Role of sp3 fraction and surface morphology on the wear mechanisms of ta-C coatings under current-carrying sliding
Bibliographic record
Abstract
This study examines how bonding structure and surface quality govern the tribological behaviour of tetrahedral amorphous carbon (ta-C) coatings under applied electrical currents, addressing their suitability for current-carrying sliding applications. Two ta-C coatings—designated as soft and hard— were deposited on high-speed steel (HSS) substrates via filtered cathodic vacuum arc (FCVA) and tested against SAE 52100 steel under currents from 100 to 1500 mA. The soft coating, deposited at 150 °C without substrate bias, had a hardness of 51 GPa, while the hard coating, grown at room temperature with a −100 V pulsed bias, reached 69 GPa. Both coatings improved the wear resistance of the substrate. Compared to pulsed vacuum arc (PVA) ta-C, the FCVA coatings—being smoother, harder, and less defective—were less prone to arc-induced damage. The soft ta-C consistently exhibited low coefficient of friction (COF) about 0.2 (rising to about 0.3 at 1500 mA) and minimal wear, while the hard ta-C degraded above 500 mA due to iron oxide-filled pores and localized arcing. With its lower pore and defect density, the soft coating resisted oxidation and showed limited current-induced damage, while Raman spectra confirmed the formation of few-layer graphene on its wear track, facilitated by its moderate sp 3 content and aromatic sp 2 structures. These results indicate that bonding structure and the ability to undergo structural transformation play key roles in governing tribological behaviour under electrical current. Coatings with smooth, low-defect surfaces and moderate sp 3 content demonstrated stable performance and low wear, supporting their suitability for current-carrying sliding applications. • ta-C coatings with smooth surfaces, low defects, and moderate sp³ content showed the lowest wear under current. • Raman 2D-band mapping indicated local graphitic domains in moderate sp³ coatings at intermediate currents. • High sp³ coatings showed limited graphitization and higher friction; porous coatings promoted arc oxidation. • Friction and wear were governed by eliminating surface defects and enabling partial graphitization. • Optimal performance required smooth surfaces and bonding that allowed controlled sp³–sp² transformation.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".