Chapter 9-Intro to material science

Component

a chemical constituent of an alloy that may be used to specify its composition

System

two meanings are possible: (1) a specific body of material being considered and (2) a new series of possible alloys consisting of the same components.

solubility limit

the maxi9mum concentration of solute that may be added without forming a new phase.

solid solution

consists of atoms of at least two different types

sugar solubility example

initially sugar is added to water, a sugar water solution or syrup forms. As more sugar is introduced, the solution becomes more concentrated until the solubility limit is reached or the solution becomes saturated with sugar. At this time if any sugar is added, it will sink to the bottom. The solubility limit of sugar depends on the temperature of the water.

when more solute can be dissolved, the system is

unsaturated

phase

a homogeneous portion of a system that has a uniform physical and chemical characteristics; every pure material is considered to be a phase

Also, when a substance can exist in two or more polymorphic forms (e.g., having both FCC and BCC structures), each of these structures is a separate blanks

phases because their respective physical characteristics differ

Phases are chemically and physically what from each other.

distinct

A solid FCC structure made from copper and nickel is an example of how many phases

one phase; Even though there are two components, the components combine to make a single solid phase.

All contents inside an open container, which is half filled with cold ice water.

three phases; Because the system is defined to include all container contents, the three phases are liquid water, solid ice, and gaseous air. The technicality between all container contents and just the mixture becomes important if the air reacts with the mixture.

A homogenous copper-nickel liquid, with a solid FCC structure made from copper and nickel.

two phases; This two phase example is similar to solid ice in liquid water. Both the solid and liquid have the same components, but the structure is different between the two phases. Additionally, the solid copper-nickel structure has a different chemical composition than the liquid.

equilibrium(phase)

the state of a system in which the phase characteristics remain constant over indefinite time periods. At equilibrium the free energy is a minimum

free energy

a thermodynamic quantity that is a function of both the internal energy and entropy (or randomness) of a system. At equilibrium, the free energy is at a minimum.

metastable

a nonequilibrium state that may persist for a very long time

a change in temperature, pressure, and/or composition for a system in equilibrium results in an increase in the free energy and in a possible spontaneous change to another state by which the free energy is lowered.

fact

Because both metastable and equilibrium phases can last for a long time, blank phases are often used when the equilibrium state cannot be reached on a small time scale.

metastable

a materials metastable state free energy is higher or lower than the phase equilibrium state free energy

higher

phase diagram

a graphical representation of the relationships among environmental constraints (e.g.. temperature and sometimes pressure), composition and regions of phase stability, typically under conditions of equilibrium

on the phase diagram, there’s a special point to remember- triple point

at this specific point only, all the sold, liquid, and vapor phases are simultaneously in equilibrium with one another.

phase transformations

the changes that occur when the temperature is altered (typically upon cooling)

isomorphous

having the same structure. in the phase diagram sense, isomorphicity means having the same crystal structure or complete solid solubility for all compositions

at temperatures below 1080 degree Celsius, copper and nickel are mutually soluble in each other in the solid state for all compositions, explain why

both Cu and Ni have the same crystal structure of (FCC) nearly identical atomic radii and electronegativities and similar valences, thus its termed isomorphous because of complete liquid and solid solubility of the two components

tie line

a horizontal line constructed across a two-phase region of a binary phase diagram; its intersections with the phase boundaries on either end represent the equilibrium compositions of he respective phases at the temperature in question

lever rule

a mathematical expression by which the relative phase amounts in two-phase alloy at equilibrium

if the temperature does or does not? change the composition of the phase will not change.

not change

Walpha and WL=?

1

the degree of displacement of the non equilibrium solidus curve from the equilibrium one depends on the rate of

cooling; the slower the cooling rate the smaller this displacement.

during nonequilibrium cooling, the initial alpha grain composition is

relatively unchanged