No abstract

The cold spray additive manufacturing process enables deposition of coatings and structures by impact bonding microparticles to surfaces through preheated, nozzle-accelerated gas flow. Most established models of gas-particle heat transfer in cold spray assume lumped thermal capacitance, which ignores particle temperature distributions and is typically valid for metals. However, recent advances in cold spray consider polymeric systems that differ categorically and considerably in thermophysical properties compared to metals. Particularly, the low Biot number (Bi) assumption may be invalid, impacting efficiency and quality of polymeric particle deposition. We describe herein a 1D transient gas-particle heat transfer model that simulates temperature profile evolution in a representative particle traveling through a cold spray nozzle. With this model, we simulated thermal histories of polymeric materials at realistic processing conditions. Polymer sprays with Bi consistently near 10 -1 or greater demonstrated thermal inhomogeneities, in some cases straddling the glass transition temperature. Thermal stratification provides insight into physical conditions of a particle before deposition, which can guide processing parameters to improve deposition efficiency and quality of polymer cold sprays.

The cold spray additive manufacturing process enables deposition of coatings and structures by impact bonding microparticles to surfaces through preheated, nozzle-accelerated gas flow. Most established models of gas-particle heat transfer in cold spray assume lumped thermal capacitance, which ignores particle temperature distributions and is typically valid for metals. However, recent advances in cold spray consider polymeric systems that differ categorically and considerably in thermophysical properties compared to metals. Particularly, the low Biot number (Bi) assumption may be invalid, impacting efficiency and quality of polymeric particle deposition. We describe herein a 1D transient gas-particle heat transfer model that simulates temperature profile evolution in a representative particle traveling through a cold spray nozzle. With this model, we simulated thermal histories of polymeric materials at realistic processing conditions. Polymer sprays with Bi consistently near 10 -1 or greater demonstrated thermal inhomogeneities, in some cases straddling the glass transition temperature. Thermal stratification provides insight into physical conditions of a particle before deposition, which can guide processing parameters to improve deposition efficiency and quality of polymer cold sprays.