Cold spray is a material deposition process where a high-pressure gas stream accelerates small particles through a supersonic nozzle and deposits them in a coating on the substrate material. The powder is typically shipped and stored before use, so degradation could occur. This research investigates the influence of time-dependent degradation of cold spray powder materials and how this affects the sprayed coatings. Conditions of four different samples of AA6061 and AA2024 powders were evaluated with Raman spectroscopy, X-Ray diffraction, and SEM-EDS over several time intervals to monitor the development of oxides and alterations in powder surfaces. Single particle launches using a laser system were performed at Mines Paris-PSL to observe the particle-scale behavior during replicated spraying experiments. A spraying test comparing three batches of AA6061 powders using two different nozzle traverse speeds provided more information for the coating behavior of the powders.

The powder condition was shown to be altering with time, though the underlying causes other than oxidation and possible phase transformation could not be identified. There were few particles adhering during the single particle experiments, and some rebounding particles left behind pieces of oxides on the substrates. The powder degradation is expected to result in higher compressive stress in the coating caused by shot-peening effect from successive rebounds and a chance of higher oxide content. ... Read more