Evaluation of the Residual Stress in the Cold Spray Technique Using Smooth Particle Hydrodynamics Modelling and Neutron Diffraction

Cold spray is a material deposition technique in which powdered metals are deposited onto metallic and glass substrates as a means of improving functionality, repair or protection of the underlying substrate. The residual stress that builds up in the material during spraying is closely linked to the coating’s integrity and the bonding mechanism. Neutron diffraction residual stresses measurements were carried out at the OPAL research reactor, ANSTO, using the KOWARI strain scanner to investigate an Al-6061 sample with a fine through-thickness resolution of 0.5 mm. The experimentally determined through thickness stress profiles of the macroscopically thick coatings were used to validate FE calculations made for 100 μm thick coatings using the Smooth Particle Hydrodynamics, SPH, techniques. A pronounced plastic strain gradient was apparent in the tested and modelled samples indicative of the significant residual macro-stresses which develop in the cladding/substrate during the deposition. Around the deposited particle’s periphery (in the jetting region) the temperatures are significant, this lends itself to the presence of grain refinement at the periphery of sprayed particles and the propagation of dynamic recrystallization which is closely coupled with the thermal softening of the particle.