Phase transition and pitting corrosion behaviour for Mo-implanted aluminium

Abstract

Molybdenum ions are implanted into aluminium with high ion flux and high dose at elevated temperatures of 200?C, 400?C and 500?C. Due to the high temperature and high flux of vacancies and interstitial atoms, the atom diffusion and chemical effects are enhanced during the ion implantation. The effects increase with increasing ion flux and dose, so that new phase formation and phase transition emerge noticeably. X-ray diffraction analysis shows that when the aluminium is implanted with Mo ions at a low ion flux (25?A/cm2), the Al5Mo alloy is formed. The atomic ratio of Mo/Al of the Al5Mo phase is close to 20%. When the aluminium is implanted with Mo ions at a high ion flux (50?A/cm2), the phase transition from Al5Mo to Al12Mo appears and the latter is dominant, which is determined to be the final phase. The ratio of Mo/Al in Al12Mo is 7.7%. Rutherford backscattering spectroscopy indicates also that the Mo/Al atom ratio is ~7% to ~8% in Mo-implanted aluminium. The atomic ratios of the constituents in Al5Mo and Al12Mo are of stoichiometric composition for these alloys. The thicknesses of the Al12Mo alloy layers for Mo-implanted Al with ion doses of 3?1017/cm2 and 1?1018/cm2 are 550nm and 2000nm, respectively. The pitting corrosion potential Vp increases obviously. It is clear that due to the formation of Al12Mo alloy layer, the pitting corrosion resistance is enhanced.