what are structure-sensitive properties
- mechanical properties that are significantly affected by changed in microstructure
what are structure insensitive properties
- mechanical properties that are not significantly affected by changed in microstructure
what are the most important structure insensitive properties
- density
- elastic modulus
- some electrical/thermal characteristics
what are the most important structure sensitive properties
- yield strength
- fracture strength
metallic bonding
- interaction between the negatively charged electron cloud and the positively charged ions resulting in a stable structure
how are metal ions arranged during metallic bonding
- packed together to give high density structures (FCC, HCP,BCC) as the metallic bond has no directionality
what are interatomic bonds
- bonds between adjacent atoms which act like small springs
why is the resulting bond energy curve asymmetrical
- the repulsive part increases faster with atom distance than the attractive
what is the equilibrium point on a resulting bond energy curve
- the lowest energy
what happens to atoms in materials above absolute zero
- they vibrate about their equilibrium positions in proportion to the temperature
what happens when energy is added to a material
- thermal vibration of the atoms causes them to oscillate about the equilibrium distance
why do most materials expand while heating
- average distance between atoms increases as temp increase because the asymmetry of the bond energy-atom distance curve
what is the relationship between bond energy atom distance curve and thermal expansion coefficient
- narrower the curve, lower the coefficient
why does a metal melt
- heating process continues causing the atoms to reach a degree of vibration causing them to separate (the bond breaks)
what is stable seperation determined by
- a balance between the attractive and repulsive forces
how to use bond force to find equilibrium distance
- when net force(dU/dr) = 0, the distance = equilibrium
how can atoms be moved from equilibrium positions
- by tensile or compressive loading
what happens when tensile/compressed load is added to atoms in eq position
- force appears that resists the stretching/compression which is closely proportional to (r-r0) for small (r-r0) for all materials in tension /compression
how to work out the stiffness of the bond (S)
- the first derivative of the bond force curve
- the second derivative of the resulting bond energy curve
how is a 3d packing structure constructed
- packing atoms 2d in atomic planes
- stack the planes on top of each other to form crystals
what are crystals
- solids in which the atoms are arranged in regular, repeating, three-dimensional patterns
when is a single layer of spheres closest packed
- in a hexagonal coordination
what are interstitial sites
- space trapped between the layers that isnt filled with spheres
what are the two different types of interstitial sites
- tetrahedral - holes with 4 nearest sphere neighbours
- octahedral - holes with 6 nearest sphere neighbours
