Nature of Metals & Alloys

What is a metal?

Form positive ion (cation) and ionic bonds with non-metals if place alloys into a suitable solution

What do metal release during ionization

electrons

Metal ions exist as free with

positive charge

What is a key factor in the behavior of metals

stability of ions

In metallic bonds, atoms are bonded by what kind of interactions

electrostatic

electrostatic ions are interactions between

the ions and electtron cloud

the nucleus in metals are surrounded by the

electron cloud

metals form what kind of ions and bonds with non metals (if alloys are placed into a suitable solution)

form positive ions (cations) and ionic bonds with non metals

during ionization, metals release

electrons

metal ions exist as free with what charges?

positive

what is a key factor in the behavior of metals and is responsible for many metallic properties that are important in dentistry

stability of ions

metals constitute nearly ___ of all elements in the periodic table

2/3

metalioids do not always form

free positive ions

what makes metalloid properties important components of many dental alloys

conductive and electronic properties

name 4 general properties of metallic elements

1. crystalline solid in normal environment

2. greater than or equal to 1800C, many would be liquid or gas

3. dense, luster, malleable, ductile, and strong

4. good thermal and electrical conductivities

define alloy

a blend of two or more metals in all their possible combinations considered as a whole

in order to form an alloy, the two metals are ___ to a liquid state

heated

when a combination of two metals is completely _____ in the liquid state, the 2 metals can form an alloy

miscible

what does a binary alloy result from

two metals and all different possible combinations are considered

what is the goal of alloys and alloy systems

1. to optimize practical properties

2. to form metallic materials with adequate strength, ductility, corrosion resistance, and biocompatibility for application in oral environment

phase changes are ___ changes

physical

what is melting

solid to liquid

what is cooling

liquid to solid

what are phase diagrams determined experimentally by

cooling rates over a range of compositions

what is a phase diagram?

temperature composition chart that indicates equilibrium phases present at a given temperature and composition

In a phase diagram the upper curve is called what

liquidus line bc the alloys in this system are entirely liquid

in the phase diagram, the lower curve is called what

solidus line bc alloys are entirely solid for temperatures and compositions below this curve

what is the solvus line in a phase diagram

represents a fixed composition of the mixture and indicates the decreasing solubility of the components in each other as the temperature decreases

what is the goal of the phase diagram

to understand and predict the alloy microstructure obtained at a given composition

the relative amounts of the two phases in the liquid-solid regino can be determined at a given temperature by the

inverse lever rule

the percentage of the material at 560C for 60% A and 40% B is

liquid is xy/xz and solid is yz/xz

in the solid state, what structure does the system have

crystal (hard ball model, unit cell, and single crystal with many unit cells)

when a mixture of two or more metals is cooled, one of three possibilities may take place:

1. solid solution

2. compound

3. eutectic alloy

what is a solid solution alloy

a solid-state solution of one or more solutes in a solvent

the crystal structure of the solvent in a solid solution alloy remains ____ by the addition of solutes

unchanged

in a solid solution alloy, the solute may incorporate into the solvent crystal in these two ways

substitutionally, or interstitially

the solid solution alloy mixture remains in a single______ phase

homogenous

what are the hume-rothery rules

describe the conditions under which an element could dissolve in a metal, forming a solid solution, if the solute and solvent have 4 characteristics

what are the 4 characteristics of the hume-rothery rules

1. atom radius

2. valence

3. chemical affinity

4. crystal structure

what are intermetallic compounds

2 metals completely miscible in liquid state and have tendency to form unique chemical compounds on solidfying

intermetallic ompounds are solid-state phase involving a more ____ structure and often a well-defined, fixed ______

ordered; stoichiometry

intermetallic compounds are harder but ____ in properties

brittle

what are eutectic alloys

upon cooling or solidification, the liquid forms 2 seperate solid phases

eutectic alloys are in ____ equilibrium. this means the liquid and 2 solid solutions all _____ at the same time

thermal; coexist

eutectic alloys have how many materials that have a eutectic composition

2+

when a eutectic alloy mets, it does at a ___ and ___ temperature

single; sharp

what is the eutectic point

where all 3 phases coexist (liquid, liquid + solid, and solid)

the most common structure of a eutectic alloy is

lamellar structure

the alloy components of eutectic alloys exhibit ___ easily

complete liquid solubility

eutectic alloys may be used in what kind of procedure

soldering

what is the lost wax casting technique

1. wax model creation

2. wax sprues are attached to wax model

3. wax model repeatedly dipped into slurry or ceramic or plaster and coated with sand (shell forms)

4. ceramic mold is heated in furnacy and wax melts leaving hollow mold

5. mold is filled with molten metal

6. metal is cooled, solidified, finished and polished

name 3 noble elements used in dental alloys

gold (Au), platinum (Pt) and palladium (Pd)

the atomic lattice is made by connections between

grains

what are grain boundaries

surface that separates the individual grains and is a narrow zone where atoms are improperly spaced and misaligned

what are dislocations

misaligned lattice points within crystal and at grain boundaries

atomic planes are ___ at grain boundaires

discontinuous

slip in each grain stops where

at grain boundaries

dislocations cannot cross from from grain into another adjacent grain so what do they do?

pile up at the grain boundaries

further deformation in grain boundaies will require greater

stressw

what kind of energy accumulates at grain boundaries

strain energy

deformation from loading is viewed in the form of what

dislocations moving to the grain boundaries (more grain boundaries = higher strength)

what 5 characteristics increase with decreasing grain size

1. hardness

2. yield strength

3. tensile strength

4. fatigue life

5. impact resistance

what characteristics decreases with decreasing grain size

ductility

what are mechanical treatments of metals and alloys

wrought, milled

what are thermal treatments of metals and alloys

cast, annealed, sintered, quenched

what are chemical treatments of metals and alloys

pickled, etched

what is cold working (strain hardening or work hardening)

process where a metal is plastically deformed below its recrystallization temp, and is achieved through mechanical processes like rolling, drawing, foraging, bending, hammeringi

in cold working, deformation of a metallic speciman is performed below what temperature

recrystallization temperature

why are metals that are cold worked are in a high energy state?

mechanical energy is absorbed in plastic deformation

what is cold working synonymous with

strain hardeningi

in cold working, because of the proximity of neighboring grains, each grain wil _____ during this process

distort

in cold working, dislocations will pile up in grain boundary of each grain and makes ___ or ____ more difficult

slipping or deformation

what properties will increase in cold working

ultimate strength, yield strength, and hardness

what properties will decrease in cold working

ductility

what are ways to reverse effects of cold working

annealing and recrystallization (can be used to restore ductility)

cold working leaves behind _____ stresses, which cause warping or distortion over time is not relieved

internal

sintering process of metals and alloys

uses metal or ceramic particles; which join without complete meltingq

quenching process of metals and alloys

cooled rapidly in order to freeze microstructure; to gain described strength and hardness

picked and etched treatment of metals and alloys

both treated with acid —> to remove contaminating substances, and brings out grains and boundaries

annealing is similar to that of ______ heat treatment

softening

what is the goal of annealing

to form new stress free crystals in a work-hardened metal through a controlled heat-treatment process

stages of successive annealing

1. recovery

2. recrystallization

3. grain growth

annealing is dependent on what two feature

temperature and time

the ________ the degree of cold work, the _______ the recrystallization temperature neededg

greater; lower

the _______ the recrystallization temperature, the ________ the heating time

higher; shorter

what is the goal of grain growth stage of annealing

to increase mean crystal size of polycrystalline metal through a controlled heat-treatment process

if recrystallized metal further anneals, what may occur

grain growth may occur to minimize grain boundary area with large grains consuming small grains

continued annealing past recrystallization temperatures leads to

grain growth with a further softening of the alloy due to increased grain size