Thermal‐cycle dependent residual stress within the crack‐susceptible zone in thermal barrier coating system

Abstract

Nondestructive and accurate measurement of residual stress in ceramic coatings is challenging, but it is crucial to the assessment of coatings failure and life. In this study, for the first time, the thermal‐cycle dependent residual stress in an atmosphere plasma sprayed thermal barrier coating system has been nondestructively and accurately measured using photoluminescence piezo‐spectroscopy. Each thermal cycle consists of a 5‐minute heating held at 1150°C and a 3‐minute water quenching. The measurement was performed within a crack‐susceptible zone in the yttria‐stabilized‐zirconia (YSZ) top coat (TC) closely above the thermally grown oxide layer. A YSZ:Eu3+ sublayer was embedded in TC as a stress sensor. It was found that the initial residual stress was compressive, with a mean value of 240 MPa, which rapidly increased to 395 MPa after 5 thermal cycles (12.5% life) and then increased gradually to the peak of 473 MPa after 25 thermal cycles (62.5% life). After 30 thermal cycles (75% life), the mean stress dropped abruptly to 310 MPa and became highly heterogeneous, with gradual reduction toward final spallation. The heterogeneous stress distribution indicates that many microcracks nucleated at different locations and the spallation occurred due to the coalescence of the microcracks.

Nondestructive measurements of residual stress in air plasma‐sprayed thermal barrier coatings

“…The objective magnitude was selected to be 10 × to ensure a laser beam spot size much larger than the grain size of TGO. 41 The laser was focused on the TBCs sample surface, and the previous study 39 confirmed an insignificant influence of the depth of focus. An in-plane area of 3 mm × 3 mm was measured point-by-point by moving the focused laser beam to generate a residual stress map.…”

“…For APS TBCs, other ions, such as Eu 3+ , was introduced into the ceramic TC as a sublayer-stress sensor. 41 However, the correlations between TGO morphology, residual stress, critical microcracks near interface and resultant delamination have not been revealed thus far, significantly limiting the further application of the PLPS method to APS TBCs. In this work, delamination in APS TBCs is indicated by measuring the TGO residual stress.…”

Crack Propagation and Effect of Mixed Oxides on TGO Growth in Thick La–Gd–YSZ Thermal Barrier Coating

“…The TBC of APS-BC for 1200 and 1300 • C failed between 10 and 300 h (C2, C3, C4, C6, C7 and C8). The TC spall off within the TC slightly above the TGO layer, which is called the crack-susceptible zone (CSZ) [44]. The spallation of TC occurred away from the TC/BC interface, within the ceramic layer and not exactly at the interface region.…”

“…The CSZ are identified as weak locations for the TBCs and failures tend to occur at this zone during real service conditions [44]. The failure mechanism of TBCs with APS-BC comes from two distinct angles: (1) TGO growth and (2) TC thickness.…”

High efficiency hierarchical porous composite microfiltration membrane for high-temperature particulate matter capturing

“…Control of material nanostructure is an effective approach to modify material properties [27][28][29] . The introduction of Nano-ZrO 2 in the high Nb-TiAl system provides a potential solution for hightemperature application because of its high melting point (2700°C), low coefficient of thermal expansion, and good creep resistance 30,31 . More specifically, a micro-scale porous microstructure was constructed by controlling self-diffusion and mutual diffusion of Ti, Al, Nb powders below 900°C, followed by building nano-scale pores on the inner surface of cell walls through chemical reaction between the porous support material and the Nano-ZrO 2 particles at 900-1350°C.…”