Ex-situ observation on the dissolution behaviour of Ni-16Cr-15Mo and Ni-30Co-16Cr-15Mo alloys in hydrofluoric acid

Ex-situ observation by laser microscopy was used to investigate the effect of plastic deformation induced by a micro-hardness tester on the corrosion resistance of both Ni-16Cr-15Mo-6Fe-0.5Si (NiCrMo) and Ni-30Co-16Cr-15Mo-6Fe-0.5Si (NiCoCrMo) alloys during immersion in hydrofluoric acid. This found that although the indentation in NiCrMo became slightly deeper and broader following immersion, this effect was far more pronounced with NiCoCrMo. Growth observed in the size of voids is attributed to preferential dissolution of SiO2 particles, as well as an accumulation of dislocations and other defects around them, with these defects also playing a key role in the subsequent coalescence of voids on the sample surface.