Ultra High Temperature Refractory Metal Based Silicide Materials For Next Generation Turbines

Transcription

1 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 CHÂTILLON (France) Office National d Études et de Recherches Aérospatiales

2 Presentation Outline Introduction The project Alloy systems Manufacturing Mechanical properties Oxidation resistance Machining Conclusion

3 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

4 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)

5 Introduction: increase temperature capability of materials + 50 C in TIT 4 5 % reduction in SFC

6 Introduction: what materials for turbine blades? Capabilities of turboengine materials, up to the most recent generation of single-crystal Ni-base superalloys

7 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

8 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

9 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

10 Alloy systems Properties of alloys are governed by: composition fast composition screening small alloy batches microstructure various microstructures various processing routes

11 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)

12 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

13 Manufacturing: Ingot metallurgy Investment casting: first trials on bars X-ray radiographs Incomplete filling of the moulds

14 Manufacturing: Ingot metallurgy Investment casting: oversized blade wax pattern blade mould cluster Improvement of process parameters defect-free cast blades

15 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

16 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

17 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

18 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) YS UTS Elongation Elongation to failure (%) T ( C) 0 DBTT ~ 1200 C Superplastic behaviour Possible forming of complex shapes by isothemal forging

19 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

20 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% True Stress (MPa) Strain rate (s -1 ) 1E-06 1E-07 1E-08 1E MPa 300 MPa 400 MPa 200 MPa 0.0% Time (s) % 0.5% 1.0% Strain (%)

21 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

22 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)

23 Oxidation resistance Nb-Ti-Hf-Cr-Al-Si alloy at 815 C (cyclic) Effect of Al content Mass variation (mg/cm 2 ) Al 4Al 8Al (Al content in at.%) Number of 1-hour cycles With increasing Al: Time for collapse increases Composition of oxide changes

24 Oxidation resistance Development of oxidation resistant coatings Performance of existing coatings on Mo-Si-B alloy at 1100 C Mass variation (mg.cm -2 ) sample 1 sample Number of 1-hour cycles Mass variation (mg.cm -2 ) Number of 1-hour cycles Fe-Cr-Si pack cementation coating (developed by NANCY) SIBOR coating (developed by PLANSEE)

25 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

26 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

27 Machining Grinding (Mo-Si-B alloys) Thread 2 Thread 1 Optimised conditions found

28 Machining Grinding (Nb-Si alloys) Optimised conditions

29 Machining Machining of complex-shaped mock-ups Fir-tree (Mo-Si-B alloys) After EDM After finishing

30 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

31 Conclusion The stand is in zone E1 ULTMAT is partially funded by EC