Phase Diagrams in Materials Science Quiz

System may refer to a specific body of material under consideration or it may relate to the series of possible alloys consisting of the same components but without regard to alloy composition.

A solid solution consists of atoms of at least two different types; the solute atoms occupy either substitutional or interstitial positions in the solvent lattice, and the crystal structure of the solvent is maintained.

For many alloy systems and at some specific temperature, there is a maximum concentration of solute atoms that may dissolve in the solvent to form a solid solution; this is called a solubility limit.

<p>Phase equilibrium refers to equilibrium as it applies to systems in which more than one phase may exist.</p> Signup and view all the answers

<p>Metastable equilibrium is reflected by a constancy with time in the phase characteristics of a system.</p> Signup and view all the answers

<p>An example of phase equilibrium using a liquid-solid system is a sugar-water syrup in contact with solid sugar.</p> Signup and view all the answers

<p>Metastable structures are often of more practical significance than equilibrium ones because some materials rely on the development of metastable microstructures for their strength.</p> Signup and view all the answers

<p>Temperature, pressure, and composition.</p> Signup and view all the answers

<p>A phase diagram displays information about the control of the phase structure of a particular system, with temperature, pressure, and composition plotted against each other.</p> Signup and view all the answers

<p>A one-component (or unary) phase diagram represents a pure substance with composition held constant and pressure and temperature as variables.</p> Signup and view all the answers

<p>The different regions delineated on a one-component phase diagram are solid, liquid, and vapor, and each of the phases exist under equilibrium conditions over the temperature–pressure ranges of its corresponding area.</p> Signup and view all the answers

<p>alpha (a) field, liquid (L) field, and a two-phase a + L field.</p> Signup and view all the answers

<p>0 wt% Ni (100 wt% Cu) on the far left horizontal extreme to 100 wt% Ni (0 wt% Cu) on the right.</p> Signup and view all the answers

<p>isomorphous.</p> Signup and view all the answers

<p>lowercase Greek letters (a, b, g, etc.).</p> Signup and view all the answers

<p>An isomorphous phase diagram is a phase diagram where the two components are completely soluble in each other in both liquid and solid states.</p> Signup and view all the answers

<p>The three types of information that can be determined from a binary system at equilibrium are the phases present, the compositions of these phases, and the percentages or fractions of the phases.</p> Signup and view all the answers

<p>In a two-phase region of a phase diagram, a tie line is a horizontal line at every temperature that extends across the two-phase region and terminates at the phase boundary lines on either side.</p> Signup and view all the answers

<p>At 1100°C and a composition of 60 wt% Ni-40 wt% Cu, only the a phase is present with a composition of 60 wt% Ni-40 wt% Cu.</p> Signup and view all the answers

<p>Microstructure refers to the arrangement of phases in a material, which can be observed using optical or electron microscopes. The properties of a material, particularly its mechanical behavior, are often influenced by its microstructure.</p> Signup and view all the answers

<p>A system is heterogeneous if it is composed of two or more phases that have different physical characteristics. A homogeneous system, on the other hand, consists of a single phase that is uniform throughout.</p> Signup and view all the answers

<p>Phase equilibrium refers to the state of a system in which its free energy is at a minimum under specific combinations of temperature, pressure, and composition. Free energy is a thermodynamic quantity that accounts for a system's internal energy and entropy.</p> Signup and view all the answers

<p>The microstructure of an alloy can be influenced by the alloying elements present, their concentrations, and the heat treatment applied to the alloy. Microstructure can be characterized by the number of phases present, their proportions, and the way in which they are distributed or arranged.</p> Signup and view all the answers

<p>A triple point is a point on a P-T phase diagram where three phases are in equilibrium, and it is defined as a point where all of the solid, liquid, and vapor phases are simultaneously in equilibrium with one another.</p> Signup and view all the answers

<p>Binary phase diagrams are maps that represent the relationships between temperature and the compositions and quantities of phases at equilibrium, which influence the microstructure of an alloy. They provide information about the relationships between temperature, composition, and the phases present in a binary alloy system.</p> Signup and view all the answers

<p>An isomorphous system is a type of binary phase diagram that is characterized by a continuous solid solution between two components. It is characterized in a binary phase diagram by a single-phase region where the two components are completely miscible.</p> Signup and view all the answers

<p>The significance of the triple point in a binary isomorphous system is that it represents the composition and temperature at which all three phases (liquid, solid, and vapor) are in equilibrium with each other, and it defines the limits of the two-phase regions on the phase diagram.</p> Signup and view all the answers

<p>The solubility limit is the maximum amount of sugar that can be dissolved in water at a given temperature. It is represented graphically as a nearly vertical line on a plot of temperature (on the ordinate) and composition (in weight percent sugar, on the abscissa).</p> Signup and view all the answers

<p>When the solubility limit of sugar in water is reached, the solution becomes saturated with sugar and is not capable of dissolving any more sugar. Further additions of sugar settle to the bottom of the container, resulting in a system consisting of a sugar-water syrup liquid solution and solid crystals of undissolved sugar.</p> Signup and view all the answers

<p>A phase is a homogeneous portion of a system that has uniform physical and chemical characteristics, including pure materials and solid, liquid, and gaseous solutions. If more than one phase is present in a given system, each will have its own distinct properties, and a boundary separating the phases will exist, across which there will be a discontinuous and abrupt change in physical and/or chemical characteristics. A phase diagram is a graphical representation of the phases of a system as a function of temperature, pressure, and composition, and helps to visualize the boundaries between different phases.</p> Signup and view all the answers

<p>The sugar-water syrup solution is a liquid phase, while solid sugar is a solid phase. They differ chemically, with the former being a solution of H2O and C12H22O11 and the latter being virtually pure sugar. They also differ physically, with the syrup solution being a liquid and the solid sugar being a solid.</p> Signup and view all the answers

<p>The lever rule is a procedure used to determine the relative amounts (as fraction or as percentage) of the phases present in a two-phase region on a phase diagram. It is applied by constructing a tie line across the two-phase region, locating the overall alloy composition on the tie line, computing the fraction of one phase by taking the length of tie line from the overall alloy composition to the phase boundary for the other phase and dividing by the total tie line length, determining the fraction of the other phase in the same manner, and multiplying each phase fraction by 100 if phase percentages are desired.</p> Signup and view all the answers

<p>The purpose of dropping perpendiculars from the intersections of the tie line and the phase boundaries to the horizontal composition axis in phase diagram calculations is to determine the composition of each of the respective phases.</p> Signup and view all the answers

<p>The composition of each phase in a two-phase region is determined using the lever rule in phase diagram calculations by computing the fraction of one phase by taking the length of tie line from the overall alloy composition to the phase boundary for the other phase and dividing by the total tie line length, determining the fraction of the other phase in the same manner, and multiplying each phase fraction by 100 if phase percentages are desired.</p> Signup and view all the answers

<p>The relative amounts of phases present at equilibrium are computed using phase diagrams in two-phase situations by constructing a tie line across the two-phase region at the temperature of the alloy, locating the overall alloy composition on the tie line, computing the fraction of one phase by taking the length of tie line from the overall alloy composition to the phase boundary for the other phase and dividing by the total tie line length, determining the fraction of the other phase in the same manner, and multiplying each phase fraction by 100 if phase percentages are desired.</p> Signup and view all the answers

<p>A solid solution consists of atoms of at least two different types; the solute atoms occupy either substitutional or interstitial positions in the solvent lattice, and the crystal structure of the solvent is maintained.</p> Signup and view all the answers

<p>For many alloy systems and at some specific temperature, there is a maximum concentration of solute atoms that may dissolve in the solvent to form a solid solution; this is called a solubility limit. The addition of solute in excess of this solubility limit results in the formation of another solid solution or compound that has a distinctly different composition.</p> Signup and view all the answers

<p>System may refer to a specific body of material under consideration (e.g., a ladle of molten steel); or it may relate to the series of possible alloys consisting of the same components but without regard to alloy composition (e.g., the iron–carbon system).</p> Signup and view all the answers

<p>The FCC crystal structure allows copper and nickel to be mutually soluble in each other in the solid state for all compositions.</p> Signup and view all the answers

<p>The two phase regions are the a + L field and the a field.</p> Signup and view all the answers

<p>The liquidus line separates the liquid and two-phase regions, while the solidus line separates the two-phase and solid regions.</p> Signup and view all the answers

<p>The copper-nickel system is termed isomorphous because of its complete liquid and solid solubility of the two components.</p> Signup and view all the answers

<p>Microstructure refers to the arrangement of the different phases present in a material. It is important because it directly affects the mechanical and physical properties of the material.</p> Signup and view all the answers

<p>A phase is a physically distinct and homogeneous part of a system that is separated from other parts by distinct boundaries. A mixture is a combination of two or more substances, which may or may not be physically distinct from each other.</p> Signup and view all the answers

<p>Equilibrium refers to the state of a system where its free energy is at a minimum under specific conditions of temperature, pressure, and composition. Free energy is a thermodynamic quantity that determines whether a system is at equilibrium or not.</p> Signup and view all the answers

<p>The microstructure of an alloy depends on several variables, including the types and concentrations of alloying elements present, as well as the heat treatment conditions (i.e., temperature, heating time, and cooling rate) that the alloy undergoes.</p> Signup and view all the answers

<p>The three externally controllable parameters that affect phase structure are temperature, pressure, and composition. Phase diagrams are constructed when various combinations of these parameters are plotted against one another.</p> Signup and view all the answers

<p>A one-component phase diagram (or unary phase diagram) is for a pure substance in which composition is held constant. It is represented as a two-dimensional plot of pressure (ordinate, or vertical axis) versus temperature (abscissa, or horizontal axis).</p> Signup and view all the answers

<p>The three different phases delineated on a one-component phase diagram are solid, liquid, and vapor. Each phase exists under equilibrium conditions over the temperature-pressure ranges of its corresponding area.</p> Signup and view all the answers

<p>Phase boundaries are the curves shown on a one-component phase diagram. At any point on one of these curves, the two phases on either side of the curve are in equilibrium (or coexist) with one another. Upon crossing a boundary (as temperature and/or pressure is altered), one phase transforms into another.</p> Signup and view all the answers

<p>The solubility limit of sugar in water is the point at which the solution becomes saturated with sugar and can no longer dissolve any more. It depends on the temperature of the water and increases slightly with rising temperature.</p> Signup and view all the answers

<p>A phase is a homogeneous portion of a system with uniform physical and chemical characteristics. It is related to the concept of a phase diagram because phase diagrams display the different phases present in a system and their properties at different conditions.</p> Signup and view all the answers

<p>A tie line is a horizontal line that connects the two-phase regions in a phase diagram and represents the compositions of the two phases in equilibrium at a specific temperature and pressure.</p> Signup and view all the answers

<p>The solubility limit line represents the maximum concentration of solute that can be dissolved in a solvent at a given temperature. It separates the regions where only a liquid solution exists from the regions where a liquid solution and solid solute coexist.</p> Signup and view all the answers

<p>The procedure is called the lever rule.</p> Signup and view all the answers

<p>The lever rule is applied by computing the fraction of one phase by taking the length of tie line from the overall alloy composition to the phase boundary for the other phase and dividing by the total tie line length. The fraction of the other phase is determined in the same manner. If phase percentages are desired, each phase fraction is multiplied by 100.</p> Signup and view all the answers

<p>The purpose is to determine the composition of each of the respective phases.</p> Signup and view all the answers

<p>The tie line is a horizontal line that connects the intersections of the phase boundaries on either side of the two-phase region.</p> Signup and view all the answers

<p>Phase equilibrium refers to equilibrium in systems where more than one phase may exist. In the sugar-water syrup example, if the system is at equilibrium, the composition of the syrup is 65 wt% C12H22O11–35 wt% H2O, and the amounts and compositions of the syrup and solid sugar will remain constant with time.</p> Signup and view all the answers

<p>Metastable equilibrium involves a system that is in a nonequilibrium or metastable state, and the rate of approach to equilibrium is extremely slow. The microstructure in a metastable state may persist indefinitely, experiencing almost imperceptible changes as time progresses. Metastable structures are often of more practical significance than equilibrium ones because some steel and aluminum alloys rely for their strength on the development of metastable microstructures during carefully designed heat treatments.</p> Signup and view all the answers

<p>In metallurgical and materials systems, microstructures necessarily include not only the phases present and their compositions, but also the relative phase amounts and their spatial arrangement or distribution. Free energy considerations and diagrams similar to Figure 9.1 provide information about the equilibrium characteristics of a particular system, but they do not indicate the time period necessary for the attainment of a new equilibrium state.</p> Signup and view all the answers

<p>It is important to understand not only equilibrium states and structures, but also the speed or rate at which they are established and the factors that affect that rate. The treatment of reaction rates and nonequilibrium structures is deferred to Chapter 10 and Section 11.9.</p> Signup and view all the answers

<p>A P-T phase diagram shows the different phases of a substance and their stability regions at different pressures and temperatures. It helps in predicting phase transformations and understanding the behavior of materials at different conditions.</p> Signup and view all the answers

<p>A triple point is a point on a P-T phase diagram where all three phases of a substance (solid, liquid, and vapor) coexist in equilibrium. Any deviation from this point can cause one or more phases to disappear. It is related to phase equilibrium because it represents the conditions at which all phases are in equilibrium with each other.</p> Signup and view all the answers

<p>A binary phase diagram is a map that represents the relationships between temperature, composition, and phases at equilibrium for a binary alloy. It is helpful in predicting phase transformations and the resulting microstructures, which may have equilibrium or nonequilibrium character.</p> Signup and view all the answers

<p>An isomorphous phase diagram is a type of binary phase diagram that is characterized by complete solid solubility of one component in another. The copper-nickel system is an example of an isomorphous phase diagram.</p> Signup and view all the answers

<p>The process for determining the phases present in a binary system at equilibrium involves locating the temperature-composition point on the phase diagram and noting the phase(s) with which the corresponding phase field is labeled. For example, an alloy of composition 60 wt% Ni–40 wt% Cu at 1100°C would be located at point A in Figure 9.3a; because this is within the α region, only the single α phase will be present. However, a 35 wt% Ni–65 wt% Cu alloy at 1250°C (point B) consists of both α and liquid phases at equilibrium.</p> Signup and view all the answers

<p>To determine the phase compositions (in terms of the concentrations of the components) in a two-phase region of a binary system, a tie line is constructed across the two-phase region at the temperature of the alloy. One may imagine a series of horizontal lines, one at every temperature; each of these is known as a tie line, or sometimes as an isotherm. These tie lines extend across the two-phase region and terminate at the phase boundary lines on either side. To compute the equilibrium concentrations of the two phases, the following procedure is used: 1. A tie line is constructed across the two-phase region at the temperature of the alloy. 2. The composition of each phase at the intersections of the tie line with the phase boundaries is determined. 3. The distance along the tie line from one intersection to the alloy composition is measured. 4. The lever rule is then used to compute the equilibrium compositions of the two phases in the alloy.</p> Signup and view all the answers

<p>An isomorphous system is a binary system that has complete solid solubility in both the liquid and solid states. In a binary phase diagram, an isomorphous system is characterized by a single-phase solid region, a single-phase liquid region, and a two-phase region in between the solidus and liquidus lines.</p> Signup and view all the answers

<p>For a binary system of known composition and temperature at equilibrium, at least three kinds of information are available: (1) the phases that are present, (2) the compositions of these phases, and (3) the percentages or fractions of the phases. The procedures for making these determinations are demonstrated using the copper-nickel system. The establishment of what phases are present is relatively simple. One just locates the temperature-composition point on the diagram and notes the phase(s) with which the corresponding phase field is labeled. To determine the phase compositions (in terms of the concentrations of the components), a tie line is constructed across the two-phase region at the temperature of the alloy, and the lever rule is used to compute the equilibrium compositions of the two phases in the alloy.</p> Signup and view all the answers