Cold sprayed bell metal: improving adhesion by substrate laser surface texturing

The improvement of bell metal repair adhesion by substrate surface treatment was studied. A high-pressure cold spray (CS) system was used to deposit Cu20Sn powder using nitrogen gas on fine- and coarse-grained Cu20Sn substrates having various surface treatments: ground, polished, off-normal CS-blasted, and laser-textured using five different patterns. The adhesion was tested by a simple, yet efficient bending method tailored for testing thick CS deposits. It was shown that the CS-blasting provides good adhesion of around 70 MPa, and even better results of approximately 120 MPa were obtained for the two best laser patterns. While the effect of substrate microstructure was not observed, the adhesion strength was partially related to the adhesion area ratio. The detailed three-dimensional fractographic analysis allowed us to describe the failure mechanism of all specimens. For the laser-texturing, this was a combination of interfacial debonding at the original substrate surface, and the deposit cohesive fracture in the recessed areas.