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Influence of microstructure and mechanical properties on the wear behavior of reactive arc deposited Zr-Si-N coatings
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
Department of Materials Science and Metallurgical Engineering, University of Barcelona, Barcelona, Spain.
Departament de Ciència del Materials i Enginyeria Metal·lúrgica, Universitat Politècnica de Catalunya, Barcelona, Spain.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Zr-Si-N coatings were grown over WC-Co substrates by an industrial reactive arc deposition technique. Si content of the coatings was varied between 0.2 and 6.3 at. % to cause a microstructural transition from a columnar to an equiaxed nanocomposite microstructure resulting in alterations of the mechanical properties such as hardness, elastic modulus, and fracture resistance. A reciprocating sliding wear test with a counter material of WC-Co shows a systematic change in wear rate as a function of Si content of the coatings. A maximum wear rate of 1.4x10-5 mm3/Nm is seen for the coating with 1.8 at. % Si (columnar microstructure), which then gradually decreases to 0.6x10-5 mm3/Nm at 6.3 at. % Si (nanocomposite structure). Electron microscopy observations of the wear track reveal tribooxidation as the dominating wear mode. The growth rate of the tribo-oxide layer is the wear rate determining mechanism. Higher growth rate of tribo-oxide layer in the columnar structured coating leads to layer delamination and high wear rate. While the lower growth rate of tribo-oxide layer in the nanocomposite coating results in reduced wear rate of the coatings. Nanocomposite coatings show superior resistance to both static and tribo-oxidation compared to the columnar structured coatings.

National Category
Natural Sciences
URN: urn:nbn:se:liu:diva-106761OAI: diva2:718616
Available from: 2014-05-21 Created: 2014-05-21 Last updated: 2014-05-21Bibliographically approved
In thesis
1. ZrN based Nanostructured Hard Coatings: Structure-Property Relationship
Open this publication in new window or tab >>ZrN based Nanostructured Hard Coatings: Structure-Property Relationship
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Ever since the hard coatings have been introduced, there has been a constant push for better mechanical properties, which motivates for deeper understanding of the microstructure-mechanical properties correlation. The aim of this thesis is to extend the knowledge on how microstructural variation influences the deformation, fracture and wear behavior of ZrN based nanostructured coatings.

Few microns thick, monolithic Zr-Si-N and multilayered Zr-Al-N coatings were deposited by reactive arc deposition and unbalanced reactive magnetron sputtering techniques respectively. The microstructures of the coatings were studied using xray diffraction, transmission electron microscopy and scanning electron microscopy. Indentation induced plastic deformation and fracture behavior was visualized by extracting the lamellae under the indent using focused ion beam milling technique combined with transmission electron microscopy. Wear behavior of the coatings were characterized by reciprocating sliding wear test following microscopic observations of the wear track.

Monolithic Zr-Si-N coating shows a systematic variation of microstructure, hardness and fracture resistance as a function of Si content. Si forms a substitutional solid solution in the cubic ZrN lattice up to 1.8 at. % exhibiting a fine columnar structure. Further Si additions result in precipitation of an amorphous SiNX phase in the form of a nanocomposite structure (nc ZrN- a SiNX) that is fully developed at 6.3 at. % Si. Dislocation based homogeneous deformation is the dominating plastic deformation mode in the columnar structure, while grain boundary sliding mediated plastic deformation causing localized heterogeneous shear bands dominates in the nanocomposite structure.

Indentation induced cracking shows the higher fracture resistance for columnar structure compared to the nanocomposite coatings. Crack branching and deflection were observed to be the key toughening mechanisms operating in the columnar structured coating. Reciprocating wear tests on these coatings show a bi-layer wear mode dominated by tribo-oxidation. Nanocomposite coatings offer superior resistance to both static and tribo-oxidation, resulting in higher wear resistance even though they are soft and brittle.

Monolithic and multilayers of Zr0.63Al0.37N coatings were grown at a deposition temperature of 700 °C. Monolithic Zr0.63Al0.37N coating shows a chemically segregated nanostructure consisting of wurtzite-AlN and cubic-ZrN rich domains with incoherent interfaces. When the same composition is sandwiched between ZrN nanolaminates, Zr0.63Al0.37N shows a layer thickness dependent structure, which results in systematic variation of hardness and fracture resistance of the coatings. Maximum hardness is achieved when the Zr0.63Al0.37N layer shows semicoherent wurtzite-AlN rich domains. While the maximum toughness is achieved when AlN- rich domains are pseudomorphically stabilized into cubic phase. Stress induced transformation of metastable cubic-AlN to thermodynamically stable wurtzite-AlN was suggested to be the likely toughening mechanism.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. 65 p.
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1664
National Category
Natural Sciences
urn:nbn:se:liu:diva-106763 (URN)10.3384/lic.diva-106763 (DOI)978-91-7519-309-0 (print) (ISBN)
2014-06-04, Visionen, B-huset, ingång 27, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Available from: 2014-05-21 Created: 2014-05-21 Last updated: 2014-05-22Bibliographically approved

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