Studies of initial oxidation of nickel–chromium alloys: Surface annealing by hydrogen ion bombardment

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Abstract
Nickel-18% chromium binary alloy and alloy 600 (77% Ni, 16% Cr, 8% Fe) have been oxidized at 600 °C for periods of several minutes under O2 pressures of <10−6 to 10−4 Torr O2. The polycrystalline surfaces were pretreated by ion bombardment with 5 kV hydrogen ions. The oxide structure developed thereafter is found to be strongly influenced by grain orientation. One major grain orientation produced a chromium-rich surface oxide, while a second orientation gave rise to a surface oxide with a high nickel concentration. On some grain surfaces, a repetitive pattern of nodule oxide growth was observed with a structural pattern which is peculiar to a specific grain orientation. On surfaces remote from H+ bombarded areas, initial surface oxide composition is more governed by local stresses which develop along scratches. It is argued that alloy surface pretreatment with H+ anneals local mechanical stresses and allows substrate crystallographic orientation effects to become important.

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