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Microstructural evolution in damaged IN738LC alloy during various steps of rejuvenation heat treatments

Hosseini, S. S ; Sharif University of Technology | 2012

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  1. Type of Document: Article
  2. DOI: 10.1016/j.jallcom.2011.09.094
  3. Publisher: 2012
  4. Abstract:
  5. IN738LC is one of the superior nickel base superalloys utilized at high temperatures in aggressive environments. However, experiencing high temperatures and stresses during service causes microstructure deterioration and degradation of mechanical properties in this alloy. To restore the microstructure and mechanical properties of the degraded alloy, rejuvenation heat treatments can be considered. In this study, the evolution of microstructural features in a creep damaged IN738LC superalloy during different stages of rejuvenation heat treatment cycles was investigated. During solution treatment stage, dissolution of coarsened γ′ precipitates, grain boundary films and transition zone around primary MC carbides took place. Solution treatment at high temperature led to lower volume fraction and smaller size of remnant γ′ precipitates and further dissolution of grain boundary films and caused MC carbides to be remained without the surrounding transition zone. In addition, fine γ′ precipitates formed during the subsequent cooling, namely cooling precipitates, were detected in higher contents after solutionizing at higher temperatures. It was found that slower cooling rates after solution treatment gave rise to coarser γ′ precipitates with higher volume fraction. Among all heat treatment cycles investigated, double solution treatment at 1190 °C/4 h/FC (furnace cooling) + 1120 °C/2 h/AC (air cooling) followed by aging at 845 °C/24 h/AC was successful to revert the microstructure back to its virgin state
  6. Keywords:
  7. Microstructure ; Aggressive environment ; Air cooling ; Cooling rates ; Degradation of mechanical properties ; Furnace cooling ; Grain boundary films ; Heat treatment cycle ; High temperature ; Higher temperatures ; Microstructural features ; Microstructure and mechanical properties ; Nickel base superalloy ; Rejuvenation heat treatment ; Solution treatments ; Solutionizing ; Subsequent cooling ; Transition zones ; Virgin state ; Carbides ; Cooling ; Dissolution ; Endocrinology ; Grain boundaries ; Grain size and shape ; Mechanical properties ; Microstructural evolution ; Stresses ; Superalloys ; Titration ; Heat treatment
  8. Source: Journal of Alloys and Compounds ; Volume 512, Issue 1 , January , 2012 , Pages 340-350 ; 09258388 (ISSN)
  9. URL: http://www.sciencedirect.com/science/article/pii/S0925838811019323