Fritz Appel

Bio: Fritz Appel is an academic researcher from University of Stuttgart. The author has contributed to research in topics: Titanium aluminide & Creep. The author has an hindex of 3, co-authored 7 publications receiving 515 citations.

Gamma titanium aluminide alloys : science and technology

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

Titanium aluminide based alloy

Abstract: The invention concerns titanium aluminide based alloys produced by using cast iron and powder metallurgy techniques. Said alloys consist of Ti - z A1 - y Nb, y corresponding to the following formula: 44.5 atom % % ≤ y ≤ 45.5 atom % and x corresponding to the following formula: 5 atom % ≤ x ≤ 10 atom %, optionally additions of B and/or of C with contents ranging between 0.05 atom % and 0.8 atom %. Said alloy is characterized in that it contains a molybdenum (Mo) content ranging between 0.1 atom % and 3.0 atom %.

Internal friction and creep of titanium aluminides with different microstructure

Abstract: A Ti-46.5 Al-4 (Cr, Nb, Ta, B) alloy (at.%) with different microstructures (fine-grained primary annealed or coarse-grained fully lamellar) was examined both by mechanical-loss (internal-friction) and creep experiments. The mechanical-loss spectra (0.01-10 Hz), ranging from 300 up to 1300 K, show two phenomena: (i) A loss peak at about 900 K (0.01 Hz) which occurs only in samples with a lamellar microstructure. The activation enthalpy, determined from the frequency shift, is 3.0 eV. The Debye-type peak is related to thermally activated reversible local movement of dislocation segments which are pinned at the lamellae interfaces and within gamma lamellae. (ii) A high-temperature damping background above 1000 K which is controlled by an activation enthalpy of 3.8 to 3.9 eV. This value agrees well with the activation enthalpy determined by creep tests and is in the range of values reported for self-diffusion of Al. These results indicate that both properties (high-temperature background and creep) are controlled by volume diffusion-assisted climb of dislocations.

Design, Processing, Microstructure, Properties, and Applications of Advanced Intermetallic TiAl Alloys†

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.

Polysynthetic twinned TiAl single crystals for high-temperature applications

Abstract: Increasing the temperature of jet engines requires materials that are stable against degradation. Towards this goal, growth of TiAl alloys with high strength and ductility, as well as superior creep resistance, is reported at high temperatures.

TiAl alloys in commercial aircraft engines

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.