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Creep Deformation of Allvac 718Plus

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Abstract

The creep deformation behavior of Allvac 718Plus was studied over the temperature range of 923 K to 1005 K (650 °C to 732 °C) at initial applied stress levels ranging from 517 to 655 MPa. Over the entire experimental temperature–stress regime this alloy exhibits Class M-type creep behavior with all creep curves exhibiting a decelerating strain rate with strain or time throughout primary creep. However, unlike pure metals or simple solid solution alloys, this gamma prime strengthened superalloy does not exhibit steady-state creep. Rather, primary creep is instantly followed by a long duration of accelerating strain rate with strain or time. These creep characteristics are common among the gamma prime strengthened superalloys. Allvac 718Plus also exhibits a very high temperature dependence of creep rate. Detailed TEM examination of the deformation structures of selected creep samples reveals dislocation mechanisms similar to those found in high volume fraction gamma prime strengthened superalloys. Strong evidence of microtwinning is found in several of the deformation structures. The presence of microtwinning may account for the strong temperature dependence of creep rate observed in this alloy. In addition, due to the presence of Nb and thus, grain boundary delta phase, matrix dislocation activity which is not present in non-Nb-bearing superalloys occurs in this alloy. The creep characteristics and dislocation mechanisms are presented and discussed in detail.

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Acknowledgments

The Allvac 718Plus material used in this study was provided by Carlton Forge Works, Paramount, CA. The authors also wish to acknowledge the insightful comments and suggestions made by the reviewer which have resulted in a significant improvement of the manuscript. R.W.H. would also like to acknowledge conversations held with Dr. Eric Ott at GE Aviation regarding the initial testing parameters for this work.

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Authors and Affiliations

  1. Metals Technology Inc, Northridge, CA, 91324, USA

    Robert W. Hayes (Principal Investagator) & Maryam Nasrollahzadeh (Researcher)

  2. Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA

    Raymond R. Unocic (Alvin M. Weinberg Fellow)

Authors
  1. Robert W. Hayes
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  2. Raymond R. Unocic
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  3. Maryam Nasrollahzadeh
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Correspondence to Robert W. Hayes.

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Manuscript submitted June 4, 2013.

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Hayes, R.W., Unocic, R.R. & Nasrollahzadeh, M. Creep Deformation of Allvac 718Plus. Metall Mater Trans A 46, 218–228 (2015). https://doi.org/10.1007/s11661-014-2564-y

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  • DOI: https://doi.org/10.1007/s11661-014-2564-y

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