THE EFFECT OF DIFFERENT SURFACE TREATMENTS ON THE MOLTEN-SALT HOT CORROSION OF IN-657 SUPERALLOY

The influence of different surface treatments (laser surface treatment , silicon nitride, and 25 wt.% Al-2(OH)(4)Si2O5-75 wl.% Na2SiO3), on t he hot corrosion behaviour of IN-657 superalloy has been studied. The corrosion tests were performed in an oxidizing atmosphere in contact w ith a molten mixture of 82% K2S2O7-18% V2O5. The effects of operation temperature and carbon residues as component of the molten mixture wer e also analyzed. The best results were obtained for the kaolin and met hasilicate mixture coating. Laser surface treatment and the CVD-silico n nitride are not recommended for surface modification of the IN-657 s uperalloy. Taking into account the results obtained, the authors sugge st the average temperature and molten salt compositions where the abov e coating can work satisfactorily.