The H up-take capacity and mobility in ultra-high strength Aermet 100 were characterized for various electrochemical charging and baking conditions. Using thermal desorption spectroscopy, the apparent H diffusivity (DH < 3 x 10-8cm2/s at 23C) was found to be more than ten times less than the values which were typical of tempered martensitic steels such as AISI4130. The value of DH decreased with decreasing temperature below 200C; with a relatively high apparent activation energy for diffusion (17.7 to 18.8kJ/mol) at the 95% confidence level. The value of DH also decreased with a decreasing diffusible H concentration which arose from less-severe charging or increased baking. Potentiostatic charging in saturated Ca(OH)2 produced total and diffusible H concentrations which increased with the (H+/H) over-potential and were significantly higher than the results for AISI4130 steel under the same conditions. A significant H concentration was produced by zero over-potential deposition. These characteristics were explained by an extensive reversible and irreversible H trapping which involved at least 3 unique trap states in the ultrafine microstructure. The former probably included coherent M2C carbides, soluble Ni, or precipitated austenite. Baking at 23 and 200C removed H from the lowest binding-energy sites.

R.L.S.Thomas, D.Li, R.P.Gangloff, J.R.Scully: Metallurgical and Materials Transactions A, 2002, 32[7], 1991-2004