The effect of N on structure, mechanical properties and tribological behaviour of TMD coatings in contact with rubber

Abstract

Transition metal dichalcogenides (TMD) coatings are solid low-friction self-lubricant materials enabling easy sliding by formation of a tribo lm at the interface in the contact region. W-S coating, which belongs to the TMDs family, was doped with N in order to combine low friction of the coating with good hardness due to addition of a third element. In this work, W-S and W-S-N coatings with di erent composition have been deposited by magnetron sputtering, characterised and evaluated with respect to the structure, mechanical properties and tribological performance. The composition was varied by changing the ow of N2 into the deposition chamber, leading to nitrogen contents ranging from 0 to 33 at.%. All coatings were deposited with Cr interlayer. Films W-S and W-S-N deposited with the lowest content of N had a crystalline structure, while coatings with the higher N content were amorphous. The coating were tribologically tested against nitrile-butadiene rubbe (NBR) balls at room temperature and 200 C using a pin-on-disc tribometer. Energy dispersive spectroscopy, optical microscopy observations and 2D pro lometry were performed after the tribological tests. The results showed that the coatings had better tribological performance at elevated temperature. The wear and friction behaviour of the coatings was interpreted as a function of several factors including: mechanical strength, structure and formation of the tribo lm. It was concluded that WS- N coatings supposedly could be material for applications requiring contact with rubber at temperatures greater than room temperature.

Os revestimentos de Dicalcogenetos de Metais de Transi c~ao (DMT) s~ao materiais s olidos, auto-lubri cantes com baixo-atrito que permitem um f acil deslizamento atrav es da forma c~ao de uma camada transfer^encia na interface da zona de contacto. Os revestimentos W-S, que pertencem a familia dos DMTs, foram dopados com N de forma a combinar o baixo atrito dos revestimentos com elevada dureza, atrav es da adi c~ao de um terceiro elemento. Neste trabalho, os revestimentos W-S e W-S-N com diferentes composi c~oes foram depositados, caraterizados e avaliados no que diz respeito o sua estrutura, propriedades mec^anicas e comportamento tribol ogico. A composi c~ao foi variada atrav es da mudan oa de uxo de N2 no interior c^amara de deposi c~ao, levando a uma varia c~ao at omica em azoto nos revestimentos de 0 a 33 %. Todos os revestimentos foram depositados com uma intercamada de Cr. Os lmes W-S-N depositados com o menor teor e sem N apresentam alguma cristalinidade, enquanto os revestimentos com maior percentagem de N s s~a amorfos. Os revestimentos foram tribologicamente testados por pino-disco com um contracorpo esf erico de borracha NBR o temperatura ambiente e a 200 C. Ap os os ensaios tribol ogicos, as amostras foram caracterizadas por EDS, microscopia otica e per lometria 2D. Os resultados demostraram que os revestimentos apresentam melhor performance a elevadas temperaturas. A taxa de desgaste e o coe ciente de atrito foram interpretados como fun c~ao de v arios fatores, incluindo: dureza, estrutura e forma c~ao da camada transfer^encia. Deste trabalho, podemos concluir que os revestimentos W-S-N podem ser usados em aplica c~oes que requeiram o contacto com borracha a temperaturas acima da temperatura ambiente havendo uma redu c~ao do atrito em rela c~ao ao deslizamento de metal borracha para as mesmas condi c~oes.