Synchrotron X-ray and neutron diffraction study on the deformation and phase transformation mechanisms in TiAl alloys: a review

Abstract

TiAl alloys are considered promising candidates for high-temperature structural applications, primarily because of their low density and good high-temperature performance. However, their broader application remains restricted due to poor ductility and inadequate deformation compatibility. The (α₂+γ) lamellar structure, which dominates the service microstructure, exhibits strong deformation anisotropy. Moreover, the large plasticity difference between the α₂ and γ phases leads to pronounced inhomogeneous deformation. Accordingly, internal stress accumulates in the α₂ phase and may initiate cracks at the α₂/γ interfaces. The formation of deformation textures further influences the microscopic deformation and complicates the analysis of stress distribution. Understanding the underlying deformation mechanisms and stress evolution requires real-time observation of these dynamic processes. To this end, synchrotron X-ray diffraction and neutron diffraction are employed for their deep penetration capability and high spatial and temporal resolution. These advanced techniques enable in situ tracking of lattice strain evolution, load partitioning, and phase transformation. This review highlights the deformation behavior of TiAl alloys, including their elastic and plastic responses, texture evolution, and internal stress accumulation. Particular attention is given to the reversible stress-induced α₂→O phase transformation, which presents promising opportunities for enhancing mechanical performance through targeted microstructural optimization.

Keywords

TiAl alloys / internal stress / lamellar structure / stress-induced phase transformation / synchrotron X-ray diffraction / neutron diffraction / orthorhombic phase

References

[1] Clemens H.Design, processing, microstructure, properties, and applications of advanced intermetallic TiAl alloys.Adv Eng Mater2013;15:191-215

[2] Appel F,Oehring M.Gamma titanium aluminide alloys: science and technology; John Wiley & Sons, 2011.

[3] Appel F,Christoph U.Recent progress in the development of gamma titanium aluminide alloys.Adv Eng Mater2000;2:699-720

[4] Sun L,Li G.High-entropy alloys in catalysis: progress, challenges, and prospects.ACS Mater Au2024;4:547-56 PMCID:PMC11565283

[5] Kim Y.Advances in gammalloy materials-processes-application technology: successes, dilemmas, and future.JOM2018;70:553-60

[6] Xu X,Wang Y,Lin Z.Effect of forging on microstructure and tensile properties of Ti-45Al-(8-9)Nb-(W,B,Y) alloy.J Alloys Compd2006;414:175-80

[7] Zhang W,Chen G.On the origin of superior high strength of Ti-45Al-10Nb alloys.Intermetallics2002;10:403-6

[8] Huang H,Xu X,Guo J.Phase transformation and microstructure evolution of a beta-solidified gamma-TiAl alloy.J Alloys Compd2021;860:158082

[9] Musi M,Clemens H.Alloying elements in intermetallic γ-TiAl based alloys-a review on their influence on phase equilibria and phase transformations.Adv Eng Mater2024;26:2300610

[10] Appel F,Staron P.The effect of residual stresses and strain reversal on the fracture toughness of TiAl alloys.Mater Sci Eng A2018;709:17-29

[11] Guo F,François M.X-ray elastic constant determination and microstresses of α₂ phase of a two-phase TiAl-based intermetallic alloy.Mater Sci Eng A2003;341:182-8

[12] Zghal S,Couret A.A quantitative TEM analysis of the lamellar microstructure in TiAl based alloys.Acta Mater1997;45:3005-15

[13] Zhu H,Maruyama K.Effect of microstructural stability on creep behavior of 47XD TiAl alloys with fine-grained fully lamellar structure.Scr Mater2005;52:45-50

[14] Riemer M,Biermann H.The internal stress state in lamellar PST-crystals of the intermetallic alloy TiAl after compressive deformation.Intermetallics1999;7:241-9

[15] Ma Y,Liu Z.Deformation behavior of PST-TiAl bicrystals at 800 °C.Mater Sci Eng A2024;915:147267

[16] Luo Y,Wang L,Cao Y.Effect of crystallographic texture on the anisotropy of fracture toughness in as-forged Ti-45Al-7Nb-0.4W-0.1B intermetallics.J Alloys Compd2025;1014:178672

[17] Cheng L,Yang G,Li J.Insights into the abnormal flow softening of lamellar γ-TiAl alloys during hot-working: experimental analysis and numerical simulation.Mater Sci Eng A2022;852:143695

[18] Inui H,Shirai Y.Low-temperature deformation of single crystals of a DO₁₉ compound with an off-stoichiometric composition (Ti-36·5 at.% Al).Philos Mag A1994;69:1161-77

[19] Umakoshi Y,Takenaka T,Yamane T.Orientation and temperature dependence of yield stress and slip geometry of Ti₃Al and Ti₃Al-V single crystals.Acta Metall Mater1993;41:1149-54

[20] Harada S,Thirathipviwat P.Lamellar orientation control of TiAl-based alloy by uniaxial compressive deformation at high-temperature in (α+β) two-phase region.J Alloys Compd2024;1003:175717

[21] Li J,Hu L.Dynamic recrystallization, phase transformation and deformation mechanisms of a novel Ti-43Al-6Nb-1Mo-1Cr alloy during the isothermal deformation.Mater Charact2023;199:112789

[22] Chen X,Wei B.Interaction between dynamic recrystallization and phase transformation of Ti-43Al-4Nb-1Mo-0.2B alloy during hot deformation.J Mater Sci Technol2025;214:130-42

[23] Yang J,Dong C.Thermomechanical instability and deformation behavior of β_o(ω) phase region in a Ti-43Al-8Nb-0.2W-0.2B alloy under high-temperature rotary-bending fatigue.Int J Fatigue2022;163:106933

[24] Liu Y,Tang B.Decomposition and phase transformation mechanisms of α2 lamellae in β-solidified γ-TiAl alloys.Acta Mater2023;242:118492

[25] Liu S,Chen R,Fu H.Evolution of rapidly grown cellular microstructure during heat treatment of TiAl-based intermetallic and its effect on micromechanical properties.Intermetallics2021;132:107166

[26] Sun T,Yang G.Twinning behavior and strengthening mechanism in a microalloyed TiAl alloy.Mater Sci Eng A2023;872:144993

[27] Huang Z.Thermal stability of Ti-44Al-4Nb-4Zr-0.2Si-1B alloy.Intermetallics2013;42:170-9

[28] Stark A,Clemens H.On the formation of ordered ω-phase in high Nb containing γ-TiAl based alloys.Adv Eng Mater2008;10:929-34

[29] Liang Z,Chi D.Compressive creep behavior of high Nb containing TiAl alloy: dynamic recrystallization and phase transformation.Intermetallics2023;163:108067

[30] Cao G,Oertel C.Microstructural evolution of TiAl-based alloys deformed by high-pressure torsion.Acta Mater2015;98:103-12

[31] Niu H,Chen Y,Liu G.Microstructural stability, phase transformation and mechanical properties of a fully-lamellar microstructure of a Mo-modified high-Nb γ-TiAl alloy.Mater Sci Eng A2020;784:139313

[32] Banerjee D.Deformation of the O and α₂ phases in the Ti-Al-Nb system.Philos Mag A1995;72:1559-87

[33] Gabrisch H,Pyczak F,Stark A.Morphology and stability of orthorhombic and hexagonal phases in a lamellar γ-Ti-42Al-8.5Nb alloy-A transmission electron microscopy study.Acta Mater2017;135:304-13

[34] Rackel MW,Gabrisch H.Screening for O phase in advanced γ-TiAl alloys.Intermetallics2021;131:107086

[35] Rackel MW,Gabrisch H,Schreyer A.Orthorhombic phase formation in a Nb-rich γ-TiAl based alloy-an in situ synchrotron radiation investigation.Acta Mater2016;121:343-51

[36] Dai C,Sun J,Vitos L.Composition and temperature dependence of α₂ phase decomposition in high Nb-containing lamellar γ-TiAl alloys: experiments and first-principles calculations.Acta Materialia2021;221:117419

[37] Liu X,Pyczak F.Stress-induced orthorhombic O phase in TiAl alloys.Acta Mater2025;286:120751

[38] Muraleedharan K,Banerjee D.Phase stability and ordering behaviour of the O phase in Ti Al Nb alloys.Intermetallics1995;3:187-99

[39] Dye D,Reed R.Intergranular and interphase microstresses.Curr Opin Solid State Mater Sci2001;5:31-7

[40] Pang J,Wright J.The generation of intergranular strains in 309H stainless steel under uniaxial loading.Acta Mater2000;48:1131-40

[41] Clausen B,Leffers T.Self-consistent modelling of the plastic deformation of f.c.c. polycrystals and its implications for diffraction measurements of internal stresses.Acta Mater1998;46:3087-98

[42] Cui Y,Zhang C.Effect of initial microstructure on the micromechanical behavior of Ti-55531 titanium alloy investigated by in-situ high-energy X-ray diffraction.Mater Sci Eng A2020;772:138806

[43] Sedmák P,Pilch J.Instability of cyclic superelastic deformation of NiTi investigated by synchrotron X-ray diffraction.Acta Mater2015;94:257-70

[44] Ma L,Nie Z.Reversible deformation-induced martensitic transformation in Al_0.6CoCrFeNi high-entropy alloy investigated by in situ synchrotron-based high-energy X-ray diffraction.Acta Mater2017;128:12-21

[45] Young M,Daymond M,Dunand D.Load partitioning between ferrite and cementite during elasto-plastic deformation of an ultrahigh-carbon steel.Acta Mater2007;55:1999-2011

[46] Wang YD,Stoica AD,Lin Peng R.Determination of the stress orientation distribution function using pulsed neutron sources.J Appl Cryst2003;36:14-22

[47] Bernier JV.A direct method for the determination of the mean orientation-dependent elastic strains and stresses in polycrystalline materials from strain pole figures.J Appl Cryst2006;39:358-68

[48] Mcnelis KP,Miller MP.A two-scale methodology for determining the residual stresses in polycrystalline solids using high energy X-ray diffraction data.J Mech Phys Solids2013;61:428-49

[49] Miller M,Dawson P.Measuring and modeling distributions of stress state in deforming polycrystals.Acta Mater2008;56:3927-39

[50] Alvarez M, Buioli C, Santisteban J, Vizcaino P. Evolution of texture and intergranular stresses of αZr and minority phases in Zr-2.5Nb pressure tube through synchrotron X-ray diffraction.Acta Mater2024;271:119802

[51] Wang YD,Zeng X.Stress-orientation distribution function (SODF)-description, symmetry and determination.MSF2000;347-9:66-73

[52] Wang Y,Mcgreevy R.A novel method for constructing the mean field of grain-orientation-dependent residual stress.Philos Mag Lett2001;81:153-63

[53] Wang Y,Wang X.Grain-orientation-dependent residual stress and the effect of annealing in cold-rolled stainless steel.Acta Mater2002;50:1717-34

[54] Miller MP,Park J.Experimental measurement of lattice strain pole figures using synchrotron x rays.Rev Sci Instrum2005;76:113903

[55] Luo S,Huang S,Mi J.Revealing in situ stress-induced short- and medium-range atomic structure evolution in a multicomponent metallic glassy alloy.Acta Mater2024;272:119917

[56] Zhang X,Xue Y.Temperature dependence of micro-deformation behavior of the porous tungsten/Zr-based metallic glass composite.J Non-Cryst Solids2016;436:9-17

[57] Cheng S,Choo H.An assessment of the contributing factors to the superior properties of a nanostructured steel using in situ high-energy X-ray diffraction.Acta Mater2010;58:2419-29

[58] Dieter GE. Mechanical metallurgy; New York: McGraw-hill, 1986. https://archive.org/details/mechanicalmetall00diet/page/n11/mode/2up (accessed 2025-09-19).

[59] Appel F,Fischer F.Modeling concepts for intermetallic titanium aluminides.Prog Mater Sci2016;81:55-124

[60] Song L,Liu W,Zhang T.{1 01} tension twins and {1 01}-{2 01}/{2 01}-{1 01} double twins in the D0₁₉ ordered hexagonal α₂-Ti₃Al phase.Acta Materialia2023;260:119335

[61] Erdely P,Maawad E,Clemens H.Lattice and phase strain evolution during tensile loading of an intermetallic, multi-phase γ-TiAl based alloy.Acta Mater2018;158:193-205

[62] Ding J,Ye T.Microstructure stability and micro-mechanical behavior of as-cast gamma-TiAl alloy during high-temperature low cycle fatigue.Acta Matera2018;145:504-15

[63] Wimler D,Kremmer T,Mayer S.Microstructure and mechanical properties of novel TiAl alloys tailored via phase and precipitate morphology.Intermetallics2021;138:107316

[64] Todai M,Liu T.Effect of building direction on the microstructure and tensile properties of Ti-48Al-2Cr-2Nb alloy additively manufactured by electron beam melting.Addit Manuf2017;13:61-70

[65] Liu X,Stark A,Zhang T.In-situ synchrotron high energy X-ray diffraction study on the internal strain evolution of D0₁₉-α₂ phase during high-temperature compression and subsequent annealing in a TiAl alloy.J Mater Sci Technol2023;163:212-22

[66] Liu X,Stark A,Zhang T.In-situ synchrotron high energy X-ray diffraction study on the deformation mechanisms of D0₁₉-α₂ phase during high-temperature compression in a TiAl alloy.J Mater Res Technol2024;33:5850-62

[67] Blackburn MJ,Promisel NE. The Science, technology, and application of titanium: proceedings; Pergamon Press, Oxford, 1970; p 633. https://books.google.com/books/about/The_Science_Technology_and_Application_o.html?id=pV98AAAAIAAJ (accessed 2025-09-18).

[68] Selvarajou B,Ramanujan R.Temperature dependent anisotropic mechanical behavior of TiAl based alloys.Int J Plast2022;152:103175

[69] Stark A,Clemens H,Schimansky F.Microstructure and texture formation during near conventional forging of an intermetallic Ti-45Al-5Nb alloy.Adv Eng Mater2009;11:976-81

[70] Stark A,Gerling R,Clemens H.Microstructure and texture formation during hot rolling of niobium-rich γ TiAl alloys with different carbon contents.Adv Eng Mater2006;8:1101-8

[71] Erdely P,Maawad E.Design and control of microstructure and texture by thermomechanical processing of a multi-phase TiAl alloy.Mater Des2017;131:286-96

[72] Erdely P,Maawad E.Effect of hot rolling and primary annealing on the microstructure and texture of a β-stabilised γ-TiAl based alloy.Acta Mater2017;126:145-53

[73] Jia M,Yu Y,Li J.Tailoring lamellar orientation and tensile properties of TNM alloy via extrusion.J. Mater Res Technol2024;28:363-70

[74] Schillinger W,Gerling R,Clemens H.Texture evolution of the γ- and the α/α₂-phase during hot rolling of γ-TiAl based alloys.Intermetallics2006;14:336-47

[75] Stark A,Mayer S.In situ high-energy XRD study of the hot-deformation behavior of a novel γ-TiAl alloy.MRS Online Proceedings Library2013;1516:71-6

[76] Wagner F,Van Landuyt O.Evolution of recrystallisation texture and microstructure in low alloyed titanium sheets.Acta Mater2002;50:1245-59

[77] Wang Z,Kang G.In-situ synchrotron X-ray tomography investigation of damage mechanism of an extruded magnesium alloy in uniaxial low-cycle fatigue with ratchetting.Acta Mater2021;211:116881

[78] Li T,Gupta M,Xia L.Quantitative investigation on the {10-12} twinning-detwinning behavior and twinning transfer of an extruded Mg-2.8Y sheet during compression-tension loading via quasi-in-situ EBSD observation.J Mater Res Technol2023;26:2957-74

[79] Banerjee D,Nandi T.A new ordered orthorhombic phase in a Ti₃Al Nb alloy.Acta Metall1988;36:871-82

[80] Banerjee D.The intermetallic Ti₂AlNb.Prog Mater Sci1997;42:135-58

[81] Bendersky L.Phase transformations in the (Ti, Nb)₃ Al section of the Ti Al Nb system-II. experimental TEM study of microstructures.Acta Acta Metall Mater1994;42:2337-52

[82] Appel F,Paul J.Nano-scale design of TiAl alloys based on β-phase decomposition.Adv Eng Mater2006;8:371-6

[83] Appel F,Paul J.A novel in situ composite structure in TiAl alloys.Mater Sci Eng A2008;493:232-6

[84] Appel F,Oehring M.Phase transformations during creep of a multiphase TiAl-based alloy with a modulated microstructure.Mater Sci Eng A2009;510-1:342-9

[85] Song L,You L,Lin J.B19 phase in Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y alloy.J Alloys Compd2015;618:305-10

[86] Musi M,Rashkova B.Evidence of an orthorhombic transition phase in a Ti-44Al-3Mo (at.%) alloy using in situ synchrotron diffraction and transmission electron microscopy.Mater Charact2019;147:398-405

[87] Bendersky L,Boettinger W.Phase transformations in the (Ti, Al)₃ Nb section of the Ti Al Nb system-I. microstructural predictions based on a subgroup relation between phases.Acta Metall Mater1994;42:2323-35

[88] Ren G.High-resolution electron microscopy characterization of modulated structure in high Nb-containing lamellar γ-TiAl alloy.Acta Mater2018;144:516-23

[89] Ren G,Mei W,Lu S.Formation and temporal evolution of modulated structure in high Nb-containing lamellar γ-TiAl alloy.Acta Mater2019;165:215-27

[90] Xu S,Lin J.The crystal structure and transformations of the omicron phase Ο in the Ti-Al-Nb system and on the ambiguity of its subvariants Ο1 and Ο2.Scr Mater2022;219:114841

[91] Mozer B,Boettinger W.Neutron powder diffraction study of the orthorhombic Ti₂AlNb phase.Scr Metall Mater1990;24:2363-8

[92] Gabrisch H,Rackel MW,Stark A.Impact of microstructure on elastic properties in the alloy Ti-42Al-8.5Nb.J Alloys Compd2023;932:167578

[93] Muraleedharan K,Banerjee S.The α₂-to-O transformation in Ti-Al-Nb alloys.Philos Mag A1995;71:1011-36

[94] Wen Y,Bendersky L.Microstructural evolution during the α₂→α₂+O transformation in Ti-Al-Nb alloys: phase-field simulation and experimental validation.Acta Mater2000;48:4125-35

[95] Wen Y,Chen L.Effect of elastic interaction on the formation of a complex multi-domain microstructural pattern during a coherent hexagonal to orthorhombic transformation.Acta Mater1999;47:4375-86

[96] Feng B,Hao S.In-situ synchrotron high energy X-ray diffraction study of micro-mechanical behaviour of R phase reorientation in nanocrystalline NiTi alloy.Acta Mater2020;194:565-76

[97] Xu K,Li C.Mechanisms of stress-induced martensitic transformation and transformation-induced plasticity in NiTi shape memory alloy related to superelastic stability.Scr Mater2022;217:114775

[98] Grabec T,Zoubková K.Evolution of elastic constants of the NiTi shape memory alloy during a stress-induced martensitic transformation.Acta Mater2021;208:116718

[99] Tyc O,Molnárová O,Šittner P.Stress induced martensitic transformation in NiTi at elevated temperatures: Martensite variant microstructures, recoverable strains and plastic strains.Acta Mater2024;279:120287

[100] Chen Y,Duchoň J.Modulated martensite in NiTi shape memory alloy exposed to high stress at high temperatures.Acta Mater2023;258:119250

[101] Iaparova E,Tyc O.Thermally induced reorientation and plastic deformation of B19’ monoclinic martensite in nanocrystalline NiTi wires.Acta Mater2023;242:118477

[102] Hao S,Jiang D.A transforming metal nanocomposite with large elastic strain, low modulus, and high strength.Science2013;339:1191-4

[103] Liu J,Hao Y.High-energy X-ray diffuse scattering studies on deformation-induced spatially confined martensitic transformations in multifunctional Ti-24Nb-4Zr-8Sn alloy.Acta Mater2014;81:476-86

[104] Song Y,Sato S.A lightweight shape-memory alloy with superior temperature-fluctuation resistance.Nature2025;638:965-71 PMCID:PMC11864968

[105] Otsuka K.Physical metallurgy of Ti-Ni-based shape memory alloys.Prog Mater Sci2005;50:511-678

[106] Li S.Superelasticity and tensile strength of Ti-Zr-Nb-Sn alloys with high Zr content for biomedical applications.Intermetallics2019;112:106545

[107] Fu J,Kim HY,Miyazaki S.Novel Ti-base superelastic alloys with large recovery strain and excellent biocompatibility.Acta Biomater2015;17:56-67

[108] Tseng L,Chumlyakov Y.Orientation dependence of superelasticity in FeMnAlNi single crystals under compression.Scr Mater2019;166:48-52.n