Competitive Growth in Spiral Grain Selector during Investment Casting of Single-Crystal Gas Turbine Blades

Transcription

1 Competitive Growth in Spiral Grain Selector during Investment Casting of Single-Crystal Gas Turbine Blades Hongbiao Dong, Manish Javahar, Huijuan Dai Department of Engineering, University of Leicester Neil D Souza Precision Casting Facility, Rolls-Royce Plc. PARSONS 2011, 5-8 September 2011, Portsmouth, UK

2 Outlines Introduction Numerical Modelling - Heat Transfer Analysis and Microstructure Modelling Experiments - Casting & EBSD Analyses What we found and what we propose Parsons 2011, 5-8 September 2011, Portsmouth UK 2

3 Grain Selection in Practice Radiation Heating Molten Metal Turbine Blade Radiation Cooling Water Cooled Chill Ceramic Mould Spiral Grain Selector Columnar Starter Block Spiral Grain Selector Starter Block V R.C. Reed, The Superalloys Fundamental and Applications, Cambridge University Press, 2006 Parsons 2011, 5-8 September 2011, Portsmouth UK 3

4 Prior Study Spiral Designs In Practice Angled Spiral (Helix) Restrictor In practice: There is no 'standard practice' for grain selection; the design of the selector rely upon trial-and-error based optimisation Parsons 2011, 5-8 September 2011, Portsmouth UK 4

5 Motivation of Our Study What are the physical processes occurring in the grain selector? What are the optimum dimensions and geometry of the grain selector? Can numerical modelling be used to answer the above questions? Can we move away from a purely empirical choice of grain selector to one which is designed and optimised? Parsons 2011, 5-8 September 2011, Portsmouth UK 5

6 Simulation Heat Transfer & Microstructure Parsons 2011, 5-8 September 2011, Portsmouth UK

7 Thermal Analysis (VeriCast Model) VeriCast Blade Investment Furnace Turbine Blade Grain Selector Parsons 2011, 5-8 September 2011, Portsmouth UK 7

8 Temperature ( C) Thermal Analysis Simulation Experiment mm 22.5mm 15mm 7.5mm 0mm Time (s) P. Carter, D.C. Cox, C.A. Gandin, R.C. Reed, Mater. Sci. Eng. A280, 2000, Parsons 2011, 5-8 September 2011, Portsmouth UK 8

9 Grain Structure Evolution Mixed Colours G <001> Parsons 2011, 5-8 September 2011, Portsmouth UK 9

10 Grain Structure Evolution Stochastic Study Linear Colours G <001> Grain Deviation Parsons 2011, 5-8 September 2011, Portsmouth UK 10

11 Average Grain Deviation the Role of Spiral? 30 Starter Block Spiral G <001> Spiral Grain Deviation Distance from the chill (mm) Starter Block Parsons 2011, 5-8 September 2011, Portsmouth UK 11

12 Quantitative Description of Spiral Size and Geometry d S T Case d T (mm) d S (mm) d C (mm) d B (mm) L P (mm) T (d C = d S T) q d B q = L P /2(d S -T) L P d S Case d T (mm) d S (mm) d B (mm) L P (mm) Case d T (mm) d S (mm) 5 15 θ d B (mm) 20 L P (mm) θ Parsons 2011, 5-8 September 2011, Portsmouth UK 12

13 Grain Selection in Spiral Selector D C B A A f e (b1) (c1) (d1) (e1) (f1) Grain Structure Evolution d c b (a) (b2) (c2) (d2) (e2) (f2) Pole Figures Along Sample <001> Parsons 2011, 5-8 September 2011, Portsmouth UK 13

14 Criteria for Determining Spiral Efficiency SX Orientation 100 % Degrees SX Height Parsons 2011, 5-8 September 2011, Portsmouth UK 14

15 SX Orientation SX Height (mm) Effect of Spiral Thickness (T) SX height INCREASES with larger spiral thickness d T (mm) 50 T d T (mm) No apparent correlation between SX orientation and spiral thickness Parsons 2011, 5-8 September 2011, Portsmouth UK 15

16 SX Orientation SX Height (mm) Effect of Spiral Diameter (d S ) SX height DECREASES with larger spiral diameter LARGER Spiral Diameter d S d S (mm) No apparent correlation between SX orientation and spiral diameter d S (mm) Parsons 2011, 5-8 September 2011, Portsmouth UK 16

17 SX Orientations SX Height (mm) Effect of Spiral Take-off Angle θ SX height INCREASES with larger take-off angle Take-off Angle SMALLER Take-off angle No apparent correlation between SX orientation and take-off angle q Take-off Angle Parsons 2011, 5-8 September 2011, Portsmouth UK 17

18 Experiments Casting & Grain Structure Parsons 2011, 5-8 September 2011, Portsmouth UK

19 Experiments Location where SX structure occurs Required SX Height INCREASES with larger take-off angle Case 13 Case 17 Case 18 Cylinder bar (28 ) (50 ) (70 ) Parsons 2011, 5-8 September 2011, Portsmouth UK 19

20 SX Height (mm) Efficiency of Grain Selection in Spiral Simulations Experiments q Take-off Angle θ ( ) Spiral becomes more efficient with a smaller take-off angle Parsons 2011, 5-8 September 2011, Portsmouth UK 20

21 Grain Orientation EBSD Grain Structure Map e d c (b) (c) (d) (e) b (a) Case 17 Geometrical Blocking Mechanism? Inverse Pole Figures along sample <001> 22 Parsons 2011, 5-8 September 2011, Portsmouth UK 21

22 Mechanism - Geometrical Blocking? R.C. Reed, The Superalloys Fundamental and Applications, Cambridge University Press, 2006, p133 Grain selection depends on the geometry of the spiral Parsons 2011, 5-8 September 2011, Portsmouth UK 22

23 Mechanism - Geometrical Blocking? Shorten L P Grain A & B survive Only grain A survives Increase q Grain A & B survive Grain selection depends on the geometry of the spiral Parsons 2011, 5-8 September 2011, Portsmouth UK 23

24 What We Found The Role of Cylindrical Base - Majority of the selection of grain orientations occurs in the cylindrical base and only a couple of grains with well aligned orientations can grow into the spiral. The Role of Spiral randomly select one grain via Geometrical Blocking Mechanism with no optimisation on grain orientations An quantitative description of the effect of the spiral on grain selection. The spiral becomes more efficient with: SMALLER Spiral Thickness; LARGER Spiral Diameter; SMALLER Take-off Angle. Parsons 2011, 5-8 September 2011, Portsmouth UK 24

25 What We Propose 2D Selector? 3D d S 2D d S d W d W L P L P q Take-off Angle (q) tanq =L P / 2 (d S -d W ) q Fully automated casting / waxassembly production line?

26 Acknowledgements modelling work: Dr. Jean-Christophe Gebelin, Prof. Roger Reed, University of Birmingham and Dr. Paul Brown, Rolls-Royce. casting experiments Dr. Yizhou Zhou, Prof. Nick Green, University of Birmingham Parsons 2011, 5-8 September 2011, Portsmouth UK 26