Strain-enhanced nanocrystallization of a CuNiTiZr bulk metallic glass coating by a kinetic spraying process

Nanocrystallization of CuNiTiZr bulk metallic glass (BMG) subjected to kinetic spraying with variable impact velocities was investigated through numerical and experimental approaches. The fraction of crystallization and activation energy of the initial feedstock and as-deposited coatings were estimated through differential scanning calorimetry and the Kissinger method, respectively. The numerical and experimental results showed that the fraction of crystallinity and activation energy for nucleation in BMG coatings is strongly related to the kinetic energy of the impacting particles. Upon high-velocity impact, the kinetic energy of the particle led to a decrease in the free energy barrier and an increase in the driving force for the amorphous-to-crystalline phase transformation. Microstructure observation revealed that the nanocrystallization of the BMG in the kinetic spray process was associated with the strain energy delivered by plastic deformation using a high strain rate.