ºÝºÝߣ

ºÝºÝߣShare a Scribd company logo

Section 3 .pptx

•
•
K
kareemhamad3

The document discusses various crystal structures including simple cubic, body centered cubic, and face centered cubic structures. It then discusses atomic packing factors for these different structures. Next, it covers alloys and phase diagrams. It defines key concepts for phase diagrams including solubility, liquidus and solidus curves, and how to determine composition using tie lines. Finally, it provides an example problem of determining the composition of phases in a Cu-40% Ni alloy at different temperatures using the phase diagram.

1 of 20
MATERIAL SCIENCE ENG. KAREEM. H. MOKHTAR
CRYSTAL STRUCTURES
• Coordination # = 6 (# nearest neighbors) SIMPLE CUBIC STRUCTURE (SC)
• Coordination # = 8 • Atoms touch each other along cube diagonals. BODY CENTERED CUBIC STRUCTURE (BCC)
• Coordination # = 12 • Atoms touch each other along face diagonals. FACE CENTERED CUBIC STRUCTURE (FCC)
ATOMIC PACKING FACTOR (APF) APF = Volume of atoms in unit cell* Volume of unit cell *assume hard spheres
close-packed directions a R=0.5a contains 8 x 1/8 = 1 atom/unit cell APF = a3 4 3 p (0.5a) 3 1 atoms unit cell atom volume unit cell volume = 0.52 ATOMIC PACKING FACTOR: SCC
ATOMIC PACKING FACTOR: BCC a APF = 4 3 p ( 3a/4)3 2 atoms unit cell atom volume a3 unit cell volume length = 4R = Close-packed directions: 3 a • APF for a body-centered cubic structure a R a 2 a 3 = 0.68
ATOMIC PACKING FACTOR: FCC maximum achievable APF APF = 4 3 p ( 2a/4)3 4 atoms unit cell atom volume a3 unit cell volume Close-packed directions: length = 4R = 2 a Unit cell contains: 6 x1/2 + 8 x1/8 = 4 atoms/unit cell a 2 a =0.74
ALLOYS
PHASE DIAGRAM A phase diagram shows the phases and their compositions at any combination of temperature and alloy composition
SOLUBILITY • how much of each material or component we can combine without producing an additional phase • Unlimited Solubility • When we pour a substance into another and stir, and only one phase is produced regardless the quantity. • Limited Solubility • when we pour a substance into another and stir, and two phases is produced after a certain amount.
CONDITIONS FOR UNLIMITED SOLID SOLUBILITY • the Hume-Rothery rules, are as follows: • 1. Size factor: The atoms or ions must be of similar size, with no more than a 15% difference in atomic radius • 2. Crystal structure: The materials must have the same crystal structure • 3. Valence: The ions must have the same valence • 4. Electronegativity: The atoms must have approximately the same electronegativity.
BINARY PHASE DIAGRAMS • When only two elements or two compounds are present in a material, a binary phase diagram can be constructed.
LIQUIDUS AND SOLIDUS CURVES Liquidus temperature is the temperature above which a material is completely liquid Solidus temperature is the temperature below which the alloy is 100% solid.
Section 3 .pptx
HOW TO DETERMINE A COMPOSITION A tie line is a horizontal line within a two-phase region drawn at the temperature of interest
QUESTION 1 Determine the composition of each phase in a Cu-40% Ni alloy at 1300°C, 1270°C, 1250°C, and 1200°C
SOLUTION 1300°C: Only liquid is present The liquid must contain 40%Ni 1270°C:Two phases are present the liquid contains 37% Ni, and the solid contains 50% Ni. 1250°C: two phases are present. the liquid contains 32% Ni, and the solid contains 45% Ni. 1200°C: Only solid is present, so the solid must contain 40% Ni.
Section 3 .pptx

More Related Content

Section 3 .pptx

  • 3. • Coordination # = 6 (# nearest neighbors) SIMPLE CUBIC STRUCTURE (SC)
  • 4. • Coordination # = 8 • Atoms touch each other along cube diagonals. BODY CENTERED CUBIC STRUCTURE (BCC)
  • 5. • Coordination # = 12 • Atoms touch each other along face diagonals. FACE CENTERED CUBIC STRUCTURE (FCC)
  • 6. ATOMIC PACKING FACTOR (APF) APF = Volume of atoms in unit cell* Volume of unit cell *assume hard spheres
  • 7. close-packed directions a R=0.5a contains 8 x 1/8 = 1 atom/unit cell APF = a3 4 3 p (0.5a) 3 1 atoms unit cell atom volume unit cell volume = 0.52 ATOMIC PACKING FACTOR: SCC
  • 8. ATOMIC PACKING FACTOR: BCC a APF = 4 3 p ( 3a/4)3 2 atoms unit cell atom volume a3 unit cell volume length = 4R = Close-packed directions: 3 a • APF for a body-centered cubic structure a R a 2 a 3 = 0.68
  • 9. ATOMIC PACKING FACTOR: FCC maximum achievable APF APF = 4 3 p ( 2a/4)3 4 atoms unit cell atom volume a3 unit cell volume Close-packed directions: length = 4R = 2 a Unit cell contains: 6 x1/2 + 8 x1/8 = 4 atoms/unit cell a 2 a =0.74
  • 11. PHASE DIAGRAM A phase diagram shows the phases and their compositions at any combination of temperature and alloy composition
  • 12. SOLUBILITY • how much of each material or component we can combine without producing an additional phase • Unlimited Solubility • When we pour a substance into another and stir, and only one phase is produced regardless the quantity. • Limited Solubility • when we pour a substance into another and stir, and two phases is produced after a certain amount.
  • 13. CONDITIONS FOR UNLIMITED SOLID SOLUBILITY • the Hume-Rothery rules, are as follows: • 1. Size factor: The atoms or ions must be of similar size, with no more than a 15% difference in atomic radius • 2. Crystal structure: The materials must have the same crystal structure • 3. Valence: The ions must have the same valence • 4. Electronegativity: The atoms must have approximately the same electronegativity.
  • 14. BINARY PHASE DIAGRAMS • When only two elements or two compounds are present in a material, a binary phase diagram can be constructed.
  • 15. LIQUIDUS AND SOLIDUS CURVES Liquidus temperature is the temperature above which a material is completely liquid Solidus temperature is the temperature below which the alloy is 100% solid.
  • 17. HOW TO DETERMINE A COMPOSITION A tie line is a horizontal line within a two-phase region drawn at the temperature of interest
  • 18. QUESTION 1 Determine the composition of each phase in a Cu-40% Ni alloy at 1300°C, 1270°C, 1250°C, and 1200°C
  • 19. SOLUTION 1300°C: Only liquid is present The liquid must contain 40%Ni 1270°C:Two phases are present the liquid contains 37% Ni, and the solid contains 50% Ni. 1250°C: two phases are present. the liquid contains 32% Ni, and the solid contains 45% Ni. 1200°C: Only solid is present, so the solid must contain 40% Ni.