Percorrer por autor "Jesus, J. de"
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- Assessment of the fatigue performance of heat-treated addictive manufactured TiAl6V4 specimensPublication . Borrego, L.P.; Jesus, J. de; Ferreira, J.A.M.; Costa, J.D.M.; Capela, C.; Capela, C.Titanium Ti6Al4V alloy has excellent mechanical properties and corrosion resistance combined with low specific weight, and is commonly used in biomedical applications, automotive and aerospace components, involving fatigue loadings. Current work studies the fatigue behavior under strain amplitude control of titanium TiAl6V4 specimens, intending to characterize fatigue strength from low to high life range after different heat treatments. Fatigue tests were carried out at room temperature, using round dog bone specimens produced by selective laser melting (SLM), where laser powder deposition occurred in layers perpendicular to the loading direction. Two batches of specimens were tested: one subjected to a stress relieve treatment and a second one treated by the hot isostatic pressing process (HIP). The material was characterized in terms of the tensile mechanical properties, cycle curve, Basquin and Coffin equations. Additional analysis of the hardness and scanning electron microscopy was carried out to complement the discussion of the results. The obtained dada showed that the stress relieved specimens exhibits significantly cyclic softening, increasing with applied strain, while HIP specimens show a practically stable cyclic behavior in relation to the monotonic curve. Material response for both treatments is well fitted by Basquin and Coffin-Manson formulations. The transition life was 187 reversals and 326 reversals, for stress relieved and HIP specimens, respectively. Fatigue life for a given strain is governed by the strain value, independently of the post manufacturing heat treatment.
- Effect of artificial saliva on the fatigue and wear response of TiAl6V4 specimens produced by SLMPublication . Jesus, J. de; Borrego, L. P.; Vilhena, L.; Ferreira, J. A. M.; Ramalho, A.; Capela, C.Additive manufactured (AM) parts made in TiAl6V4 alloy are increasingly used in medical prostheses and dental implants, because of its high strength, low weight and excellent biocompatibility. These components work under environmentally assisted cyclic loading, i.e. under corrosion-fatigue, and/or subject to wear conditions. Fatigue performance of additive manufactured alloys is significantly influenced by the porosities, residual stresses, which can reduce its strength when compared with traditional materials. This paper presents the results of a fatigue crack propagation study in titanium TiAl6V4 specimens produced by selective laser melting (SLM) under artificial saliva ambient. Tests were performed using standard 6 mm thick compact specimens (CT) tested at R=0.05 and with frequencies of 1 and 10 Hz. The main objective of the current research work was studying the corrosion effect on the fatigue crack propagation of Selective Laser Melting (SLM) specimens, and to compare the tribocorrosion behaviour of two different specimens: one produced by SLM and the other by the conventional/traditional method. The study concluded that: AM Titanium Ti6Al4V alloy exhibits a moderate effect of saliva ambient on fatigue crack nucleation and on fatigue crack propagation, the wear rate coefficients for SLM and conventional manufactured specimens is of the same order, and the mechanism of abrasive wear is mainly with grooves aligned with the direction of sliding.
- Environmental effect on the fatigue crack propagation of AM TiAl6V4 alloy specimensPublication . Borrego, L.P.; Jesus, J. de; Ferreira, J.A.M.; Costa, J.D.; Capela, C.Additive manufactured (AM) parts made in TiAl6V4 alloy are increasingly used in medical devices and in the aeronautical industry, because of its high strength, low weight and excellent biocompatibility. Most of these components work under environmentally assisted cyclic loading, i.e. under corrosion-fatigue. Fatigue performance of additive manufactured alloys is significantly influenced by the porosities, residual stresses, which can be reduced by optimizing the process parameters, thermal treatments or hot isostatic pressing (HIP). Those parameters can also influence significantly to the propagation of cracks under corrosion-fatigue, but the understanding of this subject still needs significant research work. This paper presents the results of a fatigue crack propagation study in titanium TiAl6V4 specimens produced by selective laser melting (SLM), under corrosive ambient. The environment solutions studied were: artificial saliva and 3.5%wt NaCl solution. Tests were performed using standard 6 mm thick compact specimens (CT) tested at R=0.05 and with frequency 10 Hz. The main objective was to study the effect of the environment solution on da/dN-∆K curves and on the fatigue failure mechanisms. Current work shows a very important accelerating effect on the crack nucleation and fatigue crack propagation for tests under corrosion ambient, particularly for 3.5%wt NaCl solution. Fatigue path shows an irregular path. Secondary cracking was observed in air, but not detected in corrosive ambient.