CORROSION AND WEAR RESPONSE OF Cr–B COATED 316L AUSTENITIC STAINLESS STEEL

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Abstract
Results are presented of an investigation into the corrosion and abrasion response of 316L stainless steelwith and without a surface coating of chromium boride. The coatings were produced by unbalanced magnetron sputter deposition at a pressure of 5 mtorr. Full crystallisation of the coatings was suppressed by the very low homologous deposition temperature (about 0·2Tm). The exact Cr:B ratio was not determined and all coatings were found to be semicrystalline or amorphous; hence, they are referred to in this paper by the general formula Cr–B, rather than CrB. Anodic polarisation and simple abrasive wear testing indicated an improved performance for the Cr–B coated samples. However, under the severest corrosion immersion testing, carried out in 6%FeC13 at 50°C, the coated samples proved inferior to uncoated 316L. The passive nature of the Cr–B coatings resulted in preferential corrosion of the substrate (via galvanic action) which quickly undermined the integrity of the coating.Corrosion of the coating involved the formation of large pits developed by the growth of numerous near circular or Hertzian cracks. It is proposed that this phenomenon was triggered by the accumulation of corrosion deposits at the coating/substrate interface.

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