Improvement of strain tolerance of functionally graded TBCs through laser surface micro-texturing

Abstract

Atmospheric plasma-sprayed thermal barrier coating made up of YSZ and LaMgAl11O19/YSZ was plasma-sprayed over nickel-based superalloy. The coated surfaces are textured using a picosecond pulsed laser for different groove geometries. The scanning parameters were optimised to minimise the occurrences of re-cast layer and horizontal cracks. The textured samples were subjected to thermal shock cycles to study their thermal stability. The width-to-depth ratio (Wd) and the groove spacing between the adjacent texture were varied to analyse and correlate their geometrical influence in providing thermal stress–strain tolerance. The textured samples exhibit higher lifetime compared to the YSZ and LaMgAl11O19/YSZ as-sprayed surface. The induced thermal stress and minimal strain tolerance in the as-sprayed surfaces result in the traditional interface delamination failure where the failure occurs at the bond coat–ceramic layer interface. The textured grooves having higher Wd restrain the propagation of crack across the coating thickness and provide improved strain tolerance. The horizontal cracks initiated at the edge propagates across the textured layer chipped the groove segments within the ceramic bulk layer. The LaMgAl11O19/YSZ-based textured sample having Wd of 0.8 and 300 µm groove spacing exhibits higher lifetime of 219 thermal cycles. This implies the significance of groove density in improving the thermal shock resistance of TBCs.