Microstructural characteristics and deposition mechanism of cold-sprayed Cr coatings

The Cr coatings are fabricated on 304 stainless steel substrates using cold spray and electroplating methods. The particle deposition behavior and coating formation mechanism of Cr are clarified by analyzing the surface morphology， cross-sectional microstructure， and nanomechanical properties of the cold-sprayed Cr coatings. The results show that the electroplated Cr coating contains numerous vertical cracks， while the cold-sprayed Cr coating exhibits an irregular but compact and defect-free interface with the substrate. In addition， the surface of the cold-sprayed coating presents a large number of craters， and the near-surface region consists of fine equiaxed grains. The nanohardness in the region increases by 41.37%-62.17% compared with that of undeformed Cr particles， indicating that subsequent particles produce work hardening due to shot-peening effects upon impacting the pre-deposited coating. The hardening hinders cooperative plastic deformation between incoming particles and the existing coating， thereby reducing the feasibility of further deposition. Based on the surface morphology and the gradient distribution of nanohardness， the deposition mechanism for Cr coatings on 304 stainless steel is proposed， involving the disruption of the substrate’s oxide film， the formation of the initial coating layer， and the surface morphological evolution induced by shot-peening strengthening.