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Tribological behavior of HVAF-sprayed WC-based coatings with alternative binders
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0001-8404-8180
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0001-5521-6894
Department of Engineering “Enzo Ferrari”, University of Modena and Reggio Emilia, Via Pietro Vivarelli 10/1, 41125 Modena (ITA).
University West, Department of Engineering Science. Department of Engineering “Enzo Ferrari”, University of Modena and Reggio Emilia, Via Pietro Vivarelli 10/1, 41125 Modena (ITA).
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2022 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 436, article id 128296Article in journal (Refereed) Published
Abstract [en]

The tribological performance of High Velocity Air-Fuel (HVAF) sprayed WC-based cermet coatings with binders containing no or very limited amount of cobalt was evaluated under dry sliding, erosion, and abrasion wear conditions. The wear and corrosion behaviors of WC-NiMoCrFeCo, WC-FeNiCrMoCu and WC-FeCrAl HVAF sprayed coatings were investigated and compared to standard WC-CoCr coatings as benchmark. Microstructure characterization along with XRD analysis was conducted on all powders as well as the corresponding coatings. Comprehensive post wear analysis was conducted on all coatings subjected to ball-on-disk, gas jet erosion and dry sand-rubber wheel abrasion tests. Moreover, all coatings were exposed to 3.5% (wt./vol.) NaCl aqueous solution to evaluate their corrosion performance through electrochemical testing. XRD results showed negligible phase transformation between the powders and the deposited coatings. The WC-NiMoCrFeCo coating exhibited the best sliding wear and electrochemical corrosion performance, with an average specific wear rate value of 3.1 x 10(-8) (mm(3).N-1.m(-1)) and a corrosion current density of 1.9 mu A/cm2. This coating also showed comparable abrasive wear resistance to the WC-CoCr coating. Under erosive wear conditions, too, the WC-FeNiCrMoCu and WC-FeCrAl coatings showed a comparable performance to the benchmark. Dominant wear mechanisms for the reference WC-CoCr coating, under sliding wear conditions, were abrasion (deep grooving) and surface fatigue (crack propagation and pitting). On the contrary, no pitting was observed in WC-NiMoCrFeCo and WC-FeCrAl coatings during the sliding wear test. No considerable difference was identified in the wear mechanisms of the different coatings under abrasion and erosion wear conditions. The results highlight the promise of some of the environment friendly binders studied to replace Co.

Place, publisher, year, edition, pages
Elsevier, 2022. Vol. 436, article id 128296
Keywords [en]
Sliding wear; Erosion; Abrasion; Electrochemical polarization; Cermet coatings; High Velocity Air-Fuel (HVAF)
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
URN: urn:nbn:se:hv:diva-18313DOI: 10.1016/j.surfcoat.2022.128296ISI: 000779413000001Scopus ID: 2-s2.0-85125519738OAI: oai:DiVA.org:hv-18313DiVA, id: diva2:1698696
Funder
Swedish Research Council, HiPerCOAT (Dnr. 20180197)Available from: 2022-09-26 Created: 2022-09-26 Last updated: 2023-11-09Bibliographically approved
In thesis
1. Towards more sustainable approaches for protecting surfaces against wear
Open this publication in new window or tab >>Towards more sustainable approaches for protecting surfaces against wear
2023 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

WC-Co coatings, with and without chromium additives, are widely used in the industry for severe tribological applications. However, concerns about cobalt supply and its environmental and health impacts have led industries to explore sustainable binder alternatives. As a deposition technique, high velocity air-fuel(HVAF) spraying technology offers a promising solution by producing dense WC-based coatings with minimal material degradation during spraying. Moreover, the combination of high velocity and low flame temperature in HVAF enables the deposition of finer powders, which are more susceptible to thermal damage, with minimal decarburization. This results in denser coatings with improved properties compared to conventional spraying techniques. Therefore, this thesis aims to evaluate more sustainable approaches to depositing WC-based wear resistant coatings involving (a) HVAF as a less energy-intensive technique compared to other methods like high velocity oxy-fuel (HVOF), (b) alternative Co-lean/free binders, and (c) fabrication of thin ('flash') coatings from finer feedstock powders.

In HVAF spraying, particles’ in-flight temperature and velocity can be influenced by the process variables including nozzle configuration as well as feedstock particle size distribution. On the other hand, the chemistry of metallic binder can also play a key role in determining both properties and performance of these coatings. In this thesis, characteristics and tribological behaviour of HVAF sprayed WC-CoCr coatings were investigated by spraying feedstock powders with varying particle sizes (ultra fine: 15/5, fine: 20/5, medium: 30/5 and coarse: 45/5um) employing different nozzle configurations (various lengths and divergence convergence configurations). Additionally, different WC-based feedstocks, comprising alternative binders to traditionally used CoCr (namely NiMoCrFeCo, FeNiCrMoCu and FeCrAl) were investigated. Results showed that the HVAF spraying excelled in processing WC-based powders with various size distributions, enabling the deposition of thinner coatings from fine powders ('flash' coatings) with similar properties/performance as thick coatings. This leads to reduced material usage while offering potential for considerable component life extension, both of which are important elements of sustainability. Additionally, it was concluded that the Co-lean/Co-free binders demonstrated comparable, and in some cases superior performance than the reference Co-based binder under various wear conditions. All of these together can represent a significant step forward towards more sustainable approaches for protecting surfaces against wear.

Abstract [sv]

WC-Co-beläggningar, med och utan kromtillsatser, används i stor utsträckning inom industrin i slitagekrävande applikationer. Oron för koboltförsörjningen och kobolts miljö- och hälsoeffekter har dock fått industrin att leta efter mer hållbara alternativ. Höghastighetsflamsprutning med luft (HVAF) är en lovande sprutteknik för att producera täta WC-baserade beläggningar med minimal materialpåverkan. Den låga temperaturen och den höga kinetiska energin hos partiklarna i lågan som sprutas med HVAF, kan möjliggöra användning av finare pulver, vilket potentiellt kan resultera i tätare och tunnare beläggningar med förbättrade prestanda. HVAF tekniken skulle även kunna vara en potentiell teknik för att åstadkomma koboltfria beläggningar. Slitageegenskaperna hos WC beläggningar som är koboltfria och som sprutas med HVAF är dock okänt. HVAF teknikens potential för att kunna ersätta hög hastighetsflamsprutning med syre (HVOF), som är den teknik som dominerar på marknaden idag vid sprutning av täta slitagebeständiga beläggningar är även okänt. HVAF är ett intressant alternativ till HVOF eftersom metoden kräver mindre energi jämfört med HVOF. Vid sprutning med HVAF kan partiklarnas temperatur och hastighet i lågan påverkas med hjälp av processvariabler, munstyckskonfiguration och genom att variera tillsatsmaterialets storleksfördelning. Partiklarnas hastighet och temperatur i lågan påverkar i sin tur den sprutade beläggningens mikrostruktur som i sin tur påverkar beläggningarnas egenskaper. Även den kemiska sammansättningen hos tillsatsmaterialet kan spela en stor roll för beläggningsegenskaperna.

I detta arbete utvärderas slitageegenskaper hos HVAF-sprutade WC-CoCr beläggningar där tillsatsmaterialet har olika storleksfördelning och olika munstyckskonfigurationer. Slitageegenskaperna jämförs med beläggningar som sprutats med tillsatsmaterial som saknar kobolt (NiMoCrFeCo, FeNiCrMoCu och FeCrAl).

Resultaten visar att HVAF-tekniken fungerar mycket väl för sprutning av WC baserade tillsatsmaterial med olika storleksfördelningar, vilket möjliggör produktion av tätare och tunnare beläggningar jämfört med de beläggningar som produceras industriellt idag. Resultaten visar även att koboltfria beläggningar som sprutats med HVAF ger jämförbara, och i vissa fall, överlägsna prestanda avseende slitagebeständighet. Både HVAF tekniken och utnyttjandet av koboltfria material är sålunda möjliga alternativ för att åstadkomma mer hållbara lösningar för slitagekrävande industriapplikationer.

Place, publisher, year, edition, pages
Trollhättan: University West, 2023. p. 49
Series
PhD Thesis: University West ; 59
Keywords
Wear; HVAF spraying; WC-Based Coatings; Sustainability; Binder Chemistry, Slitage; HVAF; WC-baserade beläggningar; Hållbar produktion; Bindemedelskemi
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-20914 (URN)978-91-89325-60-9 (ISBN)978-91-89325-59-3 (ISBN)
Public defence
2023-11-28, F131, Gustava Melins gata, Trollhättan, 10:00 (English)
Opponent
Supervisors
Note

Paper F is not included in the digital thesis due to the copyright.

Available from: 2023-11-09 Created: 2023-11-09 Last updated: 2024-01-15Bibliographically approved

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