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Thermal Aging Effects on IN718 Plus Nickel-base Superalloy

Chaswal, Vibhor
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1299854439

Abstract Details

2011, MS, University of Cincinnati, Engineering and Applied Science: Materials Science.
Precipitation behavior in IN718Plus superalloy has been studied after heat treatment between 923K to 1123K upto 1000h. Spherical gamma prime (γ’) precipitates transform to plate shaped eta phase (η) upon aging which is important for fatigue design of this alloy. The as received microstructure shows plate shaped grain boundary delta phase but after thermal aging titanium containing eta plates appear within the grains by transformation of γ’ along the close-packed plane through a faulting mechanism. Confirmation was obtained using transmission electron microscopy (TEM) through convergent beam electron diffraction, orientation analysis and energy dispersive X-Ray measurements. The activation energy for γ’ precipitate coarsening was calculated based on precipitate size data obtained through analysis of TEM micrographs. Coarsening kinetics of γ’and γ’ are coupled and were analyzed based on activation energy analysis and are compared with microhardness results. Coarsening of γ’ precipitates is found to deviate from LSW theory at small sizes but matches well for intermediate and bigger particles. In this study, a procedure to identify the range of validity of operative rate law is found based on JMA model. Small particle coarsening is found to exhibit a radius square dependence with time proposed [Ardell et al, Nature Materials 2005] for ordered alloys. Since number density of plate shaped precipitates increases progressively at expense of spherical γ’ with time, a general condition is derived for such systems where the content of stable daughter phase is proportional to the metastable γ' phase which it is forming from. Gamma double prime (γ’’) phase was not observed during above aging treatments. Finally, thermal relaxation of Laser Shock induced stresses in this material is compared based on SXRD, XRD and microhardness data. The main features of this study are: A. Advances knowledge of precipitation in this class of superalloy upon thermal ageing at and above service temperatures including γ’ coarsening behavior and new precipitation. We also report effects of thermal ageing on relaxation of residual stresses generated by contemporary technique of laser peening. B. This work adds confidence in long term thermal stability and addresses microstructural evolution in this alloy while attempting a general formulation of coarsening for similar systems. The precipitation of intragranular plate shaped η precipitates in IN718Plus is confirmed at temperatures under investigation, which has implications for fatigue life due to its detrimental properties. This study proposes a generalized treatment having wider applicability along with generating valuable data for this new alloy. Finally it investigates residual stress retention after Laser shock treatment upon thermal ageing in the alloy. This is vital towards estimating design life of the components subjected to high energy laser shocks for inducing residual compressive stresses which are reported to enhance fatigue life of the components upto an order of magnitude.
Vijay Vasudevan, PhD (Committee Chair)
Rodney Roseman, PhD (Committee Member)
Raj Singh, ScD (Committee Member)
115 p.
Materials Science
IN718 Plus superalloy; Thermal Aging; Precipitate coarsening; Gamma prime precipitates; Laser Shock peening; Eta Ni3Ti

Recommended Citations

Citations

  • Chaswal, V. (2011). Thermal Aging Effects on IN718 Plus Nickel-base Superalloy [Master's thesis, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1299854439

    APA Style (7th edition)

  • Chaswal, Vibhor. Thermal Aging Effects on IN718 Plus Nickel-base Superalloy. 2011. University of Cincinnati, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1299854439.

    MLA Style (8th edition)

  • Chaswal, Vibhor. "Thermal Aging Effects on IN718 Plus Nickel-base Superalloy." Master's thesis, University of Cincinnati, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1299854439

    Chicago Manual of Style (17th edition)

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This open access ETD is published by University of Cincinnati and OhioLINK.