Effects of Withdrawal Rate on the Microstructure of Directionally Solidified GH4720Li Superalloys.

Jinglong Qu,Anping Dong,Yu Gu,Zhengyang Chen,Jingshe Li,Shufeng Yang

doi:10.3390/ma12050771

Abstract

Increasing the ingot size of GH4720Li superalloys makes it difficult to control their microstructure, and the withdrawal rate is an important factor in controlling and refining the microstructure of GH4720Li superalloys. In this study, GH4720Li superalloy samples were prepared via Bridgman-type directional solidification with different withdrawal rates. The morphology and average size of the dendrites in the stable growth zone during directional solidification in each sample, morphology and average size of the γ’ phases, and microsegregation of each alloying element were analyzed using optical microscopy, Photoshop, Image Pro Plus, field emission scanning electron microscopy, and electron probe microanalysis. Increasing the withdrawal rate significantly helped in refining the superalloy microstructure; the average secondary dendrite arm spacing decreased from 133 to 79 µm, whereas the average sizes of the γ’ phases in the dendrite arms and the interdendritic regions decreased from 1.02 and 2.15 µm to 0.69 and 1.26 µm, respectively. Moreover, the γ’ phase distribution became more uniform. The microsegregation of Al, Ti, Cr, and Co decreased with the increase in the withdrawal rate; the segregation coefficients of Al, Cr, and Co approached 1 at higher withdrawal rates, whereas that of Ti remained above 2.2 at all the withdrawal rates.

Highlights

Superalloys exhibit outstanding high-temperature strength and resistance to oxidation, fatigue, and creep [1,2,3] and are key materials in the construction of high-temperature structural components in the aerospace sector
As GH4720Li superalloys are highly alloyed, increasing the ingot size makes it difficult to control their microstructure; this poses a significant threat to the safety and reliability of the superalloy [9,10]
Our findings provide a theoretical foundation for the selection of process parameters to enhance the microstructure of GH4720Li superalloys

Summary

Introduction

Superalloys exhibit outstanding high-temperature strength and resistance to oxidation, fatigue, and creep [1,2,3] and are key materials in the construction of high-temperature structural components in the aerospace sector. The GH4720Li superalloy is a new nickel-based age-hardened superalloy derived from the Udimet 720 superalloy [4,5]. As GH4720Li superalloys are highly alloyed, increasing the ingot size makes it difficult to control their microstructure; this poses a significant threat to the safety and reliability of the superalloy [9,10]. To address this issue, some researchers have studied and manipulated

Methods

Results

Conclusion