Lecture 10 Flashcards
Metals make up _____ of the periodic table
75%
Bonds in metals
A sea of moving valence e- in a network of positive ions
Properties of metals
High thermal and electrical conductivity, malleable, lustrous.
Normal metals (Al, Mg, Na) have ___ bonds
weak
Transition metals have ____ bonds.
strong
Coordination #
of nearest neighbors. Max is 12
Crystallization
isothermal evolution with heat evolution
Glass transition
gradual transition without heat evolution. L -> glass
Difference between glass and crystal
Crystal is lattice, glass is not. Crystal has Tm, glass have a glass transition point
Which lattices are the most common?
Cubic and hexagonal
What are the 2 types of solid solution alloys?
Interstitial (smaller)
Substitutional (larger)
Examples of Interstitial and Subsitutional
Int: C, N, H in steel
Sub: Ni in Cu and Fe (can be ordered or disordered)
Grains
crystal with a orientation. All the crystals have the same chemical makeup, but are ordered differently.
Defects in a material
Can only be perfect over an extremely small volume. All structures have defects, but this might not be detrimental to performance
Classifications of defects
Point defects (0D) Linear defects (1D) Surface defects (2D) Volume defects (3D)
Point defects
interstitial/substitution. Has an impact on matter transfer and electrical conductivity
Linear defects
local distortion of a perfect crystal lattice
Small burger vector results in
more like to have a dislocation
What is the burger vector
the extent of the defect
Transfer phenom.
The core a dislocation is an increase in the diffusivity path
Common 2D defects
Free surfaces, interphases, grain boundaries, twin boundaries, grain boundaries, twin boundaries, stacking faults
Interphases
energy of the interphase depends on the structure of the phases and on their crystal orientation.
Surface defects on high diffusivity paths
For atoms, diffusion Heat conduction in some materials Favor chemical reactivity Fragile, preferential crack or corrosion site Resist deformation
Volume defects
- Pore and cavities
- Foreign particles and inclusions
- Non-desired phases
3D Defects, impacts:
detrimental, concentrate stresses and initiate cracking/corrosion
Defects - synthesis
entropy associated w/ defects, influence mech and transport properties, interact between each other. Volume effects are high cost.
Lost wax casting hip implant
Mineral deposit (ore), metalic raw material in bluk form, stock shape, preliminary implant decide, final implant device, market
Quality assurance (Ndt) Dimensions
]3D multi-sensor machine (optical and mechanic)
Quality assurance (Ndt) Volumic defects
–X ray radiography station,
–Ultra sound inspection,
–fluorescent dye penetrant inspection plant ,
Quality assurance (Ndt) Surface defects
–Eddy currents,
Quality assurance (Ndt) Chemical analysis
– optical emission spectrometer, X-ray fluorescence spectrometry
– carbon-sulphur analyser.
Quality assurance (Ndt) Mechanical properties
-HRC and HV hardness machines
Dental amalgams, an almost perfect PM process and product
Reaction: 59% powder 41 vol% Hg (liquid) Powder : 60%Ag, 30 Sn,10 Cu Mercury desintegrates the particles and reacts to form Ag3Hg4, , causing the setting of the amalgam No volume change!
