Lecture 2 - Materials Science Issues Flashcards
What is an alloy?
a mixture of one metal with another or multiple elements
What are the most common metals?
lithium, beryllium, sodium, magnesium, aluminum, copper, iron, nickel, titanium
What percentage of the periodic table is metals?
~80%
Which alloys are the most popular?
FCC metallic alloys
Which alloys have poor ductility?
HCP metallic alloys due to asymmetry
How many elements are typically in multicomponent metallic alloys?
3-6
What three types of alloys are in FCC metallic alloys?
Cu-alloys, Al-alloys, Ni superalloys
What are metallic composites?
reinforced by nonmetallic elements like carbon, oxides
What do Cu-alloys consist of?
Cu-Zn (brass)
Cu-Sn (bronze)
Cu-Ni
Cu-Be
~400 other types
Why are most materials (>5500 alloys) not printable?
low/poor weldability
brittle (cracking)
low absorptivity/high thermal conductivity
What do Al-alloys consist of?
1xxx through 7xxx series
What does low absorptivity and high thermal conductivity mean?
materials cannot hold onto energy well enough to melt into desired shape
What do Ni superalloys consist of?
inconel, hastelloy
What do HCP metallic alloys consist of?
Ti-alloys (Ti-6Al-4V and variations) and Mg-alloys (biodegradable)
What do BCC metallic alloys consist of?
Fe-based alloys: carbon steel, alloy steel, stainless steel, tool steel
What are multicomponent metallic alloys?
high entropy alloys
What are the five types of metals and alloys?
FCC, HCP, BCC, multicomponent, and composite
Which metal powder is the cheapest?
Steel
Which materials are currently mostly printable?
Steel, Nickel, Titanium, Cobalt, non silicone aluminum, non-pure copper
What material properties are evaluated?
strength, ductility, creep, corrosion/oxidation resistance, dynamic/impact, thermal and electrical conductivity, biocompatibility*
Why does processing lead to unique microstructures/compositions?
recoil pressure causes evaporation of metal
impurities/pores
melting/remelting of previous layers
How do AM materials differ from commercial alloys?
different compositions
impurities
residual stresses
porosities
microstructural features
surface roughness
accident failure parts
What does oxidation during AM lead to?
degraded mechanical and functional properties
What problems does surface roughness create?
affects build and leads to machine crashing if comparable to resolution
What problems does residual stress contribute?
Loss of dimensional accuracy
limits maximum dimensions
in process failure/cracking
reduced mechanical performance
Why is the structure-property relationship difficult to understand?
need new physics and scaling laws for predictability and long-term reliability and sustainability from computer modeling
How do AM material properties compare to commercial properties?
Commercial properties are better.
What are different types of differences in microstructures?
voids
weld pools
grain sizes
textures
impurities
compositional inhomogeneity
phases
What are the typical properties of metals?
elastic (damping)
mechanical strength (yield strength, ultimate tensile strength, fracture strength, hardness)
ductility and fracture toughness
creep and fatigue
electrical and thermal conductivities
corrosion resistance
biocompatibility
What are characteristics of Al alloys?
light weight (2.7 g/cc)
good ductility
medium strength
good machinability and castability
general corrosion resistance
poor weldability
poor high temperature properties (bp - 2470C)
~$1/lb
What are application areas for Al?
aerospace
automotive
construction
packaging
electrical transmission lines
Are high-strength Al alloys easy to print?
high-strength Al alloys are one of the most difficult to print
What are the characteristics of Ni superalloys?
outstanding high temp strength and creep properties
high temp resistance to oxidation
not lightweight
$7/lb
What are the applications of Ni superalloys?
high temp in aerospace, automotive, power generation
biotechnology
What are difficulties to printing Ni superalloys?
difficult to control precipitates and single crystals
What are the characteristic properties of Cu alloys?
high ductility
good thermal and electrical
conductivity
ultrahigh vacuum compatibility
good corrosion resistance
medium strength
poor high temp properties
$4/lb
What are the applications of Cu alloys?
Electrical applications (power transmission and generation, building
wiring, telecommunication, and electrical and electronic products).
Thermal transferring systems (heat exchangers)
Marine applications - good corrosion resistance in seawater (seawater piping).
Architectures
Catalysts
What type of Cu alloy is the most difficult to print?
pure Cu
What are the characteristic properties of Fe alloys?
high strength
high ductility
high corrosion
resistance
good fatigue properties
good medium temperature properties
cheap
vacuum compatibility
biocompatibility
What are the application areas of Fe alloys?
Construction (buildings, bridges)
Transportation (vehicles, ships, rails, trains)
Oil gas pipelines
Weapons
Consumables
Nuclear and chemical plants
Why are steels not p3D printed more?
different compositions
no added value by printing
What are the characteristic properties of Ti alloys?
low elastic modulus
light weight (4.5 g/cc)
high strength
poor ductility
high corrosion resistance
good medium
temperature properties
biocompatibility
expensive
tough to process
What are applications of Ti alloys?
aerospace
medical implants
other appliances
What are the four material science issues?
- printability
- different compositions compared to commercial
- structure-property relationship is not well understood
- properties of AM materials are not good enough
What is ductility?
the ability of a material to be plastically deformed without fracture
What is yield strength?
the point at which material begins to deform plastically
What is ultimate tensile strength?
the maximum stress that a material can withstand before breaking
What is elastic deformation?
temporary deformation of a material’s shape that is self-reversing
What is plastic deformation?
permanent distortion when stresses exceed yield strength
What is fracture strength?
The stress at which a material breaks or fails
What is hardness?
the ability of a material to resist deformation
What is creep?
time dependent deformation at elevated temperature or constant stress
Why do we prefer alloys over pure elements?
properties tend to be better than their constitutional components
What are two characteristics about Ti alloys?
lucrative
many material science issues to be solved
