Calibration of the critical velocity in cold gas spraying
Publication date
2024-04-29
Document type
Konferenzbeitrag
Author
Organisational unit
Conference
International Thermal Spray Conference and Exposition 2024 (ITSC 2024) ; Milan, Italy ; April 29–May 1, 2024
Publisher
ASM International
Book title
Thermal Spray 2024 : Proceedings from the International Thermal Spray Conference
First page
67
Last page
73
Article ID
itsc2024p0067
Part of the university bibliography
✅
Language
English
Abstract
In cold gas spraying, successful bonding occurs when particle impact velocities exceed the critical velocity. The critical velocity formula depends on material properties and temperature upon impact, relying mainly on tabulated data of bulk material. However, rapid solidification of powder particles during gas atomization can result in strengths up to twice that of bulk materials, causing an underestimation of the critical velocity. Thus, a re-adjustment of the semi-empirical calibration constants could supply a more accurate prediction of the requested spray conditions for bonding. Using copper and aluminum as examples, experimentally determined particle strengths for various particle sizes were 43% and 81% higher than those of the corresponding soft bulk materials. Cold gas spraying was performed over a wide range of parameter sets, achieving deposition efficiencies ranging from 2% to 98%. Deposition efficiencies were plotted as functions of particle impact velocities and temperatures, as calculated by a fluid dynamic approach. By using deposition efficiencies of 50%, the critical velocities of the different powders and the corresponding semi-empirical constants were determined. Based on particle strengths, the results reveal slight material-dependent differences in the mechanical pre-factor. This allows for a more precise description of individual influences by particle strengths on critical velocities and thus coating properties. Nevertheless, the general description of the critical velocity based on bulk data with generalized empirical constants still proves to be a good approximation for predicting required parameter sets or interpreting achieved coating properties.
Version
Published version
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