Lesson Recap previous lecture

Nội dung text: Lesson Recap previous lecture

1. RECAP PREVIOUS LECTURE ✓ Phase ✓ Phase equilibrium ✓ Component ✓ Phase diagram ✓ Phase rule
2. PHASE DIAGRAMS AND PHASE RULE 2
3. Lecture Outline ✓ Introduction ✓ Solubility Limits ✓ Phases ✓ Phase Equilibrium ✓ Interpretation of Phase Diagrams • Binary Isomorphous Systems (Cu-Ni) • Development of Microstructure • Mechanical Properties • Binary Eutectic Systems • Development of Eutectic Alloy Microstructure 3
4. Components and Phases • Components: The elements or compounds that are mixed initially (Al and Cu). • Phases: A phase is a homogenous, physically distinct and mechanically separable portion of the material with a given chemical composition and structure ( and ). Aluminum- Copper Alloy 4
5. Phase Equilibria: Solubility Limit • Solution – solid, liquid, or gas solutions, single phase • Mixture – more than one phase Sugar/Water Phase Diagram • Solubility Limit: Maximum concentration for 100 Solubility which only a single phase L 80 Limit C) solution exists. ° (liquid) 60 L + Question: What is the S solubility limit for sugar in 40 (liquid solution water at 20°C? i.e., syrup) (solid 20 sugar) Temperature ( Temperature Answer: 65 wt% sugar. At 20°C, if C < 65 wt% sugar: syrup 0 20 40 6065 80 100 At 20°C, if C > 65 wt% sugar: syrup + sugar C = Composition (wt% sugar) Water Sugar
6. Equilibrium • A system is at equilibrium if its free energy is at a minimum, given a specified combination of temperature, pressure and composition. • The (macroscopic) characteristics of the system do not change with time — the system is stable. • A change in T, P or C for the system will result in an increase in the free energy and possible changes to another state whereby the free energy is lowered. 6
7. One Component Phase Diagram 7
8. Phase Diagrams • Indicate phases as a function of Temp, Comp and Pressure. • Focus on: - binary systems: 2 components. - independent variables: T and C (P = 1 atm is almost always used). T(°C) 1600 • 2 phases: L (liquid) 1500 L (liquid) (FCC solid solution) 1400 • 3 different phase fields: Cu-Ni L system 1300 L + 1200 (FCC solid 1100 solution) 1000 0 20 40 60 80 100 wt% Ni 8
9. Effect of Temperature & Composition (Co) • Changing T can change # of phases: path A to B. • Changing Co can change # of phases: path B to D. T(°C) 1600 1500 L (liquid) 1400 B D 1300 Cu-Ni system 1200 (FCC solid solution) 1100 A 1000 0 20 40 60 80 100 wt% Ni Cu 9
10. Determination of phase(s) present • Rule 1: If we know T and Co, then we know: --how many phases and which phases are present. • Examples: Cu-Ni phase diagram Melting points: Cu = 1085°C, Ni = 1453 °C Solidus - Temperature where alloy is completely solid. Above this line, liquefaction begins. Liquidus - Temperature where alloy is completely liquid. Below this line, solidification begins. 10