Titanium Flashcards
What are the sectors that use titanium?
Commercial aerospace
military aerospace
Power generation
CPI and Desalination
What are the advantages of titanium?
Low density
Excellent corrosion resistance
High melting point
High specific strength
Compatible with CFRP
Excellent properties at high temperatures
What are the disadvantages of Titanium
Expensive to machine
Low wear resistance
Difficult to form
Pick up of oxygen + nitrogen ^ 500*C
Expensive £25k/tonne
lots of work to remove oxygen
Why is titanium with CFRP?
Similar linear expansion coefficient
Similar electrochemical potential
Can join easily - no galvonic corrosion
Similar youngs modulus (stifnnes)
What is the order of the FFC cambridge process?
- Tio2 and MeOx
- Blend
- Press
- Sinter
- Electrochemical process
In FFC what are the components of the electrochemical process
Anode - Graphite
Cathode - TiO2/MeOx
Crucible - Titanium
Liquid - molten CaCl2 800-1100*C
What process is used for the extraction of titanium?
Kroll Process
What are the components of the Kroll process?
- Rutile + Chlorine + Coke
- Magnesium and TIckle
- MgCl2 off product
- Alloys and scrap added to sponge
- Electrode
- Melt process
What is the general processing of titanium sponge?
- Titanium sponge
- Compaction
- Manufacture electrodes
- VAR (vacuum arc remelting)
- Ingots
- Breakdown Forging
- Blooms
What are some Alpha-Stabilising elements?
Aluminium
Oxygen
Nitrogen
What are the Beta-Stabilising elements?
Molybdenum
Iron
Vanadium
Chromium
Manganese
What does increasing Alpha stabilisers do?
Promotes alpha Phase
How can you promote the beta phase
Increase the quantity of beta stabilisers
What are the properties of Alpha dominant structures?
Higher Creep strength
Improved weldability
What are the properties of beta dominant structures?
Higher density
Increased heat treatment response
Higher short term strength
Increased strain rate sensitivity
Improved fabricability
What is meant by the beta transus?
The temperature at which titanium alloy transforms from alpha to beta form
What temperature is the beta transus
883*C
What is the structure of the atoms before and after beta transus
before - BBC
after - HCP
What is the effect of increasing interstitial elements on the properties of titanium?
Increases the tensile strength
Decreases the weld joint bend elongation
What is the order of interstitial elements in terms of effect on properties?
N > O > C
How can Alpha alloys be strengthened?
- Solution Strengthening from OXYGEN
- Grain Refinement (Hall Petch)
3.Cold work
What phase are non-heat treatable products?
Alpha
composition is such that beta cannot be retained at room temp in any form.
Always alpha
Martensite formed
What are the applications of alpha alloys?
CLadding in chemical plants
Hydraulic piping
Cooling towers
What are the benefits of Alpha Alloys
Highly corrosion resistant
Low maintanence cost
What are the applications of near alpha alloys?
Compressor disks
Compressor blades
Gas turbine engines (compressor section)
Why are near alpha alloys good for creep resistance?
- Silicon pins dislocations
- Large prior beta grain size - inhibits grain boundary sliding
- Alpha Structure - slow diffusion
up to 600*C
What are the applications of
Bulk heads for F22
High performance aircraft
What are the benefits of Near beta alloys?
Good hardenability
Applications of near beta alloys?
Landing gear components
Rotor hub for helicopters
Benefits of Beta alloys
Cold formable
Omega formation surpassed
What effect does grain size have on tensile strength?
Determines strength via Hall-Petch
grain size reduction ideal
Increase phase boundaries interfere with slip .
increased Yield Strength
what effect do interstitial elements have on tensile strength
Deleterious effect on ductility
Have very potent solis solution strenghtening affect.
What affect does age hardening have on tensile strength
hinders slip and increases strength.
What is the microstructure influence on fracture toughness?
Lenticular morphologies provide a tortuous path for cracks
fine grain structure makes crack path easy
Fine grain structure have poor fracture toughness
Microstructure influence on fatigue
Fine grain structure will have good crack initiaion resistance
Once crack has grown, microstructure ideal to have large grains to reduce ease of crack propogation
Fatigue crack initiation resistance
Fine grain structure wanted
Stop crack initiation
what is the most expensive part in the Kroll process
Thermomechanical process
Heating Ti-6Al-4V above the beta transus for 4 hours followed by a furnace cool will lead to…
A single colony alpha structure and grain boundary alpha
How are medium strength levels generated in CP-Ti alpha alloys?
Cold working
