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Design Approaches for the Joining of Ceramic

Components

ADMACOM WorkshopSeptember 14-15, 2016Brussels, Belgium

Audi AG, Fraunhofer ISC Ceramic Composites, Snecma Propulsion Solide, Schunk Group

Walter Krenkel

Ceramic Materials Engineering (CME)University of Bayreuth Germany

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• Designing with Ceramics: Monolithic versus Composite Ceramics

• Challenges in Joining Monolithic Structural Ceramics

• Strain-compatible Hybrid Metal/Ceramic Structures

• Joining with Ceramic Matrix Composites

Brake Disks

Jacketed Pipes

• Summary

Outline

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Truss bridge made of steel (tensile or compressive stresses in

the bars)

Separation of functions of the different construction elements

Typical arched bridge made of brittle

stones (compressive stresses only)

Limited distance between the supports

because of high side thrust

Different Designs with Ductile and Brittle Materials

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-2,0

0,0

2,0

4,0

6,0

8,0

10,0

12,0

14,0

16,0

18,0

0 200 400 600 800 1000 1200 1400 1600

Temperature [°C]

Co

eff

icie

nt

of

therm

al

exp

an

sio

n

[10

-61/K

]

CMC (n.-ox.): C/C-SiC_XT

CMC (ox.): 720/Mullite ║CMC (ox.): 720/Mullite

CMC (n.-ox.): C/C-SiC_XT ║

Steel: St37

Nickel-base alloy: N06022

Monolithic ZrO2 (3 mol Y2O3)

Coefficent of Thermal Expansion of Ceramics Compared with Steel and Superalloys

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Ceramic Components for Gas Turbines

• Preferred ceramic

materials: SiC and Si3N4

• Prototype development

during the „ceramic fever“

in the 1980/90s

• Preferred components like

combustion chambers and

nozzles as well as hot gas

components like blades,

vanes and liners

• Unsolved problems with

insufficient damage

tolerance, reliability and

problems with the

metal/ceramic joinings

Victor Trefilov et al: Development of High-

Temperature Ceramics for Application in Gas

Turbine Engine Components (ASME, 2003)

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Attachments of Ceramic Blades

Metallic rotor with inserted RBSN blades

Stress distribution in the blade root of a metal/ceramic design

a) Ideal surface contact

b) Line contact

c) Asymmetric line contact

Mark van Roode: German Automotive Ceramic Gas Turbine Development

(ASME, 2002)

David W. Richerson: The Ceramic Gas Turbine – Retrospective,

Current Status and Prognosis (ASME, 2003)

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Integral Design of Automotive Gas Turbine Components

Blisks (Bladed Disks) of HPSN (Daimler) and integral vane rings of RBSN

(MTU) for automotive gas turbines

Mark van Roode: German Automotive Ceramic Gas Turbine Development (ASME, 2002)

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Metal-Ceramic Hybrid Blade Design (MTU)

• Concept of a tie-

rod

• Separation of

functions

• Cooled, load-

bearing cores

(metal)

• Uncooled,

compression-

loaded hollow

blades (SiSiC

ceramic)

W. Krüger et al: Ceramic Gas Turbine

Component Development at MTU (ASME, 2002)

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Compression-Loaded Rotor (Ceramic/CFRP Hybrid Concept)

Compression-loaded

blades (uncooled

monolithic ceramic)

Tensile loaded

outer ring (cooled

CFRP)

Segmented rotor

(monolithic ceramic)

Goal: Avoidance of tensile

stresses within the ceramic

material

• Shrinkage fit of high-strength

CFRP support ring to the

ceramic blades

• CFRP support ring has to be

cooled (cooling fins) and

isolated (from the rotor blades)

• Rotor and rotor blades made

of Si3N4

• Segmented rotor (to reduce

the stress level)

Quelle: DLR-Stuttgart

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Ceramic Tiles in Stationary Gasturbines

Ceramic tiles in an annular combustion chamber (Siemens)

• The liner of the combustion

chamber is exposed to only

low aerodynamic loads

(primarily:

thermomechanical and

corrosive loads)

• Reduced cooling air is

required because of the

ceramic „hot walls“

• Ceramic tiles are based on

alumina and mullite

• Microcracked structure

result in a damage-tolerant

behaviour

• The highest loads occur by

thermal shocks during rapid

coolings

C. Taut et al: Siemens KWU – Experience with Refractory

Ceramics in Stationary Gas Turbines (ASME, 2002)

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Refractory Ceramic Tiles

Segment of the ceramic heat shield (Siemens)

• Segmented design reduces the

thermally induced stresses and

facilitates the replacement of the tiles

• Gaps between the different tiles allow

an unhindered thermal expansion

• Sealing air from the compressor

prevents the penetration of hot gases

into the gaps (efficiency loss)

• Attachment of the tiles by metallic

fasteners in the grooves

Properties of the mixed ceramic:

Density 2.8 – 3.0 g/cm3

Open porosity 18 – 20 %

3 pt-bending strength 9 – 12 MPa (RT)

6 – 8 MPa (1200 °C)

Young‘s modulus 13 – 16 GPa

C. Taut et al: Siemens KWU – Experience with Refractory

Ceramics in Stationary Gas Turbines (ASME, 2002)

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X-38 – Nosecap Attachment

DLR Stuttgart

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Design

• Adjustable metal/ceramic fasteners

• Eight sets of levers on the rear side

of the cap

• Levers made of CMC

• Bearing support made of ODS alloy

DLR Stuttgart

Nosecap Attachment by Strain-Compatible Fastening System

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sleeve Screw

Friction rotor

(C/SiC)

Metallic

Bell

Force-locking

Different expansion

behaviors require large

tolerances

Stresses depending on

temperature

Force- and form-locking

Floaters for radial

expansion compensation

Additional expansion

compensation in

circumferential and axial

direction by slotted sleeves

and springs

Strain-Compatible Design of Ceramic-Metal Joinings in High Performance Brakes

Sleeve

Exploded view of the assembly

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Differential Design Applying In-situ Joining Methods (PIP and LSI Process)

Permanent Ceramic Joints made of SiC

Strength of joint almost identical with substrate strength

PrecursorPaste

C-Fabric, Felt

Joining MaterialC-Powder

Joining Material

Paste (80% Precursor / 20% C-Powder)

Optional: One Layer C-Fabric

C/C-Preparation Machining with diamond tools

Curing 135°C / 90 min / air

Siliconization 1500°C / Vacuum

Chemical Reaction: Si liquid + C solid SiC solid

Stringer/Panel + Joining Material Complex Structures

Joining Area

Detail A

Detail A

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Modular Design (Separate Manufacture of Fricion Layer and Load-Bearing Body)

Reibring

Kreissegmente

Friction ring

Friction ring

Core material (e.g. cooling ribs)

Assembly in the

carbon/carbon stage

Process-integrated joining

(reaction-bonding)

Friction ring: High COF, low wear

Core material: High strength, high thermal

conductivity and heat capacity

Separation of functions

C/SiC brake disk

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Form-locking joining between cooling ducts and friction surface

Functions of friction surfaces and load-bearing body are separated

Design studies and prototypes manufactured by DLR already in the 1990s

Internally Ventilated Brake Disks in Modular Design

DLR, Stuttgart

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Wheel Brake Disk ( 750 mm) for High Speed Trains

W. Krenkel: Hochleistungsbremsen aus Faserkeramiken,

MATERIALICA 1998

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Concept of Hybrid Ceramic/Metal Pipes (Jacketed Pipes)

Separation of Functions

• Metal pipe

Assures gas tightness and sufficient corrosion

resistance against steam oxidation

• Interphase

Compensates the tolerances of manufacturing

between metallic pipe and ceramic reinforcement

• CMC reinforcement (jacket)

Takes partially the mechanical and thermal

loads and prevents the metal pipe from creep

High mismatch of the coefficient of

thermal expansion (steel – CMC)

Steel limits the manufacture temperature

of the CMC pipe to 700 °C due to the required

on-site manufacture

© Fraunhofer HTL

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FE Simulations : Model and Variations

• FE software: ANSYS Mechanical

2D model:

– Two coaxial quarters of pipes

– Steel: inner diameter 30 mm, thickness 2 mm

– CMC: UD material C/SiC (hoop-wound)

• Loads/test conditions:

– Inner metal surface: 300 bar

– Over-all temperature: 700 °C

• Variations (pressure and temperature

are constant)

– Wall thickness ratio:

– Young’s modulus of the CMC reinforcement

– CTE of the CMC reinforcement

• Time-dependent simulation

– Gap between steel and ceramic jacket

CMC

steel

pressure

| tS|tC|

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Variation of the Young’s Modulus of the CMC pipe (ratio of wall thickness 1:1, no

gap)

steel only

E|| 75 GPa, E 7 GPa

E|| 150 GPa, E 14 GPa

E|| 187,5 GPa, E 17,5 GPa

Higher stiffness of the CMC jacket leads to higher stresses

in the steel (compressive stresses) and CMC pipes (tensile

stresses)

FE Simulations – Hoop Stress: Influence of Young’s Modulus of the CMC

Ho

op

str

es

s

All results are normed to the value of

the inner hoop stress of the steel pipe

1 2

3 4

steel CMC

1 2 3 4

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Variation of the coefficient of thermal expansion (CTE) of the CMC pipe in

circumferential direction (ratio of wall thickness 1:1, no gap)

steel only

CMC 1,6 x 10-6 K-1

CMC 7,4 x 10-6 K-1

CMC reinforcements with higher CTEs reduce the stress

level of the two coaxial pipes due to the smaller mismatch

of the thermal expansion

FE Simulations – Hoop Stress: Influence of CTE

Ho

op

str

es

s

All results are normed to the value of

the inner hoop stress of the steel pipe

1 2

3 4

steel CMC

1 2 34

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• Increase of lifetime by more than factor 4

• Local damage of the CMC jacket after 3655 h

• Non-catastrophic damage behavior due to local

creep failure of the steel pipe

• Proof of concept successful

steel pipe

local creep deformation

of steel pipe

cracked CMC pipe

CMC pipe

No separation of the CMC jacket of

the steel pipe

steel pipe

Hyb

rid

ce

ram

ic-m

eta

l p

ipe

Proof of Concept

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CMC load bearing

structure

SiSiC-tubes

Process gas (20 bar)

Exhaust gas (1 bar)

Separation of functions:

• CMC load bearing structure for high thermomechanical strength and reliability

• Monolithic ceramic tubes for gas tightness and high corrosion stability

• Interphase of high TC (BN, AlN) compensates manufacture tolerances

Full-Ceramic Heat Exchanger

Europ. Patent EP 0 996 848

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Summary

• The different CTEs of metals and ceramics require strain-compatible

attachments

• Joining of similar materials (in-situ-joining) results in lowest thermally induced

stresses

• Ceramic Matrix Composites allow the design of highly and permanently tensile

loaded structures

• The high anisotropy and the very low CTEs of CMCs still remain challenges in

designing with ceramics

• Change of Design in Ceramics: “From the compression-loaded arch to the

tension-loaded beam“