1 Chapter II: Metallurgical Fundamentals 1 Chapter II Metallurgical Fundamentals Chapter II: Metallurgical Fundamentals 2 Content • Primary Bonds (liên kết) • Secondary Bonds • Crystalline Structure • Theoretical Yield Strength • Mechanisms of Plastic Deformation • Strengthening Mechanisms • Recovery • Recrystallization 2 Chapter II: Metallurgical Fundamentals 3 Atomic Bonds • Primary Bonds: Strong atom-to-atom attractions by exchange of valence electrons • Secondary Bonds: Weak attraction between molecules (van der Waals forces) Chapter II: Metallurgical Fundamentals 4 Primary Bonds • Ionic • Covalent • Metallic 3 Chapter II: Metallurgical Fundamentals 5 Ionic Bonding Groover (2005) Ionic Bond (Combination of metallic and nonmetallic elements): Atoms either get electrons or loose electrons to make their outer shells complete so that they become positive or negative ions. Opposite charge atoms attract each other. Chapter II: Metallurgical Fundamentals 6 Covalent Bonding Groover (2005) Covalent Bond (Nonmetallic elements): Atoms share outer shell electrons. 4 Chapter II: Metallurgical Fundamentals 7 Metallic Bonding Groover (2005) Metallic Bond (Metals and their alloys): Atoms loose their outer shell electrons and become “+” ions surrounded by a free electron cloud. Free electrons act as cement to hold atoms together. Chapter II: Metallurgical Fundamentals 8 Properties of Bonds Property Ionic Bond Covalent Bond Metallic Bond Hardness High Low to Very High Low to High Ductility Brittle Brittle Ductile Melting Point Temperature High Low to Very High Low to High Electrical & Thermal Conductivity Low Low High 5 Chapter II: Metallurgical Fundamentals 9 Secondary Bonds • Dipole forces ['daipoul] Các lực lưỡng cực • London forces • Hydrogen bonding Chapter II: Metallurgical Fundamentals 10 Dipole Forces Groover (2005) Two molecules with dipole property attract each other 6 Chapter II: Metallurgical Fundamentals 11 London Forces Groover (2005) Two molecules with temporary dipole property attract each other Chapter II: Metallurgical Fundamentals 12 Hydrogen Bonding Groover (2005) 7 Chapter II: Metallurgical Fundamentals 13 Crystalline Structure Groover (2005) Body Centered Cubic (BCC) Face Centered Cubic (FCC) Hexagonal Closed Packed (HCP) Examples BCC Chromium (Cr), Iron (Fe), Molybdenum (Mo), Tantalum (Ta), Tungsten (W) FCC Aluminum (Al), Copper (Cu), Gold (Au), Lead (Pb), Silver (Ag), Nickel (Ni) HCP Magnesium (Mg), Titanium (Ti), Zinc (Zn) Chapter II: Metallurgical Fundamentals 14 Elastic and Plastic Deformations undeformed crystal deformation elast c i deformation elastic and last c p i undeformed crystal theoretical to 30 2 G G τ π = Elastic deformation of crystal 8 Chapter II: Metallurgical Fundamentals 15 Theoretical & Actual Strengths Metal Shear Modulus in MPa Theoretical Shear Strength in MPa Actual Shear Strength in MPa Steel 75,800 2,527 to 12,063 150 to 750 Aluminum Alloys 27,500 917 to 4,377 50 to 150 Copper Alloys 41,400 1,380 to 6,589 100 to 250 Titanium Alloys 44,800 1493 to 7,130 350 to 800 Chapter II: Metallurgical Fundamentals 16 Plastic deformation of crystal 2 Kinds of plastic deformation: - Slide/Slip Mechanism and - Twining Mechanism Slide/Slip Mechanism 9 Chapter II: Metallurgical Fundamentals 17 Twining Mechanism undeformed crystal deformation plast c i t w i n n i n g p l a n e t w i n n i n g p l a n e Chapter II: Metallurgical Fundamentals 18 Imperfections • Point Defects – Vacancy – Ion-Pair Vacancy – Interstitialcy – Displaced Ion • Line Defects – Edge Dislocation – Screw Dislocation • Surface Defects – Grain Boundaries Definition: Imperfections or defects refer to the deviations in the regular pattern of the crystalline lattice structure. 10 Chapter II: Metallurgical Fundamentals 19 Typical Points Defects vacancy interstitialcy displaced ion (Frenkel Defect) ion-pair vacancy Groover (2005) Chapter II: Metallurgical Fundamentals 20 Animated Point Defects DMEMS [...]...Line Defects • Edge dislocation • Screw dislocation Chapter II: Metallurgical Fundamentals 21 Animated Edge Dislocation DMEMS Chapter II: Metallurgical Fundamentals 22 11 Animated Screw Dislocation DMEMS Chapter II: Metallurgical Fundamentals 23 Plastic Deformation Mechanism Chapter II: Metallurgical Fundamentals 24 12 Yield Strength of Actual Metals Y = Y0 + ∆Ys + ∆Yd + ∆Yp... = ky Hall-Petch d relationship d is the grain size and the constant ky ranges between 15 to 24 MPa mm1/2 for common steels Chapter II: Metallurgical Fundamentals 26 13 Effect of Plastic Deformation T < 0.3 Tm Ductility Yield Stress Plastic Deformation Chapter II: Metallurgical Fundamentals 27 Recovery Heating the deformed metal in a range of 0.3 Tm < T < 0.5 Tm will activate diffusion of atoms This... and thermal properties will be recovered as well Chapter II: Metallurgical Fundamentals 28 14 Recrystallization Recrystallization Primary Secondary Ductility Yield Stress Definition: Temperature at which the whole structure is completely recrystallized within one hour is named as recrystallization temperature Time T > 0.5 Tm Chapter II: Metallurgical Fundamentals 29 Heat treatment Dislocations will... (a) ch−a ñ (c) ñ ë 5500C (b) ñ ë 5250C (d) ñ ë 6500C Chapter II: Metallurgical Fundamentals 30 15 Yield Stress n mi 10 r 1h hr 10 Mutual Effect of Temperature and Time Annealing Temperature High amount of prior cold work Yield Stress Moderate amount of prior cold work Low amount of prior cold work Annealing Temperature Chapter II: Metallurgical Fundamentals 31 Typical Recrystallization Temperatures... single crystal metal with some dislocations ∆Ys: increase in yield strength due to solid solution hardening ∆Yd: increase due to dispersion hardening ∆Yp: increase due to phase boundaries Chapter II: Metallurgical Fundamentals 25 Values of Strength Components For ferritic steel for instance Y0 is about 30 MPa where xi is the weight percentage of the alloying element and ki is a weight factor ∆Ys = ∑... C-Steel 550oC tin 0 to 40oC Pure-Al 290 to 300oC zinc 50 to 100oC Dur-Al 360 to 400oC Mo 870oC W 900-1000oC Ni 400-600oC Cu Lead 200oC (changes drastically with alloying elements) -50 to 50oC Chapter II: Metallurgical Fundamentals 32 16 . 1 Chapter II: Metallurgical Fundamentals 1 Chapter II Metallurgical Fundamentals Chapter II: Metallurgical Fundamentals 2 Content • Primary Bonds (liên. Defects DMEMS 11 Chapter II: Metallurgical Fundamentals 21 Line Defects • Edge dislocation • Screw dislocation Chapter II: Metallurgical Fundamentals 22 Animated Edge Dislocation DMEMS 12 Chapter II: Metallurgical. Dislocation DMEMS 12 Chapter II: Metallurgical Fundamentals 23 Animated Screw Dislocation DMEMS Chapter II: Metallurgical Fundamentals 24 Plastic Deformation Mechanism 13 Chapter II: Metallurgical Fundamentals 25 Yield