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Materials Engineering Materials Engineering introductory overview Materials Engineering - metals technology „Technology” Greek origin „Technos” technical „logos” logikal Theory and practice of some technical processes. Production, planning, organizations (+information and experience) Materials Engineering - metals technology Meaning changed with time Before the industrial revolution: the sum of the knowledge of a single worker. After the industrial revolution, first part of XIX century: Manufacturing industry, technical knowledge and the science are separated into various technologies. After the industrial revolution, second part of XIX century: Mass production, important technologies: Mechanization, automatization, organization Materials Engineering - metals technology Meaning changed with time Since 1960: New disciplines (electronics, informatics, computer science), various scientific background Increased productivity, the skilled labor is less important Materials Engineering Metals technology Metal producing and processing technologies machining industry Construction Product Production quality possibilities Material Technology production abilities Materials Engineering examples 1) Car body sheet rolling technology deep drawing 2) Heat exchanger: steel, stainless steel, titanium different welding technologies Materials Engineering Materials Metallic Non metallic Ferrous -> iron, steel Organic Plastics or polymers Nonferrous Wood, paper, rubber -> Al, Mg, Cu, Ni, Pb Inorganic ceramics (technical ceramics) glass Composites: utilize more than one type of material Materials Engineering Materials Engineering The properties of materials are determined by two group of factors: Internal factors determine the material’s structure - Chemical composition (impurity and alloying) - Microstructure (equilibrium or non-equilibrium phases, their amount, quality distribution, and sizes) External factors determine the service condition of a machine part - Temperature (mean value and amplitude) - Rate of deformation - Stress state - Chemical effects - Corrosion effects - Irradiation effects Materials Engineering Internal factors are determined by all the - Metal production - Form making - Forming - Heat treating - Surface treating - Joining process Materials Engineering External factors – service conditions are determined by how the machine part is used T (°C) 1000 600 e.g.: service temperature range 1950 1960 1970 1980 1990 -200 spacecraft Materials Engineering Need for better material properties because: a) To decrease the weight of the equipment b) Increasing the quality In practice 70-80,000 various types of materials are used. More than 1000 different types of steel Materials Engineering General layout of the subject Metal producing technologies: iron and steel making Producing of nonferrous metals Form making technologies: casting, pre-forming Never pure, contains by plastic deformation impurities Powder metallurgy Cast ingot, castings, rolled bloom, billet, rod, wire, strip, sheet, forged bar, block Forming processes, machining processes, heat treatments and surface treatments Joining process: Welding Materials Engineering Phase transformation Phase diagrams Phase Transformation Why is it important for us? o Temperature, chemical composition and pressure can change the properties of materials o Understanding what happens during heat treating processes o Understanding the development of the microstructure Phase Transformation Today’s topics o Terminology of phase diagrams and phase transformations o Thermodynamics of phase transformations o Phase diagrams Phase Transformation Terminology Component: Pure metals and/or compounds of which an alloy is composed. e.g. in a copper–zinc brass, the components are Cu and Zn System: Series of possible alloys consisting of the same components, but without regard to alloy composition Solid solution consists at least two different types of atoms the solute atoms occupy either substitutional or interstitial positions in the solvent lattice Phase Transformation Solubility limit A maximum concentration of solute atoms that may dissolve in the solvent to form a solid solution The solubility of sugar in a sugar–water syrup Figures from Callister, Mat. Sci. and Eng. An Introduction, 8th edition Phase Transformation Phase A homogeneous portion of a system that has uniform physical and chemical characteristics. Own distinct properties • Chemical composition • State of matter (e.g. water+ice) • Crystal structure • … 1 phase Homogeneous system: single-phase system 2 phases Heterogeneous system: two or more phases Phase Transformation Thermodynamics Internal energy U: the energy needed to create the system Enthalpy (H=U+pV): U+ energy required to make room for it by displacing its environment Enthropy (S): expression of disorder or randomness, the energy not available for work Helmholtz free energy (F=U-TS) Gibbs free energy (free enthalpy)(G=H-TS) G Equilibrium Gsolid A system is at equilibrium if its free energy is at a minimum under some specified Gliquid combination of temperature, pressure, and composition. T The characteristics of the system do not change with time. Phase Equilibrium Phase Equilibrium In an equilibrium system the ratio of phases are constant. 3 2 1 Phase Equilibrium Equilibrium Two component system (A-B) (ideal solution: exchanging any two atoms does not change the enthalpy) Entropy, S disorder or randomness Processes reduce the state of order of the initial systems. S A B Phase Equilibrium Equilibrium Two component system (A-B), ideal solution Phase Equilibrium L liquid α phase T1 T2 L L+α T3 T4 α T5 CL Cα CL Cα Phase Equilibrium L L+α α CL Cα C L Cα Phase Equilibrium Metastable state Often the state of equilibrium is never completely achieved because the rate of approach to equilibrium is extremely slow. non-equilibrium or metastable state. Metastable state or microstructure may persist indefinitely (changes only extremely slight) Often, metastable structures are of more practical significance than equilibrium ones. Phase Diagrams Phase or equilibrium diagram Information about the phase structure of a particular system. Parameters Informations • Temperature • State of the matter, crystal structure • Pressure • Phase composition • Composition • Chemical composition of the phases several different varieties (e.g. composition-Temperature, pressure-Temperature) Phase Diagrams One-component (or unary) phase diagram Simplest, one-component system p-T phase diagram Note! phases at equilibrium Pressure–temperature phase diagram for H2O. Phase Diagrams Binary phase diagrams composition-Temperature transition from one phase to another, or the appearance or disappearance of a phase. Copper–nickel phase diagram Phase Diagrams Copper–nickel phase diagram Alloy (2) Point A: T=1100°C 1 phase: α, solid sol. of Cu and Ni C CNi=60%, CCu=40% Alloy (1) Point C: T=1400°C 1 phase: L, liquid CNi=35%, CCu=65% (1) (2) Phase Diagrams Copper–nickel phase diagram Alloy (1) Point B: T=1250°C 2 phases: α + L, C solid + liquid phase Composition: CNi=35%, CCu=65% Mass fraction of phases Wα=? %, WL= ? % Composition of phases: α: CNi=? %, CCu=? % L: CNi=? %, CCu=? % (1) (2) Phase Diagrams Copper–nickel phase diagram L α L L α L α α Phase Diagrams Copper–nickel phase diagram Lever rule ~ α ~ L CL C0 Cα Mass fraction of phases 퐶0−퐶퐿 퐶훼−퐶0 푊훼 = 퐶훼−퐶퐿 푊퐿 = 퐶훼−퐶퐿 Phase Diagrams Copper–nickel phase diagram Composition of phases ~ α ~ L CL C0 Cα wt% of Ni wt% of Ni in liquid phase in α phase The chemical composition of the phases is changing with the temperature change. Phase Diagrams Copper–nickel phase diagram Liquid phase: 35% Ni α phase: - Liquid phase: 34% Ni α phase: 46% Ni Liquid phase: 32% Ni α phase: 43% Ni Liquid phase: 35% Ni α phase: 37% Ni Liquid phase: - α phase: 35% Ni 25 46 Phase Diagrams Inhomogeneous and equilibrium phase Equilibrium solidification: • only for extremely slow cooling rates. • diffusional processes (diffusion rates are lower for lower temperatures and for solid phases) High cooling rate Low cooling rate Inhomogeneous Equilibrium structure structure Phase Diagrams Inhomogeneous and equilibrium phase Figure from Callister, Mat. Sci. and Eng. An Introduction, 8th edition Phase Diagrams Eutectic reaction Liquid phase α + (solid phases) Lead-Tin system Phase Diagrams Lead-Tin system Phase Diagrams Lead-Tin system Phase Diagrams Eutectoid reaction ( solid phase) α + (solid phases) Peritectic reaction α ( solid phase) + liquid phase (solid phases) Copper–zinc phase diagram Phase Diagrams Ceramic Phase Diagrams The two components are compounds that share a common element Similar to metal–metal systems Al2O2-Cr2O3 phase diagram Figure from Callister, Mat. Sci. and Eng. An Introduction, 8th edition Ceramic Phase Diagrams ZrO2-CaZrO3 phase diagram Ceramic Phase Diagrams BaTiO3 p-T phase diagram S A Hayward and E K H Salje ,J. Phys.: Condens. Matter 14 No 36 2002 p 599-604 Materials engineering Iron and steel making Metals: rarely exist in pure state mostly in ores Ore: Metallic and other compounds, mostly oxides Metallic content: Iron ores: 30-70% Fe Copper ores: 0.1-0.8 % Cu Molybdenum: 0.01-0.1% Mo 4 basic way to gain the metallic parts from ore: Reduction by carbon Electrolytic way costs Metallotermical process Dissociation 1) Reduction by carbon MeO + C Me + CO FeO + C [Fe] + {CO} molten metals gas 3+ 2- 2) Electrolytic way Al2O3 Al2 + 3O on the cathode: Al3+ + 3e- Al 3) Metallothermical process TilCl4 + 2Mg [Ti] + 2MgCl 4) Dissociation MeX [Me] + [x] only at high energy level Iron and steel Iron and
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