Analyzing the Effects of Particle Diameter in Cold Spraying of Thermoplastic Polymers

Abstract

Cold spray deposition is a process in which bonding between solid microscale particles and a substrate occurs due to high energy impact. In this process, adhesion forms between the impacted particle and the substrate within a certain multi-parameter (material, temperature, particle size, etc.)-dependent impact velocity range. The present work analyzes the effects of particle diameter (for a range of 10-60 lm) on the adhesion of thermoplastic PEEK particles on PEEK substrates using a combined numericalanalytical approach. Our findings indicate that a maximum critical velocity (i.e., impact velocity required for a successful bond formation) of *360 m/s is required for cold spraying of 10 lm PEEK particles at room temperature. The critical velocity decreases at higher temperatures and for particle diameters in the range of 10 to 40 lm. The predicted critical velocity is shown to increase again for particles with 60 lm diameter. For PEEK particles with diameters from 10 to 60 lm, the critical velocity window is determined to be in the range of 277-360 m/s. The velocity window decreases to 208-270 m/s if the spray temperature is increased to 150°C, i.e., slightly above the nominal glass transition temperature of PEEK.

Molecular Weight Controls Interactions between Plastic Deformation and Fracture in Cold Spray of Glassy Polymers

“…The differences between the impact response of polymeric and metallic feedstock mainly originate from the significant differences in their thermo-mechanical properties, the nature of the bonds formed (e.g., metallurgical and metallic bonds in metal cold spray, which do not necessarily apply to polymer cold spray), as well as the material’s location on the crystalline-amorphous spectrum. Regardless, the occurrence of extremely high strains and strain rates in both the impacting particles and the substrate is the main driving force for a successful deposition of cold-sprayed powders. − The high local strain fields developed at the particle–substrate interface vicinity lead to adiabatic heating and substantial local thermal softening, effectively improving the mixing between the two components. − However, when both the particle and the substrate are polymers, other mechanisms can arise subsequent to the local heating: mechanical mixing, interlocking, and entanglement between the polymer in the impacting particle and the polymer constituent in the substrate. In such cases, the rheological behavior of the constituent polymer species can also play a major role in the establishment and strength of the bond. − …”

“…Manufacturing of polymers and polymer-based composites has been facilitated by concurrent advances in cold spray technology and growth in the number of applications of polymers in various industries. − When used as cold spray feedstock, polymer particles behave quite differently than metals. The differences between the impact response of polymeric and metallic feedstock mainly originate from the significant differences in their thermo-mechanical properties, the nature of the bonds formed (e.g., metallurgical and metallic bonds in metal cold spray, which do not necessarily apply to polymer cold spray), as well as the material’s location on the crystalline-amorphous spectrum.…”

“… 10 − 17 The high local strain fields developed at the particle–substrate interface vicinity lead to adiabatic heating and substantial local thermal softening, effectively improving the mixing between the two components. 9 − 11 However, when both the particle and the substrate are polymers, other mechanisms can arise subsequent to the local heating: mechanical mixing, interlocking, and entanglement between the polymer in the impacting particle and the polymer constituent in the substrate. In such cases, the rheological behavior of the constituent polymer species can also play a major role in the establishment and strength of the bond.…”

Recent advances on bonding mechanism in cold spray process: A review of single-particle impact methods

“…As the spray angle departs from the optimum, the normal velocity component contributes to the adhesion of the particle, while other velocity components contribute to the removal of the splats [ 22 , 23 ]; this causes a decline in DE till it turns zero at the highest departure from the optimum [ 24 ]. Feedstock material parameters (particle -size, -distribution, -composition, -geometry, and -temperature): Decreasing the particle size increases the critical adhesion velocity, [ 27 ]; this is postulated to be due to the high surface area-to-volume ratio in smaller particles that results in (i) lower kinetic energy [ 28 ], (ii) quicker heat conduction away from the bonding interface [ 7 ], and (iii) higher amount of adsorbents/oxides that hinder bonding [ 29 ]. Also, an increase in powder oxygen content impedes bonding and decreases the ductility of the deposit [ 10 ].…”

“…Feedstock material parameters (particle -size, -distribution, -composition, -geometry, and -temperature): Decreasing the particle size increases the critical adhesion velocity, [ 27 ]; this is postulated to be due to the high surface area-to-volume ratio in smaller particles that results in (i) lower kinetic energy [ 28 ], (ii) quicker heat conduction away from the bonding interface [ 7 ], and (iii) higher amount of adsorbents/oxides that hinder bonding [ 29 ]. Also, an increase in powder oxygen content impedes bonding and decreases the ductility of the deposit [ 10 ].…”