Tribocorrosion is a term used to describe the material degradation due to the combination of electrochemical and tribological processes. Due to a synergetic effect, the material loss can be larger than the sum of the losses due to wear and corrosion acting separately. In this thesis, the synergy of wear and corrosion was investigated for different types of material, namely the Ti-6A1-4V alloy, the SS316L stainless steel coated with a thin film of Diamond Like Carbon (DLC), and the SS301 stainless steel coated with a thin film of chromium silicon nitride (CrSiN).

A tribocorrosion apparatus was designed and constructed to conduct wear experiments in corrosive media. Sliding ball-on-plate configuration was used in this design, where the contact between the ball and the specimen is totally immersed in the test electrolyte. The specimen was connected to a potentiostat to control its electrochemical parameters, namely the potential and the current. Electrochemical techniques were used to control the kinetics of corrosion reactions, and therefore it was possible to assess separately the role of corrosion and wear in the total degradation of material, and to evaluate the synergy between them.

For Ti-6A1-4V, it was found that the corrosion and tribocorrosion depend strongly on the structure of the material. The a-equiaxed microstructure with fine dispersed p-phase exhibited the best corrosion resistance. The corrosion resistance was found to decrease when the basal plane was preferentially aligned parallel to the surface, which is attributed to a low resistance to charge transfer in the oxide films formed on this plane. On the other hand, when wear and corrosion were involved simultaneously, the oxide layer protecting the substrate against dissolution was mechanically destroyed leading to a high corrosion rate. It was found that the hardness was the most important factor determining the tribocorrosion behavior of the Ti-6A1-4V alloy;​ samples with high hardness exhibited less mechanical wear, less wear-enhanced corrosion, and less corrosion-enhanced wear.

For DLC coatings, it was found that interface engineering plays a crucial role in the tribocorrosion behavior of DLC films. DLC films with nitrided interface layer (SS\N3h\DLC) were shown to have very poor tribocorrosion resistance;​ the DLC film delaminated from the substrate after 50 cycles of sliding wear at 9 N load in Ringer's solution. It should be mentioned that a previous study performed at Ecole Polytechnique de Montreal [4] has shown that the same coating resisted 1800 cycles of dry wear at 22 N without delamination. This demonstrates clearly the effect of corrosion on the wear resistance of DLC films. The use of a-SiN:​H bond layer between the SS316L substrate and the DLC film improved significantly the tribocorrosion behavior of the coating. This layer acts as a barrier against corrosion reaction;​ the polarization resistance was 5.76 GQ.cm² compared to 27.5 MQ.cm² and 1.81 MQ.cm² for the DLC-coated SS316L with nitrided interface layer and the bare substrate, respectively.

For CrSiN coatings, it was also shown that nitriding treatment of the substrate prior to deposition reduces significantly the tribocorosion resistance of the CrSiN-coated SS301 substrates. This is attributed to the peculiar morphology of the nitrided surface prior to deposition. The high relives at the grain boundaries of the substrate may be the reason for the generation, during sliding wear, of defects in the film, which makes the infiltration of the liquid easier, and consequently leads to the destruction of the CrSiN film.

La tribocorrosion est un terme utilise pour decrire la degradation des materiaux due a la combinaison des actions electrochimiques et tribologiques. Due a un effet synergetique, la perte des materiaux peut etre plus important que la somme des pertes dues a l'usure et la corrosion prises separement. Dans cette these, la synergie entre l'usure et la corrosion est etudiee pour differents types de materiaux ;​ Palliage de titane Ti-6A1-4V, l'acier inoxydable SS316L couvert d'une couche mince de Diamond Like Carbon (DLC), et l'acier inoxydable SS301 couvert d'une couche mince de nitrure de chrome avec silicium (CrSiN).

Un dispositif experimental a ete concu et construit pour faire des tests d'usure dans des milieux corrosifs. La configuration bille-sur-plat, en mode glissant, a ete utilisee dans ce dispositif, ou le contact entre la bille et l'echantillon est completement immerge dans l'electrolyte. En plus, l'echantillon est connecte a un potentiometre pour pouvoir controler ses parametres electrochimiques, tel que le potentiel et le courant. Des techniques electrochimiques ont ete utilisees pour controler la cinetique des reactions de corrosion, pour en consequence evaluer separement les roles de la corrosion et de l'usure dans la degradation totale du materiau, et pour evaluer aussi la synergie entre eux.

Pour l'alliage Ti-6A1-4V, on a constate que la corrosion et la tribocorrosion dependent fortement de la structure du materiau. La microstructure equiaxe de a avec dispersion de phase p en forme de particules nodulaires dans les grains a, presente la meilleure resistance a la corrosion. En plus, on a trouve que la resistance a la corrosion diminue quand le plan basal etait preferentiellement aligne parallelement a la surface, ce qui est due a une resistance de transfert de charge moins important pour ce plan. De 1'autre part, quand l'usure et la corrosion sont impliquees simultanement, la couche d'oxyde qui protege le substrat contre la dissolution est detruite mecaniquement conduisant a une corrosion plus importante. On a constate que la durete de la surface etait le parametre le plus important determinant le comportement a la tribocorrosion de l'alliage T1-6A1-4V ;​ les echantillons ayant une grande durete ont montre moins d'usure mecanique, moins de corrosion assitee par l'usure, et moins d'usure assistee par la corrosion.

Pour les couches DLC, on a trouve que l'ingenierie de 1'interface joue un role crucial dans le comportement de la couche DLC a la tribocorrosion. Les couches DLC avec une couche d'acier inoxydable nitruree comme interface (SS\N3h\DLC) avaient un mauvais comportement a la tribocorrosion;​ la couche DLC s'est detachee du substrat apres 50 cycles d'usure avec une force normale de 9N dans la solution Ringer. If faut mentionner qu'une etude effectuee prealablement a l'Ecole Polytechnique a montre que ce meme depot a resiste 1800 cycles d'usure seche avec une force normale de 22N sans detachement, ce qui montre clairement l'effet de la corrosion sur les proprietes tribologiques de la couche DLC. L'utilisation de la couche a-SiN:​H comme couche d'interface a ameliore d'une maniere significative le comportement de la couche DLC a la tribocorrosion. Cette couche agit en tant qu'une couche barriere contre les reactions de corrosion ;​ la resistance a la polarisation etait 5.76 Gfi.cm comparee a 27.5 MQ.cm et 1.81 MQ.cm² pour les substrats couverts d'une couche de DLC sans a-SiN:​H et les substrats nus respectivement.

Pour les couches de CrSiN, on a aussi constate que le traitement de nitruration du substrat avant le depot diminue d'une maniere significative le comportement de ces couches a la tribocorrosion. Ceci est attribue a la morphologie de la surface nitruree. Les reliefs eleves sur les joints de grains peuvent etre la raison de la creation, durant le test d'usure, des defauts dans la couche, ce qui rend 1'infiltration du liquide a travers la couche plus facile, et par consequence mene a la destruction de la couche CrSiN.