Tair-I Wu

Use of thiourea to inhibit the incorporation of hydrogen in Ti and Ti-6Al-4V alloy

Commercially pure titanium and a Ti-6Al-4V alloy covered with a thin thermal oxide film derived from hot rolling were electrolytically hydrogenated in 1N aqueous sulfuric acid solution (H2SO4(aq)) to see the influence of thiourea (H2N-CS-NH2) on the hydrogen uptake of both metals under atmospheric conditions. The inhibitive effect of thiourea was evaluated through quantitative composition analyses (by using a glow discharge spectrometer, GDS) and qualitative microstructural examinations (by using XRD). Thiourea acts as a hydrogenation inhibitor irrespective of the applied current densities. However, the inhibitive effect is more evident at lower charging current densities for longer operating periods.

Effect of sodium sulfide on hydrogen absorption of Ti-6% Al-4% V alloy

Abstract The hydrogenation inhibitive effect of sodium sulfide (Na2S) on Ti-6% Al-4% V alloy (UNS R56400) in aqueous sulfuric acid solution (H2SO4[aq]) was investigated qualitatively and quantitatively using optical microscopy, x-ray diffraction (XRD), and glow-discharge spectrometry (GDS). Introduction of Na2S into the electrolyte resulted in an obvious inhibitive effect of hydrogen absorption on as-received (covered with a thin thermal oxide film < 0.5 μm) and abraded specimens (free of thermal oxide film) irrespective of applied current density and operating period. The contrary effect of Na2S on Ti-6% Al-4% V alloy vs ferrous alloys could have resulted from the fact that molecular hydrogen sulfide (H2S), which adsorbed on the titanium surface as on the iron surface, facilitated formation of a thin layer of E titanium hydride (TiH2). TiH2 effectively retarded ingress of hydrogen.

Study of the Behavior of Titanium Alloys as the Cathode for Photovoltaic Hydrogen Production

CP-Ti and Ti-153 were adopted in this study to observe their electrochemical behavior in serving as the cathode for photovoltaic hydrogen production. The designed cyclic hydrogenation-solution heat treating processes were performed to increase the hydrogen uptake for both alloys. The results are as follows. (1) Both arsenic trioxide and thiourea showed hydrogenation promotive effect on CP-Ti, while thiourea was an inhibitor for Ti-153 under the applied conditions. (2) Arsenic trioxide showed hydrogenation promotive effect on both Ti-153 and CP-Ti in this study. (3) Ti-153 demonstrated superiority to CP-Ti when serves as the cathode for photovoltaic hydrogen production. The hydrogen mass payload for Ti-153 is 68 times larger than that for CP-Ti.

Interdiffusion Coefficients of Fe and Si Measured from Si/IF Steel Coating System

We adopted sputtering techniques to produce Si thin films on IF (interstitial free) steel sheets in this study to obtain diffusivity of O and interdiffusion coefficients of Si and Fe in sputtered Si film. The microstructure of the coating system was analyzed by using XRD (X-ray diffractometry) and Raman spectroscopy. The compositional variations and the phase transformation within the diffusion zone at the end of diffusion annealing were inspected by employing GDOS (glow discharge optical spectrometry) and XPS (X-ray photoelectron spectroscopy). The diffusivities of Fe and Si for the Si-Fe diffusion couple calculated based on the Boltzmann-Matano method and the depth profiles from GDOS were found to vary from 2.40×10−15 to 4.24×10−14 cm2/s and 5.77×10−15 to 6.59×10−14 cm2/s, respectively. The diffusivity of O in the Si thin film, 2.19×10−14 cm2/s, was however obtained by employing Grube method. Low diffusivities of O and Fe within the Si film are the reason why sputtered Si film is suitable to serve as an anti-oxidation barrier for the IF substrate at 400°C.

Surface Hardening of Ti-15V-3Al-3Cr-3Sn Alloy after Cyclic Hydrogenation and Subsequent Solution Treatment

The as-received and preheated (1000°C-30 min. and 500°C-30 min.) sheets of Ti-15V-3Al-3Cr-3Sn alloy (Ti-153) were treated according to the predetermined process including a cyclic electrolytic hydrogenation (at 50 mA/cm2 for 1 hr and at 5 mA/cm2 for 10 hrs) combining a subsequent solution treatment to see the effects of various operating parameters on the evolution of microstructure and the variations of hardness. The hardening effect deriving from solid-solution strengthening of hydrogen eventually overrode that from precipitation hardening. The maximum hardness elevation was from 236.9 to 491.1 VHN.

Electrolytic hydrogenation technique: New approach for the modification of Ti-film mechanical properties and MEMS applications

This study reports a novel low temperature electrolytic hydrogenation technique to modify mechanical properties of metal films. To demonstrate the feasibility of this approach, various current densities and cathodic charging periods of electrolytic hydrogenation processes were implemented to modify the mechanical properties of Ti-film. Preliminary results demonstrate the feasibility of modulating the Youngs modulus, residual stress, and hardness, of Ti-film. Note: the electrolytic hydrogenation technique can be applied for other metal films. Since electrolytic hydrogenation process is simple and low temperature, it is a promising approach to modulate mechanical characteristics of MEMS structures.