Efeito da adição de alumínio e de magnésio na estabilidade do composto Ti6Si2B.

Abstract

Ti-Si-B alloys containing the Ti6Si2B phase have potential for high-temperature structural applications, because exhibit oxidation resistance and low crystallographic anisotropy. The presented work aims to investigate the effect of Al and Mg addition on the Ti6Si2B stability and oxidation resistance of the (67-x)Ti-xAl-22Si-11B, (67-x)Ti-xMg-22Si-11B alloys produced by high-energy ball milling and subsequent sintering. The Al and Mg contents varied in 2 and 7%-at. The elemental powder mixtures were prepared in a planetary ball mill. The powder mixtures were processed at different times: 20, 60, 180, 300, 420 and 600 min, to understand on effect of high-energy milling. Powders milled for 600 minutes were used to prepare round samples with 6 mm diameter by uniaxial pressing followed by sintering in argon atmosphere (1100ºC for 240 min). The milled powders and the sintered samples were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) techniques. Heating in air up to 900 and 1100 oC for 240 min was conducted to determine the oxidation resistance of the sintered alloys, while the Vickers hardness measurements were performed in order to determine the chemical and microstructural homogeneities of these materials. XRD results indicated the presence of extended solid solution during milling of Ti-Al-Si-B and Ti-Mg-Si-B powder mixtures. In the sintered Ti-Mg-Si-B alloys, it was noted the reduced Ti6Si2B amount with increase of Mg content in alloy, and the Ti5Si3 and TiB phases were preferentially formed during sintering. For alloys containing aluminum, there was a reduction in Ti6Si2B phase’s formation with the increasing of added element content, having the Ti5Si3 phase’s formation for the alloy containing 7(at.%) of aluminum.