Diamond-like carbon and ceramic materials as protective coatings grown by pulsed laser deposition

A rather large number of nitride, carbide, and oxide thin films are used as hard and wear-resistant coatings, for optical, corrosive, and refractory applications that are of crucial importance. Additional requirements place even more stringent conditions on the deposition processes. The properties of coatings deposited by pulsed laser deposition are determined by the deposition parameters, the composition of the PLD plasma and its ionization states, the substrate conditions, etc.. In this way, the advantageous properties of PLD can be used with the general aim to increase the adhesion of the high quality PLD thin films to offer new applications where the hard, optical, and/or thermal coatings are required to contribute to surface engineering. A first objective has been to shine some light on the optical and mechanical properties of smooth, homogeneous, and adherent SiNx ceramic coatings which have been deposited on different substrates such as glass, silicon wafer, tool steels, and tungsten carbide (WC-10%Co) at various processing gas pressures and different laser fluences. The r.f. plasma and the PLD-plasma using Si3N4 target have been analyzed during the deposition of SiNx coatings revealing as well as Si° atoms, Si+ ions, No atoms, and N+ ions with these species working actively in the dissociative recombination processes in the nitrogen r.f. and PLD plasmas to promote the physical and chemical adsorption on the substrate surfaces and on the nitridation layer to grow finally the SiNx thin films. Some optical properties measured from the SiNx coating as the refractive index show an increase as the nitrogen processing gas pressure decreases. A general increase in the refractive index is detected as the laser fluence is increasing. Considering Si and its compounds as nucleates for diamond and DLC coatings, SiNx was used as buffer layer to improve the adherence of DLC hard coatings on metallic and tungsten carbide substrates. The influence of the substrate materials on the nucleation and growth of DLC coatings and the adherence of this superhard coating to different substrates was investigated. The deposition of DLC coatings on substrates (tool steels and WC-10%Co) with high Co-content (known as an anti-nucleate element for the sp3-bond) has been achieved by using a polishing process with diamond disk and diamond solution, and the subsequent chemical etching to produce an amorphous layer of CoO/CoSO4 which is removed from the surface by argon r.f. plasma. The DLC coatings with an application-like mechanical properties are deposited (60% sp3-content), but a poor adherence is obtained and the coatings showing spontaneous delamination from the substrates. By using SiNx coatings as buffer layer the adherence of the hard DLC films is improved. The process consisted in the nitridation of the surface by r.f. nitrogen plasma and a subsequent deposition by PLD of a SiNx ceramic in nitrogen processing gas pressure directed towards different substrates such as metals, ceramics, and polymers. Finally smooth, homogeneous, and adherent DLC coatings on tool steels and on WC-10%Co substrates are obtained. The chemical bonds of the DLC coatings characterized from Raman spectra and calibrated by EELS, indicate that the sp3-content in the DLC films increases with increasing laser fluence, and decreasing processing gas pressure. By increasing the number of sp3-bonds in the DLC coatings with the change in the deposition parameters by PLD, the hardness and Young's modulus increase with a direct improvement in the mechanical properties. The adhesion of DLC coatings with a large sp3-content deposited on WC-10%Co has been improved. The failure mode is quite different to the DLC coatings on tool steels, which show an adhesive failure due to the plastic deformation of the metallic substrates. Based on the actual demands for stable and nondegradeable refractory coatings a more general goal is to understand the crystallization of Al2O3-ZrO2 composite coatings associated to the PLD deposition parameters and annealing. In the past the deposition of complex refractory materials and diverse composites was not possible until recently. Advances in the pulsed laser deposition technique have now made it possible to produce such special thin films, which enable a variety of diffusion and other kinetic studies to be carried out. The smooth, homogeneous and adherent alumina-zirconia composite coatings in a relation of 85:15 (Al2O3-ZrO2) are deposited on silicon wafer, stainless steels, and CMSX-2 substrates with a substrate temperatures up to 800°C playing no role in the crystallization of the composite Al2O3-ZrO2 coatings. A homogeneous deposition of amorphous composite materials can be transformed to more stoichiometric crystalline coatings by increasing the kinetic energy supply during the annealing. After annealing the composite coatings exhibit a higher level of crystallization of a-alumina and cubic-zirconia with decreasing oxygen processing gas pressure, and with increasing the laser fluence, associated to the subsequent change of the coating thickness at constant target-substrate-distance, due to the expansion of the plasma plume and the removal of more particles with the transfer of energy into the laser-induced plasma.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2004

Author dc:creator

• Perera Mercado, Yibran Argenis

Contributors dc:contributor

• Poprawe, Reinhart

• info:eu-repo/classification/ddc/530
• Siliciumnitrid
• Impulslaserbeschichten
• Dünne Schicht
• Stoffeigenschaft
• Diamantähnlicher Kohlenstoff
• Aluminiumoxide
• Physik
• Zirkoniumdioxid
• Verbundwerkstoff
• Diamond-like carbon
• DLC
• Al2O3-ZrO2
• SiNx
• Coatings
• Pulsed Laser Deposition
• PLD

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-123657%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:62059