Materials Science and Engineering --- MY2100 Chapters 1 and 2 Metals and Metal Structures Key Concepts  Major Engineering Alloy Systems  The Design Process  Metal Structures and Terms (Polymorphism, Solutions, Phase, Boundaries, Phase Morphology)

Materials Science and Engineering --- MY2100 Generic Iron-Based Metals

Materials Science and Engineering --- MY2100 Generic Copper-based Metals Generic Nickel--based Metals

Materials Science and Engineering --- MY2100 Generic Aluminum-based Metals

Materials Science and Engineering --- MY2100 Generic Titanium-based Metals

Materials Science and Engineering --- MY2100 Product/Process Realization Design Concept (Approximate Generic Data) Design Concept (Handbook and Supplier Data) Prototype (Material Verification Testing) First Article (Quality Assurance)

Materials Science and Engineering --- MY2100 Types of Material Properties  Structure-Insensitive—Properties which are nearly independent of microstructure: Density, Young’s Modulus, thermal expansion, specific heat  Structure-Sensitive—Properties which vary strongly with processing and detailed alloy composition Yield and tensile strength, ductility, fracture toughness, creep and fatigue strength

Materials Science and Engineering --- MY2100 Hierarchy of Structure (Metals) FeatureTypical Scale (m) Engineering Structures.003 m – 1000 m Aggregates of grains (crystals)0.01 mm – 10 mm Individual grains & phases (Size and shape) 0.1  m – 1000  m Grain and phase boundaries 0.01  m Atomic arrangements (crystal structure; solutions) 0.1 nm – 1 nm Subatomic structure  0.1 nm

Materials Science and Engineering --- MY2100 Crystal Structures of Selected Pure Metals  Face Centered Cubic (FCC) Aluminum (Al) Copper (Cu) Nickel (Ni)  Close packed hexagonal (CPH) Titanium Magnesium  Body Centered Cubic (BCC) Iron (Fe) Chromium (Cr) Tungsten (W)

Materials Science and Engineering --- MY2100 Polymorphism  Polymorphism  “Many Forms”  Some metals (and ceramics) change crystal structure as they are heated or cooled.  Behavior can affect: Forming operations Heat treatment and residual stresses Service characteristics  Can be “manipulated” through cooling rate and alloy chemistry  Examples include austenitic stainless steels and  +  titanium alloys

Materials Science and Engineering --- MY2100 Polymorphism in Alloys Austenitic stainless: FCC form stabilized with Ni Ti-6Al-4V: BCC form stabilized with aluminum

Materials Science and Engineering --- MY2100 Solid Solutions Solute atoms can dissolve in a solid solvent metal in two ways: Interstitial Solution o Solvent atoms fit within interstitial voids of the solvent crystal o Examples: C in iron; O in titanium Substitutional Solution o Solvent atoms replace atoms on solvent lattice o Examples: Ni in iron; Cu in aluminum

Materials Science and Engineering --- MY2100 Solid Solutions--II

Materials Science and Engineering --- MY2100 Material Phases  Phase-A region of material with uniform chemical and physical properties Pure, Liquid Water Water + Ice Ice Salt Water Solution Oil/Water Emulsion (1 Phase) (2 Phases) (1 Phase) (1 Phase--Solution) (2 Phases)

Materials Science and Engineering --- MY2100 Grain Boundaries  Separate regions of different crystal orientation  Low bond density (energy ~ 0.5 J/m 2 )  Open Structure (fast diffusion/impurity segregation)  Influence mechanical properties Low T  Increase strength & ductility High T  Decrease strength

Materials Science and Engineering --- MY2100 Phase Boundaries  Interfaces which separate regions of different chemical and physical properties.  Coherent boundaries Difference in chemical composition but not crystal structure Very low energy (~0.05 J/m2) May have coherency strain due to differences in lattice spacing.(increases boundary energy)

Materials Science and Engineering --- MY2100 Semi-Coherent and Incoherent Boundaries  Semi-Coherent Difference in composition and small difference in crystal structure Higher energy--more effective strengthening Periodic dislocations compensate for differences in atomic spacing  Incoherent Difference in composition and large difference in crystal structure Energy similar to grain boundary

Materials Science and Engineering --- MY2100 Semi-Coherent and Incoherent Boundaries-II

Materials Science and Engineering --- MY2100 Shapes of Grains & Phases Soap Bubbles  Processing, composition and energy relationships determine shape  “Equilibrium” shape Flat faces joined at 120 o “Bubble Raft” analogy

Materials Science and Engineering --- MY2100 Phase Morphology