Influence of Cooling Scenarios on the Evolution of Microstructures in Nickel-Based Single Crystal Superalloys

Zhengxing Feng,Zhixun Wen,Yanchao Zhao,Guangxian Lu

doi:10.3390/cryst12010074

Abstract

The reprecipitation and evolution of γ’ precipitates during various cooling approaches from supersolvus temperature are studied experimentally and via phase field simulation in nickel-based single crystal superalloys. The focus of this paper is to explore the influence of cooling methods on the evolution of the morphology and the distribution of γ’ precipitates. It is demonstrated that small and uniform spherical shape γ’ particles formed with air cooling method. When the average cooling rate decreases, the particle number decreases while the average matrix and precipitate channel widths increase. The shape of γ’ precipitates which changed from spherical to cubic and irregular characteristics due to the elastic interaction and elements diffusion are observed with the decrease of the average cooling rate. The phase field simulation results are in good agreement with the experimental results in this paper. The research is a benefit for the study of the rejuvenation heat treatment in re-service nickel-based superalloys.

Highlights

Scenarios on the Evolution ofAs an important high-temperature structural material, nickel-based single crystal superalloys have excellent high-temperature mechanical properties and are widely used as turbine blade materials for modern aviation gas turbine engines [1]
The results demonstrated that bimodal particle distribution can be achieved at an intermediate cooling rate due to the coupling between diffusion and undercooling
In order to simulate the evolution of the precipitates for different cooling scenarios, the same concentration and order parameters are introduced for the initial conditions

Summary

Introduction

As an important high-temperature structural material, nickel-based single crystal superalloys have excellent high-temperature mechanical properties and are widely used as turbine blade materials for modern aviation gas turbine engines [1]. The excellent mechanical properties of this kind of single crystal superalloys mainly come from the precipitation strengthening effect of the γ’ precipitates in the microstructure composed of the L12 type Ni3 Al phase (γ’ precipitates) and the fcc Ni-rich phase (γ matrix). Precipitates, such as shape, size, volume fraction and spatial arrangement, play an extremely important role in the mechanical properties of nickel-based single crystal superalloys during application [2,3,4,5]. The dissolution and reprecipitation of the γ’ precipitates will always accompany the heat treatment process. By optimizing the process parameters in the heat treatment process, the mechanical properties of the material can be improved. It is very necessary to study the precipitation kinetics of the γ’

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Discussion

Conclusion