Papers by Author: S.L.G. Petroni

Abstract: The use of hydrogenated titanium powders combined with traditional PM techniques may lead to a significant reduction in the manufacturing costs of titanium components. In this work, the advantages and limitations of the use of TiH₂ powder consolidated through the conventional press-and-sinter method were investigated. Processing parameters related to the compaction and sintering were studied for a TiH₂ powder in the particle sizes <355 μm, <150 μm and <45 μm. Optimized compaction conditions were achieved by using admixed lubricant and compaction pressure of 800 MPa. The mechanisms involved in the compaction of powders were detailed through the fit of compressibility data to a theoretical model originally developed for titanium powders. Densification of samples was favored by the reduction in particle size and increase in sintering temperature up to 1300 °C. The positive effects of hydrogen release during dehydrogenation were verified through the results of sintered densities and the reduction of oxygen levels. Limitations were observed mainly regarding the flowability of powders and the difficulty to achieve full densification.

Abstract: The use of hydride powders in titanium powder metallurgy (P/M) is a low cost alternative for the manufacture of titanium alloys. However, due to the high reactivity of these powders, parts produced using this technique may contain interstitial impurities such as oxygen, nitrogen and carbon. In this work a factorial design approach was used to evaluate the influence of some stages of P/M upon the levels of these elements in sintered samples of Ti-6Al-4V. Milling time of titanium hydride powders, sintering temperature and holding time were evaluated. The effect of milling time was detected as the most significant for the increase in oxygen levels. The contents of all elements were affected by the increase of sintering temperature from 1200 °C to 1400 °C. Holding time was shown to be significant only for the carbon absorption in the samples sintered at 1400 °C.

Abstract: The titanium alloys are used for applications that demand high performance, including surgical implants and aerospace applications. Powder metallurgy is an advantageous alternative for titanium parts production with complex geometries at a relative low cost. Despite that, it is verified that the introduction of interstitial elements (oxygen, nitrogen and carbon) wile processing these alloys, though can increase hardness and mechanical resistance, which is frequently related to the reduction of ductility and fragility increase. The objective of this work is to investigate the influence of the interstitial elements in commercially pure Ti and Ti-13Nb-13Zr alloy produced by powder metallurgy (P/M). Samples were produced by the mixing of hydrided metallic powders followed by uniaxial and cold isostatic pressing with subsequent densification by sintering at 1400 °C, in vacuum. Sintered samples were characterized for phase composition, microstructure and microhardness by X-ray diffraction, scanning electron microscopy and Vickers indentation, respectively. The interstitial content was analyzed by Leco equipment. It was shown that the samples were sintered to high densities with a Widmanstatten microstructure. The oxygen and nitrogen contents are above the ELI (Extra Low Interstitial) and the critical issues were identified in the original blended elemental route.