Study On The Electrochemical Hydrogen Permeation Behavior Of B2 Phase FeAl

Al-containing intermetallic compounds have a wide range of application in the fields of aerospace,automobile industry,and thorium engineering system because of their outstanding oxidation resistance,corrosion resistance,sulfuration resistance,high specific strength,and melting point.Among them,iron aluminide(FeAl)are regarded as an alternative to stainless steel because of its low cost and low density.However,the hydrogen brittleness at room temperature causes extremely low plasticity which makes FeAl alloy difficult to shape and severely limits its application and development.Therefore,starting from the hydrogen embrittlement problem of FeAl alloy,this paper focuses on the permeation behavior of hydrogen in B2 phase FeAl prepared by powder metallurgy by using electrochemical methods at room temperature.Surface pretreatment of specimen,influence of hydrogen-charged current on FeAl alloy hydrogen permeation and the permeation kinetics of hydrogen were obtained systematically in this work.The results of the study laid the foundation for the hydrogen embrittlement of intermetallic compounds,and it is significance to improve the theory of hydrogen damage of metallic materials.Mainly get the following conclusions:(1)Compared with FeAl alloy prepared by introduction melting method,the B2 phase FeAl alloy prepared by powder metallurgy has more dense structure,showing less impurities,small holes and features,and the phenomenon of segregation appears in microstructure.The black and white substructure of B2 phase FeAl alloy in microstructure is similar to that of pearlite because of the tendency of Al to accumulate together in high temperature and pressure environment.At the same time,the substructure makes the grain growth greater.(2)The surface of the FeAl alloy was plated with Pd film by chemical plating and electroplating.Long or short time of chemical plating will make the electroplating coating irregular growth,30min is ideal chemical plating time.In the subsequent electroplating,excessive current density results in excessively high growth rate,and holes or cracks are likely to appear on the surface of the Pd film,while small current density results in a slower growth rate,resulting in a loose film surface and low coverage.A flat,dense and non-porous Pd film was obtained with a density of 5 mA/cm2.(3)The hydrogen permeation behavior of FeAl alloy at room temperature was obtained by electrochemical method.At 293±2K,the hydrogen permeation flux of hydrogen,hydrogen diffusion coefficient and hydrogen solubility increase with the hydrogen charging current.At a current density of 0.318 A/cm2,the effective diffusion coefficient and solubility of hydrogen in B2 phase FeAl alloy are 1.610 × 10-bcm2/s and 9.898x 10-6mol/cm3,consistent with the literature report results.(4)The kinetics of hydrogen permeation in FeAl alloy was obtained with the IPZ kinetic model.The adsorption rate constant of hydrogen on FeAl surface was 7.939×10-10 mol·cm-3·s-1,and the desorption rate constant of hydrogen was 3.043×10-7 mol·cm-3·s-1.The rate constant of the desorption is much greater than the rate constant of the adsorption,which indicates that the adsorption of hydrogen on FeAl surface is slow.Most of H at the hydrogen-charged surface is bound by H2,very small amount of H can penetrate in the FeAl alloy.