Ultra High Temperature Refractory Metal Based Silicide Materials For Next Generation Turbines Dr. Stefan DRAWIN ONERA (French aerospace research centre) Metallic Materials and Processing Department 92320 CHÂTILLON (France) Office National d Études et de Recherches Aérospatiales www.onera.fr
Presentation Outline Introduction The project Alloy systems Manufacturing Mechanical properties Oxidation resistance Machining Conclusion
Introduction: increase engine performance Environmental impact efficiency (SFC, ) emissions (CO 2, NO x, ) noise Reliability Costs (Rolls-Royce) Long term goals (from ACARE): 20% reduction in SFC 80% reduction in NO x emissions 50% reduction in CO 2 emissions
Introduction: increase temperature capability of materials Increase thermal efficiency Increase combustion temperature through Advanced engine architectures Advanced cycle designs Novel combustor designs Optimised aerodynamics New cooling concepts Increased airfoil material temperature capability (cfmi)
Introduction: increase temperature capability of materials + 50 C in TIT 4 5 % reduction in SFC
Introduction: what materials for turbine blades? Capabilities of turboengine materials, up to the most recent generation of single-crystal Ni-base superalloys
The Project ULtra high Temperature MATerials for Turbines Develop Mo- and Nb silicide-based multiphase alloys Develop cost-effective fabrication processes, based on PM or IM Design coatings with improved oxidation resistance Establish a database to benchmark against current materials, and provide data for specific turbine operating conditions Identify the critical material properties, processing requirements and other factors (cost, etc.) governing production feasibility Manufacture prototypes to validate machining and joining processes Carry out a preliminary assessment to introduce these materials in high-performance turbines, and study implications for future component/turbine design
The project ULtra high Temperature MATerials for Turbines ONERA (coordinator) University of Magdeburg PLANSEE SE IRC Univ. of Birmingham Turbomeca University of Surrey University of Nancy Snecma Walter Engines Electricité de France Rolls-Royce Avio France Germany Austria UK France UK France France Czech Republic France UK Italy 12 partners 6 countries Started: January 2004 Duration: 48 months
Alloy systems Key properties Replicate the properties of superalloys ( 1100 C) at T 1300 C tensile creep (< 1% in 125 h at T > 1200 C and σ > 175 MPa) tensile strength RT toughness oxidation resistance ( e < 25 µm in 100 h at 1300 C) fatigue behaviour and phase stability at T > 1300 C density < 7.5 g.cm -3 processing at industrial scale
Alloy systems Properties of alloys are governed by: composition fast composition screening small alloy batches microstructure various microstructures various processing routes
Alloy systems Mo-Si-B Mo(ss) Mo 3 Si Mo 5 SiB 2 Nb-Si Nb(ss) Nb 5 Si 3 Nb 3 Si Powder metallurgy (PM) Ingot metallurgy (IM)
Manufacturing: Ingot metallurgy Vacuum arc melting (SURREY, ONERA) Plasma melting: up to 50 kg (IRC) Shaped parts: investment casting (IRC) main difficulty: high melting point ( > 1700 C) Investment casting: first trials on bars
Manufacturing: Ingot metallurgy Investment casting: first trials on bars X-ray radiographs Incomplete filling of the moulds
Manufacturing: Ingot metallurgy Investment casting: oversized blade wax pattern blade mould cluster Improvement of process parameters defect-free cast blades
Manufacturing: Powder Metallurgy (PM) PM process Powder (raw material) CIP Sintering Hot Isostatic Pressing Wrought Processing Elemental Powder Blend Sintered Bar Material Consolidated Billet Mill Product HIP ed extruded forged
Manufacturing: Powder metallurgy PM process: influence of powder preparation Mo(ss) Microstructure after HIP ing eutectic x 1000 gas-atomised powder (Ar) mechanically alloyed powder finer (< 1µm) better homogeneity co-continuous
Mechanical properties Main properties used for alloy screening: HT compressive strength HT compressive creep RT toughness MT and HT oxidation resistance Others properties: tensile properties impact resitance physical properties thermal properties fatigue properties
Mechanical properties HT compressive strength 500 Mo-Si-B alloy (HIP ed) 50 Mo-Nb-Si-B alloy (HIP ed) 1400 C, strain rate = 10-4 s -1 Strength (MPa) 400 300 200 100 YS UTS Elongation 40 30 20 10 Elongation to failure (%) 0 800 1000 1200 1400 1600 T ( C) 0 DBTT ~ 1200 C Superplastic behaviour Possible forming of complex shapes by isothemal forging
Mechanical properties HT compressive creep IFW Dresden (Germany) INSTRON machine; low vacuum (0.01 mbar) laser extensometry ONERA Châtillon (France) Lever arm machine; secondary vacuum (10-5 mbar) conventional extensometry (on compression platens) 3 x 3 x 6 (mm) T = 1050 C to 1315 C
Mechanical properties HT compressive creep Load increment: 100 to 400 MPa save time and specimens increment load when stationary creep is reached validated with constant load experiments Strain (ξ L/L0) 2.0% 1.5% 1.0% 0.5% 200 300 400 200 400 340 280 220 True Stress (MPa) Strain rate (s -1 ) 1E-06 1E-07 1E-08 1E-09 200 MPa 300 MPa 400 MPa 200 MPa 0.0% 0 72 000 144 000 Time (s) 160 0.0% 0.5% 1.0% Strain (%)
Mechanical properties HT compressive creep Mo-Nb-Si-B alloy HIP ed Grain size: < 1 µm Heat treated (1700 C 10 h) Grain size: 4 7 µm
Oxidation resistance Two oxidation regimes «Pesting» at 600 C 850 C Internal oxidation of Nb Volatilisation of oxides: Mo + O 2 MoO 3 (g) Too slow kinetics of: silicide + O 2 silica High temperature oxidation at T > 1100 C Control of the protective oxide layer formation Control of substrate / oxide CTE mismatch Adherence of oxide to prevent spalling (cyclic oxidation)
Oxidation resistance Nb-Ti-Hf-Cr-Al-Si alloy at 815 C (cyclic) Effect of Al content Mass variation (mg/cm 2 ) 0-10 -20-30 -40 2Al 4Al 8Al (Al content in at.%) 0 50 100 Number of 1-hour cycles With increasing Al: Time for collapse increases Composition of oxide changes
Oxidation resistance Development of oxidation resistant coatings Performance of existing coatings on Mo-Si-B alloy at 1100 C Mass variation (mg.cm -2 ) 8 6 4 2 0 sample 1 sample 2 0 1 000 2 000 3 000 Number of 1-hour cycles Mass variation (mg.cm -2 ) 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0 200 400 600 800 Number of 1-hour cycles Fe-Cr-Si pack cementation coating (developed by NANCY) SIBOR coating (developed by PLANSEE)
Machining Determine which parameters play a significant role in terms of tool wear and workpiece productivity during main operations required on blades and vanes: EDM (electro-discharge machining) Grinding Turning Milling Drilling
Machining Turning (Mo-Si-B alloys) Thread spalled 6 th trial 3 rd trial Surface finishing in 3 rd and 6 th trial (Mo-Si-B) Optimised conditions found Brittleness
Machining Grinding (Mo-Si-B alloys) Thread 2 Thread 1 Optimised conditions found
Machining Grinding (Nb-Si alloys) Optimised conditions
Machining Machining of complex-shaped mock-ups Fir-tree (Mo-Si-B alloys) After EDM After finishing
Conclusion is a fast-track programme to evaluate the potential of Mo- & Nb-silicide based materials. At mid-project, very encouraging results are obtained in many fields: - Definition of alloy compositions - Processing techniques: PM and IM - Improvement of oxidation resistance - Development of coatings - Manufacturing: parameters and mock-ups
Conclusion The stand is in zone E1 www.ultmat.onera.fr ULTMAT is partially funded by EC