REPOSITÓRIO P.PORTO
Repositório Científico do Politécnico do Porto
Entradas recentes
Microstructure, Mechanical, and Tribological Properties of Mo2N/Ag-SiNx Nanomultilayers with Varying Modulation Periods
Publication . Fernandes, Filipe; Luan, Jing; Wang, Lei; Dong, Songtao; Ferreira, Fábio; Mo, Changpan; Cavaleiro, Albano; Ju, Hongbo; Kiryukhantsev-Korneev, Philipp
The multilayered Mo2N/Ag-SiNx self-lubricant films were designed and deposited using a
DC (Direct Current) magnetron sputtering system under mixed gas atmosphere of N2 and
Ar. The modulation ratio (thickness ratio of Mo2N to Ag-SiNx) was fixed at 2:1, while the
modulation periods (thickness of Mo2N and its adjacent Ag-SiNx layer) were set at 20, 40,
and 60 nm. The results indicated that all multilayer films, regardless of modulation period,
exhibited a combination of face-centered cubic (fcc) and amorphous phases. Specifically,
fcc-Mo2N was detected in the Mo2N layers, while fcc-Ag and amorphous SiNx co-existed
in the Ag-SiNx layers. The multilayered architecture induced residual stress and interface
strengthening, resulting in hardness values exceeding 21 GPa for all films. Compared
to Mo2N and Ag-SiNx monolayer films, the multilayer structure significantly enhanced
tribological properties at room temperature, particularly in terms of wear resistance. The
Mo2N/Ag-SiNx multilayer films exhibit ~25% lower friction than Ag-SiNx, ~3% lower
than Mo2N, and achieve remarkable wear rate reductions of ~71% and ~85% compared to
Ag-SiNx and Mo2N, respectively, demonstrating superior tribological performance. The
synergistic effects of both modulation layers and relative high hardness were key factors
contributing to the enhanced tribological behavior.
Nitrogen alloyed MoSe2 coatings – Role of optimized morphology, structure and mechanical properties on diverse environment sliding performance
Publication . Fernandes, Filipe; Yaqub, Talha Bin; Nadeem, Irfan; Yaqoob, Khurram; Kalin, Mitjan; Cavaleiro, Albano
Transition metal dichalcogenide (TMD) coatings are gaining increasing interest among the scientific community as eco-friendly solutions for reducing friction, improving energy conservation, and lowering carbon footprints. N-alloyed MoSe2 coatings (MoSeN), a subset of TMDs, remain largely underexplored, with no research on their frictional performance across various sliding environments. Herein, an in-depth analysis of DC-magnetron sputtered MoSeN coatings is presented, with N content varying from 0 to 42 at%. Investigation of composition, morphological features, crystal structure, mechanical strength and sliding performance are accessed. Our findings revealed that N additions resulted in increased compactness, amorphous structure and hardness of ∼4.6 GPa, and these improvements remained consistent despite compositional variations. The sliding competency was evaluated under six different conditions, revealing promising results in ambient-air and dry-N2 atmospheres at room conditions and 100 °C. At 200 °C, the sliding performance in ambient-air was better than dry-N2. Friction coefficient for N-alloyed coatings was relatively close, ranging between 0.03 and 0.06, except for a dry-N2 environment at 200 °C. Nevertheless, wear rate showed slight variations, with higher values observed in dry-N2 at 100 °C and 200 °C but remained within a specific range of 1–7 × 10−7 mm3/Nm for all other conditions. This study highlights the potential of MoSeN coatings to be scaled for industrial applications, offering a roadmap for reducing the inherent limitations of PVD sputtering.
Mutually enhanced mechanical and tribological properties in magnetron sputtered Mo2N/Ag-SiNx self-lubricating multilayered films via epitaxial growth design
Publication . Fernandes, Filipe; Luan, Jing; Wang, Lei; Dong, Songtao; Choukourov, Andrei; Yang, Junfeng; Kalin, Mitjan; Cavaleiro, Albano; Ju, Hongbo; Vincenzini, P.
Achieving simultaneous enhancement of both mechanical and self-lubricating properties by incorporating soft lubricants into nitride films has been a longstanding challenge in the development of solid lubricant materials. This paper introduced a novel approach to overcome this challenge by developing coherent-structured Mo2N/Ag-SiNx multilayered films using radio frequency (RF) magnetron sputtering. The multilayer films were designed with a fixed modulation period of 30 nm, while the modulation ratio (γ) was varied from 1:9 to 1:1. The Mo2N layers exhibited a single fcc-Mo2N phase, while the Ag-SiNx layers formed a dual-phase structure comprising fcc-Ag nanoparticles embedded in an amorphous SiNx matrix. At a modulation ratio of 1:9, the Ag-SiNx layer epitaxially grew on the Mo2N template, resulting in a coherent structure. This coherent structure significantly enhanced both the hardness and elastic modulus, reaching approximately 36 GPa and 230 GPa, respectively. The improved wear resistance at room temperature can be attributed to the coherent strengthening effect, which not only elevated the film's hardness but also eliminated sharp interfaces between modulation layers, thereby reducing crack initiation sites. In temperature-cycling tribo-testing from room temperature to 600 °C, the film with a γ of 1:9 maintained a stable coefficient of friction around 0.2, except during the initial room temperature, where it was 0.4. The wear rate could not be accurately calculated due to the adhered tribolayer on the top of the wear track following the initial tribo-test at 600 °C. The excellent tribological properties across temperature cycles were attributed to the synergistic lubricant characteristics of both layers and the formation of self-lubricating tribo-phases. The optimized Mo2N/Ag-SiNx multilayered films provide an effective balance of lubrication and mechanical stability under extreme conditions, making them highly promising for high-performance engineering applications.
Performance evaluation of TiAlSiN and TiSiN/TiSiVN coatings during high-speed dry turning of AISI 316 L considering the role of vanadium-based tribo-oxides
Publication . Fernandes, Filipe; Kumar, Ch. Sateesh; Lacalle, Luis Norberto López de; Cavaleiro, Albano; Cavaleiro, Diogo; Kalin, Mitjan; Prajapati, Ramanand
This study investigates the tribo-mechanical performance of uncoated, TiAlSiN-coated, and TiSiN/TiSiVN multilayer-coated Al2O3/SiC ceramic tools during dry turning of AISI 316 L austenitic steel across three successive passes at varying cutting speeds. Key machining outputs, including cutting forces, surface roughness, cutting temperature, and tool wear (flank and crater), were analyzed with a focus on oxide formation and selflubricating mechanisms. The TiSiN/TiSiVN-coated tool exhibited the most favorable performance, showing only ~15 % increase in cutting force across passes, ~9 % improvement in flank wear resistance compared to TiAlSiN, and ~ 17 % lower wear progression relative to the uncoated tool at 350 m/min. Surface roughness and cutting temperature trends further confirmed the coating’s superiority, attributed to the formation of V₂O₅ tribo-oxides, which reduce friction and thermal degradation. EDS and SEM analyses validated the wear protection mechanisms, highlighting the adaptive role of vanadium-based layers in mitigating adhesion and thermal fatigue. The results establish TiSiN/TiSiVN as a promising candidate for high-speed dry machining due to its superior mechanical-chemical synergy and wear resistance.
Ensinar e aprender na era da Inteligência Artificial Generativa
Publication . Cruz, Mário; Queirós, Ricardo
Este livro analisa criticamente a integração da Inteligência Artificial Generativa no ensino superior, assumindo-a como uma questão pedagógica, epistemológica e ética, e não apenas tecnológica. A obra problematiza discursos tecnodeterministas e abordagens instrumentais, propondo uma leitura informada e situada da IA enquanto fenómeno sociotécnico que intervém em práticas centrais da vida académica, como a escrita, a avaliação, a produção de conhecimento e a mediação pedagógica. Ao longo dos capítulos, são mobilizados contributos da pedagogia crítica, das teorias da aprendizagem e de referenciais éticos internacionais, articulando evidência científica, reflexão conceptual e propostas de análise da prática docente. O livro dirige-se a docentes do ensino superior e foi concebido para aprendizagem autónoma, promovendo o desenvolvimento de literacia crítica em Inteligência Artificial, a reflexão sobre integridade académica e a construção de posicionamentos pedagógicos conscientes e responsáveis face ao uso da IA generativa em contextos de ensino superior.