Metal Microstructure Quiz
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Questions and Answers

What is the term used for the process in which metal solidifies into many small crystals rather than a single crystal?

  • Homogeneous solidification
  • Microcrystalline formation
  • Nucleation spread
  • Heterogeneous nucleation (correct)
  • Which of the following best describes the effects of rapid solidification on grain size?

  • It leads to coarse and irregular grains.
  • It has no effect on grain size.
  • It produces a larger grain size.
  • It typically leads to a finer grain size. (correct)
  • What are the imperfections in the crystal structure of metals called that occur due to the interaction of grains?

  • Phase boundaries
  • Crystal defects
  • Grain boundaries (correct)
  • Atomic voids
  • What is the primary method by which the microstructure of a metal can be visually examined?

    <p>Optical microscopy (C)</p> Signup and view all the answers

    In wrought processes, what is the predominant characteristic of the grain structure of deformed metals?

    <p>Elongated grains aligned in the direction of deformation (A)</p> Signup and view all the answers

    What is the purpose of using etchants when examining metal microstructures?

    <p>To attack regions of high stress and reveal grain boundaries (C)</p> Signup and view all the answers

    Why are alloys preferred over pure metals in practical applications?

    <p>Alloys can be tailored to improve specific properties such as strength and corrosion resistance. (B)</p> Signup and view all the answers

    What primarily influences the variation in properties of metals at the microstructural level?

    <p>The presence of grain boundaries and atomic arrangement irregularities (A)</p> Signup and view all the answers

    What is the maximum copper solubility in silver as indicated in the Ag-Cu system phase diagram?

    <p>8.8 wt% at 780°C (A)</p> Signup and view all the answers

    What is the significance of the eutectic point in the Ag-Cu system?

    <p>It is a point where three phases are in equilibrium. (A)</p> Signup and view all the answers

    What process occurs at 723°C in the Fe-Cu system phase diagram?

    <p>Eutectoid transformation (B)</p> Signup and view all the answers

    During rapid cooling of alloys, what is likely to happen to the phase with the highest melting temperature?

    <p>It will solidify first. (B)</p> Signup and view all the answers

    What structural feature is commonly observed in the final solid structure due to non-equilibrium conditions?

    <p>Dendrites (D)</p> Signup and view all the answers

    What does compositional segregation refer to in the context of alloy solidification?

    <p>Non-uniform composition in the final structure (A)</p> Signup and view all the answers

    Which of the following statements about phase diagrams is correct?

    <p>They show equilibrium conditions. (B)</p> Signup and view all the answers

    Which type of phase involves a mixture of more than one metallic element?

    <p>Alloy (A)</p> Signup and view all the answers

    What best describes equiaxed grain structures?

    <p>Grains equal in all dimensions (A)</p> Signup and view all the answers

    Which of the following accurately defines solidification?

    <p>The transformation from liquid to solid state (C)</p> Signup and view all the answers

    In the context of alloys, what is true about a binary alloy?

    <p>Contains two metallic elements (C)</p> Signup and view all the answers

    Which grain structure is characterized by its elongation along a specific direction?

    <p>Radial (C)</p> Signup and view all the answers

    What does the freezing diagram illustrate?

    <p>The changes from liquid to solid substances (D)</p> Signup and view all the answers

    Which of the following is NOT a type of grain structure?

    <p>Heterogeneous (B)</p> Signup and view all the answers

    What effect does etching have on a metal's surface as shown in the figures?

    <p>It affects the reflection of incident light. (A)</p> Signup and view all the answers

    How do grain structures change during solidification?

    <p>They depend on the solidification conditions. (D)</p> Signup and view all the answers

    What is true about intermetallic compounds in relation to phases?

    <p>They are defined as structurally homogeneous regions. (C)</p> Signup and view all the answers

    What characterizes the solidification process of pure metals compared to alloys?

    <p>Pure metals have a defined melting point. (B)</p> Signup and view all the answers

    In the copper-nickel system, what does the phase diagram allow you to determine?

    <p>The solid and liquid phases for specific compositions and temperatures. (C)</p> Signup and view all the answers

    Which temperature is defined as the liquidus in the cooling curve of alloys?

    <p>The temperature where solid begins to form. (D)</p> Signup and view all the answers

    What thermodynamic concept is reflected in both the cooling curves and the phase diagrams?

    <p>Latent heat of fusion. (B)</p> Signup and view all the answers

    What is a key reason why copper and silver exhibit partial solid solubility in each other?

    <p>Their atomic sizes differ significantly. (D)</p> Signup and view all the answers

    What is a characteristic difference between the solidus and liquidus in alloy cooling curves?

    <p>The solidus is the temperature where the last liquid solidifies. (B)</p> Signup and view all the answers

    Why do alloys solidify over a range of temperatures rather than at a single temperature like pure metals?

    <p>The presence of different sized atoms causes a range of solidification temperatures. (D)</p> Signup and view all the answers

    What happens to latent heat during the phase transition from liquid to solid?

    <p>It is released to the surrounding environment. (D)</p> Signup and view all the answers

    What does a mixture of 50Cu 50Ni at 1300°C primarily consist of?

    <p>A copper-rich liquid and a nickel-rich solid. (B)</p> Signup and view all the answers

    What must be true for a substitutional solid solution to form?

    <p>The atoms must have similar valencies and the same crystal structure. (B)</p> Signup and view all the answers

    In an interstitial solid solution, what is a requirement for the solute atom's size relative to the solvent atom?

    <p>It must be less than 60% of the solvent atom's diameter. (C)</p> Signup and view all the answers

    Which of the following is an example of an intermetallic compound?

    <p>Silver-tin alloy (A)</p> Signup and view all the answers

    What does a binary phase diagram represent?

    <p>The phases present in an alloy at various temperatures and compositions. (B)</p> Signup and view all the answers

    Which type of solid solution can be described as atoms fitting into the spaces between solvent atoms?

    <p>Interstitial solid solution (B)</p> Signup and view all the answers

    Which of the following pairs can form a substitutional solid solution?

    <p>Gold and copper (B)</p> Signup and view all the answers

    What is true about the atomic diameters of gold (Au) and copper (Cu)?

    <p>They both have the same crystal structure. (B)</p> Signup and view all the answers

    Which of the following statements accurately describes the atomic sizes of metals that can form substitutional solid solutions?

    <p>They must be within 15% of each other. (A)</p> Signup and view all the answers

    Which metal is widely known to form interstitial solid solutions when combined with iron?

    <p>Carbon (B)</p> Signup and view all the answers

    Which of the following characteristics is NOT required for forming a substitutional solid solution?

    <p>Hisotropic atomic shapes (B)</p> Signup and view all the answers

    Flashcards

    Unit Cell

    The smallest repeating unit in a crystalline structure.

    Homogeneous Nucleation

    The process of forming a new crystal from a liquid, typically initiated by atoms losing thermal energy and forming a unit cell.

    Heterogeneous Nucleation

    The process of forming a new crystal from a liquid, initiated by impurities within the metal.

    Grain Boundaries

    The boundaries between individual crystals in a metal, which are imperfections in the crystal structure.

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    Wrought Metals

    Metals that are deformed by processes like hammering, rolling, or pressing.

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    Working (Metals)

    The process of shaping metals by deformation, which can change the size and arrangement of grains.

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    Alloy

    A mixture of two or more metals, or metals and nonmetals, engineered to achieve specific desired properties.

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    Microstructure

    The microscopic structure of a material, visible under a microscope, which can reveal information about its properties.

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    What is a 'phase' in materials science?

    A structurally homogeneous region within a system that's physically distinct from other regions.

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    What is an alloy?

    A mixture of two or more metallic elements (possibly with non-metallic elements), often produced by fusion at temperatures above their melting points.

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    What is the difference between a binary and a ternary alloy?

    A binary alloy contains two elements, and a ternary alloy contains three.

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    What is an equiaxed grain structure?

    Grain structures are roughly equal in all dimensions.

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    What is a radial grain structure?

    Grain structures are elongated along a specific direction.

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    What is solidification?

    The process of a substance changing from a liquid to a solid state.

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    What is homogeneous nucleation?

    The process of forming a new crystal from a liquid, typically initiated by atoms losing thermal energy and forming a unit cell.

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    What is heterogeneous nucleation?

    The process of forming a new crystal from a liquid, initiated by impurities within the metal.

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    What is a freezing diagram?

    Shows typical changes from liquid to solid substances, with nuclei of crystallization.

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    What are grain boundaries?

    The boundaries between individual crystals in a metal, which are imperfections in the crystal structure.

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    Substitutional Solid Solution

    A mixture of elements at the atomic level, where solute atoms replace solvent atoms at the lattice sites. This happens when atoms have similar valencies, crystal structures, and size differences within 15%.

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    Interstitial Solid Solution

    A mixture of elements at the atomic level, where solute atoms fit into the spaces between solvent atoms. This occurs when the solute atom is significantly smaller than the solvent atom.

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    Intermetallic Compound

    A compound formed when two or more metals combine in a specific, fixed ratio (stoichiometry).

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    Phase Diagram

    A graphical representation of the phases present in an alloy at different temperatures and compositions. Usually, temperature is on the vertical axis and composition on the horizontal axis.

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    Binary Phase Diagram

    A type of phase diagram that shows the phases present in an alloy composed of two elements at different temperatures and compositions.

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    Solid Solubility

    The ability of two elements to mix and form a homogeneous solid solution.

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    Solubility Limit

    The maximum amount of solute that can dissolve in a solvent at a specific temperature.

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    Electronegativity Difference

    A measure of the difference in electronegativity between two elements. It indicates the tendency for elements to form ionic bonds.

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    Ionic Bonding Tendency

    The tendency of elements to form ionic bonds. It increases with the electronegativity difference between the elements.

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    Crystal Structure Tendency

    The tendency of metals to crystallize into specific structures (e.g., FCC, BCC).

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    Eutectic Point

    A specific composition of an alloy where three phases (solid, solid, and liquid) coexist at a specific temperature. It signifies a point of equilibrium where the alloy can transition between these three phases.

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    Eutectoid Transformation

    A transformation where a solid solution (gamma) transforms into two different solid solutions (alpha and Fe₃C) at a specific temperature. This is a common reaction in iron-carbon alloys.

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    Solidification

    The process of a liquid turning into a solid. During solidification, the phase with the highest melting point crystallizes first, shaping the final structure of the metal.

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    Compositional Segregation

    The phenomenon where the composition of a metal is uneven, resulting in different concentrations of elements in different parts of the material. This occurs often during rapid cooling.

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    Dendrites

    Tree-like structures that can form in metals during rapid cooling. They result from the non-uniform composition created by compositional segregation.

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    Liquidus

    The temperature at which a molten metal begins to solidify upon cooling. Think of it as the starting point of crystallization.

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    Solidus

    The temperature at which the last liquid completely solidifies upon cooling. The final point of the transition.

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    Latent Heat of Fusion

    The energy absorbed or released during a phase change between solid and liquid states. Think of it as the heat needed for melting or freezing.

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    Solubility

    The ability of one material to dissolve into another. Think of how sugar dissolves in water.

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    Cooling Curve of a Pure Metal

    A cooling curve for a pure metal has a plateau at the melting point, meaning the temperature stays constant because the heat released during solidification balances the cooling effect. Think of a flat line.

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    Cooling Curve of an Alloy

    The cooling curve of an alloy shows a temperature range for solidification because the mixture of metals solidifies progressively with different compositions. Think of a slope.

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    Equilibrium Phase Diagram

    A phase diagram displays the equilibrium phases at various temperatures and compositions in a metal system, allowing you to predict the phases present for any composition at a given temperature. Think of a map.

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    Partial Solid Solubility

    This type of phase diagram illustrates the limited solubility of some materials, meaning they do not fully mix at an atomic level. Think of oil and water.

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    Composition Range in Cu-Ni Alloys

    The size difference between copper and nickel atoms causes a range of compositions in the final solid, as copper and nickel solidify at different rates. Think of sorting marbles by size.

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    Phase Diagram Construction

    Phase diagrams are created by plotting cooling curves for various compositions. These curves show the temperature and composition at which phases change, defining the boundaries on the phase diagram.

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