Influence of slip correction factor, back pressure, standoff distance, and nozzle expansion ratio on impact conditions of fine copper particles in vacuum sold spray
Bibliographic record
Abstract
Vacuum cold spray is an additive manufacturing technique used to produce metal and ceramic thick films. In this process, metal or ceramic powders smaller than 5 μm are accelerated to high velocities through a converging-diverging (de Laval) nozzle in a supersonic flow and deposited onto a solid substrate in a vacuum chamber. The vacuum environment minimizes the velocity loss of submicron particles by reducing supersonic spray jet impingement effects, which enables dense deposition of fine metal and ceramic powders through metallurgical and mechanical adhesion mechanisms. However, most existing studies on vacuum cold spray focus on ceramic materials and operate at inlet gas pressures below 1 bar. Impact conditions of metal particles less than 5 μm under inlet pressure ranging between 2 bar and 35 bar in full vacuum of 0 Pa, partial vacuum of 5066.3 and 10132.5 Pa remain largely unexplored. In this study, a series of CFD simulations were conducted to investigate the impact behavior of fine copper particles injected at 2, 10, 20, and 35 bar into three different vacuum levels of 0, 5066.3, and 10132.5 Pa with the Cunningham correction factor applied to account for slip effects. Standoff distances and nozzle expansion ratios were varied to examine their influence on impact conditions. Results showed that the application of Cunningham correction factor was crucial for capturing slip effects on particles, particularly in the nozzle expansion region. Under full vacuum conditions, copper particles as small as 100 nm can theoretically achieve deposition when the inlet pressure exceeds 2 bar. Furthermore, high pressure nozzles with large expansion ratio of 10 and 15 operated in partial vacuum can yield particle impact velocities significantly higher than compared to nozzles operated in open atmosphere for fine copper particles in the range of 1 µm to 5 µm. The results of this study are expected to be influential in understanding and designing high pressure vacuum cold spray nozzles, gas dynamic conditions, and large nozzle expansion ratios for achieving high impact velocities and improved deposition qualities.--Author's abstract
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| 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".