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Tribological behaviour of HVAF-sprayed WC-based coatings:: Role of process variables and binder chemistry
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0001-8404-8180
2021 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Tungsten carbide (WC) based metallic matrix coatings sprayed using high velocity air fuel (HVAF) technique have attracted increasing attention as they show excellent tribological performance in various wear conditions. In the HVAF method, particles’ in-flight temperature and velocity can be influenced by the process variables including nozzle configuration as well as feedstock particle size range. 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-based coatings were investigated employing four different nozzle configurations (4L2, 4L4, 5L2and 5L4), and three different feedstock particle sizes of WC-CoCr feedstock powder (5/20, 5/30 and 15/45 μm). Also, characteristics and performance of coatings processed with four different WC-based feedstocks comprising alternative binders to traditionally used CoCr (namely CoCr, NiMoCrFeCo,FeNiCrMoCu and FeCrAl) were investigated. Characteristics of the coatings were explored by conducting scanning electron microscopy observations, microindentation testing and X-ray diffraction analysis. Performance of the coatings was evaluated by conducting sliding wear, dry jet erosion wear and sand rubber wheel abrasion wear testing. Moreover, material removal mechanisms in the coatings subjected to the above tests were investigated through post wear analysis.

X-ray diffraction analysis showed that no considerable phase change compared to the starting feedstock was observed in any of the coatings sprayed by HVAF technique. It was revealed that decrease in powder particle size range can result in an improvement in microstructural characteristics, such as homogeneity and density, as well as hardness of the coatings. Besides, it can lead to a substantial improvement in wear performance of the coatings. It was shown that using various nozzle configurations does not result in any considerable change in characteristics or performance of the HVAF-sprayed WC-CoCr coatings. It was further shown that, by decreasing particle sizes from coarse to medium or fine, a significant difference can be observed. While wear mechanisms for medium and fine feedstock coatings were dominated by ploughing and fracture of individual carbide grains, for the coarse feedstock coatings ploughing and grooving along with the local removal of coating material were observed.

Hardness values for all the four coatings with different binder chemistries were in a narrow range of 1100 – 1300 HV0.3. WC-NiMoCrFeCo and WC-FeNiCrMoCu coatings showed better or comparable sliding wear performance compared to WC-CoCr coating (as reference). WC-FeNiCrMoCu and WC-FeCrAl coatings showed comparable performance under erosion conditions while all the three binder alternatives yielded slightly inferior coating performance under abrasion wear, compared to the reference coating. While ploughing was the common wear mechanism in all the four coatings, pitting was noted in coatings with CoCr and FeNiCrMoCu binders in case of sliding wear.

Abstract [sv]

Populärvetenskaplig Sammanfattning

Cermet-beläggningar består av WC-partiklar inbäddade i ett metallbindemedel,sprutat med High Velocity Air Fuel (HVAF) uppvisar utmärkt tribologiskprestanda under olika slitage förhållanden. Med HVAF-tekniken kan partiklarnasflygtemperatur och hastighet påverkas av konfigurationen av den utrustning somanvänds såväl som partikelstorleksintervallet för råmaterialet. Därtill kan kemin hos det metalliska bindemedlet spela en nyckelroll för beläggningarnas egenskaper och prestanda. I denna avhandling undersöktes egenskaper och tribologiskt beteende hos HVAF-besprutade WC-baserade beläggningar. Undersökningen gjordes genom att använda fyra olika uppsättningar av ändra sprutparametrar förHVAF-processen där fyra olika munstyckskonfigurationer (4L2, 4L4, 5L2 och5L4) och tre olika partikelstorleksintervaller av WC-CoCr råvarupulver (5/20,5/30 och 15/45 μm). Studieegenskaper och prestanda för alla deponerade beläggningar, påverkan av processvariabler (olika munstyckskonfigurationer och olika partikelstorlekar) undersöktes. Dessutom undersöktes egenskaper och prestanda för tre olika WC-baserade råvaror med alternativa bindemedel till CoCr (NiMoCrFeCo, FeNiCrMoCu och FeCrAl) och jämfördes med WC-CoCrbeläggningsom referens. Beläggningens egenskaper undersöktes genom att genomföra SEM-analys, mikroindragningstest och röntgenanalys. Beläggningens prestanda utvärderades genom att utföra glidförslitning, erosionsslitage under torra förhållanden och test med torr sand/gummihjulanordning. Vidare undersöktes mekanismer för materialavlägsning i beläggningarna med ovanstående tester genom analys efter slitage.

Ingen avsevärd fasförändring observerades för alla beläggningar som besprutades med HVAF-teknik. Det avslöjades att minskning av pulvrets genomsnittliga partikelstorlek resulterade i en förbättring av mikrostrukturella egenskaper, såsom homogenitet och densitet, samt beläggningarnas hårdhetsvärde. Dessutom leder det till en avsevärd förbättring av beläggningens slitageförmåga. Det visades att användning av olika munstycken till HVAF-processen inte resulterar i en avsevärd förändring i egenskaper eller prestanda hos WC-CoCr-beläggningarna. När det gäller förslitningsmekanismer visades det att genom att minska partikelstorleken från grov till medium eller fin sågs en avsevärd skillnad. För beläggningar besprutade med fina och medelstora partiklar dominerades förslitningsmekanismer av plöjningsslitage och sprickor av enskilda hårdmetallkorn. För grova beläggningar observerades plöjningsslitage och spårning tillsammans med avlägsnande av material.

Ingen signifikant skillnad i mikrostruktur eller fasförändring observerades i alla beläggningar med alternativa bindemedel såväl som WC-CoCr som referensbeläggning. Hårdhetsvärdet för alla de fyra beläggningarna låg inom x intervallet 1100 - 1300 HV0.3. NiMoCrFeCo och FeNiCrMoCu visade bättre eller jämförbar glidförmåga med referensbeläggningen. FeNiCrMoCu och FeCrAl visade jämförbara prestanda under erosionsförhållanden och alla de tre undersökta beläggningsmaterialen visade något sämre prestanda under nötningsslitage jämfört med referensbeläggningen. Medan plöjningsslitage var den vanliga förslitningsmekanismen i alla de fyra beläggningarna noterades gropning i beläggningarna CoCr och FeNiCrMoCu vid glidförslitning.

Place, publisher, year, edition, pages
Trollhättan: University West , 2021. , p. 97
Series
Licentiate Thesis: University West ; 35
Keywords [en]
Tribological Behaviour, HVAF; WC-Based Coatings; Process Variables; Binder Chemistry
Keywords [sv]
Tribologisk Prestanda; HVAF; WC-baserade Beläggningar; Parametervariabler; Bindemedelskemi
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
URN: urn:nbn:se:hv:diva-17484ISBN: 978-91-89325-02-9 (print)ISBN: 978-91-89325-01-2 (electronic)OAI: oai:DiVA.org:hv-17484DiVA, id: diva2:1596637
Presentation
2021-10-08, Sal J113, Zoom, Trollhättan, 10:00 (English)
Supervisors
Available from: 2021-10-08 Created: 2021-09-23 Last updated: 2023-11-09Bibliographically approved
List of papers
1. Influence of Test Conditions on Sliding Wear Performance of High Velocity Air Fuel-Sprayed WC–CoCr Coatings
Open this publication in new window or tab >>Influence of Test Conditions on Sliding Wear Performance of High Velocity Air Fuel-Sprayed WC–CoCr Coatings
2021 (English)In: Materials, E-ISSN 1996-1944, Vol. 14, no 11, article id 3074Article in journal (Refereed) Published
Abstract [en]

Sliding wear performance of thermal spray WC-based coatings has been widely studied. However, there is no systematic investigation on the influence of test conditions on wear behaviour of these coatings. In order to have a good understanding of the effect of test parameters on sliding wear test performance of HVAF-sprayed WC–CoCr coatings, ball-on-disc tests were conducted under varying test conditions, including different angular velocities, loads and sliding distances. Under normal load of 20 N and sliding distance of 5 km (used as ‘reference’ conditions), it was shown that, despite changes in angular velocity (from 1333 rpm up to 2400 rpm), specific wear rate values experienced no major variation. No major change was observed in specific wear rate values even upon increasing the load from 20 N to 40 N and sliding distance from 5 km to 10 km, and no significant change was noted in the prevailing wear mechanism, either. Results suggest that no dramatic changes in applicable wear regime occur over the window of test parameters investigated. Consequently, the findings of this study inspire confidence in utilizing test conditions within the above range to rank different WC-based coatings.

Place, publisher, year, edition, pages
Basel: MDPI, 2021
Keywords
Tests conditions, sliding wear, HVAF, WC–CoCr, ball-on-disk, wear mechanism
National Category
Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:hv:diva-16509 (URN)10.3390/ma14113074 (DOI)000660279500001 ()2-s2.0-85108228061 (Scopus ID)
Available from: 2021-06-10 Created: 2021-06-10 Last updated: 2024-07-04Bibliographically approved
2. Influence of nozzle configuration and particle size on characteristics and sliding wear behaviour of HVAF-sprayed WC-CoCr coatings
Open this publication in new window or tab >>Influence of nozzle configuration and particle size on characteristics and sliding wear behaviour of HVAF-sprayed WC-CoCr coatings
Show others...
2021 (English)In: Surface and Coatings Technology, ISSN 0257-8972, Vol. 423, p. 1-16, article id 127585Article in journal (Refereed) Published
Abstract [en]

In this study, effect of feedstock particle size and nozzle configuration on deposition, microstructural features, hardness and sliding wear behaviour of high velocity air fuel (HVAF)-sprayed WC-CoCr coatings was evaluated. Three different WC-CoCr powders with nominal particle sizes of 5/20 μm (fine), 5/30 μm (medium) and 15/45 μm (coarse) were sprayed employing a HVAF gun with four distinct DeLaval nozzle configurations involving different lengths and/or exit diameters. Microstructure, phase constitution and mechanical characteristics of the coatings were evaluated using SEM, EDS, XRD and micro indentation testing. Specific wear rate for all the samples was determined under sliding conditions and a comprehensive post wear analysis was conducted. X-ray diffraction analysis showed negligible decarburization in all the HVAF-sprayed coatings. It was shown that decrease in particle size of employed feedstock results in discernible changes in microstructural features of the coatings as well as considerable improvement in their performance. Also, notable changes in wear mechanisms were identified on reducing particle size from coarse to medium or fine. Fine and coarse feedstock powders were found to be sensitive to the type of nozzle used while no major difference was observed in coatings from powders with medium cut size sprayed with different nozzles.

Place, publisher, year, edition, pages
Elsevier, 2021
Keywords
Particle size, Nozzle configuration, HVAFWC-CoCr, Sliding wear
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-17483 (URN)10.1016/j.surfcoat.2021.127585 (DOI)000697566200017 ()2-s2.0-85108196054 (Scopus ID)
Available from: 2021-09-22 Created: 2021-09-22 Last updated: 2023-11-09Bibliographically approved

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Torkashvand, Kaveh

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