No abstract

Absorption of interstitial elements during the processing of Ti-13Nb-13Zr alloy using hydride powders was investigated. Oxygen, nitrogen and carbon contents were quantified in the steps of hydriding and milling of powders and after sintering of green compacts. The influence of the hydriding treatment was analysed regarding the interstitial contents in the raw materials. Milling and sintering were evaluated according to a 3 3 factorial design considering the effects of milling time of titanium hydride from 1 to 11 h, sintering temperature between 1000 and 1400uC and holding time from 1 to 5 h. The results showed that the oxygen contents in sintered samples are strongly affected by the hydriding and milling of powders. The effects of the sintering temperature and holding time were found to be significant mainly for the increase in nitrogen and carbon contents. The results of the factorial design, along with the study of microstructural evolution allowed the optimisation of the process parameters in order to obtain the alloy with the lowest possible contents of interstitial elements and homogeneous microstructure.

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.

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.