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: hollie.heard@cvd.co.uk/h.heard@surrey.ac.uk

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

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1: C

VD

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3: R

eentry

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8: H

ot-fire

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TAE th

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Figure 10: Ta sample EDX analysis

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9: Ta

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g S

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Table 1: ZrB2 EDX Quantitative results

Expansion nozzle

Thruster chamber

Injector assembly

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Chamber

segment 1

Chamber

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13: Z

rB2 E

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(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

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High temperature

selective solar absorbers

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12: Z

rB2 S

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