Simone Vezzù

Effect of Cold Spray Deposition of Similar Material on Fatigue Behavior of Al 6082 Alloy

In this study the effect of cold spray deposition of similar material on the Al 6082 alloy substrate is investigated. High deposition pressure which enhances coating cohesion and peening effect was used for cold spraying. Micro-structural observation, micro-hardness measurements and X-Ray diffraction (XRD) measurement of residual stress were performed on the sprayed material. Rotating bending fatigue limit of the cold sprayed specimen was experimentally determined and compared with the as-received specimens. The results showed that the cold spray process developed significant compressive residual stress in both deposited material and the substrate. Cold spray Coating is able to increase the fatigue limit by 14.7 %. No significant delamination between coating and substrate was found by scanning electron microscopy observation of the fractured surface. The result of this paper confirms that the cold spray coatings can successfully contribute to carrying applied loads. This affirms the possible application of the cold spray process of the similar materials for repairing the damage parts.

Characterisation of Cold Spray Titanium Coatings

Cold spray is a solid state spray deposition process utilizing a supersonic De Laval nozzle to accelerate fine particles to high velocities. Particles plastically deform on impact to the substrate and to each other to create dense well adhered structures. In this study, the microstructure and mechanical properties of cold spray Titanium coatings deposited using nitrogen gas at different gas temperature and pressure were examined. In general, it was found that gas-atomised CP-titanium powder is capable of producing dense coating structures on aluminium alloy (Al6061) substrates. The micro-hardness, oxygen and nitrogen content of the coatings were found to be slightly higher than powder in the as-received condition. It was also found the coating residual stress was purely compressive when cold spray is conducted at high gas pressure and temperature.

Effect of Shot Peening on Residual Stresses and Surface Work-Hardening in Cold Sprayed Coatings

Coating deposition processes such as cold spraying are commonly employed to increase wear and fatigue resistance and consequently to enhance longevity of engineering components. Such processes typically introduce residual stresses into the coated surface, which in turn affect efficiency of coatings and play an important role in coating durability. Present study describes alteration of residual stress state and surface work-hardening of two types of aluminum coatings that are cold sprayed onto aluminum substrate, and subsequently treated by air blast shot peening (ABSP). Residual stress measurements have been made by means of X-ray diffractometer (XRD) on coated samples both before and after shot peening process. The results indicate that that the effect of shot peening is more marked in terms of surface work-hardening than of residual stresses and allow some consideration to correctly orient the choice of peening parameters in practical application.