Microstructure and Thermal Fatigue Mechanism of K403 Alloy High Pressure Guide-Vane

Author of the article:ZHOU Zhongbo1,2, YANG Mingbo1 , ZHANG Jianzhong2 , WEI Haobo1

Author's Workplace：1. Materials Science and Engineering College, Chongqing University of Technology, Chongqing 400054, China; 2. Chongqing Sannai Technology Co., Ltd., Chongqing 401135, China

Key Words：K403 alloy; high pressure guide-vane; thermal shock; microstructure; thermal fatigue crack

Abstract：To speed up the verification of the reliability of the K403 alloy high pressure guide vane manufactured by the new process, a thermal shock test was used to simulate the actual service environment of the blade. The microstructure of the blade before and after thermal shock and the initiation and propagation mechanism of thermal fatigue cracks were also analysed. The results show that the secondary dendrite spacing increases significantly, the γ-matrix becomes wider, and the γ′ phase content decreases from 53% to 45.1%. Fatigue cracks not only originate from the stress concentration part of the blade surface, but also form the source of cracks when the large carbides inside the blade body are ruptured due to the action of cold and heat cycles. The fatigue crack growth rate gradually slows down due to the release of thermal stress in the early stage of the thermal shock test, and the γ′ strengthening phase tends to decrease in the middle and late stages of the thermal shock test, which reduces the resistance to crack growth and accelerates the crack growth rate.