Cold gas dynamic spray is increasingly used for dimensional repair in the aerospace sector as it is capable of producing dense, oxide-free deposits of significant thickness and with good levels of adhesion and inherent mechanical strength. There is significant interest in extending the application of cold spray deposits to include structural, load-bearing repairs. However, particularly for high strength aluminium alloys, cold spray deposits can exhibit high levels of porosity and micro-cracks, leading to mechanical properties that are inadequate for most load bearing applications. In this work, heat treatment was investigated as a potential means of improving the properties of a cold sprayed Al alloy C355 deposit. C355 alloy deposits were produced using two process gas temperatures (350°C and 500°C) and three gas pressures (40, 50 and 60 bar) using a commercially available HPCS system. Microstructural analysis of the coatings revealed that the optimal microstructure (ca. 1% porosity) was obtained at 500°C and 60 bar. Therefore, coatings produced with process conditions of 500°C and 60 bar were heat treated at 175, 200, 225, 250°C for 4h in air and the evolution of the microstructure and microhardness was analysed. The results show that heat treatment at 225°C can decrease porosity (<0.2%) and retain high hardness (105 HV0.05 vs 130 HV0.05 as-sprayed). Further investigation was performed on as-sprayed and 225°C heat treated deposits. The results show that this heat treatment can halve residual stress (-50 MPa vs -100 MPa as-sprayed), and improve tensile properties (UTS). Therefore, this work has demonstrated that the heat treatment of C355 cold sprayed deposits at 225°C can significantly improve their properties.

For well over a hundred years, hardness testing has provided engineers a quick measure of the mechanical properties of a material or coating. However, the technique has also been fraught with potential artifacts, many of which are related to a phenomenon known as the “indentation size effect”. Unlike bulk materials, experimental studies on the hardness measurements of cold spray coatings in different load regimes shows strong dependency on the indentation size in a manner different from the Nix–Gao model. In cold spray coating additional parameters such as porosity and cohesive strength between cold sprayed particles affect the hardness measurements. As a result the hardness loss was observed by increasing the indentation load. To interpret the experimental observation, a two dimensional model was developed taking into consideration the inter particle damage. Ductile damage initiation in combination with the linear damage evolution model has been used. The deviation of load-displacement curves in the material with inter particle defects in comparison to bulk material was studied to explain the mechanism involved in hardness loss.

This study evaluates the influence of shot peening on the fatigue life of cold spray aluminum alloy 6082 coatings. A pneumatic blast machine with standard steel shot was used to peen both uncoated and coated substrates. Six test groups representing different treatment protocols were characterized in terms of residual stress, roughness, and rotating bending fatigue. The results show that the best fatigue performance is obtained by intense shot peening prior to cold spraying. Post-treatment shot peening, in contrast, had a detrimental effect as a large portion of the kinetic energy is absorbed in the coating, resulting in surface damage rather than further work hardening.

Surface treatment has become an effective method to improve corrosion resistance of magnesium alloys which are the lightest commercial structural alloys with superior specific strength and stiffness. Low pressure cold spraying is used to locally deposit aluminium on AZ31 in order to enhance general and galvanic corrosion of magnesium. This study is aimed at numerical estimation of the residual stress profile due to cold spray coating using FEM. The impact of particles on the substrate is modelled in Abaqus Explicit. The challenge of AZ31 simulations is the intrinsic yield asymmetry and anisotropy which results different behaviour of the material along different direction both in tension and compression. On the other hand, there is no precise material model capable of considering the yield asymmetry and anisotropy experienced by AZ31 in Abaqus. This paper studies the effect of anisotropy of the AZ31 on residual stress induced by cold spray. The results are compared with experimental X-Ray diffraction measurements. It is suggested that an isotropic analysis in the dominant stress direction of AZ31 may result in good estimation of the residual stress profile.

Titanium and titanium alloy coatings have high potential for applications in several industrial fields such as aerospace, bio-medical and chemical industries. Its eligibility for each single application depends on physical, chemical and mechanical properties. Cold spray as a deposition technique for titanium coating is growing because there is no need for vacuum or protective atmospheres. The properties of cold spray titanium coatings can be tailored by controlling and optimizing the process parameters. In this study the effect of the gas pressure and temperature on the deposition process and the coatings properties were examined. Cold spray CP-titanium coatings were produced using nitrogen as propellant gas at different gas pressures (from 2.0 MPa to 3.5 MPa) and temperatures (from 400°C to 800°C). Morphology and the microstructure of the CP titanium powder and coatings were studied by scanning electron microscope (SEM) and light optical microscope (LOM). Micro-hardness measurements and oxygen and nitrogen contents of titanium powder and the coatings were performed. As a final step, residual stress analysis of deposits were measured by means of X-ray diffraction.

In this work, the influence of the substrate temperature on the deposition efficiency and on the coating properties and residual stress was investigated. Pure Al coatings were deposited on Al 6061 alloy substrates using CGT Kinetics 3000 deposition system. The substrate temperature was ranged between 20°C (room temperature) and 375 °C and was kept nearly constant during the deposition while all the other deposition parameters were unchanged. The deposited coatings were quenched in water (within one minute from the deposition) and then characterized. The residual stress was determined by Almen gage method (Ref 1, 2, 3), Modified Layer Removal Method (Ref 4, 5, 6), and XRD (Ref 7) in order to identify both the mean coating stress and the stress profile through the coating thickness from the surface to the coating- substrate interface. The residual stress results obtained by these three methods were compared and discussed. The coating morphology and porosity were investigated using optical and scanning electron microscopy.

In the present work, pure Al and Al-Al 2 O 3 composite coatings are deposited by cold spraying while measuring in-flight particle velocities. Residual stresses, evaluated using the Almen curvature method, X-day diffraction, and modified layer removal, are correlated with particle velocity, coating thickness, and alumina content. Peening stresses due to plastic deformation were estimated to be less than 100 MPa and are shown to be nearly constant through the thickness of the coatings.