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ORIGINAL PAPER

Cyclic oxidation behavior of NiCoCrAlY/YSZ@Ni composite coatings fabricated by laser cladding Hai-zhong Zheng1,2 • Pei-feng Zhou2 • Gui-fa Li2 • Ping Peng3 Received: 17 August 2019 / Revised: 27 December 2019 / Accepted: 29 December 2019 / Published online: 6 October 2020 Ó China Iron and Steel Research Institute Group 2020

Abstract Composite coating on GH4169 alloy is prepared by laser cladding yttria-stabilized zirconia (YSZ)@Ni core–shell powders mixed with NiCoCrAlY alloy powders. The cyclic oxidation behavior of the coatings, especially the growth process of the oxide layer, is investigated based on experimental research and first-principle calculations. The results indicate that the oxidation resistance of coated GH4169 alloy is better than that of uncoated GH4169 alloy. The coating has three layers: a cellular dendrite outer layer, a planar YSZ interlayer, and an inner layer composed of Cr2O3 formed during laser cladding. After oxidation at 1000 and 1050 °C, as the oxidation time increases, the cellular dendrite outer layer becomes thicker, and the planar yttria-stabilized zirconia interlayer becomes thinner. Between the planar interlayer and Cr2O3 inner layer, an Al2O3 layer formed. Notably, cracks formed in the interface of Al2O3/Cr2O3 owing to their weak interface strength, which led to the failure of the composite coating. Keywords Laser cladding  NiCoCrAlY/YSZ@Ni composite coating  Cyclic oxidation  Oxidation mechanism  Crack nucleation

1 Introduction Yttria-stabilized zirconia (YSZ) is widely used in thermal barrier coatings (TBCs) owing to its low density (6.4 g/ cm3) and thermal expansion coefficient, which can reduce the working temperature of a turbine blade [1–6]. To improve their cohesive strength and reduce the difference in the thermal expansion coefficients between TBCs and matrix superalloys, bonding coatings that are mainly composed of NiCoCrAlY alloy are used [7, 8]. During the service of TBCs in a high-temperature environment, oxygen will permeate into TBCs and react with NiCoCrAlY alloy to form a thermal growth oxide (TGO, mainly composed of Al2O3) layer, which can induce the failure of & Hai-zhong Zheng [email protected] 1

School of Materials Science and Engineering, Beihang University, Beijing 100191, China

2

School of Material Science and Engineering, Nanchang Hangkong University, Nanchang 330063, Jiangxi, China

3

School of Material Science and Engineering, Hunan University, Changsha 410082, Hunan, China

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TBCs owing to the internal stress between two interfaces [9, 10]. In recent decades, considerable efforts have been devoted to slowing down the growth rate of TGO layers to relieve their internal stresses [11–13]. For example, in order to improve the high-temperature oxidation resistance of TBCs, researchers have used laser remelting technology to reprocess TBCs [11, 14]. Further, TBCs have a dense structure with less porosity and fewer oxygen diffusion channels, which greatly slows down the permeability of oxyge