Low pressure cold spraying under 6 bar pressure deposition: Exploration of high deposition efficiency solutions using a mathematical modelling

Abstract

Abstract This paper investigates the improvement of the deposition efficiency (DE) for low pressure cold spraying. In the literature, some possibilities were studied (a long preheating of the powder feedstock, the use of irregular shaped particles, the combination of metallic particle with ceramics, or the laser assisted heating) but the DE is still weak, in the range of 10%, when working at around 6 bar. In this paper, the improvement possibilities depending on the gas conditions, the particle size and the nozzle geometry are explored. The deposition of spherical copper powder onto a copper substrate is considered. Experimental investigations evidence a low DE of about 0.1 and virtual tests computing the one-dimensional flow of the gas through the nozzle and the interaction with the particles are used to identify potential solutions increasing the DE. Air or nitrogen propellant gas has led to similar DE. The highest achieved value remains low even working at the maximum capacity of the low pressure system, i.e. a gas with an inlet pressure of 12 bar and a preheating temperature of 630 °C. Factors of improvement are suggested for the specific case of the standard pressure of 6 bar. Fine particles cause clogging and larger particles are difficult to be efficiently deposited. Successful combinations promoting the DE include a nozzle expansion ratio in between 1.2 and 2, a diverging part length in between 200 mm and 300 mm and the helium propellant gas preheated at 600 °C. Hence the DE can reach up to 100% for 10 μm sized copper particles according to the computation. If using larger particles (20 μm, 30 μm or 40 μm), the maximum DE is respectively 0.7, 0.5 or 0.3 approximately. This results give indications for the suitable conditions promoting the highest achievable DE for low pressure cold spraying.