Thermal shock resistance of thermal barrier coatings modified by selective laser remelting and alloying techniques

Abstract

Aiming to improve the thermal shock resistance of thermal barrier coatings (TBCs), the plasma-sprayed 7YSZ TBCs were modified by selective laser remelting and selective laser alloying, respectively, in this study. A self-healing agent TiAl 3 was introduced into the 7YSZ TBCs by selective laser alloying to fill cracks during thermal cycling. The thermal shock experiments of the plasma-sprayed, laser-remelted, and laser-alloyed TBCs were conducted by a means of heating and water-quenching method. Results revealed that some segmented microcracks were distributed on the surface of the laser-remelted and the laser-alloyed zones, showing a dense columnar crystal structure. After thermal shock tests, the numbers of segmented microcracks on the laser-remelted coating increased, whereas, in the laser-alloyed condition, some irregular particles formed, leading to the decreased numbers of segmented microcracks. The laser-alloyed coating exhibited the best thermal shock resistance, followed by the laser-remelted condition, with the thermal shock lifetime 3.3 and 2.7 times higher than that of the as-sprayed coating, respectively. On the one hand, both columnar grains and segmented microcracks in the laser-treated zone could effectively improve the strain tolerance of coatings. On the other hand, the oxidation products of TiAl 3 under high-temperature condition could seal the microcracks to postpone the crack connection. Thus, the thermal shock resistance of the laser-treated coatings was significantly improved.

Role of nano‐zones in enhancing the performance of YSZ coatings under thermal shock conditions

“…28,29 During thermal shock conditions, the strain mismatch between the topcoat and substrate induces significant stress, although the magnitude is generally lower than the residual stress in the TGO layer. [30][31][32] In such conditions, the limited dwell time at high temperatures restricts TGO growth, making the primary mechanism of coating damage the CTE mismatch transmitted to the topcoat. Additionally, other sources of coating damage include hot corrosion, calcium-magnesium-alumino-silicate (CMAS) damage, foreign object damage, and others.…”

Effect of material parameters on thermal shock crack of ceramics calculated by phase‐field method

“…Ceramics are extensively used in the aerospace industry instead of metals because of their excellent hightemperature properties. [1][2][3][4] However, due to the brittleness of ceramics, it is easy to fail due to thermal shock when the ambient temperature changes sharply, which is the inherent disadvantage of ceramic materials. 3,4 Due to the complexity of the multi-field coupling fracture in thermal shock, the simulation analysis of fractureinduced failure plays an important role in designing materials or structures.…”

“…[1][2][3][4] However, due to the brittleness of ceramics, it is easy to fail due to thermal shock when the ambient temperature changes sharply, which is the inherent disadvantage of ceramic materials. 3,4 Due to the complexity of the multi-field coupling fracture in thermal shock, the simulation analysis of fractureinduced failure plays an important role in designing materials or structures. In recent 10 years, there have been some theoretical models to study thermal shock crack initiation and propagation of ceramics, including phase-field, 5-10 meso-damage, 11,12 energy minimization, 13 nonlocal failure, 14 bond-based peridynamic, 15 and gradient damage.…”

“…Ceramics are extensively used in the aerospace industry instead of metals because of their excellent high‐temperature properties 1–4 . However, due to the brittleness of ceramics, it is easy to fail due to thermal shock when the ambient temperature changes sharply, which is the inherent disadvantage of ceramic materials 3,4 …”