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© Rolls-Royce plc 2010The information in this document is the property of Rolls-Royce plc and may not be copied or communicated to a third party, or used for any purpose other than that for which it is supplied without the express written consent of Rolls-Royce plc.This information is given in good faith based upon the latest information available to Rolls-Royce plc, no warranty or representation is given concerning such information, which must not be taken as establishing any contractual or other commitment binding upon Rolls-Royce plc or any of its subsidiary or associated companies.
Trends and Issues - Titanium Alloy use in Gas Turbines
Professor Dave RuggCorporate Specialist – Compressor and Nuclear Applications
Royal Society Industrial Fellow
2
Talk Structure History
Load regimes / material limitations Elastic regimes Elastic-plastic regimes Plastic regimes
The way forward Process / structure relationships Structure / property relationships
Conclusions
3
Engineering Challenge - The Gas Turbine
4Rolls-Royce Ti overview Ti Alloys account for 1/3 of gas turbine weight
Over 2000 tonnes per year used by RR >$100M PA
‘Conventional’ alloys Form a significant part of research
Improved component lifing Introduction via improved design and improved
manufacturing processes Seeking improvements in buy to fly ratio (near nett shape
technology) Academic interaction
Extensive collaboration with Academia Direct contract Via nationally funded programmes
5
Disc alloy temperature capabilityTemperatureCapability (C)
1960 1970 1980 1990 2000
350
600
α-β Alloys
High strength α-β Alloys
Near-α Alloys
Aerofoil ‘fire line’
6
Titanium in Discs – 3 shaft history
Increasing temperatureDecreasing space= Increased Ni alloy use
1980 1990 2000 2010
HP
IP
Ti685 Ti829 Ti834
Fan
7If titanium was your child - (global perspective)
Approx 50 years to mature
Half the typical growth rate (with respect to adoption through the engine)
Cost £2,000,000 per year whilst maturing(or £50,000 per mm of growth)
8Load regimes and material limitations
9Elastic properties (Texture)
•Fan blade untwist
-arise from centrifugal loads
-blades manufactured with ‘over-twist’
-running tip deflection > 15mm
-Tip angle controlled to < 1°
Shape = Mass flow = Thrust
Parallel rolling
Engine type (property differential L to T %) Trent xyz (1.4%)Trent xyz (1.8%)
Trent xyz (2.8%)
Trent xyz (3.5%)
RB211 derivative1 (8%)
10Elastic Properties - Resonance•Resonance
-blade design to minimise exposure and magnitude of HCF stress.
-design to 109 cycles is common.
-criteria based on stress threshold, not
cyclic life….
Modal frequency = HCF load = Product integrityIP compressor blade - high order resonantmode stress contour plot.Resonant frequency 18 KHz
11
Matls070289P
Hollow Fan Technology
Trent
MILITARY
Cross-Section ofHollow Blade
12Elastic – Plastic properties
Cold Dwell Fatigue
Notch Fatigue
Macrozone vs Effective Structural unit size…
13Plastic properties – the great divide ?
Strain rate
UTS(Quasi static)
UTS(High rate)
Low (Hours / days)
Medium(seconds)
High(milliseconds)
‘Yield’
‘Failure’
‘cyclic’yield
‘tensile’yield
Stre
ss
Notes;In all regimes strength level is controlled by degree of micro-structural refinement.Many alloys have similar cyclic yield strength.
Room temp props are dictated byDislocation creep….
relaxation
14Plastic Properties contd.
1970 1980 1990 2000
RB211-22B & 524
RB211-535E4
TRENT 700
TRENT 800
TRENT 500
TRENT 900
Medium Bird
1.5lb
30min Run-on
4lb Large Bird
Medium Bird
2.5lb
20min Run-on
4lb Large Bird
Medium Bird
2.5lb
20min Run-on
8lb Large Bird
Medium Bird
2.5lb
20min Run-on
8lb Large Bird
Medium Bird
2.5lb - 20min Run-on
8lb Large Bird, AND new
5.5lb Large Flocking Bird
20min Run-on
Medium Bird
1.5lb
5min Run-on
4lb Large Bird
Also consider containment,FOD, trailing blade integrity,Surface treatments (peening)etc.
15Titanium – other criteria…
Compressor blade fire(Temp / mass flow criteria)
Compressor disc oxidation(Temp limit – alpha case cracking)
Residual stress(section size /total stress consideration)
Adaibatic shear(structural unit size)
Disc / blade contact fatigue(crushing stress)
Repair(microstructural control)
16The way forward
17Experimental techniques and models now available… (Imperial, Manchester,Oxford,Swansea)
0
200
400
600
800
1000
1200
0 2 4 6
Position (micron)
Stre
ss yy
(MPa
)
time=0.01stime=0.02s
F Dunne
A Wilkinson
M Bache
M Preuss, J Fonseca
D Dye
18Local Microtexture - cross rolled plate;
AX
19Understanding and modelling properties - overview
Measure Represent Model Validate Use / interface
SAWEBSDBeam line
What / how tomeasure ?
How accurate Do the measurementsHave to be ?
Poly crystalrepresentation
When does strain /Slip reversal becomeA crack ?
Databank ?
Length scales
Misorientation distribution
texture
Aspect ratioTopographyGB type /area fraction
CRSSStrain rateElastic props
Failure criteria Hydrostatic stress
Boundary conditionsFrom continuum FE
Coherent framework is required to allow adoption by the end user. A similar logic can be applied to modelling TMP.
20Structural variables – real world issues…
Grain Boundary Morphology
Forge temperature, strain and strain rate,
transfer time and media for post forge
cooling
Primary Alpha Laths
Transfer time and media on post forge cooling,
Solution heat treatment temperature and time
Prior Beta Grain
Billet* preheat, temperature, time and
ramp rate, transfer time to press, strain and strain rate during forging, press
time and hold periods
Secondary “Fine” Alpha
Transfer time and media for post solution heat treatment cooling, Ageing temperature and time
Retained Beta
Transfer time and media for post solution heat treatment cooling, Ageing temperature and time
* Billet itself sets starting bulk chemistry, initial partitioning, macro/microstructure and crystallography
Grain Boundary Morphology
Forge temperature, strain and strain rate,
transfer time and media for post forge
cooling
Primary Alpha Laths
Transfer time and media on post forge cooling,
Solution heat treatment temperature and time
Prior Beta Grain
Billet* preheat, temperature, time and
ramp rate, transfer time to press, strain and strain rate during forging, press
time and hold periods
Secondary “Fine” Alpha
Transfer time and media for post solution heat treatment cooling, Ageing temperature and time
Retained Beta
Transfer time and media for post solution heat treatment cooling, Ageing temperature and time
* Billet itself sets starting bulk chemistry, initial partitioning, macro/microstructure and crystallography
21Symmetry variables – real world issues
Slip transmission function of:
(i) Relative orientation of αΙ and β and β to αΙΙgiving favourable or unfavourable alignment of preferred slip systems.
(ii) Orientation angle, θ
(iii) Stress, either macro applied or local due to crystal plasticity.
(iv) Length scale and slip planarity
(v) Loading rate
(vi) Local chemistry, driven by alloy partitioning, changing CRSS for individual slip systems
σ
σ
Slip
αΙ
β
αΙΙ
θ
Slip transmission function of:
(i) Relative orientation of αΙ and β and β to αΙΙgiving favourable or unfavourable alignment of preferred slip systems.
(ii) Orientation angle, θ
(iii) Stress, either macro applied or local due to crystal plasticity.
(iv) Length scale and slip planarity
(v) Loading rate
(vi) Local chemistry, driven by alloy partitioning, changing CRSS for individual slip systems
σ
σ
Slip
αΙ
β
αΙΙ
Slip transmission function of:
(i) Relative orientation of αΙ and β and β to αΙΙgiving favourable or unfavourable alignment of preferred slip systems.
(ii) Orientation angle, θ
(iii) Stress, either macro applied or local due to crystal plasticity.
(iv) Length scale and slip planarity
(v) Loading rate
(vi) Local chemistry, driven by alloy partitioning, changing CRSS for individual slip systems
σ
σ
Slip
αΙ
β
αΙΙ
θ
E = 145
E = 100
Elastic and plastic asymmetry;from single crystal to real engineering(complex) structures….
22Understanding and modelling the evolution of texture, structure and properties.
Important for the material supplier AND end user; Process route optimisation (large gains possible) Assessing manufacturing change and concessions Design for ‘local area properties’ Advanced micro-structural standards are coming...
Possible options; Physics based Statistics based Neural network Phase field
In reality, a combination of techniques is probable..
23Conclusions. Some limits for titanium application defined;
Max temperature in discs Max temp in aerofoils
Significant gains still to be had; Process improvements Improved component lifing ‘new’ manufacturing practice and repair All require detailed fundamental understanding combined
with the appropriate modelling framework
‘Joined up’ programmes and extensive interaction with Academia and supply chains are critical in achieving these gains.
Trends and Issues - Titanium Alloy use in Gas TurbinesTalk StructureEngineering Challenge - The Gas TurbineRolls-Royce Ti overviewDisc alloy temperature capability�Titanium in Discs – 3 shaft historyIf titanium was your child - (global perspective)Load regimes and material limitationsElastic properties (Texture)Elastic Properties - ResonanceSlide Number 11Elastic – Plastic propertiesPlastic properties – the great divide ?Plastic Properties contd.Titanium – other criteria…The way forwardExperimental techniques and models now available… (Imperial, Manchester,Oxford,Swansea) Local Microtexture - cross rolled plate;�Slide Number 19Slide Number 20Symmetry variables – real world issuesUnderstanding and modelling the evolution of texture, structure and properties.Slide Number 23
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