New vision of convection induced freckle formation theory in nickel-based superalloys by electron microscopy

Abstract

Freckles, one of the common defects in blades used in heavy-duty gas turbines, hugely deteriorate the mechanical properties and liability of blades under service conditions. The thermal-solutal convection theory is a widely adopted formation mechanism, but few solid experimental pieces of evidence have been reported. Here, the grain microstructure in freckle chains taken from four different Nickel-based superalloys with either single-crystal or directionally solidified alloy is analyzed for the first time. The relationship between the internal stress and the misorientation throughout the freckle chains is studied by means of state-of-the-art electron microscopy. The results supply new experimental evidence of the thermal-solutal convection theory, which is further supported by the fact that borides at the boundary are randomly orientated to alloys. Therefore, this research enriches the methodology of freckle study, providing new insight into the formation mechanism of casting defects.

Keywords

Nickel-based superalloy / freckle / dendrite fracture / orientation / strain

References

[1] Broomfield RW,Bhangu JK.Development and turbine engine performance of three advanced rhenium containing superalloys for single crystal and directionally solidified blades and vanes. Proceedings of the ASME 1997 International Gas Turbine and Aeroengine Congress and Exhibition. 1997 Jun 2-5; Orlando, USA. New York: ASME; 1998.

[2] Gasson PC.The superalloys: fundamentals and applications. R. C. Reed Cambridge University Press, The Edinburgh Building, Shaftesbury Road, Cambridge, CB2 2RU, UK, 2006. 372pp. Illustrated. £80. ISBN 0-521-85904-2.Aeronaut j2008;112:291

[3] Pollock T.Creep resistance of CMSX-3 nickel base superalloy single crystals.Acta Metall Mater1992;40:1-30

[4] Versnyder FI.The development of columnar grain and single crystal high temperature materials through directional solidification.Mater Sci Eng1970;6:213-47

[5] Quested PN.Mechanical properties of conventionally cast, directionally solidified, and single-crystal superalloys.Mater Sci Technol1986;2:461-75

[6] Giamei AF.On the nature of freckles in nickel base superalloys.Metall Trans1970;1:2185-92

[7] Chmiela B,Cwajna J.Identification and evaluation of freckles in directionally solidified casting made of PWA 1426 nickel-based superalloy.Arch Metall Mater2012;57:559-64

[8] Worster MG.Instabilities of the liquid and mushy regions during solidification of alloys.J Fluid Mech1992;237:649-69

[9] Ramirez JC.Evaluation of a rayleigh-number-based freckle criterion for Pb-Sn alloys and Ni-base superalloys.Metall Mater Trans A2003;34:1525-36

[10] Valdés J,Liu X.On the formulation of a freckling criterion for Ni-based superalloy vacuum arc remelting ingots.Metall Mater Trans A2010;41:2408-16

[11] Frueh C,Felicelli S.Predicting freckle-defects in directionally solidified Pb-Sn alloys.Mater Sci Eng2002;328:245-55

[12] Wang F,Zhang J,Bührig-polaczek A.Solidification behavior of a Ni-based single crystal CMSX-4 superalloy solidified by downward directional solidification process.Mater Charact2015;101:20-5

[13] Li Q,Qin L,Yue X.Effect of traveling magnetic field on freckle formation in directionally solidified CMSX-4 superalloy.J Mater Process Technol2019;274:116308

[14] Li Q,Qin L.Investigation on local cooling in reducing freckles for directionally solidified superalloy specimens with abruptly varying cross-sections.Mater Charact2017;130:139-48

[15] Xiao J,Han D,Lu Y.Evolution of crystallographic orientation and microstructure in the triangular adapter of grain continuator of a 3rd-generation single crystal superalloy casting during directional solidification.J Alloys Compd2022;898:162782

[16] Genereux PD. Characterization of freckles in a high strength wrought nickel superalloy. Superalloys 2000;2000:19-27. Available from: https://www.tms.org/superalloys/10.7449/2000/Superalloys_2000_19_27.pdf [Last accessed on 20 Dec 2023]

[17] Pollock TM,Goldman EH,Tu JS. Grain defect formation during directional solidification of nickel base single crystals. Superalloys 1992;1992:125-34. Available from: https://www.tms.org/superalloys/10.7449/1992/Superalloys_1992_125_134.pdf [Last accessed on 20 Dec 2023]

[18] Sarazin JR.Channel formation in Pb-Sn, Pb-Sb, and Pb-Sn-Sb alloy ingots and comparison with the system NH₄CI-H₂O.Metall Trans A1988;19:1861-71

[19] Karagadde S,Shevchenko N,Lee P.3-D microstructural model of freckle formation validated using in situ experiments.Acta Mater2014;79:168-80

[20] Ren N,Panwisawas C,Dong H.Thermal-solutal-fluid flow of channel segregation during directional solidification of single-crystal nickel-based superalloys.Acta Mater2021;206:116620

[21] Amouyal Y.An atom-probe tomographic study of freckle formation in a nickel-based superalloy.Acta Mater2011;59:6729-42

[22] Tin S,King WT. Carbon additions and grain defect formation in high refractory nickel-base single crystal superalloys. Superalloys 2000;2000:201-10. Available from: https://www.tms.org/Superalloys/10.7449/2000/Superalloys_2000_201_210.pdf [Last accessed on 20 Dec 2023]

[23] Tin S,Murphy W.Stabilization of thermosolutal convective instabilities in Ni-based single-crystal superalloys: carbon additions and freckle formation.Metall Mater Trans A2001;32:1743-53

[24] Amouyal Y.The role of hafnium in the formation of misoriented defects in Ni-based superalloys: an atom-probe tomographic study.Acta Mater2011;59:3321-33

[25] Karagadde S,Cai B.Transgranular liquation cracking of grains in the semi-solid state.Nat Commun2015;6:8300 PMCID:PMC4579839

[26] Cai B,Kao A.4D synchrotron X-ray tomographic quantification of the transition from cellular to dendrite growth during directional solidification.Acta Mater2016;117:160-9

[27] Reinhart G,Abou-khalil L.Impact of solute flow during directional solidification of a Ni-based alloy: in-situ and real-time X-radiography.Acta Mater2020;194:68-79

[28] Ren N,Li J,Dong H.Solute enrichment induced dendritic fragmentation in directional solidification of nickel-based superalloys.Acta Mater2021;215:117043

[29] Isensee T.Convective effects on columnar dendritic solidification - a multiscale dendritic needle network study.Acta Mater2022;234:118035

[30] Mullis A.Growth induced dendritic bending and rosette formation during solidification in a shearing flow.Acta Mater1999;47:1783-9

[31] Dragnevski K,Walker DJ.Mechanical deformation of dendrites by fluid flow during the solidification of undercooled melts.Acta Mater2002;50:3743-55

[32] Billia B,Thi HN,Gastaldi J.Cumulative mechanical moments and microstructure deformation induced by growth shape in columnar solidification.Phys Rev Lett2004;93:126105

[33] Niederberger C,Jacot A.Origin of intragranular crystallographic misorientations in hot-dip Al-Zn-Si coatings.Acta Mater2008;56:4002-11

[34] Yuan L.A new mechanism for freckle initiation based on microstructural level simulation.Acta Mater2012;60:4917-26

[35] Ananiev S,Eckert K.Dendrite fragmentation by catastrophic elastic remelting.Acta Mater2009;57:657-65

[36] Boden S,Willers B.X-ray radioscopic visualization of the solutal convection during solidification of a Ga-30 Wt Pct In Alloy.Metall Mater Trans A2008;39:613-23

[37] Appolaire B,Combeau H.Free growth of equiaxed crystals settling in undercooled NH₄Cl-H₂O melts.Acta Mater1998;46:5851-62

[38] Hu X,Ma X.Crystallographic account of nano-scaled intergrowth of M₂B-type borides in nickel-based superalloys.Acta Mater2014;68:70-81

[39] Ge H,Zheng S.Boride-induced dislocation channeling in a single crystal Ni-based superalloy.Mater Lett2019;235:232-5

[40] Du B,Yang J.M5B3 boride at the grain boundary of a nickel-based superalloy.J Mater Sci Technol2016;32:265-70

[41] Wang Y,Gauvin R.Line-rotated remapping for high-resolution electron backscatter diffraction.Ultramicroscopy2022;242:113623

[42] Wilkinson AJ,Dingley DJ.High-resolution elastic strain measurement from electron backscatter diffraction patterns: new levels of sensitivity.Ultramicroscopy2006;106:307-13

[43] Mingard K,Bennett E.Comparison of EBSD and conventional methods of grain size measurement of hardmetals.Int J Refract Hard Met H2009;27:213-23

[44] Mottura A.What is the role of rhenium in single crystal superalloys?.MATEC Web Conf2014;14:01001

[45] Huang M.An overview of rhenium effect in single-crystal superalloys.Rare Met2016;35:127-39

[46] Wang S,Guo Z.In situ high speed imaging study and modelling of the fatigue fragmentation of dendritic structures in ultrasonic fields.Acta Mater2019;165:388-97

[47] Wright SI,Field DP.A review of strain analysis using electron backscatter diffraction.Microsc Microanal2011;17:316-29

[48] Gottstein G.Physical foundations of materials science. Berlin:Springer;2004.

[49] Callister W.Materials science and engineering: an introduction (2nd edition).Mater Des1991;12:59

[50] Floreen S.The effects of b and Zr on the creep and fatigue crack growth behavior of a Ni-base superalloy.Metall Trans A1983;14:895-901

[51] Li X,Wang M,Ma Y.Effect of boron addition on the microstructure and mechanical properties of K4750 nickel-based superalloy.J Mater Sci Technol2021;60:177-85

[52] Kontis P,Pedrazzini S.On the effect of boron on grain boundary character in a new polycrystalline superalloy.Acta Mater2016;103:688-99