competitive growth in spiral grain selector during ... 1520 dong.pdf · competitive growth in...

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

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


Grain Selection in Practice

Ceramic Mould

Molten

Metal

Water

Cooled Chill

Radiation

Cooling

Radiation

Heating

Columnar

Starter Block

V

Spiral Grain

Selector

Turbine

Blade

Spiral Grain

Selector

Starter

Block

R.C. Reed, ‘The Superalloys Fundamental and Applications’, Cambridge University Press, 2006


Prior Study

Spiral Designs

In practice: There is no 'standard practice' for grain selection;

the design of the selector rely upon trial-and-error based optimisation

In Practice

Angled Spiral (Helix) Restrictor


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?

Simulation

Heat Transfer

&

Microstructure

Parsons 2011, 5-8 September 2011, Portsmouth UK


Thermal Analysis (VeriCast Model)

Investment Furnace Turbine Blade Grain Selector

VeriCast Blade

8

0 50 100 150 200 250 300 350 4001250

1300

1350

1400

1450

1500

Tem

pera

ture

Time (s)

30mm

22.5mm

15mm

7.5mm

0mm

Thermal Analysis

P. Carter, D.C. Cox, C.A. Gandin, R.C. Reed,

Mater. Sci. Eng. A280, 2000, 233-246

(˚C

)

ExperimentSimulation



Grain Structure Evolution

Mixed Colours

G <001>



Stochastic Study

Linear Colours

G

Grain

Deviation

<001>


the Role of Spiral?

Starter

Block

Spiral

10

3738

29

43

G

Grain

Deviation

2

5

Distance from the chill (mm)

0

5

10

15

20

25

30

1 2 3 4 5 6 7

Avera

ge G

rain

Devia

tio

n

2 5 10 29 37 38 432 5 10 29 37 38 43

Starter Block Spiral

<001>


Quantitative Description of Spiral Size and Geometry

T

Case 1 2 3 4 5 6 7

d T (mm) 2 3 4 5 6 7 8

d S (mm) 12 13 14 15 16 17 18

d C (mm)

d B (mm)

L P (mm)

20

10.5

10

(dC= dS – T)

dS

θ

Case 8 9 10

d T (mm)

d S (mm) 13 15 17

d B (mm)

L P (mm)

5

20

10.5

Case 11 12 13 14 15 16 17 18

d T (mm)

d S (mm)

θ 20 25 28 29 35 40 50 70

d B (mm)

L P (mm) 7.5 9.3 10.5 11.2 14 17 24 55

5

15

20

q

dB

dS

T

LP

q = LP/2(dS-T)


bc

d

e

f(d1) (e1) (f1)(b1) (c1)

(d2) (e2) (f2)(b2) (c2)(a)

A

B

C

A

D


Pole Figures Along Sample <001>

Grain Selection in Spiral Selector


Criteria for Determining Spiral Efficiency

SX Height

SX Orientation

%100

15 30 40 550 15 30 40 550

27.8˚

Degrees


2 3 4 5 6 7 80

10

20

30

40

50

SX

Ori

enta

tio

n

dT (mm)

2 3 4 5 6 7 80

2

4

6

8

10

12

14

16

18

20

22

SX

Hei

gh

t (m

m)

dT (mm)

No apparent correlation

between SX orientation and

spiral thickness

SX height INCREASES

with larger spiral thickness

Effect of Spiral Thickness (T)

T


13 14 15 16 175

10

15

20

25

30

35

40

45

50

SX

Ori

enta

tion

dS (mm)

13 14 15 16 1713

14

15

16

17

18

19

20

21

SX

Heig

ht

(mm

)

dS (mm)

SX height DECREASES

with larger spiral diameter


between SX orientation and

spiral diameter

Effect of Spiral Diameter (dS)

LARGER

Spiral Diameter

dS


20 30 40 50 60 70

1012141618202224262830323436384042

SX

Hei

gh

t (m

m)

Take-off Angle

20 30 40 50 60 705

10

15

20

25

30

35

40

45

SX

Ori

enta

tio

ns

Take-off Angle

Effect of Spiral Take-off Angle θ

SX height INCREASES

with larger take-off angle


between SX orientation

and take-off angle

SMALLER

Take-off angle

qq

Experiments

Casting

&

Grain Structure



Case 13

Experiments

Case 17 Case 18 Cylinder bar

Location where SX

structure occurs

(28˚) (50˚) (70˚)

Required SX Height

INCREASES

with larger take-off angle


0 10 20 30 40 50 60 70 800

10

20

30

40

50

Take-off Angle θ (° )

SX

Heig

ht

(mm

)Simulations

Experiments

Efficiency of Grain Selection in Spiral

Spiral becomes more efficient with a smaller take-off angle

qq


22°

EBSD Grain Structure Map

Inverse Pole Figures along sample <001>

b

c

d

e

(a) Case 17

(d) (e)(b) (c)

Grain Orientation

Geometrical Blocking

Mechanism ?


Mechanism - Geometrical Blocking?

Grain selection depends on the geometry of the spiral

R.C. Reed, ‘The Superalloys Fundamental and Applications’,

Cambridge University Press, 2006, p133


Mechanism - Geometrical Blocking?

Shorten LP Increase q

Grain A & B survive Grain A & B survive

Only grain A survives

Grain selection depends on the geometry of the spiral


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.

What We Propose – 2D Selector?

dS

tanq =LP / 2 (dS-dW)

Take-off Angle (q)

3D 2D

dW

LP

dW

dS

LP

qq

Fully automated casting / wax-

assembly production line?


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

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