EFFECTS OF STRAIN CYCLING ON BUCKLING, CRACKING AND SPALLING OF A THERMALLY GROWN ALUMINA ON A NICKEL-BASED BOND COAT

摘要

Strain cycling has been used to studyvarious events that occur in association with analumina　 thin layer thermally grown on a Ni-based bondcoat. There are three main findings. (i) Bucklespropagate　 with a growth per cycle suggestive ofeffects of cycling on the friction acting at theseparated interfaces. (ii)　 Cracking of the thermallygrown oxide (TGO) occurs within buckles having highellipticity, subject to a　 flexural strength typicalof fine-grained Al2O3, with small stressed volume.Such cracking has implications　 for oxygen ingress andrapid degradation. (iii) Spalling occurspreferentially in those buckles that previously crack.The measurements are analyzed using the mechanics ofbuckle propagation, bending and　 kinking.