. The atomic Cr/Ti ratio was determined by EDX analysis and 1,71 was obtained. The H2 sorption/desorption measurements by Sievert apparatus were carried out. After different tests varying temperature and pressure, a protocol measurement was established; and a H2 sorption value of 0,4 wt% at 200 °C/10 bar with a fast kinetic at 5 bar (Dwt% of about 0,3 wt%) were obtained. Hydrogen desorption measurements performed in the same conditions of T confirmed a totally reversible trend. A confirm of metal hydride formation was recorded by XRD, in fact, comparing X-Ray patterns before and after volumetric tests a notable difference was recorded

VHCF response of heat-treated SLM Ti6Al4V Gaussian specimens with large loaded volume

Abstract Among the materials used for the production of components through Additive Manufacturing (AM) processes, the Selective-Laser-Melting (SLM) Ti6Al4V alloy is widely employed in aerospace applications for its high specific strength and in biomedical applications for its good biocompatibility. Actual structural applications are generally limited to static loading conditions where the large defects originating during the SLM process do not play a significant role for the static failure. On the contrary, the same defects strongly affect the fatigue response of the parts since they act as crack initiation sites that rapidly lead to fatigue failure. In the literature, a lot of research has been carried out to investigate the quasi-static and the High-Cycle Fatigue properties of the SLM Ti6Al4V alloy but there are still few studies on its Very-High-Cycle Fatigue (VHCF) response. In the paper, the VHCF response of Ti6Al4V specimens, which are vertically orientated during the SLM building and then subjected to a conventional heat treatment (2 hours heating in vacuum at 850°C), is experimentally assessed. Ultrasonic VHCF tests are carried out on Gaussian specimens with a large risk-volume (2300 mm3). Fracture surfaces are investigated for revealing the defect originating the fatigue failure. The Stress Intensity Factor Threshold associated to the experimental failures is finally estimated

Phase Transformations in the CeO2-Sm2O3System : A Multiscale Powder Diffraction Investigation

The structure evolution in the CeO2-Sm2O3system is revisited by combining high resolution synchrotron powder diffraction with pair distribution function (PDF) to inquire about local, mesoscopic, and average structure. The CeO2fluorite structure undergoes two phase transformations by Sm doping, first to a cubic (C-type) and then to a monoclinic (B-type) phase. Whereas the C to B-phase separation occurs completely and on a long-range scale, no miscibility gap is detected between fluorite and C-type phases. The transformation rather occurs by growth of C-type nanodomains embedded in the fluorite matrix, without any long-range phase separation. A side effect of this mechanism is the ordering of the oxygen vacancies, which is detrimental for the application of doped ceria as an electrolyte in fuel cells. The results are discussed in the framework of other Y and Gd dopants, and the relationship between nanostructuring and the above equilibria is also investigated

High performance shape memory effect (hp-sme): un innovativo percorso termo-meccanico per lo sviluppo di attuatori sma ad elevate prestazioni

Recentemente è stato proposto un percorso termo-meccanico innovativo per l’utilizzo di leghe a memoria diforma basato sul ciclaggio termico della martensite indotta da sforzo. Questo fenomeno viene chiamato HighPerformance Shape Memory Effect (HP-SME). Questa soluzione consente di utilizzare elementi austenitici conun notevole incremento del carico necessario al funzionamento dell’attuatore a memoria di forma e di mantenereuna elevata capacità del materiale di recupero della deformazione. Attuatori basati su questo principio mostranoproprietà funzionali migliorate rispetto agli attuatori convenzionali basati sull’effetto a memoria di forma (Shapememory effect, SME). In questo lavoro vengono riportati i risultati dei test di recupero della deformazione a caricocostante di fili sottili austenitici e confrontati con quelli di fili martensitici dello stesso diametro

Application of martensitic SMA alloys as passive dampers of GFRP laminated composites

This paper describes the application of SMA (Shape Memory Alloy) materials to enhance the passive damping of GFRP (Glass Fiber Reinforced Plastic) laminated composite. The SMA has been embedded as reinforcement in the GFRP laminated composite and a SMA/GFRP hybrid composite has been obtained. Two SMA alloys have been studied as reinforcement and characterized by thermo-mechanical tests. The architecture of the hybrid composite has been numerically optimized in order to enhance the structural damping of the host GFRP laminated, without significant changes of the specific weight and of the flexural stiffness. The design and the resultant high damping material are interesting and will be useful in general for applications related to passive damping. The application to a new designed lateral horn of railway collector of the Italian high speed trains is discussed

Application of martensitic SMA alloys as passive dampers of GFRP laminated composites

This paper describes the application of SMA (Shape Memory Alloy) materials to enhance thepassive damping of GFRP (Glass Fiber Reinforced Plastic) laminated composite. The SMA has been embeddedas reinforcement in the GFRP laminated composite and a SMA/GFRP hybrid composite has been obtained.Two SMA alloys have been studied as reinforcement and characterized by thermo-mechanical tests. Thearchitecture of the hybrid composite has been numerically optimized in order to enhance the structural dampingof the host GFRP laminated, without significant changes of the specific weight and of the flexural stiffness. Thedesign and the resultant high damping material are interesting and will be useful in general for applicationsrelated to passive damping. The application to a new designed lateral horn of railway collector of the Italianhigh speed trains is discussed

Beta Titanium Alloys Processed by Laser Powder Bed Fusion: a Review

In bTi-alloys, some advances and developments have been reached toward optimizing their mechanical performance and their processability. However, the applications of these alloys via laser powder bed fusion (LPBF) are still under investigation. In this work, the processing of bTi-alloys via LPBF and their properties is reviewed with a focus on six selected metallurgical systems which are expected to be top performance materials in applications in the aeronautical and biomedical contexts. These six systems promise a better mechanical and functional performance considering different in-service environments for medical implants and structural applications. After literature analysis, the applicability of bTi-alloys to be processed via LPBF is then discussed considering the relevant fields of applications

La microforatura laser del titanio

In this work some of the main results dealing with laser drilling of titanium are reported. After the presentation of the state of the art of the present issue, three specific cases were defined and discussed. In the first part the main results concerning the laser drilling using a nanosecond laser source was descrived, reporting the principal performances of the process as well as the heat damages of the material machined; in the second discussion a comparison among the properties of two titanium plates, having different initial microstructure, was proposed: it was shown that different initial properties can affect significantly the final performances of the material machined, like the thermal process can do. Finally, the third discussion reports some preliminary results concerning the laser drilling with ultrashort pulses; here, the limitation of the thermal damages can be seen in the sensible reduction in the melted material produced and in improving the hole precision and quality

Spatter reduction in nanosecond fibre laser drilling using an innovative nozzle

Pulsed wave fibre lasers are becoming a popular industrial tool in microprocessing due to their many positive features, such as high beam quality, high reliability and high productivity, which are fundamental to machining small, precise features of industrial applications. However, the lasers’ use in the machining of ultra-precise features, such as small holes, is hindered by the fact that commercial pulsed wave fibre lasers commonly operate with pulse durations in the nanosecond regime. Such long pulse durations mean that the material is thermally removed, which results in the production of a melted layer and thermal damage in the bulk material. Consequently, the typical thermal defects of the melting regime, such as spattering of recast material around the hole, taper, heat-affected zone and poor hole circularity, are found in materials machined with these lasers. This paper proposes a design for an innovative nozzle that combines the high productivity of nanosecond fibre lasers with an improvement in the quality of the machined holes by reducing the spatter production in titanium laser percussion drilling. The innovative nozzle is based on the suction effect created by the Venturi principle that prevents the deposition of melted and vaporised material on the workpiece surface. The influence of the nozzle configuration and shielding gas on hole quality is investigated after the laser percussion drilling of 0.5 mm-thick titanium sheets, in which the process conditions that allow maximum productivity are used. The innovative nozzle produces a remarkable decrease in spatter on the entrance hole surface without affecting the other quality features, such as hole diameter, circularity and taper, while preserving the high productivity obtainable with a standard nozzle