Abstract

Directionally solidified (DS) nickel-based superalloys are widely used in manufacturing turbine blades, which may fail due to wear and/or material loss during service. Laser metal deposition (LMD) has been considered to be a promising technology in repairing the damaged components thanks to the high temperature gradient formed, which is conducive to the growth of directional microstructure. Intergranular liquation cracking in the heat-affected zone (HAZ) has been one of the major problems in LMD of the DS superalloys. In this paper, the influences of two cooling conditions (conventional cooling and forced cooling) on the microstructure development and liquation cracks were studied for the laser deposition of a DS superalloy IC10. The experimental results showed that, as compared to the conventional cooling, both number and length of the liquation cracks in HAZ were notably reduced under the forced cooling condition. The effects of cooling conditions on temperature and stress fields were analyzed through a thermo-elastoplastic finite element analysis. It was revealed that the maximum tensile stress and high tensile stress region in the substrate were effectively minimized while using the forced cooling measure. The forced cooling on the substrates is a promising method for mitigating the liquation cracking in LMD of DS superalloys.

Highlights

  • Solidified (DS) nickel-based superalloys have been widely employed in manufacturing the critical hot-section parts, such as blades in aeroengines and gas turbines with working temperatures higher than 1000 ◦ C

  • Cracks can be seen in both samples, which are located around the interface regions, deposition process

  • It can from be found from thecracks enlarged that are shown7 that these cracks extend across the interface bonding zones between substrates and deposits, and in Figure 7 that these cracks extend across the interface bonding zones between substratesalong and the grain and boundaries between the directional solidified columnar dendrites both substrates and deposits, along the grain boundaries between the directional solidified in columnar dendrites in deposits

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Summary

Introduction

Solidified (DS) nickel-based superalloys have been widely employed in manufacturing the critical hot-section parts, such as blades in aeroengines and gas turbines with working temperatures higher than 1000 ◦ C. Various defects, such as wear, cracks, and burn-through, may take place in these superalloy parts during service under the crucial working conditions (high temperature, high centrifugal force, and corrosion), which make the parts fail. Among various repairing processes for turbine blades, such as gas tungsten arc deposition, plasma arc deposition, etc., laser metal deposition (LMD) has been considered as a promising technology thanks to the more concentrated heat input, lower stress and distortion, high precision, and high flexibility in production. The ideal LMD microstructures of the deposits on the DS superalloys should be defect-free columnar grains that are directionally grown in the same crystallographic orientation

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