Mesoscale Modeling of Cold Spray Deposition of Tantalum Powders

Cold spray (CS) deposition of metal powders has recently emerged as a leading kinetic spraying technique for additive manufacturing and repair of metallic systems. The CS process involves accelerating metal powders towards a solid substrate, wherein, particle impacts result in high strain rate particle deformation and metallurgical bonding with the substrate/deposit. The deformation is concentrated in the region at the interface between the incoming particle and the underlying substrate/deposit, and the shear component of this deformation is far more significant at the periphery of the interface than in the center of the impact site. Predicting the deformation behavior of powders during impact with the substrate/deposit requires the capability to model evolution of microstructure at the length and timescales of experiments. Typical powders span lengths of tens of microns and the deformation/bonding processes span times of tens of nanoseconds. CS deposition of BCC metal powders poses the challenge to accurately capture the interplay between slip and deformation twinning during high strain rate deformation. Such a challenge can be overcome by using quasi-coarse-grained dynamics (QCGD) to extend the capabilities of classical MD to the mesoscales relevant to cold spray deposition. In this work, the QCGD simulations are carried out to investigate the deformation behaviors during the impact of multiple 20 um pure Tantalum powders onto a pure Tantalum substrate. Detailed analyses of the evolution of pressure, temperature, and shear strain are conducted to reveal jet initiation at the particle-particle and particle-substrate interfaces. Grain size distributions for initial and final splat microstructure are also obtained using an atom orientation clustering technique to identify recrystallization. The presentation will discuss the mesoscale modelling using QCGD, the mechanisms of bonding, and the evolution of microstructure during the cold-spray deposition of Tantalum powders at the length/time scales of experiments. The simulations provide insights into the plasticity contributions from slip and twinning on the dynamic recrystallization behavior at the particle/substrate and particle/particle interface during CS deposition.