Grain Refinement of Ti-6Al-4V Alloy by Gas Phase Hydrogenation

• Main Authors: J. P. Wu, 吳榮賓
• Other Authors: 吳建國
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/39712717879009362098

碩士 === 國立臺灣海洋大學 === 材料工程研究所 === 95 === Hydrogen was regarded as a harmful element for some general metallic materials in traditional concepts, but it can enhance the mechanical properties of titanium alloys through different thermochemical procedures . By the presence of hydrogen, hydrogen diffuses into titanium to form solid solution or hydride. Titanium and titanium alloys have large affinity for hydrogen and dissoluted hydrogen can be easily to removed by vacuum annealing. The dissolving and removing processes of hydrogen in titanium alloy is reversible, as a results grain refinement of their alloys. In this study, that hydrogenation in several effective parameters has been discussed, including： temperature, hydrogen pressure and hydrogenation time, by gas phase hydrogenation. The results indicates that it can supply large hydride dissolution site increasing with hydrogen concentration after hydrogenation, as a results enhance the efficiently of grain refinement, it has the best efficiency under the hydrogen concentration about 1 wt％. TCT(thermochemical treatment) was developrd by Froes in 1990s and then renamed and modified as THP(thermohydrogen processing). It can be evaluated through the microstructure variation and enhance the mechanical processability of titanium alloys by grain refinement. The results indicates it mainly refine the α phase and its microstructure still maintain Widmanstatten structure after TCT procedure；the THP procedure can refine the β phase and its microstructure likes equi-axed α phase. For mechanical property, the hardness of THP procedure is higher than TCT procedure. Finally, we developed a cyclic thermohydrogen processing(CTHP) to refine the microstructure by different cycles of hydrogenation -dehydrogenation and significant improvement on mechanical properties of titanium alloys have been obtained. The results indicates it can enhance its mechanical property after a cyclic thermohydrogen processing increase with cycle times, but it can not have many cycles owing to many cracks.