Deformation mechanisms in a precipitation-strengthened ferritic superalloy revealed by in situ neutron diffraction studies at elevated temperatures

Abstract The ferritic superalloy Fe–10Ni–6.5Al–10Cr–3.4Mo strengthened by ordered (Ni,Fe)Al B2-type precipitates is a candidate material for ultra-supercritical steam turbine applications above 923 K. Despite earlier success in improving its room-temperature ductility, the creep resistance of this material at high temperatures needs to be further improved, which requires a fundamental understanding of the high-temperature deformation mechanisms at the scales of individual phases and grains. In situ neutron diffraction has been utilized to investigate the lattice strain evolution and the microscopic load-sharing mechanisms during tensile deformation of this ferritic superalloy at elevated temperatures. Finite-element simulations based on the crystal plasticity theory are employed and compared with the experimental results, both qualitatively and quantitatively. Based on these interphase and intergranular load-partitioning studies, it is found that the deformation mechanisms change from dislocation slip to those related to dislocation climb, diffusional flow and possibly grain boundary sliding, below and above 873 K, respectively. Insights into microstructural design for enhancing creep resistance are also discussed.

[1]  Yanfei Gao,et al.  Intergranular strain evolution near fatigue crack tips in polycrystalline metals , 2011 .

[2]  Gerhard Sauthoff,et al.  The strengthening effect of (Ni, Fe)Al precipitates on the mechanical properties at high temperatures of ferritic Fe–Al–Ni–Cr alloys , 2005 .

[3]  Yanfei Gao,et al.  In Situ Neutron-Diffraction Studies on the Creep Behavior of a Ferritic Superalloy , 2011, Metallurgical and Materials Transactions A.

[4]  David C. Dunand,et al.  Creep properties and microstructure of a precipitation-strengthened ferritic Fe–Al–Ni–Cr alloy , 2014 .

[5]  R. Taillard,et al.  The precipitation of the intermetallic compound NiAl in Fe-19wt.%Cr alloys , 1982 .

[6]  Huajian Gao,et al.  Recoverable creep deformation due to heterogeneous grain-boundary diffusion and sliding , 2007 .

[7]  D. Miracle.  Overview No. 104 The physical and mechanical properties of NiAl , 1993 .

[8]  Chuin-Shan Chen,et al.  Effects of grain boundary heterogeneities on creep fracture studied by rate-dependent cohesive model , 2012 .

[9]  Fan Zhang,et al.  New NiAl-strengthened ferritic steels with balanced creep resistance and ductility designed by coupling thermodynamic calculations with focused experiments , 2012 .

[10]  J. R. Weertman,et al.  Coarsening and morphology of β′ particles in Fe-Ni-Al-Mo ferritic alloys , 1988 .

[11]  Huajian Gao,et al.  Enhanced strain-rate sensitivity in fcc nanocrystals due to grain-boundary diffusion and sliding , 2008 .

[12]  Michael K Miller,et al.  Characterization of nanoscale NiAl-type precipitates in a ferritic steel by electron microscopy and atom probe tomography , 2010 .

[13]  M. Ashby,et al.  Deformation-Mechanism Maps: The Plasticity and Creep of Metals and Ceramics , 1982 .

[14]  G. Sauthoff,et al.  Ferritic Fe–Al–Ni–Cr alloys with coherent precipitates for high-temperature applications , 2004 .

[15]  Alan Needleman,et al.  An analysis of nonuniform and localized deformation in ductile single crystals , 1982 .

[16]  E. Kenik,et al.  Room temperature ductility of NiAl-strengthened ferritic steels: Effects of precipitate microstructure , 2012 .

[17]  P. Dawson,et al.  Influence of directional strength-to-stiffness on the elastic–plastic transition of fcc polycrystals under uniaxial tensile loading , 2010 .

[18]  A. Bower,et al.  A two-dimensional finite element method for simulating the constitutive response and microstructure of polycrystals during high temperature plastic deformation , 2004 .

[19]  A. Mortensen.  Concise encyclopedia of composite materials , 2007 .

[20]  P. Liaw,et al.  Thermodynamic modeling and experimental validation of the Fe-Al-Ni-Cr-Mo alloy system , 2012 .

[21]  H. Prask,et al.  Calculation of Single-Crystal Elastic Constants for Cubic Crystal Symmetry from Powder Diffraction Data , 1998 .

[22]  C. J. Smithells,et al.  Smithells metals reference book , 1949 .

[23]  Alexandru Dan Stoica,et al.  First In Situ Lattice Strains Measurements Under Load at VULCAN , 2011 .

[24]  Bjørn Clausen,et al.  Neutron-diffraction study and modeling of the lattice parameters of a NiAl-precipitate-strengthened Fe-based alloy , 2012 .

[25]  R. Reed,et al.  On the generation of microstrains during the plastic deformation of Waspaloy , 1999 .

[26]  J. D. Eshelby.  The determination of the elastic field of an ellipsoidal inclusion, and related problems , 1957, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[27]  D. J. Dever,et al.  Temperature dependence of the elastic constants in α‐iron single crystals: relationship to spin order and diffusion anomalies , 1972 .

[28]  M. Preuss,et al.  Evidence of variation in slip mode in a polycrystalline nickel-base superalloy with change in temperature from neutron diffraction strain measurements , 2007 .

[29]  K. Masuda,et al.  Elastic and viscoelastic properties of α iron at high temperatures , 1995 .

[30]  Huajian Gao,et al.  Recoverable creep deformation and transient local stress concentration due to heterogeneous grain-boundary diffusion and sliding in polycrystalline solids , 2008 .

[31]  Chuin-Shan Chen,et al.  A micromechanics study of competing mechanisms for creep fracture of zirconium diboride polycrystals , 2013 .

[32]  M. Daymond,et al.  Microstrain evolution during creep of a high volume fraction superalloy , 2005 .

[33]  Mark Asta,et al.  Calculation of impurity diffusivities in α-Fe using first-principles methods , 2010 .

[34]  P. Withers,et al.  Introduction to the Characterization of Residual Stress by Neutron Diffraction , 2005 .

[35]  Peter K. Liaw,et al.  Effects of Al on the microstructure and ductility of NiAl-strengthened ferritic steels at room temperature , 2010 .

[36]  Alexandru Dan Stoica,et al.  VULCAN—The engineering diffractometer at the SNS , 2006 .