Cracking, Microstructure and Tribological Properties of Laser Formed and Remelted K417G Ni-Based Superalloy

Shuai Liu,Jinguo Li,Changsheng Liu,Xue Zhang,Suiyuan Chen,Haixin Yu,Yang Wang

doi:10.3390/coatings9020071

Shuai Liu, Jinguo Li + Show 5 more

Open Access

https://doi.org/10.3390/coatings9020071

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Journal: Coatings	Publication Date: Jan 24, 2019
Citations: 8	License type: CC BY 4.0

Affiliation: Northeastern University, Chinese Academy of Sciences

Abstract

The K417G Ni-based superalloy is widely used in aeroengine turbine blades for its excellent properties. However, the turbine blade root with fir tree geometry experiences early failure frequently, because of the wear problems occurring in the working process. Laser forming repairing (LFR) is a promising technique to repair these damaged blades. Unfortunately, the laser formed Ni-based superalloys with high content of (Al + Ti) have a high cracking sensitivity. In this paper, the crack characterization of the laser forming repaired (LFRed) K417G—the microstructure, microhardness, and tribological properties of the coating before and after laser remelting—is presented. The results show that the microstructure of as-deposited K417G consists of γ phase, γ′ precipitated phase, γ + γ′ eutectic, and carbide. Cracking mechanisms including solidification cracking, liquation cracking, and ductility dip cracking are proposed based on the composition of K417G and processing characteristics to explain the cracking behavior of the K417G superalloy during LFR. After laser remelting, the microstructure of the coating was refined, and the microhardness and tribological properties was improved. Laser remelting can decrease the size of the cracks in the LFRed K417G, but not the number of cracks. Therefore, laser remelting can be applied as an effective method for strengthening coatings and as an auxiliary method for controlling cracking.

Highlights

Because of the objective reality of enhancing aeroengine performance, blades must work in an environment of high temperature, overloading, and high frequency vibration [1]
The results indicate that Ti and Mo elements are significantly segregated between the dendrites, while Cr and Co are evenly distributed in the dendrites
The K417G Ni-based superalloy has been prepared on as-cast K417G substrate by the Laser forming repairing (LFR) process

Summary

Introduction

Because of the objective reality of enhancing aeroengine performance, blades must work in an environment of high temperature, overloading, and high frequency vibration [1]. The Ni-based superalloy K417G containing a high content of Al + Ti (>7.0 wt.%) is widely used in aeroengine turbine blades for its excellent high-temperature properties and relatively low fabricating cost [2,3,4,5]. The turbine blade root with fir tree geometry experiences early failure frequently, because of the wear problems occurring in the working process [1]. From an efficiency and economic point of view, it is more appealing and significant to repair the defected or damaged blades instead of replacing them with new ones. It can be applied to form a repaired coating that recovers complex or various defected parts up to certain degree and to form a metallurgical bond between substrate and coating, without degrading the inherent service properties of the parts [6,7,8]

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Results

Conclusion