Effect of Surface Condition and Microstructure on Hydrogen Uptake in Metastable β Titanium Alloys
The use of hydrogen as a temporary alloying element within the heat treatment (Thermo-HydrogenProcessing) requires reliable information about hydrogen diffusion and hydrogen equilibrium solubility. The basic idea of THP is to utilize the stabilizing effect of hydrogen on the bcc β-phase in order to enhance mechanical properties by means of microstructure modification. Therefore, well-defined hydrogen concentrations have to be established in order to achieve designated transition temperatures. In the framework of THPstudies on metastable β-titanium alloys Ti 38-644 and Ti 10-2-3,the hydrogen uptake kinetics and equilibrium concentrations were determined experimentally by means of volumetric measurements. The results indicate clearly that within the hydrogenation temperature range applied the hydrogen uptake is affected or even controlled by the surface reaction especially at the lower temperatures. Therefore,samples were coated electrochemically with thin Pd-or PdNi-layers promoting hydrogen uptake by a catalytic effect on the hydrogen dissociation. The degree of acceleration of hydrogen uptake was shown by a comparison with the behavior of samples with uncoated surfaces and further by calculating the rate of diffusion-controlled hydrogen uptake by means of FEM-analyses. Accurate values of the hydrogen diffusion coefficient were obtained by analyzing hydrogen concentration profiles of annealed samples in which a hydrogen concentration step profile was established using electrochemical charging prior to diffusion annealing. In order to study microstructure effects on hydrogen diffusion systematically, samples were heattreated differently prior to hydrogenation. The results of the electrochemical charging experiments revealed that hydrogen diffusion is essentially affected by the existence and morphology of the or phase, whereas hydrogen diffusion in pure βmicrostructures seems to be nearly unaffected by β-grain size,chemical composition and residual deformation structures of the particular β-titanium alloy.
Thermohydrogen processing beta titanium alloys Sievert s law hydrogen absorption hydrogen diffusion coefficient
Peter Schmidt Hans-Jürgen Christ
Institut fur Werkstof ftechnik,Universit(a)t Siegen,57068 Siegen,Germany
国际会议
The 12th World Conference Titanium(第十二届世界钛会 Ti-2011)
北京
英文
508-513
2011-06-19（万方平台首次上网日期，不代表论文的发表时间）