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Journal ArticleDOI

Advanced Intermetallic TiAl Alloys

01 Nov 2016-Materials Science Forum (Trans Tech Publications Ltd)-Vol. 879, pp 113-118
TL;DR: The 3rd generation TiAl alloys, such as the TNM alloy described in this paper, are complex multi-phase alloys which can be processed by ingot or powder metallurgy as well as precision casting methods as mentioned in this paper.
Abstract: Challenging issues concerning energy efficiency and environmental politics require novel approaches to materials design. A recent example with regard to structural materials is the emergence of lightweight intermetallic TiAl alloys. Their excellent high-temperature mechanical properties, low density, and high stiffness constitute a profile perfectly suitable for their application as advanced aero-engine turbine blades or as turbocharger turbine wheels in next-generation automotive engines. Advanced so-called 3rd generation TiAl alloys, such as the TNM alloy described in this paper, are complex multi-phase alloys which can be processed by ingot or powder metallurgy as well as precision casting methods. Each process leads to specific microstructures which can be altered and optimized by thermo-mechanical processing and/or subsequent heat treatments.
Citations
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Journal ArticleDOI
TL;DR: This strategy to realize high strength and high plasticity simultaneously in Cr-rich γ-TiAl-based intermetallic alloys via introducing high-density deformation nanotwins through introducing twinning deformation mechanism can be applied to other brittle alloys with a favorable twinningDeformation mechanism.
Abstract: Intermetallic alloys with high melting point can mostly serve as promising high-temperature structural materials, but their intrinsic brittleness limits their further application. Herein, we developed a strategy to realize high strength and high plasticity simultaneously in Cr-rich γ-TiAl-based intermetallic alloys via introducing high-density deformation nanotwins. Non-equilibrium continuous casting followed by annealing in the (α + γ) phase region generated numerous Shockley partial dislocations and stacking faults as well as a number of α2 nanoparticles in the γ-TiAl phase. The substantial Shockley partial dislocations and stacking faults acting as effective heterogeneous nucleation sites favored the generation of high-density nanotwins in the as-annealed alloys during deformation, especially within the γ lamellae. This strategy can also be applied to other brittle alloys with a favorable twinning deformation mechanism and paves the way for the development of high-strength and high-ductility materials.

42 citations

Journal ArticleDOI
30 Apr 2019-Wear
TL;DR: In this paper, the high-temperature sliding wear behavior of the γ-based TiAl alloy TNM-B1 was investigated using a pin-on-disk apparatus up to 800°C in air under variation of the counterpart material.

26 citations

Journal ArticleDOI
01 Jun 2018-Vacuum
TL;DR: In this paper, the effects of brazing temperature on the interfacial microstructure and mechanical properties of the Ti60/Cu75 P/t/Ti2AlNb brazed joints were investigated.

18 citations

Journal ArticleDOI
TL;DR: The bulging of the γ phase boundaries, the decomposition of α2 lamellae and the disappearance of γ/γ interfaces were considered as the main coarsening mechanisms of the lamellar microstructure.
Abstract: A β-solidifying Ti-43Al-2Cr-2Mn-0.2Y alloy was directionally solidified by the optical floating zone melting method. The microstructure is mainly characterized by γ/α2 lamellae with specific orientations, which exhibits straight boundaries. The β phase is randomly distributed in the lamellar microstructure, indicating that the β phase cannot be directionally solidified. The directional solidification of γ/α2 lamellae was not affected by the precipitation of the β phase. Hot compression tests show that the deformation behavior of the β-containing lamellar microstructure also exhibits the anisotropic characteristic. The deformation resistance of the lamellae is lowest when the loading axis is aligned 45° to the lamellar interface. Microstructural observation shows that the decomposition of the lamellar microstructure tends to begin around the β phase, which benefits from the promotion of a soft β phase in the deformation. Moreover, the deformation mechanism of the lamellar microstructure was also studied. The bulging of the γ phase boundaries, the decomposition of α2 lamellae and the disappearance of γ/γ interfaces were considered as the main coarsening mechanisms of the lamellar microstructure.

17 citations

References
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Journal ArticleDOI
TL;DR: In this article, a general survey of engineering γ-TiAl based alloys is given, but concentrates on β-solidifying alloys which show excellent hot-workability and balanced mechanical properties when subjected to adapted heat treatments.
Abstract: After almost three decades of intensive fundamental research and development activities, intermetallic titanium aluminides based on the ordered γ-TiAl phase have found applications in automotive and aircraft engine industry. The advantages of this class of innovative high-temperature materials are their low density and their good strength and creep properties up to 750 °C as well as their good oxidation and burn resistance. Advanced TiAl alloys are complex multi-phase alloys which can be processed by ingot or powder metallurgy as well as precision casting methods. Each process leads to specific microstructures which can be altered and optimized by thermo-mechanical processing and/or subsequent heat treatments. The background of these heat treatments is at least twofold, i.e., concurrent increase of ductility at room temperature and creep strength at elevated temperature. This review gives a general survey of engineering γ-TiAl based alloys, but concentrates on β-solidifying γ-TiAl based alloys which show excellent hot-workability and balanced mechanical properties when subjected to adapted heat treatments. The content of this paper comprises alloy design strategies, progress in processing, evolution of microstructure, mechanical properties as well as application-oriented aspects, but also shows how sophisticated ex situ and in situ methods can be employed to establish phase diagrams and to investigate the evolution of the micro- and nanostructure during hot-working and subsequent heat treatments.

791 citations

BookDOI
21 Sep 2011
TL;DR: In this paper, the Binary Ti-Al Phase Diagram is used to study the behavior of single-phase and two-phase alloys with a modulated microstructure.
Abstract: Preface INTRODUCTION CONSTITUTION The Binary Ti-Al Phase Diagram Ternary and Multicomponent Alloy Systems THERMOPHYSICAL CONSTANTS Elastic and Thermal Properties Point Defects Diffusion PHASE TRANSFORMATIONS AND MICROSTRUCTURES Microstructure Formation on Solidification Solid State Transformations DEFORMATION BEHAVIOR OF SINGLE-PHASE ALLOYS Single-Phase Gamma(TiAl) Alloys Deformation Behavior of Single-Phase Alpha2(Ti3Al) Alloys Beta/B2 Phase Alloys DEFORMATION BEHAVIOR OF TWO-PHASE ALPHA(Ti3Al) + GAMMA(TiAl) ALLOYS Lamellar Microstructures Deformation Mechanisms, Contrasting Single-Phase and Two-Phase Alloys Generation of Dislocations and Mechanical Twins Glide Resistance and Dislocation Mobility Thermal and Athermal Stresses STRENGTHENING MECHANISMS Grain Refinement Work Hardening Solution Hardening Precipitation Hardening Optimized Nb-Bearing Alloys DEFORMATION BEHAVIOR OF ALLOYS WITH A MODULATED MICROSTRUCTURE Modulated Microstructures Misfitting Interfaces Mechanical Properties CREEP Design Margins and Failure Mechanisms General Creep Behavior The Steady-State or Minimum Creep Rate Effect of Microstructure Primary Creep Creep-Induced Degradation of Lamellar Structures Precipitation Effects Associated with the Alpha2 -> Gamma Phase Transformations Tertiary Creep Optimized Alloys, Effect of Alloy Composition and Processing Creep Properties of Alloys with a Modulated Microstructure FRACTURE BEHAVIOR Length Scales in the Fracture of TiAl Alloys Cleavage Fracture Crack-Tip Plasticity Fracture Toughness, Strength, and Ductility Fracture Behavior of Modulated Alloys Requirements for Ductility and Toughness Assessment of Property Variability FATIGUE Definitions The Stress-Life (S-N) Behavior HCF Effects of Temperature and Environment on the Cyclic Crack-Growth Resistance LCF Thermomechanical Fatigue and Creep Relaxation OXIDATION BEHAVIOR AND RELATED ISSUES Kinetics and Thermodynamics General Aspects Concerning Oxidation Summary ALLOY DESIGN Effect of Aluminum Content Important Alloying Elements - General Remarks Specific Alloy Systems Summary INGOT PRODUCTION AND COMPONENT CASTING Ingot Production Casting Summary POWDER METALLURGY Prealloyed Powder Technology Elemental-Powder Technology Mechanical Alloying WROUGHT PROCESSING Flow Behavior under Hot-Working Conditions Conversions of Microstructure Workabiliy and Primary Processing Texture Evolution Secondary Processing JOINING Diffusion Bonding Brazing and Other Joining Technologies SURFACE HARDENING Shot Peening and Roller Burnishing Residual Stresses, Microhardness, and Surface Roughness Surface Deformation Due to Shot Peening Phase Transformation, Recrystallization, and Amorphization Effect of Shot Peening on Fatigue Strength Thermal Stability of the Surface Hardening APPLICATIONS, COMPONENT ASSESSMENT, AND OUTLOOK Aerospace Automotive Outlook

540 citations


"Advanced Intermetallic TiAl Alloys" refers background in this paper

  • ...IN 625 and Rene 95 are Ni based superalloys, whereas IMI 834 represents a so-called near α Ti based alloy [3,4]....

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  • ...2 g/cm3, depending on composition), high specific yield strength, high specific stiffness, good oxidation resistance, resistance against ”titanium fire”, and good creep properties up to high temperatures [1-4]....

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  • ...Generally, the influence of microstructure on mechanical properties of γ-TiAl based alloys can be summarized as follows: coarse-grained “fully lamellar” (FL) and “nearly lamellar” (NL) microstructures exhibit relatively high fracture toughness and creep resistance, but poor tensile ductility and strength especially at room temperature [1-4]....

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  • ...In this section the industrial scale processing routes established for wrought engineering γ-TiAlbased alloys are treated, where the focus is put on ingot metallurgy (IM) and forging [2-4]....

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Journal ArticleDOI
TL;DR: In this paper, the authors describe aspects of the science and technology of titanium aluminide (TiAl) alloy system and summarise the low and high temperature mechanical and environmental properties exhibited by different alloy generations.
Abstract: The present article will describe aspects of the science and technology of titanium aluminide (TiAl) alloy system and summarise the low and high temperature mechanical and environmental properties exhibited by different alloy generations. In terms of processing developments, conventional gravity casting and near net shape casting would be discussed in detail. Also newer and non-conventional forging and additive manufacturing routes would be briefly highlighted. Extensive investigations of TiAl alloys have enabled their commercial implementation in aerospace and automotive industries. The GEnx™ engine is the first commercial aircraft engine that used TiAl (alloy 48–2–2) for their low pressure turbine blades. Among non GE engines, recently, new β-stabilised TiAl alloy (TNM) is being used to manufacture LPT blades for PW1100G™ engines. TiAl materials and design processes can reduce engine weight and improve engine performance.

408 citations


"Advanced Intermetallic TiAl Alloys" refers background in this paper

  • ...stationary gas turbines [4,14,15]: 1) γ-TiAl has a specific elastic stiffness 50% greater than structural materials commonly used in aircraft engines....

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  • ...For more information the reader is referred to [15]....

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  • ...%) in the low pressure turbine (LPT) of the GEnx TM engine, because this section of the engine offers the highest weight reduction potential [15]....

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Journal ArticleDOI
TL;DR: In this article, electron beam melting (EBM) is used to realize a selective densification of metal powder by melting it in a layerwise manner following a CAD design, and microstructure, the residual porosity and the chemical composition of the samples have been investigated both immediately after EBM and after heat treatments.

377 citations