Thermal charging effects of Hydrogen in Copper and CuAl alloys

Abstract

Thermal charging of hydrogen into copper at 1000°C followed by a rapid quench produces hardening and a slight decrease in the positron Doppler peak parameter P relative to control samples. Deformation of copper after thermal charging of hydrogen produces an extra hardness increase relative to argon as well as an increase in P. In Cu4Al alloy (actual composition, 3.69 wt.% Al and balance copper), thermal charging of hydrogen followed by deformation produces only one-third of the hardness increase produced by thermal charging alone. A slight increase in P is found in the alloy in both deformed and undeformed regions of charged samples. For copper it takes 3 h at 1000°C in hydrogen to observe fully the decrease in P and 4 h in ambient temperature air for the decrease in P to recover. In the Cu4Al alloy, proton pinning of stacking faults results in very effective hardening of annealed material but the protons in this case are not very effective in screening the defects from positrons, presumably because of the low probability of positron trapping close to a proton site in a widely extended fault. In copper, however, protons can quite effectively screen dislocations from detection by positrons. This provides a very effective way of studying hydrogen-defect interactions and hydrogen egress from dislocation traps.