Tribological Performance Study of HVOF-Sprayed Microstructured and Nanostructured WC-17wt.%Co Coatings
Bibliographic record
Abstract
Abrasive and erosive wear of components and machinery is an ongoing challenge in the oil sands industry in northern Alberta, Canada. To improve the wear resistance by increasing surface hardness of steels, heat treatments and deposition of hard layers of metal alloys (such as stellite) by fusion welding techniques are traditionally used. However, these deposition techniques are not applicable to all shapes and add considerable weight to the final component. Thermal spraying techniques such as the use of high velocity oxy-fuel (HVOF) composite coatings based on WC-Co cermet system offer better wear resistance and greater flexibility in applications. This study presents work on two feedstock powders, namely nanocrystalline and microcrystalline WC-Co cermets, with identical matrix phase content: WC-17wt.%Co. The novelty of the research is that an engineered duplex Co coated WC-17wt.%Co cermet particle designed to withstand coating spalling under elevated loads as well as to limit abrasive debridement during wear is introduced for the first time to produce a more homogeneously-dispersed coating microstructure. The engineered particle has 6wt.% of the ductile phase material mixed into the core to insure that the reinforcement WC phase is discontinuous to limit the debridement during wear, while remainder (11wt.%) of the Co is applied as a coating on the particle to improve the ductility. The mechanical properties of the overall particle are further improved by controlling the size of the reinforcing phase (WC) in the matrix (Co). This resulted in a WC-17wt.%Co particle containing a characteristic WC grain in the order of 350 nm in the core with the Co outer coating of 1–2 μm thick, making the powder particle as nanocrystalline. HVOF deposited coatings of the nanocrystalline and microcrystalline powders were examined for microhardness, fracture toughness, sliding abrasion (ASTM G133-05) and dry-sand rubber wheel abrasion (ASTM G65-04) wear performance. The wear rate under various loads and sliding distances was studied. In both the coatings, it was found that the wear rate increased with increasing applied loads, while it decreased with increasing sliding distances. 3D surface analysis of the wear tracks using atomic force microscopy (AFM) revealed two distinctive mechanisms associated with the two coatings after abrasive wear. The improved wear resistance was attributed to the higher hardness value of the nanostructured WC-17wt.%Co coating. It was also found that the nanostructured WC-17wt.%Co coating has about twice the toughness of the conventional microstructured coating counterpart. The extent of the WC decarburization and the dissolution of Co in the coatings were also studied.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 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) | 0.001 | 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 source (direct Gemma or distilled Codex), 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".