Influence of solution treatment on microstructure and stress rupture properties of K439 nickel-base superalloy

  • Jin Xu State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi´an 710072, China
  • Mingjun Zhang Science and Technology on Advanced High Temperature Structure Materials Laboratory, Beijing Institute of Aeronautical Materials, Beijing 100095, China
  • Xin Tang Science and Technology on Advanced High Temperature Structure Materials Laboratory, Beijing Institute of Aeronautical Materials, Beijing 100095, China
  • Guangyu Yang State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi´an 710072, China
  • Jingyang Chen Science and Technology on Advanced High Temperature Structure Materials Laboratory, Beijing Institute of Aeronautical Materials, Beijing 100095, China
  • Qing Li Science and Technology on Advanced High Temperature Structure Materials Laboratory, Beijing Institute of Aeronautical Materials, Beijing 100095, China
  • Chengbo Xiao Science and Technology on Advanced High Temperature Structure Materials Laboratory, Beijing Institute of Aeronautical Materials, Beijing 100095, China
Keywords: K439; Solution treatment; Microstructure; Stress rupture properties

Abstract

The isochronal solution treatment (4h) in the 1080-1190°C range with air cooling are performed to investigate the effects of solution temperature on the microstructure and stress rupture properties of K439 alloy. The detailed as-cast and solution treated microstructures were analyzed through optical microscopy (OM), scanning electron microscopy (SEM) and differential scanning calorimeter (DSC). The experimental results show that the as-cast alloy exhibited a typical dendritic structure with five phases of γ, γ´, γ/γ´, η and MC. After solution heat treated at 1080°C, although all of the γ´ particles in the dendritic cores were dissolved, there were still some of these precipitates in the interdendritic regions beside η phase. With the solution temperature increasing to 1150°C, all of the γ´ and η solutioned and a uniform microstructure was observed. Furthermore, increasing the temperature to 1210°C, a small amount of incipient melting occurred in the alloy. The stress rupture life of K439 alloy at 760°C/530MPa increased with the rising of solution temperature and reached to the top value under the solution temperature of 1150°C. The optimum solution treatment considered to be 1150 C/4 h followed by air cooling.

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Published
2018-06-24
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ARTICLES