Berzins lecture 1

metal

electropositive element

general properties of metals

-luster
- good thermal and electrical conductors
-high fracture toughness
- stronger, more ductile, and denser than nonmetals

alloy

A mixture of two or more metals (sometimes with nonmetals)

classification of metals

elemental vs alloy
cast vs wrought
noble vs non-noble
application and composition

bonding and structure of metals

metallic bonding, crystalline

crystal systems of metals

simple cubic
face centered cubic
body centered cubic
hexagonal close-packed
etc

noble metals in dentistry

Palladium
Ruthenium
Osmium
Gold
Rhodium
Iridium
Platinum

3 major noble metals

gold, palladium, platinum

metals used as grain refiners

ruthenium and iridium

pure base metal vs pure noble metal in mouth

base metals have a greater tendency to corrode in the mouth compared to noble metals

high noble alloy

gold > 40% wt
noble metal content > 60wt%

Titanium and Titanium Alloys

titanium > 85%wt

noble alloys

noble metal content > 25% wt

predominantly base alloys

noble metal content

ADA type I alloy

hardness: soft
tensile yield strength:

ADA type II alloy

hardness: medium
tensile yield strength: 140-200
elongation (%): 18

ADA type III alloy

hardness: hard
tensile yield strength:201-340
elongation (%): 12

ADA type IV alloy

hardness: extra-hard
tensile yield strength: >340
elongation (%): 10

ADA alloy classification by physical properties

from type I to IV, hardness and tensile yield strength increases, elongation decreases

application of ADA alloy type I

sustainable stress: low, no occlusion
use: inlays

application of ADA alloy type II

sustainable stress: moderate, light occlusion
use: inlays and onlays

application of ADA alloy type III

sustainable stress: high, full occlusion
use: crowns, short-span FPD

application of ADA alloy type IV

sustainable stress: very high
use: thin veneers, long-span FPD, RPD

homogenous nucleation

solid forms from the liquid, sometimes requires 'supercooling'

solidification of metals

pure metals have a melting point, alloys have a melting range

grain boundaries

The boundaries between crystals (grains) in a polycrystalline material.

raid vs slow cooling of metals

rapid cooling --> more nuclei --> smaller grains

slow cooling --> fewer nuclei --> larger grains

grain refiners

method used to reduce grain size
- add

finer grain size (vs larger grains)

increased yield strength, composition uniformity, and corrosion resistance

dendrites

in pure metals, the dendrite formation is through thermal supercooling
- dendrite growth is along specific crystallographic directions

solid solution

created with incorporation of foreign atoms (solute) into a crystal structure of the matrix atoms (solvent)
- may be a wide range of compositions

substitutional solid solution

B atoms replace where A atoms should be (disordered and ordered)

interstitial solid solution

B atoms fit in-between the A atoms

disordered vs ordered substitutional solid solution

amount of solute 'in solution' depends on:

1. size
2. crystal structure
3. valence
4. chemical reactivity

size of solute

- substitutional solubility decreases as size difference increases (

crystal structure and solubility

greater solubility if same (eg FCC)

valence and solubility

greater solubility if same
-eg. Mn2+ and Zr4+ are similar size but charge makes solution improbable

eutectic point

liquid solidifies into two solid phases

intermetallic compound

differ from solid solutions int that they exist as fixed anatomic ratios
eg. NiTi, Ti2Ni, TiNi3

point defect

substitution or interstitial atoms, vacancies, self-interstitial

vacancy

vacant lattice site

self-interstitial

a matrix atom in an interstitial site

dislocations

line imperfections in crystalline solids
- atoms missing or extra-half-planes of atoms are formed
- decrease the strength

plastic deformation of metals

hinder dislocation movement --> increase strength

strengthening mechanisms of metals

- solid solution strengthening
- strain or work hardening
- precipitation hardening
- transformation strengthening

solid solution strengthening of metals, general features

1. higher strength and hardness, but less ductile than either pure metal
2. melting range, melt below highest melting point of the pure metals
3. higher corrosion resistance than multi-phase alloy

Strain hardening (cold working)

strength and hardness increase, ductility decreases
-- with plastic deformation, it becomes more difficult to deform more
-- increase in number and interaction between dislocations

annealing

heat treatment used to soften metals and refine their grains

Recrystallization

above a certain temp new grains nucleate

precipitation hardening of metals

solute atoms are not dissolved but form separate 2nd phase particles dispersed in the matrix

transformation strengthening of metals

change in the morphology of the lattice structure which occurs upon heating or cooling
- titanium: BCC to HCP
--- strained lattice retards dislocation movement