Abstract: The effect of long-term ageing on degradation of tensile properties and mechanism of a directionally-solidification superalloy DZ409 were studied, to simulate servicing of heavy industrial gas turbine blades during the long-term aged at 900℃ and 980℃. The results show that the spherical secondary γ' phase dissolves rapidly, the cubic γ' phase becomes smooth, and some γ' phases merge at 900℃ and 980℃. γ' phase coarsened continuously during long-term ageing, and the coarsening rate at 980℃ was much higher than that at 900℃. The MC carbides gradually transform into M₂₃C₆ and γ' phases. At 900℃ to 1000h and 980℃ to 100h, M₂₃C₆ began to precipitate at the MC/γ' interface. When (γ+γ') eutectic structure coexists with MC, M₂₃C₆ particles are gradually precipitated. No TCP phase was found after aged at 900℃/20000h and 980℃/3000h. Both the yield and tensile strength of the alloy at RT, 650℃ and 900℃ can be divided into three stages after aged at 900℃. The first stage (0~100/200h) has a rapid decline in strength, mainly due to the rapid dissolution of the spherical secondary γ' phase. In the second stage (100/200~2000h), the decline rate of the strength continued to slow down, mainly due to the coarsening of the γ' phase and the decrease of the cubic degree of the γ' phase, which led to the decrease of the mismatch of γ/γ', and the decomposition of MC carbide began. In the third stage (2500~8000h), the strength tends to be stable, which is because of the negative effect of continuous coarsening and merging of γ' phase on the deformation resistance of the alloy. The positive effect of M₂₃C₆ carbide formation on the pinning of dislocation and the inhibition of grain boundary slip makes the tensile properties of the alloy stable. Compared with the long-term aged at 900℃, the damage regularity of microstructure evolution and tensile properties of the alloy after 980℃ ageing is similar, but the change rate is faster.

Keywords: Long-term ageing, property degradation, directionally solidified superalloy DZ409, microstructure evolution.

Biography: Prof. Lei Wang currently is a Distinguished Professor of Northeastern University, specialized in materials science and engineering. He obtained BEng in 1982 and MEng in 1985 from Northeastern University, China, PhD in 1997 from Toyohashi University of Technology, Japan. He has taught at 3 national universities for more than six years as a senior lecturer, an associate professor and a deputy professor in Japan. He has been the Director of Institute of Advanced Material Technology, Northeastern University, Vice President of Heat Treatment Society of China, an executive committee member of Materials Branch of Chinese Society of Mechanical Engineering, a visiting professor of IMR at Tohoku University, Japan. He has been selected as a Taishan Industry Leading Leader in 2018, a special government allowances of the State Council (China) in 2020. Prof. Wang’s research is focused on the strengthening and toughening of advanced materials with microstructural controlling. He also has many research achievements in the field of mechanical behavior of materials under dynamic loading and other environments. He has published more than 430 scientific papers and 12 books.