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

摘要

Aluminized and thermally oxidized superalloy 690 substrates forming Al _2O_3 layer on (NiCr)Al + Cr_5Al_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_2O _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_2O_3 along with NiAl and Cr _5Al_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.