滲氫時間及化學添加劑對Ti-6Al-4V合金在1N H2SO4溶液中電解氫化作用之影響

The Influence of Charging Time and Chemical Additives on Electrolytic Hydrogenation of Ti-6Al-4V Alloy in 1N H2SO4 Solution

本研究探討Ti-6Al-4V合金在1N硫酸水溶液中施以陰極電流密度100 mA/cm2進行不同時間之電解滲氫效果。由定性X光繞射術（X-ray diffractometry; XRD）與定量輝光放電光譜術（glow discharge optical spectrometry; GDOS）分析結果得知，滲氫48小時後有較多之滲氫量及較深之氫分布，但就滲氫效率而言，以滲氫12小時最佳。感應耦合電漿質譜分析術（inductively coupled plasma-mass spectroscopy; ICP-MS）分析發現，滲氫前一階段（12小時）鋁元素（α-相）有較明顯之溶釋（dissolution）現象，此一現象肇因於滲氫作用使近表面層α-相中析出之氫化物體積逐漸擴大膨脹，最後剝落而溶於硫酸水溶液，也因此造成長時間之滲氫效率未隨滲氫時間增加而增加。為擴大滲氫效果，以12小時滲氫條件加入不同重量之滲氫促進劑（Na2S2O3‧5H2O）於電解液中，XRD與GDOS分析結果顯示添加0.5 g/L Na2S2O3‧5H2O產生明顯的促進作用，其滲氫效果更勝於無添加劑、滲氫48小時之製程。

Ti-6Al-4V sheet specimens were cathodically charged at a constant current density (100 mA/cm2) in 1N H2SO4 aqueous solution for various periods. Qualitative and quantitative analyses performed by employing XRD (X-ray diffractometry) and GDOS (glow discharge optical spectrometry) showed that the specimens hydrogenated for 48 hrs exhibit higher hydrogen uptake and deeper diffusion depth, however, those hydrogenated for 12 hrs exhibited the highest hydrogen uptake efficiency. Preferential dissolution of α phase for specimens processed less than 12 hrs were revealed by using ICP-MS (inductively coupled plasma-mass spectroscopy). Hydrides having precipitated in the α-phase at the near surface peeled off (due to volume expansion) into the electrolyte, and thus resulted in reduced HUE for specimens having experienced longer charging periods. In order to increase HUE, the hydrogenation promoter, Na2S2O3 ．5H2O, was added into the electrolyte to see the effect on the hydrogen absorption. It was found by XRD and GDOS that hydrogen uptake efficiency obtained at 100mA/cm2 for 12hrs with adding 0.5 g/L Na2S2O3 ．5H2O into the electrolyte was significantly increased over those processed for 48 hrs without adding the promoter.