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Chapter 6

Chapter 6. Phase Diagrams. Phase Diagrams • Binary Phase Diagrams • Ternary Phase Diagrams.

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Chapter 6

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  1. Chapter 6 Phase Diagrams Phase Diagrams • Binary Phase Diagrams • Ternary Phase Diagrams

  2. A substitutional solid solution is formed when atoms of a solute metal substitute for atoms of a solvent metal. Interstitial solid solution is formed when the interstitial atoms fit into the interstices of the solvent metal crystal structure.

  3. Porosity, which is caused by shrinkage at the center of a solidified ingot, is an impurity in the microstructure and is revealed by macroetching a slice taken through an ingot.

  4. An isothermal transformation is shown as an arrest on the cooling curve, during which time the phase transformation occurs. A continuous cooling transformation does not show an arrest, but the gradient of the cooling curve changes during the phase change.

  5. The length of the specimen, which changes abruptly during a phase transformation, is continuously monitored as it is heated or cooled to determine the temperature of the phase transformation.

  6. A binary phase diagram plots temperature on the y-axis and alloy composition on the x-axis.

  7. The melting point of a pure metal is indicated by an isothermal transformation on the cooling curve.

  8. The liquidus and solidus are the upper and lower boundaries between completely liquid and completely solid alloys.

  9. A tie line indicates the compositions of phases in an alloy coexisting at a specific temperature.

  10. As an alloy solidifies, each layer of solidifying metal deposited on the growing dendrites has a slightly different composition.

  11. Coring in cast Monel metal is removed by hot working and annealing, which homogenizes the structure. Etching reveals coring that is caused by the variable composition gradient in the grains of the alloy.

  12. The lever rule is used to figure the proportion of liquid phase transforming to eutectic phase, which occurs on crossing the eutectic reaction temperature.

  13. Hypoeutectic alloy compositions are located to the left of the eutectic composition, and hypereutectic alloy compositions are located to the right of the eutectic composition.

  14. When an alloy crosses the solvus during cooling, it undergoes a continuous cooling transformation. The solvusrepresents the limits of solubility for a solid phase.

  15. The intermediate phase divides a phase diagram into two parts, each of which contains a eutectic reaction.

  16. The copper-rich end of the copper-aluminum phase diagram indicates several electron compounds, which are illustrated by Greek letters.

  17. The silver-platinum alloy system exhibits a peritectic reaction.

  18. The room temperature microstructure of a 60% Ag and 40% Pt alloy exhibits a peritectic reaction that is uncompleted.

  19. A monotectic reaction occurs in the copper-lead phase diagram. L1 and L2 are two immiscible liquid phases.

  20. The pure titanium phase diagram exhibits an allotropic change at 883ºC. The low- and high-temperature solid solutions based on the allotropic forms of titanium are alpha and beta.

  21. The order-disorder transformation for a copper with 40% Zn alloy occurs at 465°C (870°F).

  22. Widmanstättenprecipitation occurs in the Ti-6Al-4V alloy as it cools from the beta-phase region into the alpha-plus-beta-phase region. A typical Widmanstätten structure has the microstructural appearance of geometrically interlacing needles.

  23. Precipitation hardening is a form of delayed precipitation. In a copper-aluminum alloy with 4% Al, precipitation hardening is achieved by quenching from the alpha-phase region and reheating in the alpha-plus-theta-phase region.

  24. The eutectoid region is the most important region of the iron-carbon diagram. This region is the iron-iron carbide diagram.

  25. Three ways to depict ternary phase diagrams are on triangular coordinates, on binary coordinates, and on three-dimensional coordinates.

  26. The percentages of each component of a ternary alloy are obtained by drawing lines through the alloy composition point parallel to the sides of the isotherm. The sum of the percentages must equal 100%.

  27. A space diagram illustrates the appearance of the component isotherms of a ternary solid solution alloy. Isotherms indicate a specific temperature during the cooling of the alloy when liquid phase and alpha phase are in equilibrium.

  28. A space diagram illustrates the appearance of the component isotherms of a ternary eutectic alloy. Isotherms represent points during the cooling of alloys in the system.

  29. Isothermal lines indicate the boundaries of the liquidus surface at different temperatures.

  30. The two methods of constructing isopleths are constant ratio and constant proportion.

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