Microstructure and Nanoindentation Evolution of (Ni,Pt)Al Coating on IC21 Substrate at 1100 °C

Abstract

In this study, a ~20 μm (Ni,Pt)Al coating was applied to an IC21 substrate via electroplating followed by aluminizing. A thermal exposure test at 1100 °C in air was used to investigate the microstructure evolution and nanoindentation behavior of samples with and without coating. The experimental results show that the (Ni,Pt)Al coating caused a phase change from β-(Ni,Pt)Al to Ni3Al, and the Topologically Close-Packed (TCP) phase at the interdiffusion zone grew larger after thermal exposure for 200 h at 1100 °C, while a layer of γ’ phase was formed on the surface of the IC21 substrate. The nanoindentation test indicated that the elastic modulus was reduced in both annealed samples (with and without coating), and after annealing the sample with coating had higher elastic modulus than the sample without coating. This result reveals that the coating effectively prevented the precipitation of refractory metal elements and the coarsening of the microstructure in the substrate, and thus shows that the coating had advantages not only in terms of improving the high-temperature oxidation properties of the substrate, but also played a significant role in improving the mechanical properties of the substrate.

Effect of Pt on Stress Rupture Properties of Pt-Modified Nickel Aluminide Coatings at 1100 °C

“…To study the effect of the coating thickness on the stress rupture properties of the PtAl-coated superalloy, it is worthwhile to estimate the impact on the stress rupture life of the substrate superalloy after depositing different PtAl coatings by the creep stress of each layer in the coatings. It was reported that Pt plays a major role in the superior high-temperature oxidation resistance of the PtAl coatings [2][3][4][5][6][7], but an increasing Pt content results in a significant stress rupture life decline of the PtAl-coated superalloys (Figure 3a) in this paper. The abnormal variation in the stress rupture properties among the specimens may result from the increasing coating thickness or the different ways of crack formation and propagation.…”

“…Pt-modified nickel aluminide (PtAl) coatings are widely applied to nickel-based superalloy components operating in hot sections of advanced gas turbine engines, owing to their excellent high-temperature oxidation resistance [1]. The superior oxidation resistance is mainly derived from the role of Pt in the coating, which promotes the formation and healing of protective alumina scales [2][3][4][5][6][7]. However, investigating the durability of PtAl coatings in complex service environments, such as the interactions of temperature, stress, and chemical field, based solely on the oxidation resistance of the coatings is still not sufficient.…”

“…In this paper, the effect of Pt on the stress rupture properties of the PtAl-coated superalloys under 1100 • C/100 MPa was investigated. An unexpected result was found that a coating with a high Pt content had worse stress rupture properties despite being thought to perform well in resisting oxidation [2][3][4][5][6][7]. To further understand the relationship between the composition of PtAl coatings and the high-temperature service performance of coated superalloys, a detailed study was carried out.…”