Beta titanium alloys produced from titanium hydride: effect of alloying elements on titanium hydride decomposition

The use of titanium hydride as a raw material has been an attractive alternative for the production of titanium components produced by powder metallurgy, due to increased densification of Ti compacts, greater control of contamination and cost reduction of the raw materials. However, a significant amount of hydrogen that often remains on the samples could generate degradation of the mechanical properties. Therefore, understanding decomposition mechanisms is essential to promote the components' long life. Several studies on titanium hydride (TiH2) decomposition have been developed; nevertheless, few studies focus on the effect of the alloying elements on the dehydrogenation process. In this work, the effects of the addition of different amounts of Fe (5 and 7 wt. %) and Nb (12, 25, and 40 wt. %) as alloying elements were evaluated in detail. Results suggest that α→β transformation of Ti occurs below 800 °C; β phase can be observed at lower temperature than the expected according to the phase diagram. It was found that β phase transformation could take place during the intermediate stage of dehydrogenation. A mechanism was proposed for the effect of allying elements on the dehydrogenation process.This research was funded by the Regional Government of Madrid (program ADITIMAT-CM, ref. S2018/NMT-4411), and by the Ministry of Economy and Competitiveness of Spain (program MINECO, ref. PCIN-2016-123 project BIOHYB, and Ramón y Cajal contract RYC-2014-1504).Publicad

A promising method to develop TiO2-based nanotubular surfaces on Ti-40Nb alloy with enhanced adhesion and improved tribocorrosion resistance

Although TiO2 nanotubes have unique properties making them attractive for variety of applications, their poor adhesion to the substrate is a major limitation. In order to overcome this limitation, a facile route, combination of a two-step anodic treatment and heat treatment was applied in order to develop a well-adhered TiO2-based nanotubular surface on Ti-40Nb alloy. The adhesion of the nanotubular layer was evaluated by Daimler-Benz Rockwell C test. Corrosion and tribocorrosion behavior was investigated in phosphate-buffered saline solution (PBS) at body temperature. Corrosion behavior was examined by potentiodynamic polarization and electrochemical impedance spectroscopy whereas tribocorrosion behavior was evaluated by reciprocating sliding against an alumina ball at open circuit potential. Results showed that the adhesion, corrosion, and tribocorrosion behavior of the nanotubular layer was drastically improved with the combination of a two-step anodic treatment and heat treatment.This work was supported by FCT national funds, under the national support to R&D units grant, through the reference project UIDB/04436/2020 and UIDP/04436/2020, together with M-ERA-NET/0001/2015 and PCIN-2016-123 project. I. Çaha is grateful for the financial support through a Ph.D. grant under the NORTE-08-5369-FSE-000012 project, and mobility program under INTERREG VA España Portugal (POCTEP) territorial cooperation programme (Project ref: 0300_NANOGATEWAY_6_P)

Atomic-scale investigations of passive film formation on Ti-Nb alloys

This study extensively investigates the passive film formation mechanisms on Ti-xNb alloys by using several electrochemical techniques, including electrochemical impedance spectroscopy (EIS) before and after potentiostatic polarization at the passive zone, and Mott-Schottky (MS) measurements in 9 g/l NaCl electrolyte at 37 °C, together with X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) analysis. Overall, the Ti40Nb presented lower corrosion resistance due to a thinner passive film as compared to commercial pure Ti (grade 2) and Ti12Nb. The passive film formed on Ti12Nb and Ti40Nb alloys at a steady-state condition (+0.5 VAg/AgCl for 60 min) is composed of amorphous phases of TiO, Ti2O3, TiO2, Nb2O5, and crystalline phases of TiO2 (anatase) and Nb2O5.This work is supported by FCT with the reference project UID/EEA/04436/2019, together with M-ERA-NET/0001/2015, and by MINECO (Spain) through the program PCIN-2016-123, the Ramón y Cajal project RYC-2014-15014 and the regional government of Madrid by S2018/NMT-4411, as well, by the CASOLEM project (028917) "Correlated Analysis of Inorganic Solar Cells in and outside an Electron Microscope", co-funded by FCT and ERDF through COMPETE2020