hollieheard.files.wordpress.com€¦ · author: hollie heard created date: 9/28/2015 4:23:30 pm
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Introduction
The project aims to develop chemical vapour deposition, (CVD), processes to produce coatings suitable for extreme operating conditions to improve performance and component lifetime.
Deposition optimisation is achieved through an iterative process of practical coating trials and subsequent analysis through techniques such as optical microscopy, SEM/EDX/WDX and XRD.
Zirconium diboride, (ZrB2)
Innovate UK feasibility study for development of ZrB2
coating by CVD currently unavailable in the EU. Coating applicable to UHTCs, spaceplanes, hypersonic & re-entry vehicles and for concentrating solar power receivers.
Process defined then developed through coating trials and SEM/EDX/WDX analysis. Structure similar to in literature and EDX results show atomic ratios of ≈2:1 suggesting diboride stoichiometry. Boron clearly identified in EDX then confirmed with WDX.
Iridium
Anti-oxidation iridium coating on niobium alloy for new ESA High Thrust Apogee Engine, (HTAE), under development by Moog. Coating aims to increase operating temperature leading to improved thrust performance.
MOCVD process using Ir(acac)3 precursor and novel evaporator system developed by Ionbond. Coating trials due to start Oct 2015, some initial testing has been completed and SEM/EDX analysis indicating presence of Ir deposition. Test pods will be coated and then hot-fire tested at Moog under real-world thruster conditions to test coating performance.
Tantalum
Initial coating trials conducting in collaboration with Cranfield university to develop Ta coating on SS and Ni alloy substrates for corrosion resistant coatings. Process uses direct chlorination of Ta metal which is then reduced with hydrogen to form the deposited coating. Analysis shows conformal and cohesive coverage of samples, high purity bcc Ta coating with little-no contamination and presence of possible alloying zone in between the coating and the substrate.
Future collaborative project planned with
Cranfield University and industrial partner to scale-
up process to commercial level with development
towards UK based Ta coating centre.
Coatings by Chemical Vapour Deposition for
Extreme Environment Applications
Conclusions & Further Work
Initial coating trials have been successful in producing cohesive, conformal and moderately pure coatings on a variety of substrates. Next steps for the project include;
Start of MOCVD iridium coating trials Preparation of Ir coated Nb alloy test pods for
hot-fire testing Ta coating development through collaborative
project towards commercialisation for corrosion resistant coatings
Further analysis of ZrB2 coatings for
stoichiometry, of C/SiC substrates and production of ZrB2-SiC-C/SiC multi-layer coatings
Analysis of composite coatings and continuation
of development of ZrB2 coating process
Mechanical and functional testing of all coatings
Corresponding author: [email protected]/[email protected]
Acknowledgements: The author would like to thank Dr Christine Chalk, (Cranfield University), for the additional SEM/EDX and XRD analysis of preliminary tantalum samples. [1] Naicker, L, Wall, R and Perigo, D, (2014), An overview of development model testing for the LEROS 4 high thrust apogee
engine, Space Propulsion 2014 Conference, Cologne, Germany, 19-22 May 2014 [2] Afloresm, (2007), "PS10 solar power tower" by - SOLUCAR PS10 [online] available at https://commons.wikimedia.org/wiki/
File:PS10_solar_power_tower.jpg#/media/File:PS10_solar_power_tower.jpg
H Heard, Dr M Baker, Dr M Whiting & C Prentice
: University of Surrey, Guildford, Surrey, GU2 7XH, : Archer Technicoat Ltd, Progreess Road, High Wycombe, Bucks, HP12 4JD
What are ‘extreme environments’? Those which induce some of the harshest operating conditions on components and can have a life and performance limiting impact such as; Ultra-high temperatures
Highly corrosive & oxidising conditions
What is CVD?
The delivery of a vapour phase precursor, which then through a series of mechanisms, processes and reactions forms a solid coating on a substrate.
Depending on the process and conditions used there are many variants of CVD such as;
▪ MOCVD, PECVD, LPCVD, CVI and ALCVD
Coating optimisation occurs through continual, iterative practical trials, complimentary analysis of coatings and adjustment of process parameters.
Advantages of CVD process include;
▪ Fast coating rate, applicable to a wide variety of substrates, net coverage, controllable, scalable, dense and high purity coatings
Element Source Norm
Wt. %
Norm Wt.
% Err
Atom % Atom %
Err B K EDS 19.59 ±1.34 62.85 ±4.29
C K EDS 2.63 ±1.45 7.58 ±4.18
Zr L EDS 77.78 ±0.98 29.57 ±0.37
Total 100 100
Fig
ure
1: C
VD
pro
cess
Fig
ure
3: R
eentry
Fig
ure
8: H
ot-fire
testin
g o
f thru
ster
Fig
ure
7: H
TAE th
ruste
r [1]
Figure 10: Ta sample EDX analysis
Fig
ure
9: Ta
coatin
g S
EM
image
Table 1: ZrB2 EDX Quantitative results
Expansion nozzle
Thruster chamber
Injector assembly
Fig
ure
2: O
ptim
isatio
n o
f CVD
pro
cess
Chamber
segment 1
Chamber
segment 2 Nozzle
segment 1
Fig
ure
13: Z
rB2 E
DX
(2) Ta coating (1) Alloy zone at interface
Figure 11: Ta sample XRD analysis (Credit: Cranfield University)
(110)
(220)
(211)
(200)
≈45μm
(1)
(2)
bcc α-Ta
Fig
ure
5: P
ipe co
rrosio
n
High temperature
selective solar absorbers
Fig
ure
6: C
once
ntra
ting so
lar p
ow
er
tow
er [2
] Fig
ure
4: H
yperso
nic v
ehicle
Fig
ure
14: Z
rB2 W
DX B
oro
n re
sults
Fig
ure
12: Z
rB2 S
EM
images