Effect of Vacuum Heat Treatment on the High-Temperature Oxidation Resistance of NiCrAlY Coating

Jiahui Zheng,Yang Gao,Deming Yang

doi:10.3390/coatings10111089

Abstract

NiCrAlY coatings were prepared using high-velocity oxygen fuel spraying (HVOF), and the coatings were removed from the substrate to achieve a uniform shape. Vacuum heat treatment (VHT) of the as-sprayed coatings was conducted at different temperatures (1000, 1100, and 1200 °C), and the specimens were subjected to isothermal oxidation exposure testing in air at 1100 °C for up to 21 h. The results show that the high temperature oxidation resistance of the coating increased gradually with the increase in VHT temperature, and the coating of VHT1200 had higher oxidation resistance. The high temperature oxidation resistance of the coating was related to the microstructure transformation of the coating. In VHT coatings, β-NiAl became a dispersed irregular block morphology. The γ’-Ni3Al in VHT1000 presented a granular morphology. However, in VHT1100 and VHT1200, γ’-Ni3Al became a lamellar morphology. This transformation of microstructure promotes the form of exclusive α-Al2O3 scale. With the increase in VHT temperature, the content of yttrium on coatings’ surface was increased and the pores were gradually eliminated. The concentration of yttrium on coatings’ surface prevented the formation of θ-Al2O3 and low porosity was beneficial in improving the internal oxidation of the coating.

Highlights

To improve the efficiency of aviation turbine engines, the hot components must endure an extreme environment, including high temperature and pressure
The β-NiAl became highly discrete, and its morphology changed as the Vacuum heat treatment (VHT) temperature increased (Figure 4b–d)
After VHT, some irregular block β-NiAl phases appeared in the coating (Figure 4c,d)

Summary

Introduction

To improve the efficiency of aviation turbine engines, the hot components must endure an extreme environment, including high temperature and pressure. An advanced thermal barrier coating technology is required. The thermal barrier coating consists of two parts: a ceramic thermal barrier coating and a bond coat. MCrAlY (M = Ni, Co, NiCo) coatings have been widely used as a bond coat for thermal barrier coatings or as a high-temperature protective coating alone [1,2,3,4,5,6,7,8]. The advantages of MCrAlY coatings have been researched by Saeidi et al [6]

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