Ti-6Al-4V alloy is employed in implants because of its good mechanical strength, excellent biocompatibility, and good resistance to corrosion in biological environments. Herein, a composite (HAp-TiO2, 50% by volume of both components) coating surface employing Ti-6Al-4V was characterized. Samples were analyzed post fabrication and post heat treatment to analyze the coating recrystallization, phases, crystallinity, porosity, and roughness. The coating showed rutile crystalline and amorphous Hap phases with crystallinity, porosity, and roughness of 55.6%, 13.6 ± 1.0%, and 4.2 ± 0.6 µm; whereas, after heat treatment, it showed a rutile hydroxyapatite phase and β-TCP with values 75.6%, 13.9 ± 1.9%, and 3.8 ± 0.2 µm, respectively. The composite exhibited 874 ± 26 HV100 hardness and 30 ± 2 MPa adhesion strength after heat treatment, which agree with previously reported data on other bioactive coatings. Therefore, this composite becomes much more crystalline after heating at 750 °C for 1 h.

Abstract The thermal processing of iron ore pellets in pelletizing plants is a decisive stage regarding final product quality and knowledge of its characteristics has a fundamental importance in its process optimization. This study evaluated the variable sensitivity involved in pellet bed formations and their permeability using the artificial neural networks method. The model stated that standard diameter deviation, sphericity and pellet bed height mostly affect bed permeability. The computational model was able to predict pellet bed backpressure by means of pellet geometrical features, thus allowing improving green pellet generation, in order to ensure fuel and energy consumption reduction, final quality improvement and better productivity.

Abstract This study evaluated the influence of plastic deformation during hot strip rolling in the size of TiN precipitates in an industrial Ti microalloyed dual phase steel. TiN is usually used for pinning austenitic grain boundaries during recrystallization and its efficiency depends on factors such as size of the precipitates and Ti precipitated fraction. During the slab reheating process, there occurs a partial dissolution of TiN precipitates that subsequently reprecipitates during the hot rolling process. However, this reprecipitation preferentially takes place at crystalline defects which act as nucleation sites. These sites increase with the amount of applied plastic deformation, resulting in smaller precipitates, due to the partial dissolution of larger particles or due to reprecipitation in the nucleation sites. Results indicate a reduction of about 28 % in the average size of the precipitates for samples extracted from hot bands (with deformation) and, therefore, a significant reduction in austenitic grain size, when compared with samples extracted from slabs (with no deformation).

AbstractThe controlled rolling of high strength low alloy steel has been widely used in the production of large diameter pipes for the oil and gas industry. The thermo-mechanical control process (TMCP) is used to maximize grain refinement and achieve both higher strength and toughness in the steels. In this sense, API 5L X80 micro-alloyed Nb-Ti steel was submitted to hot torsion tests to evaluate its hot deformation behavior. The critical temperatures (Tnr, Ar3 and Ar1) were obtained by testing with multiple strains in continuous cooling. From the flow stress curves generated in the isothermal tests, it was possible to obtain a critical strain that starts dynamic recrystallization, the peak strain for temperatures ranging from 1150ºC to 850ºC, and the strain rates at 0.2; 0.4 and 0.8s-1. The results showed that peak and critical stress values increase as the temperature decreases and strain rate increases.

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%).