Thermal Spray Coatings For Industrial Applications · 2018. 9. 25. · 13 rticle re big particles,...
Transcript of Thermal Spray Coatings For Industrial Applications · 2018. 9. 25. · 13 rticle re big particles,...
Thermal Spray Coatings
For Industrial Applications
INSTM Research Unit “Roma La Sapienza”
Dept. of Chemical and Materials Engineering (ICMA)
Sapienza University of Rome
Giovanni Pulci
INSTM - Italian Consortium
on Materials Science
and Technology
Le nuove frontiere delle tecnologie al plasma - Esempi di applicazioni industriali
Consorzio Innova FVG - 24 Settembre 2018
Coatings for severe operating environment
Heavy combination of mechanical stresses and aggressive environment
Temperature
Mechanicalstress
OxidationCorrosion
Wear
Coatings for severe operating environment
Aim of presentation:
Description of case studies related to innovations and R&D in thermal spray field
R&D plays a key role for component working in critical operating conditions
R&D
Improvementof performance
Costs reduction
R&D
Introductioninto the market
Design
Existing product New product
energy
heat/energy source
material
material feed/flow
atomizing
gas or air
material spray
substrate
coating
molten particlesspray equipment
A thermal spray process can be divided into four sections:
heat/energy source (thermal energy for heating and melting)
material feed/flow
material spray (kinetic energy for propelling dispersion)
material deposition
Surface engineering by thermal spray process
Surface engineering by thermal spray processes
Surface engineering by thermal spray processes
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• An inert gas is passed through a potential differential.
• An arc is formed between the two dipoles.
• The gas is ionized and recombines after going through a free expansion.
• The recombination effect releases heat and creates a plasma flame (“plume”).
• Powder is inserted into the flame and is propelled towards the substrate.
Plasma spraying
9
Plasma spraying
10
• Max. plume temperature ≈ 12000 °C
• Impact speed of particles 200-400 m/s
• In-flight time of particles ≈ 10-3 s
• Heating/cooling rate ≈ 107 K/s
Plasma spraying
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• Plasma (Primary) gas flow
• Secondary gas flow
• Plasma power
• Spray distance
• Injector angle, length and size
• Carrier gas flow
• Gun spray angle
powder injection
molten particle stream
plasma
spray gun
plasma
flame or
plume
Plasma spraying
Process parameters
12
• Primary gases (Ar, N2): plasma
stability and transport properties
• Secondary lighter gases (He, H2),
enthalpy adjustment.
• N2 and H2 are diatomic gases.
These plasmas have higher
energy contents for a given
temperature than argon and
helium because of the energy
associated with dissociation of
molecules.
gas e
nerg
y c
on
ten
t [W
h/S
CF
]
N2 H2Ar
He
gas temperature [°C]
0
100
200
300
400
500
600
0 2200 4400 6600 8800 11100 13300 15500 17800 20000
dissociation
H2 2 H
dissociation
N2 2 N
Plasma spraying
Plasma gases
13
pow
de
r p
art
icle
tem
pera
ture
big particles,
high powder density
small particles,
low powder
density
flow
te
mp
era
ture
part
icle
ve
locity
Ar/H2
N2/H2 N2/H2
flo
w v
elo
city
Plasma spraying
Spray distance
14
part
icle
ve
locity
N2/H2
29 kW
20 kW(same gas comp.)
oxid
e c
on
ten
tsu
rfa
ce
ro
ugh
ne
ss
cold particles
Plasma spraying
Spray distance
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Controlled Atmosphere Plasma Spray
chamber is backfilled after evacuation, either at
• near vacuum (1 - 10 mbar) VPS
• reduced pressure (> 50 mbar) LPPS
• standard pressure APS
• elevated pressure (up to 4 bar) HPPS
• with a substitute atmosphere (reactive (CxHy), inert (Ar)) RPS / IPS
VPS / LPPS / LVPS
➢ spraying in near vacuum or under reduced pressure conditions
➢ spray particles are unimpeded by frictional forces of the atmosphere
Plasma spraying
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• Ceramics (high melting point)
• Al2O3, Al2O3/TiO2, Cr2O3, ZrO2 -Y2O3, La2Zr2O7, ecc.
• ZrB2, TiB2, SiC (non standard)
• Metals (refractory, oxidation control is mandatory, controlled
atmosphere)
• MCrAlY, Ni-and Mo-based alloys
• Cermets
• Cr3C2 - based (high T, generally NiCr matrix)
• WC - based (better mechanical properties, Tmax 500 °C
(decarburation), Co - CoNiCr - based matrix)
Plasma spraying
Materials
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• Low porosity
• Lamellar microstructure, partially molten ceramic phase
Cermet Cr3C2 – Ni-Cr
Plasma spraying
HVOF deposition
Plasma Spray HVOF
• Max. jet temperature ≈ 2800 °C
• Particles impact speed 400-700 m/s
• In-flight time ≈ 10-3 s
• Heating/cooling rate ≈ 107 K/s
Applications
Wear and corrosion resistant coatings
(Mechanical, chemical, aerospace, textile industries)
- Cermet (WC, Cr3C2 or TiC in Co, Co-Cr or Ni-Cr metal matrix);
- Ceramics (Cr2O3, Al2O3-TiO2);
- Metallic (Ni or Co base, e.g. NiCrBSiC).
Thermal barrier coatings (TBC)
(Aerospace, energy industries)
- ZrO2 - Y2O3.
High temperature oxidation resistant coatings
(Aerospace, energy, chemical industries)
- Ni - Cr – Al base (e.g. NiCoCrAlY).
Biocompatible coatings
Porous Ti , hydroxy apatite (Ca10(PO4)6(OH)2
Materials and Surface Engineering Lab
Research partners and clients
Aircraft engines and power gas turbines
Max gas temperature in turbine:
900 - 1400 °C
Rise in gas temperature in turbine
Improvement of thermodynamic
efficiency
Max service temperature
of superalloy!
Turbine blades protection
High temperature and combustion products (e.g. SO2, SO3, V2O5) cause
surface damages on the Ni-base superalloy
High temperature
oxidation (T > 1000°C)
Hot corrosion
(700 – 925 °C)
(SO3 attack, sulphides
formation)
Erosion
(Solid particles in
gas stream)
Protective ceramic overlay
Thermal Barrier Coating (TBC)
Top Coat (ZrO2–6-8%Y2O3)• Thermal insulation• Erosion protection
Bond Coat (Ni/Co-CrAlY) •Enhanced adhesion•Hot corrosion resistance
TGO (a-Al2O3) • Oxidation barrier
Substrate (Ni–base superalloy) •Thermo-mechanical loading
ZrO2 permeable to O2
(through open porosity & by ionic conduction)
Thermal Barrier Coatings (TBC)
Innovative materials for gas turbines
Strategies to improve turbines performance:
use of CMC materials
Modification of substrate-coating system
Innovative materials for gas turbines
Strategies to improve turbines performance:
use of CMC materials
Modification of substrate-coating system
Innovative materials for gas turbines
Strategies to improve turbines performance:
use of CMC materials
GE Rolls-Royce – development of F136 engine (second choice for
F-35 aircraft)
3rd low pressure stage – stator in SiC/SiC
Modification of substrate-coating system
Innovative materials for gas turbines
Strategies to improve turbines performance:
use of CMC materials
Modification of substrate-coating system
Innovative materials for gas turbines
Strategies to improve turbines performance:
use of CMC materials
Problem:
- Active oxidation of SiC/SiC, expecially in presence of H2O
steam: Thermal & Environmental Barrier Coatings
Environmental Barrier Coatings
EBC deposited by APS (examples)
- HfO2-Y2O3-Gd2O3-Yb2O3
- Barium-Strontium-Alumino-Silicate (BSAS)
Innovative materials for gas turbines
Need for innovation in surface engineering
Case study: Hard chrome replacement
Hard Chrome plating is an electrolytic method of depositing chrome for
engineering applications, from a chromic acid solution.
Cr 6+ compounds
EU classification
Need for innovation in surface engineering
Hard chrome replacement
- HIGH HARDNESS
Typical values of 850 - 1050 HV
- LOW COEFFICIENT OF FRICTION –
coefficient against steel of 0.16 (0.21 dry),
- WEAR RESISTANCE
extremely good resistance to abrasive
and erosive wear
- CORROSION RESISTANCE
extremely high resistance to atmospheric
oxidation, and a good resistance to most
oxidising and reducing agents- MACHINING
Can be successfully finished
Properties of hard chrome:
Case study
Hard chrome replacement in marine engine components
Wärtsilä aims to be the leader in power
solutions for the global marine markets
Case study
Hard chrome replacement in marine diesel engine components
Case study
Hard chrome replacement in marine diesel engine components
Case study
Hard chrome replacement in marine diesel engine components
Valves problems:
• High temperature
• Wear
• Cold and hot corrosion
Wear and cold corrosion
from sulphur compounds
Fatigue
Thermo-
mechanical fatigue
Hot-corrosion and oxidation
Creep
Case study
Hard chrome replacement in marine diesel engine VALVES
Problem:
Wear and cold corrosion in
exhaust and intake valves stem
Hard chrome on stem has a short
service-life
Case study
Hard chrome replacement in marine diesel engine valves
Ceramic-metal (cermet) HVOF coatings
Hard ceramic phase:
wear resistance
Metal matix:
toughness and corrosion
resistance
2 phases - microstructure
Cr3C2 – 25 (Ni-Cr)✓
WC-CoCrNi✓
(WC-Co)-NiCrSiFeBC ✓
Case study
Hard chrome replacement in marine diesel engine valves
Materials (Sulzer powders):
Facility:
HVOF – JP5000 gun
Wärtsilä requirements and constrain
Cermet HVOF coatings
• Thickness higher than150 µm
• Porosity as low as possible
• Hardness higher than 900 HV
• High deposition efficiency
Optimization of deposition
parameters by
Design of Experiment (DoE)
2 factors 3 levels
1) Kerosene - O2 flow
2) Spray distance
1) Low
2) Medium
3) High
32 parameter sets
Keros. (gph) – O2 (scfh)
5,5-1700 6-1850 6,5-2000
Dis
tan
ce
(mm
)
320
355
380
Phase 1- HVOF coatings optimization (DoE)
Investigated properties
• Deposition efficiency
• Porosity as a function of total flow and spray distance
• Hardness
Weighted combination of these properties
provide the “desirability function”
DESIGN-EXPERT Plot
Actual Factors:
X = O2 mass flow
Y = Distance
0.096
0.281
0.466
0.651
0.836
Des
irabil
ity
1700
1775
1850
1925
2000
320
335
350
365
380
O2 mass flow
Distance
DESIGN-EXPERT Plot
Actual Factors:
X = O2 mass flow
Y = Distance
0.096
0.281
0.466
0.651
0.836
Des
irability
1700
1775
1850
1925
2000
320
335
350
365
380
O2 mass flow
Distance
WC-CoCrNi
Properties Optimized value
Deposition efficiency
(um/pass)24,3
Hardness (HV100) 1610
Porosity (%) 3,04
Desirability 0,84
Keros. (gph) – O2 (scfh)
5,5-1700 6-1850 6,5-2000
Dis
tan
ce
(mm
)
320
355
380
Optimized
parameters
DESIGN-EXPERT Plot
Actual Factors:
X = O2 mass flow
Y = Distance
0.000
0.206
0.412
0.619
0.825
Des
irabil
ity
1700.00
1775.00
1850.00
1925.00
2000.00
340.00
355.00
370.00
385.00
400.00
O2 mass flow
Distance
(WC-Co) - NiCrSiFeBC
Properties Optimized value
Deposition efficiency
(um/pass)10,8
Hardness (HV50) 1053,5
Porosity (%) 1,79
Desirability 0,82
Keros. (gph) – O2 (scfh)
5,5-1700 6-1850 6,5-2000
Dis
tan
ce
(mm
)
400
370
340Optimized
parameters
DESIGN-EXPERT Plot
Actual Factor
X = O2 mass flow
1700.00 1775.00 1850.00 1925.00 2000.00
0.000
0.249
0.498
0.747
0.996
X: O2 mass flow
Y: Desirability
One Factor Plot
Cr3C2 – 25 (Ni-Cr)
Properties Optimized value
Deposition efficiency
(um/pass)34,3
Hardness (HV100) 1369
Porosity (%) 4,06
Desirability 0,996
Keros. (gph) – O2 (scfh)
5,5-1700 6-1850 6,5-2000
Dis
tan
ce
(mm
)
320
355
380
Optimized
parameters
Phase 1- HVOF coatings optimization (DoE)
Optimized coatings
WCN
WSF
CRC
Phase 2- optimized coatings characterization
Corrosion tests Wear tests
Phase 2- optimized coatings characterization
Corrosion tests
1 hour immersion test – boiling 5% H2SO4 solution
8,29 6,26 0,065
191,02
0
50
100
150
200
CRC WSF WCN HC
Mas
s lo
ss (
mg
/cm
2 )
Corrosion test - mass lost
Not protective
Phase 2- corrosion tests
Hard chrome
No surface damage
detectable
Phase 2- corrosion tests
WCN coatings
0,42
0,49
0,14 0,13
0,02 0,030,07 0,08
0,230,27
0,16
0,22
0,01 0,01 0,01 n.c.0,00
0,10
0,20
0,30
0,40
0,50
0,60
Wear
(m
m3)
Senza attacco corrosivo
Con attacco corrosivo
As sprayed
Post corrosion attack
Phase 2- optimized coatings characterization
Wear tests - Load: 91 N
- Sliding distance: 2000 m
- Speed: 1 m/s
Phase 3- coating selection for valve deposition
WC-CoCrNi:
- Highest hardness
- Lowest wear rate
- Lowest corrosion rate
- Good density
- High deposition efficiency
- WC-CoCrNi coating was selected
- Coated valves tested for 3 years on a
Wartsila test engine
Innovative coatings for hot corrosion
Case study: Hot corrosion on marine diesel engines valves
Aggressive environment produced by high impurity contents within
the fuel: V, Na, S.
Innovative coatings for hot corrosion
Multiphase cermet coatings: CrystalCoat
Innovative coatings for hot corrosion
Multiphase cermet coatings: CrystalCoat
Metal alloy SiO2 Basalt Oxide Other silicates
CRYSTALCOAT
Innovative coatings for hot corrosion
Case study: Hot corrosion on marine diesel engines valves
Aim: development of innovative thermal spray coatings
alternative to Crystal Coat
Commercial
(non standard)
tested solutions
Development of
innovative
solutions
✓ Cr3C2 – NiCr
✓ Cr3C2 – NiCrAlY
✓ Cr3C2 – CoNiCrAlY
✓ Cr3C2 – self fusing alloy
✓ Mullite – nano SiO2 – NiCr
Phase 1- coatings optimization (DoE)
Innovative coatings for hot corrosion
2 factors 3 levels
1) Kerosene - O2 flow
2) Spray distance
1) Low
2) Medium
3) High
32 parameter sets
Keros. (gph) – O2 (scfh)
5,5-1700 6-1850 6,5-2000
Dis
tan
ce
(mm
)
320
355
380
• Thickness higher than150 µm
• Porosity as low as possible
• High deposition efficiency
Optimization of deposition
parameters by
Design of Experiment (DoE)
Very low porosity (< 1 %)
Ceramic phase dispersed in multiphase metallic matrix
Example: optimization of Cr3C2 - self fusing alloy
Optimized coating
Innovative coatings for hot corrosion
✓ Mullite – nano SiO2 – NiCr
Powder agglomeration – spray drying
Nano-SiO2 cover completely
the spray dried agglomerates
Innovative coatings for hot corrosion
✓ Mullite – nano SiO2 – NiCr
Coating deposition
Coatings retain the
nano-structure
100 h
50 h
5 h
Innovative coatings for hot corrosion
Hot corrosion tests
• Temperature: 750 °C• Environment: Na2SO4 – V2O5 molten salt• Exposure time: up to 100 h
Oxide scale
evolution
Innovative coatings for hot corrosion
Hot corrosion tests
Nanostructured coating
25 h
Innovative coatings for hot corrosion
Hot corrosion tests
Comparison between nanostructured and self fusing coatings
Nano 25 hCr3C2 – self fusing alloy 25 h
Thinner oxide scale in nano-coating
0
10
20
30
40
50
60
70
80
90
0 20 40 60 80 100 120
Thic
kne
ss [μ
m]
Time [h]
Scale growth kinetics
Carbide-NiCr Carbide-MCrAlY/2 Carbide-Self flux
Carbide-MCrAlY/1 Cer-nano/oxide-NiCr
Corrosion kinetics
Faculty of EngineeringSapienza University of Rome