Role of Hydrogen in the Process of Sintering of Titanium Powders
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ROLE OF HYDROGEN IN THE PROCESS OF SINTERING OF TITANIUM POWDERS D. H. Savvakin,1, 2 M. M. Humenyak,1 M. V. Matviichuk,1 and O. H. Molyar1
UDC 669.295:669.788
We perform the experimental investigation the role of hydrogen in the production of samples of commercially pure titanium by the method of pressing and sintering of titanium and titanium-hydride powders. The comparative analysis of their behavior shows that the changes in the mechanical properties under the conditions of hydrogenation of the material determine the formation of a specific fine-porous microstructure in the case of pressing of a hydrated powder. As an important specific feature of hydrated titanium as compared with the titanium powder, we can mention its dehydrogenation in the process of heating, which leads to the activation of sintering, decreases the oxygen content of the final material, and, hence, improves the mechanical characteristics of sintered commercially pure titanium. Keywords: titanium, titanium hydride, phase transformations, sintering of powders, microstructure.
Powders of hydrated (hydrogenated) titanium can be successfully used for the production of commercially pure titanium and synthesis of its alloys [1–4] by the method of pressing and sintering of powders based on the solid-phase diffusion. In [1, 2], it was established that powders of TiH 2 titanium hydride, i.e., titanium hydrogenated to 3–4 wt.% H, have significant advantages over the customary titanium powders because they guarantee the possibility of production of alloys with higher relative density and improved mechanical characteristics. The physical foundations of the application of hydrogenated titanium are based on the unique ability of hydrogen to be a reversible (temporary) alloying admixture for titanium, i.e., to saturate titanium to the required concentrations with an aim of getting positive influence on the physicomechanical and microstructural characteristics and then to be completely removed from titanium in the course the vacuum heating. The main mechanisms of the positive action of hydrogen on the material were established as a result of the comprehensive experimental investigations of the specific features of the dehydrogenation of titanium hydride in the course of heating [5]. The bulk effects and phase transformations occurring as the concentration of hydrogen in titanium decreases lead to the increase in the number of defects in the crystal structure. Moreover, atomic hydrogen released from the crystal lattice to the surface of powder particles reduces the surface oxide films. This leads to the activation of diffusion processes, improved sintering of particles, and the formation of massive low-porosity materials with density maximally close to the theoretical value (98–99%). The second important consequence of the reduction of surface oxides is the decrease in the oxygen content of titanium as a result of dehydrogenation. All these factors positively affect the material. As a result, the physicomechanical properties of titanium alloys of various com
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