Formation of diffusion barrier coating on superalloy 690 substrate and its stability in borosilicate melt at elevated temperature

Abstract Aluminized and thermally oxidized superalloy 690 substrates forming Al 2 O 3 layer on (NiCr)Al + Cr 5 Al 8 types aluminides and bare substrates were exposed in sodium borosilicate melt at 1248 K for 192 h. SEM–EDXS analysis along the cross-section of bare substrate with adhered glass revealed formation of a continuous, thick Cr 2 O 3 layer at the substrate/glass interface due to its low solubility in borosilicate melt. XRD on aluminide coated and thermally oxidized specimen revealed existence of Al 2 O 3 along with NiAl and Cr 5 Al 8 type phases after the exposure in borosilicate melt. SEM–EDXS analysis along the cross-section of aluminide coated and thermally oxidized sample with adhered glass indicated good stability of coating in borosilicate melt without any phase formation at the coating/glass interface. However, some Al enrichment in glass phase adjacent to interface was noticed without any significant Ni or Cr enrichment.