Caracterização de ligas de Ti e Ti-Nb sinterizadas por ultrafast high-temperature sintering(UHS)

Abstract

The ultra-high temperature (UHS) sintering method, a recent innovation, significantly transforms materials processing by heating compacted powder samples in a matter of seconds, enabling superior densification and faster phase transformation. The process consists of applying a high current for a short time to the sample through a carbon felt, in which it is wrapped, enabling rapid heating. Initially developed for advanced ceramics, its scope has expanded to include metallic materials. Titanium alloys are valued for their exceptional properties, including a high strength-to-weight ratio, corrosion resistance, and biocompatibility, making them key in aerospace, automotive, and biomedical applications. This research delves into applying the UHS method in Ti and Ti-20Nb alloys. A UHS device sintered green parts formed by compacting elementary powders with different current and time parameters. The results demonstrated that achieving a high densification rate (up to 96%) within a maximum sintering time of 120 seconds was possible. These samples’ microstructure and hardness were analyzed using different software and experimental methods, such as optical microscopy, image analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD), Archimedes porosity test, and Vickers microhardness test. Maximum porosity values of around 26% were found for the Ti samples and 34.5% for the Ti-20Nb samples, with higher hardness values generally being associated with samples with fewer pores. The XRD results indicated the presence of titanium carbide - Ti2C - on the surface of the alloys, which was formed during sintering due to the diffusion of carbon from the felt into the sample. In addition, the comparative evaluation of the Ti and Ti-20Nb alloys highlights the formation of a beta-titanium phase with the addition of niobium, which is accentuated at high sintering temperatures, in contrast to the formation of an alpha phase in the Ti alloys. However, contrary to expectations, the expected increase in hardness attributed to the incorporation of niobium did not occur, with the Ti-20Nb alloys exhibiting hardness values similar to those of the Ti alloys. This study sheds light on the intricate interplay of variables in the sintering of titanium and titanium-niobium alloys by the UHS method, providing valuable insights for advancing material manufacturing techniques and optimizing alloy properties.