Biomecânica e otimização topológica com H-adaptatividade em implantes dentários nitretados a plasma em cátodo oco

In recent years there has been a significant growth in technologies that modify implant surfaces, reducing healing time and allowing their successful use in areas with low bone density. One of the most widely used techniques is plasma nitration, applied with excellent results in titanium and its alloys, with greater frequency in the manufacture of hip, ankle and shoulder implants. However, its use in dental implants is very limited due to high process temperatures (between 700 C o and 800 C o ), resulting in distortions in these geometrically complex and highly precise components. The aim of the present study is to assess osseointegration and mechanical strength of grade II nitrided titanium samples, through configuration of hollow cathode discharge. Moreover, new formulations are proposed to determine the optimum structural topology of the dental implant under study, in order to perfect its shape, make it efficient, competitive and with high definition. In the nitriding process, the samples were treated at a temperature of 450 C o and pressure of 150 Pa , during 1 hour of treatment. This condition was selected because it obtains the best wettability results in previous studies, where different pressure, temperature and time conditions were systematized. The samples were characterized by X-ray diffraction, scanning electron microscope, roughness, microhardness and wettability. Biomechanical fatigue tests were then conducted. Finally, a formulation using the three dimensional structural topology optimization method was proposed, in conjunction with an hadaptive refinement process. The results showed that plasma nitriding, using the hollow cathode discharge technique, caused changes in the surface texture of test specimens, increases surface roughness, wettability and microhardness when compared to the untreated sample. In the biomechanical fatigue test, the treated implant showed no flaws, after five million cycles, at a maximum fatigue load of 84.46 N. The results of the topological optimization process showed well-defined optimized layouts of the dental implant, with a clear distribution of material and a defined edge

Desgaste corrosivo-cavitativo-erosivo de um aço-carbono em meio aquoso com frações de sal (NaCl), CO2 e particulados sólidos (SiO2)

A batch of eighty-four coupons of low carbon steel were investigated at laboratory conditions under a corrosive, cavitative-corrosive (CO2) and corrosive-erosive (SiO2 + CO2) in an aqueous salt solution and two levels of temperature. The following measurements were made on Vickers (HV0,05, HV0,10, HV0,20) Microhardness tests at three levels of subsurface layer. A turbulent flow collided on the cylindrical sample, with and without mechanical stirring and gas bubbling, with and without fluid contamination by solid particles of SiO2, at two temperatures. Surface Roughness and Waviness, under two conditions "as received, after machining" and "after worn out", as well as gravimetric and electrochemical parameter were measured on the two opposite generatrices of each cylindrical sample, on the flow upstream (0°) and downstream (180°) by Profilometry, Mass Variation and Linear Polarization Resistance (LPR). The results of the Microhardness and Surface Texture of all coupons were subjected to statistical comparison, using the software Statgraphics® Centurion XVI, 95% statistical certainty, and significant differences were observed in some arrays of measurements. The corrosive wear rate measured by LPR and mass variation shown to be sensitive to the presence of bubbles and hydrodynamic fluctuations inside the cell, considering the temperature and contamination of corrosive fluid by solid particles. The main results of visual inspection relative to some topologies of the surface damages involving different mechanisms that were seen to give explanation for some fluctuations in wear rates of the steel experimentally investigated