Lecture 5 - Titanium Alloys Flashcards
What is CP-Ti?
commercial purity Ti
What is the crystal structure of beta-Ti?
bcc
What is the crystal structure of alpha-Ti?
hcp
What is the density of ti?
4.5 g/cm3 (low)
What is the melting temperature?
1668C
What is the boiling point?
3287C
What is the Young’s Modulus of Ti?
110GPa (low)
What are the four types of Ti alloys?
alpha
alpha + beta
beta meta stable
beta stable
Why are Ti alloys used?
good specific tensile strength at elevated temperatures
excellent corrosion resistance
What is the density of Ti-6Al-4V?
4.429 g/cc (lower than normal titanium)
Which type of titanium is used for medical grade?
Ti-6Al-4V, extra low interstitials
What does an increased amount of Al (alpha stabilizer) do?
increases beta transus
Which elements have a neutral effect on Ti?
Sn, Zr
Which elements have an alpha-stabilizing effect on Ti?
Al, O, N, C
Which elements have an beta-isomorphous effect on Ti?
Mo, V, Ta, Nb
Which elements have a beta-eutectoid effect on To?
Fe, Mn, Cr, Co, Ni, Cu, Si H
What are the Ti-Al-x alloys?
alpha and alpha + beta
What are the Ti-transition-metal-based?
beta meta stable and beta stable
Alpha alloys have a higher _____ than pure Ti
beta transus
Addition of oxygen can raise _______ 4x
yield strength
Al-Sn additions are effective ________________
strengtheners
___________ values for Ti alloys are 2x higher than that of Al alloys
Klc (plane strain fracture toughness)
What is a martensitic transformation?
diffusion-less solid-to-solid phase transitions
What is the angle needed to change BCC to HCP?
10.6 degrees
Which phase is diffusion slower in?
alpha phase (hcp)
What does diffusion affect in AM
elemental partition
How do O and Al differ for AM?
powders have higher O and lower Al
What is the yield strength and ductility of AM Ti-6Al-4V?
yield strength is high, ductility is small
What are the five strengthening mechanisms for L-PBF in Ti64?
phase
solid solute
dislocation
boundary
pores
What happens to the tensile ductility when 90 degrees from build direction?
drops dramatically
voids play a role in _________ of PBF Ti64
necking and fracture behavior
Why are Ti alloys tough to print via L-PBF?
martensitic phase transformation during 3D printing
What challenges remain difficult to overcome?
impurities and pores
What does a majority of 3D printed Ti64 alloys have?
poor ductility
where are the studies of corrosion resistance and biocompatibility at?
ongoing
what limits aerospace applications for 3d printed Ti64 alloys?
elevated temperature properties (creep) and fatigue properties
What is BCC?
body centered cubic
What is FCC?
face centered cubic
What is HCP?
hexagonal close packing
What is unique about titanium phases?
multiple phases unlike steels
How does beta Ti compare with alpha Ti?
more ductile (alpha-Ti is brittle)
What are the properties of alpha + beta Ti?
mix of ductile and brittle
How does Ti do in low temperatures?
very good tensile strength
How does Ti compare in weight?
very light
What does ELI mean?
extra low interstitials (low oxygen levels)
What happens when you add too much Al?
creates brittle Ti3Al
Why do you want the beta transition temperature as low as possible?
avoid brittle material when cooling
What are the gamma and omega phases?
too brittle, shatter
What does alpha-stabilizing and beta-stabilizing mean?
the more of these elements you add, the more alpha/beta there is
What happens if you add too much beta-stabilizing elements?
heavier, lose corrosion resistance
what is the downside to beta Ti Alloys?
not as ductile as alpha + beta
What happens to the shear strength from beta to alpha?
introduces tan(10.6 degrees) = .187 shear strength (18.7%)
Which structures have the best close packing?
FCC and HCP
What shape has the best diffusivity?
BCC
What the cooling rates for the three quenching processes from highest to lowest?
water quench, air cooled, furnace cooled
What is the typical L-PBF cooling rate?
10^7 K/s
Why does iron get into the L-PBF build?
chamber is made of iron
Why is beta identified as pre-beta?
it used to be beta but now is alpha’
Where are impurities Fe and V located?
beta lines
higher energy input means what for V?
higher quenching rate, less time for V to diffuse
What does heat treatment do to V?
helps break it up
What happens to Ti when repeated heating and cooling?
twinning and dislocations
How does L-PBF/SLM compare to EBM in properties?
more alpha than beta, higher cooling rate, more yield strength, less ductility
What happens if you use an insufficient energy input on Ti?
reduce fatigue cycle
What are the optimal temperatures for annealing Ti5553?
300 and 800C
