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Development, microstructure and mechanical characterisation of nickel-based ceramic reinforced metal matrix composites manufactured by laser powder bed fusion
Thesis (PhD)--Stellenbosch University, 2025.
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Stellenbosch : Stellenbosch University
2026
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| _version_ | 1867614126627356672 |
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| access_status_str | Open Access |
| author | Mwambe, Polline |
| author2 | Sacks, Natasha |
| author_browse | Mwambe, Polline Sacks, Natasha |
| author_facet | Sacks, Natasha Mwambe, Polline |
| author_sort | Mwambe, Polline |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (PhD)--Stellenbosch University, 2025. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/134729 |
| institution | Stellenbosch University (South Africa) |
| last_indexed | 2026-06-10T12:47:05.324Z |
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| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2026 |
| publishDateRange | 2026 |
| publishDateSort | 2026 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/134729 Development, microstructure and mechanical characterisation of nickel-based ceramic reinforced metal matrix composites manufactured by laser powder bed fusion Mwambe, Polline Sacks, Natasha Stellenbosch University. Faculty of Engineering. Dept. of Industrial Engineering. Additive manufacturing Nickel alloys -- Mechanical properties Laser sintering Metal matrix composites Thesis (PhD)--Stellenbosch University, 2025. Mwambe, P. 2025. Development, Microstructure and Mechanical Characterisation of Nickel-based Ceramic Reinforced Metal Matrix Composites Manufactured by Laser Powder Bed Fusion. Unpublished doctoral dissertation. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/f3730403-3874-4793-88b6-d06fc416421b ENGLISH ABSTRACT: Pure nickel (Ni) is a ductile and malleable metal known for its excellent corrosion resistance, magnetic properties, and high electrical and thermal conductivity [1]. However, its poor mechanical properties limit its industrial application, and often small amounts of alloying elements are added to improve its properties and extend its application range [2]. This study aimed to enhance the mechanical properties of pure Ni by addressing its inherent limitations of low hardness and low strength, without compromising its desirable properties. This was achieved by developing two metal matrix composites (MMCs) namely Ni-10wt%TiC and Ni-10wt%TiCN. The two ceramics are known to have high hardness and excellent wear resistance [3,4]. By adding small amounts of these ceramics to Ni, its mechanical properties can be enhanced thereby potentially extending the lifespan of the material during industrial application. Laser powder bed fusion (LPBF) has been successfully used to manufacture MMCs, however its application to create high-content Ni-based TiC and TiCN MMCs does not appear to have been explored yet. Hence a LPBF manufacturing strategy was developed to produce the Ni-10wt%TiC and Ni-10wt%TiCN MMCs with pure Ni as the benchmark. Optimisation of the LPBF process parameters was carried out using response surface methodology with a central composite design of experiments. Laser power and scanning speed were the primary variable factors, while layer thickness and hatch spacing were held constant. Relative density and Vickers hardness were maximised as the response variables. The optimal deposition parameters were then used to produce samples for detailed analyses. Microstructures were characterised while the mechanical, thermal expansion and sliding wear properties were evaluated to investigate the impact of the ceramic particles. The optimal process parameters for Ni-10wt%TiC and Ni-10wt%TiCN were laser powers of 190 W and 195 W and scanning speeds of 500 mm/s and 400 mm/s, respectively, resulting in high-quality parts with relative densities above 99%. Phase analysis showed peak shifting indicating lattice distortion, especially in Ni-10wt%TiC, due to residual stress and fine-scale precipitated particles, with no new phase formation. Microstructural characterisation revealed new grain formation with TiC and TiCN addition, with a mixture of cellular, columnar and dendritic structures. Furthermore, the TiC reinforcement reduced the microstructural anisotropy observed in pure Ni. While the TiC reinforcement led to nearly uniform grain sizes with random texture, the TiCN maintained the texture orientation but showed larger grains in the build direction. The hardness of Ni-10wt%TiC and Ni-10wt%TiCN increased by 133% and 106%, respectively, compared to that of pure Ni which is 163 HV. Ni-10wt%TiC exhibited better thermal expansion properties by 3% at low temperatures, while Ni-10wt%TiCN demonstrated better overall thermal stability by 8%. The ultimate tensile strength and yield strength of the Ni-10wt%TiC increased by 132% and 112%, respectively, whereas that of the Ni-10wt%TiCN increased by 112% and 79%, respectively compared to pure Ni (UTS 354.0 MPa, YS 306.8 MPa). However, ductility decreased by 43% for Ni-10wt%TiC and 25% for Ni-10wt%TiCN making the latter more suitable for applications where ductility is preferred. Ni-10wt%TiC exhibited improved wear resistance with a 45% reduction in wear rate compared to pure Ni, while Ni-10wt%TiCN showed a 2% increase in wear rate, indicating no improvement in wear resistance. Between the two MMCs, although both enhanced the mechanical strength of pure Ni, Ni-10wt%TiC demonstrated the greatest overall improvement, achieving the highest strength enhancement. The study concluded with a conceptual framework designed for developing Ni-ceramic-based MMCs using the LPBF process, which can be extended to other high-content Ni-based MMCs and serves as a guide for understanding process-microstructure-property relationships influenced by reinforcement additions. AFRIKAANSE OPSOMMING: Suiwer nikkel (Ni) is 'n rekbare en smeebare metaal wat bekend is vir die uitstekende korrosieweerstand, magnetiese eienskappe en hoë elektriese en termiese geleidingsvermoë wat dit bied [1]. Die swak meganiese eienskappe beperk egter die industriële toepassing daarvan, en dikwels word klein hoeveelhede legeringselemente bygevoeg om die eienskappe te verbeter en die toepassingsreeks daarvan verleng [2]. Hierdie studie het ten doel gehad om die meganiese eienskappe van suiwer Ni te verbeter deur die inherente beperkings van lae hardheid en lae sterkte aan te spreek, sonder om die gewenste eienskappe in die gedrang te bring. Dit is bereik deur twee metaalmatrikssamestelling (MMS’s) te ontwikkel, naamlik Ni-10 gew.%TiC en Ni-10 gew.%TiCN. Dit is bekend dat dié twee keramiek hoë hardheid en uitstekende slytasieweestand het [3,4]. Deur klein hoeveelhede van hierdie keramiek by Ni te voeg, kan die meganiese eienskappe daarvan verbeter word, en sodoende die lewensduur van die materiaal tydens industriële toepassing moontlik verleng. Laserpoeierbedfusie (LPBF) is suksesvol gebruik om MMS’s te vervaardig, maar die toepassing daarvan om hoë-inhoud Ni-gebaseerde TiC- en TiCN- MMS’s te skep, blyk nog nie ondersoek te wees nie. Daarom is 'n LPBF-vervaardigingstrategie ontwikkel om die Ni-10wt%TiC en Ni-10wt%TiCN MMS’s met suiwer Ni as die maatstaf te produseer. Optimalisering van die LPBF-prosesparameters is uitgevoer met behulp van responsoppervlakmetodologie met 'n sentrale saamgestelde ontwerp van eksperimente. Laser krag en skanderingspoed was die primêre veranderlike faktore, terwyl laagdikte en arsiëringspasiëring konstant behou is. Relatiewe digtheid en Vickers-hardheid is gemaksimeer as die responsveranderlikes. Die optimale afsettingsparameters is toe gebruik om monsters vir gedetailleerde ontledings te produseer. Mikrostrukture is gekenmerk terwyl die meganiese, termiese uitsetting en gly-slytasie-eienskappe geëvalueer is om die impak van die keramiekdeeltjies te ondersoek. Die optimale prosesparameters vir Ni-10wt%TiC en Ni-10wt%TiCN was laserkragte van 190 W en 195 W en skanderingspoed van onderskeidelik 500 mm/s en 400 mm/s, wat gelei het tot hoëgehalte-onderdele met relatiewe digthede bo 99%. Fase-analise het piekverskuiwing getoon wat roostervervorming aandui, veral in Ni-10wt%TiC, as gevolg van oorblywende spanning en fynskaal neergesette deeltjies, sonder enige nuwe fasevorming. Mikrostrukturele karakterisering het nuwe korrelvorming met TiC- en TiCN-byvoeging aan die lig, met 'n mengsel van sellulêre, kolomvormige en dendritiese strukture. Verder het die TiC-versterking die mikrostrukturele anisotropie wat in suiwer Ni waargeneem is, verminder. Terwyl die TiC-versterking gelei het tot byna eenvormige korrelgroottes met ewekansige tekstuur, en die TiCN het die tekstuuroriëntasie behou, maar groter korrels in die bourigting getoon. Die hardheid van die Ni-10wt%TiC en Ni-10wt%TiCN het onderskeidelik met 133% en 106% toegeneem in vergelyking met dié van suiwer Ni met 'n hardheid van 163 HV. Ni-10wt%TiC het beter termiese uitsettingseienskappe met 3% by lae temperature vertoon, terwyl Ni-10wt%TiCN beter algehele termiese stabiliteit met 8% getoon het. Die uiteindelike treksterkte en vloeigrens van die Ni-10wt%TiC het met onderskeidelik 132% en 112% toegeneem, terwyl dié van die Ni-10wt%TiCN met onderskeidelik 112% en 79% toegeneem het in vergelyking met suiwer Ni (UTS 354.0 MPa, YS 306.8 MPa). Rekbaarheid het egter met 43% afgeneem vir Ni-10wt%TiC en 25% vir Ni-10wt%TiCN, wat laasgenoemde meer geskik maak vir toepassings waar rektiliteit verkies word. Ni-10wt%TiC het verbeterde slytasieweerstand getoon met ’n 45% vermindering in slytasietempo in vergelyking met suiwer Ni, terwyl Ni-10wt%TiCN ’n 2% toename in slytasietempo getoon het, wat geen verbetering in slytasieweerstand aandui nie. Tussen die twee MMS's, hoewel beide die meganiese sterkte van suiwer Ni verbeter het, het Ni-10wt%TiC die grootste algehele verbetering getoon en die hoogste sterkteverbetering behaal. Die studie het afgesluit met 'n konseptuele raamwerk wat ontwerp is vir die ontwikkeling van Ni-keramiek-gebaseerde MMS’s met behulp van die LPBF-proses, wat uitgebrei kan word na ander hoë-inhoud Ni-gebaseerde MMS’s en dien as 'n riglyn vir materiaalkeuse en die begrip van proses-mikrostruktuur-eienskap-verhoudings wat beïnvloed word deur versterkingstoevoegings. Doctoral 2026-01-05T13:20:56Z 2026-01-05T13:20:56Z 2025-12 Thesis https://scholar.sun.ac.za/handle/10019.1/134729 Stellenbosch University xxii, 189 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Additive manufacturing Nickel alloys -- Mechanical properties Laser sintering Metal matrix composites Mwambe, Polline Development, microstructure and mechanical characterisation of nickel-based ceramic reinforced metal matrix composites manufactured by laser powder bed fusion |
| title | Development, microstructure and mechanical characterisation of nickel-based ceramic reinforced metal matrix composites manufactured by laser powder bed fusion |
| title_full | Development, microstructure and mechanical characterisation of nickel-based ceramic reinforced metal matrix composites manufactured by laser powder bed fusion |
| title_fullStr | Development, microstructure and mechanical characterisation of nickel-based ceramic reinforced metal matrix composites manufactured by laser powder bed fusion |
| title_full_unstemmed | Development, microstructure and mechanical characterisation of nickel-based ceramic reinforced metal matrix composites manufactured by laser powder bed fusion |
| title_short | Development, microstructure and mechanical characterisation of nickel-based ceramic reinforced metal matrix composites manufactured by laser powder bed fusion |
| title_sort | development microstructure and mechanical characterisation of nickel based ceramic reinforced metal matrix composites manufactured by laser powder bed fusion |
| topic | Additive manufacturing Nickel alloys -- Mechanical properties Laser sintering Metal matrix composites |
| url | https://scholar.sun.ac.za/handle/10019.1/134729 |
| work_keys_str_mv | AT mwambepolline developmentmicrostructureandmechanicalcharacterisationofnickelbasedceramicreinforcedmetalmatrixcompositesmanufacturedbylaserpowderbedfusion |