Estudo do comportamento tribológico de um aço texturado, revestido com filmes TMD

Dissertação de Mestrado Conjunto Europeu em Tribologia de Superficies e Interfaces apresentada à Faculdade de Ciências e TecnologiaA texturização de superfície é uma das técnicas amplamente utilizadas em vários componentes de máquinas, como pistão/cilindros, de modo a evitar sua quebra precoce e aumentar sua funcionalidade. A textura na superfície auxilia na lubrificação e reduz o coeficiente de atrito (COF) e o desgaste. O funcionamento da textura na superfície depende de vários parâmetros, como o método de texturização, a forma da textura, condições de operação, etc. Da mesma forma, o revestimento da superfície também é outra técnica usada para melhorar as propriedades da superfície dos materiais. O revestimento de uma superfície atua como um lubrificante sólido na mesma em caso de desgaste e reduz o COF. Uma vez que o aprimoramento das propriedades tribológicas dos materiais pistão/cilindro num motor de combustão interna é importante para beneficiar a economia de combustível e o desempenho do motor. A lubrificação adequada nesses sistemas é, assim, uma característica fundamental que pode melhorar seu desempenho tribológico. O objetivo deste trabalho consiste na redução significativa do atrito em diferentes regimes de lubrificação, em particular, em regimes de lubrificação limite (BL), lubrificação mista (ML) e lubrificação hidrodinâmica (HL). Os novos revestimentos de lubrificantes sólidos combinados com a texturização da superfície podem diminuir o atrito sem prejudicar o meio ambiente com aditivos de óleo. O efeito sinérgico dos revestimentos de dichalcogenetos de metais de transição (TMD) aplicados em superfícies texturizadas pode ajudar a atingir esse objetivo. O procedimento de texturização consistirá em duas etapas: (i) texturização de elétrodos, utilizando tecnologia laser com três padrões geométricos diferentes (dois retangulares e uma circular) e (ii) texturização de corpos de prova por ECP (processamento eletroquímico) / EDM (usinagem por descarga elétrica) utilizando esses elétrodos texturizados. As técnicas de texturização utilizadas nesta investigação são ECP e a texturização dupla com EDM+ECP em combinação com revestimentos TMD (WSC e MoSeC) por deposição física de vapor (PVD). O efeito destas três geometrias de textura e dos revestimentos baseados em TMD foram analisados com teste tribológico de bloco sobre anel para ver o efeito das diferentes texturas, dos processos de texturização, revestimentos e o efeito combinado de texturização com os revestimentos. A maior melhoria em termos de redução de COF para corpos de provaContents [Manoj Rajankunte Mahadeshwara] iii[STUDY OF THE TRIBOLOGICAL BEHAVIOR OF THE TEXTURED STEEL COATED WITH TMD FILMS] texturizados, foi observada em amostras de covas circulares em regime BL com baixas velocidades de deslizamento e em regime ML e HL a altas velocidades de deslizamento.Surface texturing is one of the techniques which is widely used on various machine components such as piston/cylinders to prevent their early breakage and increase their functionality. The texture on the surface aids the lubrication and reduces the coefficient of friction (COF) and wear. The functioning of the texture on the surface is varied by various parameters such as the method of texturing, shape of texture, operating conditions etc. Similarly, surface coating is also another technique for enhancing the surface properties of the materials. Surface coating acts as a solid lubricant on the surface in case of wear and tear and reduces COF. Since enhancing the tribological properties of the piston/cylinder materials in an internal combustion engine is important to benefit the fuel economy and performance of the engine. Proper lubrication in these systems is a key feature which can improve their tribological performance. The objective of this work is the significant reduction in friction in different lubricated regimes in particular boundary lubrication (BL), mixed lubrication (ML) and hydrodynamic lubrication (HL) regimes. The novel solid lubricant coatings combined with surface texturing can decrease the friction without harming environment with oil additives. The synergetic effect of transition metal dichalcogenides (TMD) coatings applied onto textured surfaces can help to achieve this goal. Texturing procedure will consist in 2 steps: (i) texturing of electrodes using laser technology with three different geometric patterns (two rectangular and one circular) and (ii) texturing of specimens by ECP (electrochemical processing) / EDM (electric discharge machining) using these textured electrodes. The texturing techniques used in this investigation are ECP and dual texturing with EDM+ECP in combination with TMD coatings (WSC and MoSeC) via physical vapor deposition (PVD). The effect of these three texture geometries and TMD- based coatings were analyzed with block-on-ring tribological test to see the effect of different textures, texturing processes, coatings and combined effect of texturing and coatings. The biggest improvement in terms of COF reduction for textured-coated specimen was observed in circular dimpled specimen in BL regime at low sliding speeds and in ML and HL regime at high sliding speeds

Synergic effect of TMD coating on textured steel using micro-EDM

Modifying the surface of materials through texturing and coating can have a significant impact on their tribological properties. In the present study, a hybrid surface modification process, texturing combined with coating, has been applied to a steel surface and the tribological behavior in lubricated conditions was studied. The surface of the steel was textured using micro-electric discharge machining (micro-EDM) to create two distinct patterns (rectangular and circular). Following this, transition metal dichalcogenides (TMD); tungsten-sulphur‑carbon (WSC) coating was applied to the surface using magnetron sputtering. To evaluate the specimens, they were subjected to tribological testing in various lubrication conditions using a block-on-ring configuration. The results were corroborated using a reciprocating sliding test and compared to those of a smooth uncoated specimen. The findings revealed that the tribological properties of the textured and coated specimens were enhanced, particularly in specimens with circular dimple patterns. The WSC coated circular dimple specimens showed a reduction of the COF by 7–12 %, in the boundary lubrication regime and by 9–25 %, in the mixed and hydrodynamic lubrication regimes as compared to the untreated specimen.The authors record sincere thanks to the University of Minho, Instituto Pedro Nunes and CEMMPRE for extending its facilities. This work is sponsored by FEDER and by National funds through FCT- Fundação para a Ciência e a Tecnologia under the projects: ON-SURF ref. “POCI-01- 0247-FEDER-024521”, ATRITO-0 ref. “POCI-01-0145-FEDER-030446”, CEMMPRE ref. “UIDB/00285/2020” and ARISE ref. “LA/P/0112/ 2020”

Investigating the Synergistic Effect of Electrochemical Texturing and MoSeC Coatings on the Frictional Behaviour of Lubricated Contacts

The materials used for the piston cylinders of automobile engines, or the ring and tappets of various mechanical components, are continuously experiencing lubricated sliding motions. These surfaces are prone to damage due to the various tribological aspects of friction and wear. Hence, enhancing their surface properties would contribute to increasing their life and saving energy and resources. For many decades surface texturing and surface coating technology have been studied to improve the surface tribological behaviours of the materials. In the present study, the steel surface was textured with electrochemical processing (ECP) and post-coating with transition metal dichalcogenides (TMD) using a molybdenum-selenium-carbon (MoSeC) film. A comparative study was conducted to investigate the synergistic effect of surface texturing and coating to improve frictional properties on the steel surface. The block-on-ring experiments were performed under lubricated conditions to understand the improvement of COF at different lubrication regimes. It has been seen that the MoSeC-coated circular patterns exhibited improvements in the frictional properties at all the lubricated conditions if compared with smooth surfaces