Microstructural features of the hydrogenation process in Ti grade 2

This paper reports the first studies made with the final aim of obtaining Ti powder by the hydrogenation-dehydrogenation process. The hydrogenation of Ti grade 2, with two different initial microstructures, equiaxed and acicular alpha, was performed in a Sieverts' device, at temperature higher than 600 degrees C and pressures close to 0.1 MPa. The evolution of the hydrogenating process was studied by comparing the microstructure changes and the variation of hydrogen pressure. For both analyzed microstructures, the process progresses by growing of a surface P phase layer with an absorption rate of 10(-5) to 10(-4) g cm(-2) s(-1). Then, Ti hydride precipitates on the surface and the rate decreases two orders of magnitude. Under this condition, obtaining of a fully hydrided material (atomic fraction: 1.6 H/Ti) becomes too slow. Although samples with 1.1 H/Ti are not so brittle as Ti hydride, it can be easily milled at room temperature and can be used to produce titanium powder at a competitive cost. (c) 2005 Elsevier B.V. All rights reserved.