Hydride formation under cathodic charging of titanium and TiAl-based alloys in alkaline solutions
- PDF / 643,033 Bytes
- 6 Pages / 595.276 x 793.701 pts Page_size
- 84 Downloads / 269 Views
HYDRIDE FORMATION UNDER CATHODIC CHARGING OF TITANIUM AND TiAl-BASED ALLOYS IN ALKALINE SOLUTIONS E. Lunarska, O. Chernyaeva, and D. Lisovytskii The electrochemical methods and the data of X-ray diffraction analysis are used to determine the parameters of cathodic polarization for the hydrogenation of α – Ti and alloys based on the TiAl intermetallic phase without formation of the hydride phase or with formation of hydrides. In α – Ti, the increasing cathodic polarization in a 0.1 M NaOH solution leads to the dissolution of hydrogen in the metal lattice and its modification and to the increase in the amount of hydrides. The hydride phase is not recorded TiAl-based alloys even for much higher levels of absorption of hydrogen as compared with pure titanium. However, hydrogen affects the phase composition of alloys and the lattice parameters of the phases.
The increase in the plasticity of Ti–Al alloys, including those based on the γ-TiAl intermetallic, would extend their applicability and decrease workability. The high-temperature hydrogen treatment allows us to increase the plasticity of the Ti alloys [1] by promoting the transformation of the low-temperature α phase into the β phase of higher plasticity [2]. Some recent results have shown that the hydrogen charging can also soften the αTi [3]. The hydrogen solubility in α-Ti is quite low and the hydride is easily formed in this phase [2]. Therefore, it is not clear whether hydrogen-induced softening occurs due to the intrinsic effect of hydrogen dissolved in the lattice or due to the hydride formation, which has been recently found to decrease the elastic modulus of Ti [4]. The hydride phase has also been found to form in the γ-TiAl intermetallic [5], which may also suggest the possibility of hydrogen-induced softening of this material. The increase in the plasticity of the low temperature α-Ti phase and the γ-TiAl-based alloys by hydrogen charging at the ambient temperature seems to be very attractive. In order to check this possibility, the effects of the electrochemical hydrogen charging on the phase composition of alloys and on the individual phases should be thoroughly analyzed. In present work, the hydrogen absorption under cathodic polarization in alkaline solutions at RT and the effect of the absorbed hydrogen on the phase composition and the crystallographic structure of the α-Ti and the TiAl-based alloys are evaluated and the conditions providing hydrogen dissolution and hydride formation are selected. Materials and Experimental Procedure The 99.99% α-Ti and the alloys containing 47.4, 50, and 53.5 at.% Al were studied. As testing electrolytes, the alkaline solutions (0.1 M NaOH with pH 11.8 and 2 M NaOH with pH 13.5), less aggressive than the acid solutions, were selected. The hydrogen uptake was evaluated by the potentiodynamic anodic desorption after hydrogen charging at the potentiostatic cathodic polarization for 30–60 min [6]. The height of the anodic peak formed on the polarization curve after the cathodic charging ( Δ iH ) was adopted as the meas
Data Loading...
