8.1TheGasTurbine-UniversitàdegliStudidiTrento.docVIP

UNIVERSITA’ DEGLI STUDI DI TRENTO Facoltà di Ingegneria Corso di laurea Specialistica in Ingegneria dei Materiali Metallurgia dei metalli non ferrosi Docente: Prof. Diego Colombo Nickel-based superalloys and their application in the aircraft industry Alexander Glage Anno accademico 2006-2007 Contents 1. Introduction 3 2. Fundamentals of nickel-base superalloys 4 3. Microstructure of nickel based superalloys 5 3.1 ? and ?′?phase 5 3.2 Carbides 6 3.3 Topologically Close-Packed Phases 8 4. Chemical Compositions 9 5. Possibilities for strengthening 12 5.1 The ??mixed – crystal 12 5.2 The ?′ precipitant 12 5.3 Carbide Precipitation ( Grain Boundary Strengthening ) 13 5.4??′′ Precipitation 14 5.5 Strength at high temperatures 14 5.6 Behaviour of dislocations 15 6. Heat treatments 16 6.1 Stress Relieving 16 6.2 Annealing 17 6.3 Heat treatment for strengthening 18 6.3.1 Solution treating 18 6.3.2 Quenching 19 6.3.3 Aging 19 7. Coatings 19 8. Applications 20 8.1 The Gas Turbine 20 8.2 GAS TURBINE BLADE CASTING 22 8.2.1 Directional solidification (DS) 23 8.2.2 Single crystal (SX) casting 23 8.3 Turbine Discs 24 8.4 Turbochargers 25 Bibliography 26 1. Introduction A superalloy is a metallic alloy which is developed to resist most of all high temperatures, usually in cases until 70 % of the absolute melting temperature. All of these alloys have an excellent creep, corrosion and oxidation resistance as well as a good surface stability and fatigue life. The main alloying elements are nickel, cobalt or nickel – iron, which can be found in the 8th group of the periodic system of the elements. Figure 1 Main alloying and partioning elements [3] Fields of application are found particularly in the aerospace industry and in the nuclear industries, e.g. for engines and turbines. The development of these advanced alloys allows a better exploitation of engines, which work at high temperatures, because the Turbine Inlet Temperature ( TIT ) depends on the temperature ca