Defects producing formation of micro-cracks in aluminum during electrochemical charging with hydrogen

SIMS study of deuterium distribution in chemically charged aluminum containing oxide layer defects and trapping sites

“…This dissolution is slower in acid than in alkaline solutions [15]. On the metal-oxide interface in aluminum, atomic hydrogen combines to form molecular hydrogen in the porous hydroxide layer [33]. This process effectively coherences the interface and, as a result, surface film blistering (surface bubbles) is initiated.…”

“…8b and c) after electrochemical and chemical charging is negative, i.e., there is a contraction of the lattice. X-ray techniques (Laue, small angle X-ray scattering (SAXS) [14], small angle neutron scattering measurements (SANS) [13,32], transmission electron microscopy (TEM) [14] and scanning electron microscopy (SEM)), all showed the formation of defects (vacancies, voids, surface bubbles (blisters), volume bubbles and micro-cracks [33]) in plasma, gas, electrochemical and chemical hydrogen charged aluminum samples. The results suggest that the lattice expansion is much less in Al than in other FCC metals and intrinsic defect formations can take place in these kinds of materials.…”

Hemispherical bubbles growth on electrochemically charged aluminum with hydrogen

“…The depth of the volume defects was controlled by the charging process and depended on the charging time [11]. Hydrogen weakly entered the aluminum lattice interstitially [8,[11][12][13]. A small contraction, in the lattice parameter resulted when high hydrogen concentrations were introduced into the aluminum matrix [13].…”

“…The deuterium depth is controlled by the electrochemical charging conditions and the length of time of charging. The effective diffusivity parameter of the deuterium (hydrogen) depends on the interstitial and traps defects (vacancies, voids, dislocations and micro-cracks [12]) as well as on the hydroxide bubble formation and growth on the surface of the charged aluminum.…”

“…This hydrogen buildup is at a rate which is many times greater than that required for discharge at the surface or dissolution into the bulk of the metal during the aging process after electrochemical charging. The experiments [4,5,8,[11][12][13] reveal the existence of a significant distribution of hydrogen voids and bubbles on and under the surface, produced during electrochemical charging. The depth distributions of these defects are controlled by charging process and depend on the charging time and the internal traps in the aluminum matrix [11].…”