Metallurgical Engineering

Metallurgical Engineering

Effect of service expose on microstructure and creep mechanisms of gas turbine blades made of IN738LC

Document Type : Research Paper

Authors
Ali Mohammad Kolagar 1
Mohammad Cheraghzadeh 2
Narges Tabrizi 3
Mohammad saeed shahryari 4
1 Research and development Manager
2 Deputy of engineering
3 Expert of Research and Development Department
4 Expert of product engineering Department
10.22076/me.2017.41681.1065
Abstract
Turbine blades operate on the different temperature and stress conditions. The variousmechanismscontribute to the creep process and lead to turbine blade failure. The characterization of the creep mechanisms is critical to predict the creep behavior and design the useful life of turbine blade. This paper compares the creep behaviors of new and used blades (worked 3000 equal operating hours) based on IN738 superalloys by investigating the microstructure and using the creep models. Optical and scanning electron microscopes were applied to study the volume fraction, size of the primary and secondary precipitated phases (γ'), change of the precipitated phases morphology (ex. formed continuous carbide in grain boundaries or coarsening γ')and the formation of the creep pores. Furthermore, the dominated creep mechanisms are identified and comparedthe new blades with used blades at different stress rupture tests and real work conditions. The results show that at760 oC/586 MPa, the active creep mechanismsincludes cutting and Orowan for both new and used blades. Whereas at 982 oC/152 MPa , the dislocations climb, diffusion creep and grain boundary gliding are active for new blades and Orowan and the dislocations climb are operative for used blades.
Keywords
"Gas turbine lade"
"used blade"
"creep mechanisms"
"IN738LC Ni-based superalloys"
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  • Receive Date 31 May 2016
  • Revise Date 21 June 2016
  • Accept Date 21 June 2016