For the first time, the influence of gas mixture on first damage resistance of a plasma nitrided DIN 18MnCrSiMo6-4 bainitic steel was investigated. Samples were nitrided at 500 °C with three different N2-H2 gas mixtures, containing 5, 24, and 76 vol.% N2. Samples were characterized concerning the resulting roughness, microstructure, compound layer’s phase composition, residual stresses in the diffusion zone, and surface hardness. Tribological ball-on-flat tests were carried out in reciprocal mode using zirconia as ball material for friction coefficient and the compound layer resistance until the first damage. The test results were evaluated statistically by analysis of variance (ANOVA). As the amount of nitrogen in the gas mixture decreases, the ε-Fe2-3(C)N content in the compound layer decreases. A γ’-Fe4N monophasic compound layer was achieved at 5 vol.% N2 gas mixture. The diffusion zone as expected presented compressive residual stresses with the highest values near the surface. In the tribological tests, better results were obtained for 5 and 24 vol.% N2 in the gas mixture as higher amounts of γ’-Fe4N were formed. The 76 vol.% N2 gas mixture led to a brittle behavior, due to the biphasic compound layer (γ’-Fe4N and ε-Fe2-3(C)N) with a predominant content of ε-Fe2-3(C)N.

RESUMO: A ingestão de corpos estranhos, principalmente metálicos (CEM), pelos bovinos é frequente e pode levar à sua morte. Para fins diagnósticos, as provas de dor reticular são usados de forma rotineira, sendo ainda pouco usual a ferroscopia, mesmo como auxílio diagnóstico. Neste trabalho procurou-se validar a aplicação do detector de metais (DM), marca GMS 120 Professional BOSCH® no reconhecimento de CEM na espécie bovina, além de descrever seu uso em casos a campo. CEM (n=50) de forma, tamanho e peso variados foram selecionados e avaliados com o DM, inicialmente sobre uma superfície plana e inerte e depois in vivo em uma vaca com fístula ruminal. Retrospectivamente, acessou-se um banco de dados dos anos 2000 a 2017 com 122015 bovinos, com 31865 bovinos atendidos após a introdução do DM no ano de 2013. Prospectivamente, avaliaram-se 15 vacas positivas para o teste de dor reticular, oito vacas foram diagnosticadas com CEM através do DM. A distância média para a melhor detecção dos CEM na superfície inerte foi de 4,6 cm. Em vaca fistulada não foi possível detectar nenhum CEM, independentemente do tamanho e peso do material. A campo, após a introdução do uso do DM aumentou a capacidade de detecção dos CEM. O DM pode ser considerado um auxílio diagnóstico em situações específicas. Dependendo da condição corporal do bovino, falsos negativos podem ocorrer com o uso do aparelho GMS 120 Professional Bosch®.

ABSTRACT: The ingestion of foreign bodies, mainly metallic (MFB- metallic foreign body), by cattle is frequent and can lead to death. For diagnostic purposes, reticular pain tests are routinely used, and ferroscopy is still unusual, even as a diagnostic aid. The objective of this study was to validate the application of the GMS 120 Professional BOSCH® metal detector (MD) in the detection of MFB in the bovine species and describe its use in field cases. Fifty MFBs of varying shape, size, and weight were evaluated with an MD, initially on a flat and inert surface, and then in a permanent rumen fistulated cow. Retrospectively, a database from 2000 to 2017 with 122015 cattle was accessed, of which 31865 were examined after the introduction of MD usage in 2013. Fifteen cows positive for reticular pain tests were prospectively evaluated and eight cows were diagnosed with MFB through MD usage. The mean distance for MFB best detection on the inert surface was 4.6 cm. In the fistulated cow, it was not possible to detect any MFBs, regardless of the size or weight of the material. The MFB detection capacity increased with MD use, which can be considered a diagnostic aid in specific situations. Depending on the body condition of the bovine, false negatives may occur with the use of GMS 120 Professional Bosch® metal detector.

Wire Electrical Discharge Machining (WEDM) is one of the most important production technologies to manufacture very accurate small components and tools on any electrical conductive material. Titanium and its alloys have been widely used in automobile and aerospace industry as well as in medical engineering field. Small components and tools with complex geometrical shapes are difficult to be produced on titanium alloys by both conventional and nonconventional machining technologies. In this work an experimental investigation on the influences of wire electrode type and electrical variables when WEDM a thin plate of Ti6Al4V alloy has been carried out. Uncoated brass wire and copper wire with a diffused zinc coating were used for the experiments. Interval time, wire run-off speed, discharge duration and dielectric inlet pressure were evaluated in order to achieve adequate process parameter settings. Characteristics of surface integrity were also investigated. The best technological results for all tested WEDM parameters were attained for copper wire with a diffused zinc coating. The recast layer of the samples WEDMachined with the copper wire presented a smaller thickness and more compact than that obtained with uncoated brass wire. For WEDM with both types of wire, the existence of thermal cracks was observed.