RESUMO
From a scientific point of view, heat transfer is different in solar furnaces compared with classical ones and the influence of direct concentrated solar radiation on sintered parts needs to be studied in detail to determine the feasibility of solar furnaces in manufacturing small workpieces. This study was performed on cylindrical samples with controlled morphology obtained by a powder metallurgy 3D printing technique. All samples were heated with a heating rate of 120 ± 10 °C/minute, with 0, 1, 2, 3, 4 and 5 min holding times at 900 °C and 930 °C. The morphology of the samples was analyzed microscopically, the microhardness was determined before and after sintering, and the results were correlated with the sintering parameters (temperature, heating rate and holding time). The best results were obtained at 930 °C with 5 min holding time from the microhardness value and microstructure point of view.
RESUMO
The utilization of polymer-based materials is quickly expanding. The enterprises of today are progressively seeking techniques to supplant metal parts with polymer-based materials as a result of their light weight, simple support and modest costs. The ceaselessly developing requirement for composite materials with new or enhanced properties brings about the preparation of different polymer mixes with various arrangements, morphologies and properties. Fused filament fabrication processes such as 3D-printing are nowadays shaping the actual pathway to a full pallet of materials, from art-craft to biomaterials. In this study, the structural and mechanical behavior of three types of commercially available filaments comprised of synthetic poly(acrylonitrile-co-butadiene-co-styrene) (ABS), poly(lactic acid) (PLA) and poly(lactic acid)/polyhydroxyalkanoate reinforced with bamboo wood flour composite (PLA/PHA BambooFill) were assessed through mechanical testing and optical microscopy, aiming to understand how the modifications that occur in the printed models with internal architecture are influencing the mechanical properties of the 3D-printed material. It has been determined that the material printed from PLA presents the highest compression strength, three-point bending and shock resistance, while the ABS shows the best tensile strength performance. A probability plot was used to verify the normality hypothesis of data for the tensile strength, in conjunction with the Anderson-Darling statistic test. The results of the statistic indicated that the data were normally distributed and that there is a marked influence of the internal architecture of the 3D-printed models on the mechanical properties of the printed material.
RESUMO
This paper discusses the structure morphology and the thermal and swelling behavior of physically crosslinked hydrogels, obtained from applying four successive freezing-thawing cycles to poly (vinyl alcohol) blended with various amounts of κ-carrageenan. The addition of carrageenan in a weight ratio of 0.5 determines a twofold increase in the swelling degree and the early diffusion coefficients of the hydrogels when immersed in distilled water, due to a decrease in the crystallinity of the polymer matrix. The diffusion of water into the polymer matrix could be considered as a relaxation-controlled transport (anomalous diffusion). The presence of the sulfate groups determines an increased affinity of the hydrogels towards crystal violet cationic dye. A maximum physisorption capacity of up to 121.4 mg/g for this dye was attained at equilibrium.
RESUMO
The appropriate selection of implant materials is very important for the long-term success of the implants. A modified composition of AISI 316 stainless steel was treated using solar energy in a vertical axis solar furnace and it was subjected to a hyper-hardening treatment at a 1050 °C austenitizing temperature with a rapid cooling in cold water followed by three variants of tempering (150, 250, and 350 °C). After the heat treatment, the samples were analyzed in terms of hardness, microstructure (performed by scanning electron microscopy), and corrosion resistance. The electrochemical measurements were performed by potentiodynamic and electrochemical impedance spectroscopy in liquids that simulate biological fluids (NaCl 0.9% and Ringer's solution). Different corrosion behaviors according to the heat treatment type have been observed and a passivation layer has formed on some of the heat-treated samples. The samples, heat-treated by immersion quenching, exhibit a significantly improved pitting corrosion resistance. The subsequent heat treatments, like tempering at 350 °C after quenching, also promote low corrosion rates. The heat treatments performed using solar energy applied on stainless steel can lead to good corrosion behavior and can be recommended as unconventional thermal processing of biocompatible materials.
RESUMO
The development of novel Ti-based amorphous or ß-phase nanostructured metallic materials could have significant benefits for implant applications, due to potentially improved corrosion properties, and mechanical characteristics (lower Young's modulus, better wear performance, improved fracture toughness) in comparison to the standardized α+ß titanium alloys. Moreover, the devitrification phenomenon, occurring during heating, could contribute to lower input power during additive manufacturing technologies. Ti-based alloy ribbons were obtained by melt-spinning, considering the ultra-fast cooling rates this method can provide. The titanium alloys contain Zr, Nb, and Si (Ti60Zr10Si15Nb15, Ti64Zr10Si15Nb11, Ti56Zr10Si15Nb19) in various proportions. These elements were chosen due to their reported biological safety, as in the case of Zr and Nb, and the metallic glass-forming ability and biocompatibility of Si. The morphology and chemical composition were analyzed by scanning electron microscopy and energy-dispersive X-ray spectroscopy, while the structural features (crystallinity, phase attribution after devitrification (after heat treatment)) were assessed by X-ray diffraction. Some of the mechanical properties (hardness, Young's modulus) were assessed by instrumented indentation. The thermal stability and crystallization temperatures were measured by differential thermal analysis. High-intensity exothermal peaks were observed during heating of melt-spun ribbons. The corrosion behavior was assessed by electrocorrosion tests. The results show the potential of these alloys to be implemented as materials for biomedical applications.
