MEEEN 360 Ch 10: Solid Solutions and Phase Equilibrium

Isomorphous Phase diagram Gibbs phase rule

1 + C = F + P

When temperature and pressure can vary, Gibbs phase rule says ___ _ ___ _ ___ _ ___

2+C=F+P

______ - A metal made by taking a pure metal and adding another material to it

Alloy

_______ - the elements which make up an alloy

Components

________ - the elemental make up, often by weight %, volume %, or atomic %

Composition

_____________ occurs over a large distance, such as the surface and center of the casting

Macrosegregation

______________ occurs over short distances, often between dendrite arms

Microsegregation

Non - equilibrium structures are often produced during rapid cooling of alloys - ___ ________ ____ ____ __________

Not enough time for diffusion

Limited solubility: after the ______ _______, additional atoms form a new compound • Two solid phases ______

solubility limit, coexist

________ _________: regardless of the ratio of atoms, only one phase is produced upon combining elements

Unlimited solubility

_Solid solution strengthening_ The degree of strengthening depends on two factors: 1. A large difference in ___ _____ results in increased strength of the alloy. 2. The greater the amount of the ____ ______ that is added, the greater the strengthening.

atomic sizes, alloying element

(Microsegregation) The compositions differ over short regions - Leads to poor ________ properties

casting

In metals, forming a solid solution often results in solid-solution strengthening, due to increased resistance to ______ _______.

dislocation motion

(Microsegregation) It can also cause _____ ________, which is the melting of interdendritic lower melting point material below the equilibrium solidus

hot shortness

(Macrosegregation) It cannot be eliminated by homogenization due to large diffusion distances, but it can be reduced by ____ _______.

hot working

Solid-solution strengthening affects properties. (1) σY, σUTS, H of the alloy ______ compared to pure metal (2) Ductility ______ compared to pure metal (3) Electrical conductivity ________ compared to pure metal (4) Resistance to _____ and strength at high temperatures increases compared to pure metal.

increase, decreases, decreases, creep

Equilibrium solidification of a solid-solution alloy • Both ________ and _____ are required • The tie lines dictate the _________ of the first solid to form (at the liquidus line), which requires _________ until the composition is achieved

nucleation, growth, composition, diffusion

A _______ is any portion of a system that is physically homogeneous and bounded by a surface that separates it from other distinct portions

phase

_Equilibrium cooling curves_ For alloys, the latent heat of fusion is removed over a ______ ___ __________. The cooling curve shows a _____ _______ instead of a plateau.

range of temperatures, changing slope

Characteristics of phases 1. The ____ _______ or atomic arrangement throughout 2. Roughly the ____ ______ and properties throughout 3. A definitive _____ ______ _____ _____ and any surrounding phases.

same structure, same composition, interface between the phase

In practice, cooling rates are quite rapid, so composition differences (from equilibrium) exist in the alloy. This is called ___________.

segregation

_________ is the nonuniform composition produced by nonequilibrium solidification

segregation

Separate phases do not have to be _____ ____ ____ _______ (solid, liquid, gas) - e.g. iron can have 2 coexisting solid phases: FCC and BCC

separate states of matter

Hume-Rothery Rule: For an alloy system to have an unlimited solid solubility. Size - must be ____ with <15% difference in atomic radius • Crystal structure - must be the _____ • Valence - must be the ____ (or close) • Electronegativity - must be approximately the ______

similar, same, same, same

In order to achieve an equilibrium final structure, the cooling rates must be _____ (fast/slow). - To allow for _______ between phases to produce the compositions given by the phase diagram.

slow, diffusion

Heating the casting to below the nonequilibrium ____ for a few hours eliminates most of the composition differences ('__________')

solidus, homogenization

Solid solutions • One or more _____ in a solvent - Homogeneous arrangement composed of ____ ___ _______. - The crystal structure of the _____ remains unchanged - A solid solution is ____ a mixture in the chemistry sense

solutes, only one phase, solvent, NOT

Solutions could refer to two elements or ____ _______.

two compounds