Titanium Alloys Flashcards
What rank is titanium in the most abundant elements on the earths crust?
4th
What kind of layer does titanium naturally form?
A stable adherant oxide film.
What are the three reasons titanium is compatible with carbon fibre reinforced polymers?
1-titanium and graphite have similar linear thermal expansion coefficients
2-Both at cathodic end of electrochemical scale, this avoids galvanic corrosion.
3-Similar youngs modulus to unidirectional carbon fibre which eases residual stresses.
Thermomechanical processing accounts for what percentage of the cost for titanium?
50%
Describe the Kroll Process.
Titanium Ore (Rutile) is combined with Chlorine and Coke to produce Titanium tatrachloride (Tickle). Tickle is then added to magnesium to produce Titanium sponge and Magnesium Chloride. The sponge is then added to alloying elements and Ti scrap before being formed into compacts and welded together into an electrode. The electrode is then vaccum arc melted to form ingots. It can then be hot forged to break its core structure.
What is the modern FFC “Metalisis” Process?
A disruptive process from cambridge that mixes Titanium Oxide with and additional metal Oxide. Its then blended, pressed and sintered into a cathode where the electrochemical process occurs. Here oxygen elements react with the anode leaving a pureish metal cathode.
What are the benefits of the FFC process?
- Very homogenous output
- Small grain size that would take mass hot forging to produce after the Kroll process.
- Can produce some alloys the Kroll process cant (Tungsten)
What are the names of new processes that can form Titanium powder straight from ore?
Armstrong Process
MER Process
The metallurgy of titanium changes at a transus temperature. What is this property called?
Allotropic
What is Titaniums transus temp?
883 celsius
What are the two titanium crystal structures?
Alpha HCP phase
Beta BCC phase
What do stabalising elements do?
Change the transus temperature.
State some Alpha stabalisers.
Aluminium, Oxygen
State some Beta stabalisers.
Vanadium, Molybdinum, Niobium, Iron, Silicon
What affect does a small addition (<0.5wt%) interstitials have on Titanium?
Massively increases strength but at the same time drastically reduces elongation to failure.
What affect does adding beta stabalisers have on the composition range of Titanium?
They open up a wide Alpha + Beta composition field which allows for hot working (controlling grain size)
What is the difference between martensitic and equilibrum alpha?
There’s no difference
How is martensite formed in titanium?
By quenching, martensite created by thermal displasive process
Alpha alloys are non-heat treatable. How can they be strengthened?
Solid solution strengthening (eg Oxygen)
Grain Refinement
Cold working
What are the benefits of Alpha alloys?
High corrosion resistance
Weldable
Typically used as cladding in power stations
What are the benefits of Near Alpha alloys?
High creep resistance due to alpha structure
High fatigue resistance
Diffusion in the Beta phase is how many times faster than in Alpha?
100 times
Which Beta stabaliser inhibits disclocation creep?
Silicon
What three aspects make near alpha alloys have great creep resistance?
Silicon pins dislocations.
Large prior Beta grain size prohibits grain boundary sliding
Alpha structure slows diffusion
What is the most commonly used Ti alloy?
Ti-6Al-4V, used in F22 bulkheads and engine pylons
What are the benefits of alpha/beta alloys?
Superplastic
Good overall mechanical properties
Where can images of the wide range of microstructures of alpha/beta alloys be found?
Ti lecture
What are the benefits of near Beta alloys?
Good hardenability (precipitaion hardening) Very strong, good for landing gear
Where are near Beta alloys proccessed?
In the Alpha/Beta range, just like near alpha alloys, to avoid the formation of embrittling products.
What are the benefits of Beta alloys?
Cold formable, ductile
Good for sheets
Why are lamellar important for fracture toughness?
They provide a tortuous route for crack propogation
As Ti alloys move from Alpha to Beta what happens to the density?
It increases
