Ultra-Fine Grain Refinement of Titanium Materials by Hydrogen Treatment

Hydrogen treatment is one of the few possible methods for producing a fine-grain size of 0.3 to 0.5 μm in α+β Ti-6Al-4V alloys. The process of hydrogen treatment involves hydrogen absorption, quenching, hot rolling and hydrogen desorption. However, ultra-fine grain refinement of other titanium materials by this treatment has not yet been examined. In this study, the optimum hydrogen treatment conditions for ultra-fine grain refinement of two phase α+β Ti-3Al-2.5V, two phase α+β Ti-1Fe-0.35O and single phase α titanium were investigated in order to expand the application of this effective treatment to the grain refinement of other titanium materials. Tensile tests were also carried out at room and high temperatures to investigate the tensile properties of the grain-refined materials. The experimental results that were obtained are as follows. An ultra-fine grain size in the range of 0.5 to 1 μm was produced in the Ti-3Al-2.5V and Ti-1Fe-0.35O alloys by controlling the hydrogen treatment conditions, particularly the content of hydrogen absorbed and hot rolling conditions. However, ultra-fine grain refinement of pure titanium was not observed. It is thought that one of the reasons for this lies with the differences in the morphology of the martensite obtained when quenching Ti-3Al-2.5V and Ti-1Fe-0.35O alloys. The proof stress of the ultra-fine-grained Ti-3Al-2.5V and Ti-1Fe-0.35O alloys was improved by the hydrogen treatment. According to the tensile tests carried out at 1098 K, ultra-fine-grained Ti-3Al-2.5V exhibited very large elongations of more than 9000%.