Abstract In this work, a ternary composite of epoxy filled with ND and MS was produced for abrasive applications. Surfactants (oleic acid (OA), sodium dodecyl sulfate (SDS) and Triton TX-100 (TX-100)) were used to improve the particle dispersion and, consequently, the composite properties. The elastic modulus increased up to 76% for the sample with 1 wt% ND and 5 wt% ND using TX-100 (1ND5MS-TX100). Regardless of the filler concentration, the particles did not modify the thermal degradation behavior of the epoxy. Thermogravimetric (TGA) and dynamic mechanical (DMA) analyses suggest a strong particle-matrix interface, also evidenced in scanning electron microscope (SEM) micrographs. The composites presented superior tribological performance. 1ND5MS-TX100 presented a wear rate of 2.19 x 10-3 mm3.Nm-1, 61.3% lower than the epoxy. Also, all composites significantly reduced the roughness of the marble, being proportional to the abrasives concentration. Overall, composites with TX-100 presented improved wear behavior.

Abstract Despite the AISI 304 stainless steel has high corrosion/oxidation resistance, its tribological properties are poor, being one of the barriers for use in severe wear applications. Thus, there is a wide field for studying technologies that aim to increase the surface hardness and wear resistance of this material. In this work, hardness and wear resistance for AISI 304 stainless steel submitted to the thermochemical treatment by low temperature plasma carburizing (LTPC) in a fixed gas mixture composition of 93% H2 and 7% CH4 are presented. Through the evaluation of the carburizing layers, it was possible to observe a substantial improvement in tribological properties after all temperature and time of treatment. This improvement is directly related to the increase of the process variables; among them temperature has a stronger influence on the wear resistance obtained using LTPC process.

Studies regarding biodegradable nanocomposites to be used as orthopedics devices have been intensified. This work aims to investigate the influence of ND dispersion on thermal and mechanical properties of a biocomposite of poly(3-hydroxybutyrate) (P(3HB)) reinforced with nanodiamonds (ND) intended to be used as orthopedics devices, with advantages as biodegradability. In order to improve its dispersion, P(3HB) has encapsulated ND in three different mass ratios: P(3HB):ND(16:1), (12:1) and (8:1). However, for all formulations, NDs are presented as agglomerates, in different intensities. In order to relate the distribution of ND within the polymer matrix and biocomposite properties, TGA, DSC, and DMA analysis were done. The formulation with higher content of ND, P(3HB):ND(8:1), presents larger aggregates; thus, decreasing its properties. With smaller and more distributed agglomerates, the 12:1 ratio composite displayed superior storage modulus and glass transition temperature, probably due to better polymer chain restriction.

Several studies of biodegradable polymers and copolymers have been carried for different applications in the biomedical area. This current study aims to develop a biocomposite to be used as an orthopedic device, using poly(3-hydroxybutyrate-co-3-hydroxyvalerate) P(HB-HV), a biodegradable copolymer, with 94%HB and 6%HV, as matrix; and nanodiamonds (ND) with primary grains of 4-6nm, as reinforcement. The nanodiamonds were previously encapsulated by P(HB-HV) and specimens were prepared using a hydraulic press and injection molding machine, in order to evaluate which method presents a better performance. Thermal and mechanical analyses were done to compare their behavior. The biocomposite and pure P(HB-HV) samples were analyzed by flexural testing, nanoidentation, DMA, XRD, TGA. The distribution of nanodiamonds on the specimen fracture surface were investigated by SEM. The SEM micrographs allowed us to concluded that the encapsulation of nanodiamonds by P(HB-HV) was successfully performed, promoting a better interface and distribution in the polymeric matrix. The presence of ND in the polymeric matrix decreased the P(HB-HV) crystallinity, inhibiting the crystallite growth. The mechanical properties obtained from flexural test, nanoidentation and DMA of the injection-molded specimens were superior to compression-molded, due to its homogeneous and continuous structure. In vitro analysis was performed to evaluate the samples cytoxicity.

As mudanças no comportamento de amaciamento que ocorrem durante a deformação a quente de um aço estão diretamente ligadas a parâmetros como deformação, taxa de deformação, temperatura, tempo de espera entre passes e taxa de resfriamento. Um aço estrutural foi estudado através de ensaio de torção a quente. Os corpos de prova foram usinados a partir de esboços do aço, sendo retirados após a laminação de desbaste. Foram realizados ensaios de torção isotérmicos e ensaios de torção com múltiplas deformações em resfriamento contínuo no laboratório de conformação mecânica do CETEC, em Belo Horizonte-MG. Através das curvas de escoamento plástico, geradas pelos ensaios de torção isotérmicos, foram determinadas a tensão e a deformação de pico para temperaturas variando de 1150ºC à 650ºC e foram realizadas análises metalográficas das amostras para se verificar o comportamento do tamanho de grão do material. Foi realizado cálculo das temperaturas críticas (Tnr e Ar3), através da utilização de equações disponíveis, na literatura. Tal cálculo foi comparado com os valores obtidos durante o ensaio com múltiplas deformações em resfriamento contínuo e verificado que a variação não passou de 1,8%.

The softening behavior changes that occur during hot deformation of steel is directly related to processing parameters such as strain, strain rate, temperature, interpass time and cooling rate. A structural steel was analyzed by hot rolling simulation using hot torsion tests. The specimens were machined from work piece after roughing mill. Isothermal torsion and multiple strains in continuous cooling torsion tests were performed in hot deformation laboratory of CETEC, in Belo Horizonte-MG. Peak stress and strain for temperatures ranging from 1150ºC to 650ºC were determined through flow curves generated by isothermal torsion tests and metallographic analysis were performed to verify the behavior of grain size of the material. The critical temperatures (Tnr and Ar3) were calculated by equations available in literature and compared to values obtained from the test flow curves (the variation did not exceed 1.8%).