Mechanical property improvement induced by nanoscaled deformation twins in cold-sprayed Cu coatings

Nanoscaled deformation twins have been observed in cold sprayed Cu coatings and the coating hardness has been improved by this kind of tiny twins. Strain rate up to 10⁹ s⁻¹ at the impact interfaces can be achieved at the cold spray process, and the maximum shearing compressive stress and tensile stress are 392 MPa and 397 MPa, respectively, obtained from impacting simulations. They are larger than the required shearing stress for the formation of deformation twins in Cu. The orientation relationship between the stripes can be determined to be (111¯)_M∥(111¯)_T and (1¯10)_M∥(101)_T both in coatings prepared by cold spray Cu particles annealed at 700 °C and 250 °C, respectively. The hardness of the coatings is higher than that of the corresponding substrates which indicates the improvement by the work hardening effect in the cold spray process. Though the misorientation of the deformation twins in the coatings slightly deviates from 60°, the existence of nanoscaled deformation twins improves its hardness significantly.