Cold spray technique employs the kinetic energy of the feedstock to generate coatings while maintaining the original microstructures of the particles during deposition. Inconel 718 is well-known for its high tensile strength and corrosion resistance at elevated temperatures thanks to a complex alloying chemistry. Cold spraying Inconel 718 often demonstrates porosity and delamination due to limited plastic deformation. Hence, we looked into improving and understanding the deformability of such particles by modifying feedstock microstructures through solution treatment at two temperatures. At 950 degrees C, the gamma(y) phase transforms into a stable delta precipitate, while at 1050 degrees C, a near-complete solution transition is observed through X-ray diffraction (XRD), electron backscatter diffraction (EBSD) mapping, and electron channelling contrast imaging (ECCI). Cold-sprayed, solution-treated Inconel 718 at 950 degrees C exhibits porosity reduction by approximately 60 % compared to the as-sprayed feedstock. ECCI micrographs suggest enhanced particle-substrate bonding and jet formation at the interface. Conversely, depositing Inconel 718 solution-treated at 1050 degrees C decreases coating hardness by around 23 % compared to that at 950 degrees C. Coatings' microstructures denote differences in dislocation accumulation mechanisms, suggesting potential dislocation formation scenarios.

This research aims to enhance the deformability of Inconel 718 by modifying the feedstock microstructures prior to deposition through solution treatment process at 950 °C and 1050 °C. It was observed that the gamma phase has transformed into a stable delta precipitate at 950 °C. Higher treatment temperature at 1050 °C shows a complete solution transition, proven by EBSD phase map, and electron channelling contrast imaging (ECCI).

In this study, laser-assisted cold spray (LACS) of titanium alloy Ti6Al4V onto Ti6Al4V substrates has been investigated in two phases: (i) single-track deposits on substrates preheated to 400 °C, 600 °C, and 800 °C, respectively, and (ii) single-layer (multi-track) deposits on substrates preheated to 600 °C with three different track spacings (1 mm, 2 mm, and 3 mm). Cross-sectional microstructures of the single-track deposits showed intimate contact at the interfaces, especially extensive interfacial mixing for specimens with substrate preheating at 600 °C and 800 °C. Cross-sectional area porosity content in single layer LACS coatings was found to be around 0.4%, which is significantly lower than the standard or conventional cold spray (CS) process having ~2.3% porosity. The microstructure reveals that the LACS process has improved the adhesion and cohesion of the deposits, in addition to the other advantages of the CS process. The average microhardness values of LACS deposits were found to be in the range of 388–403 HV (the highest hardness with the lowest track spacing), which is approximately 6–10% lower than that of the CS deposits without laser substrate preheating. Tensile residual stresses were found in all three LACS coatings, which was due to elevated process gas temperature along with high heat input during laser preheating of the substrate. It was observed that the higher the track spacing, the higher the stress magnitude, i.e., 31 MPa, 135 MPa, and 191 MPa in the longitudinal direction when deposited with 1 mm, 2 mm, and 3 mm track spacings, respectively. Heat treatments induced varied microstructures in LACS coatings, encompassing fully equiaxed or lamellar α-phase within the β-phase, or a bimodal microstructure, with characteristics linked to track spacing variations. Key contributions of this study include enhanced coating-substrate adhesion through extensive interfacial mixing, a substantial reduction in cross-sectional area porosity compared to CS, insights into the effects of residual stresses, and, ultimately, advancing the comprehension of LACS and its potential advantages over conventional CS process.

This study aims at investigating the effect of various post-deposition thermal treatments on improving tensile properties of cold spray (CS) deposited titanium alloy Ti6Al4V. Dogbone-shaped tensile specimens were designed considering two application scenarios: ‘fully CS’ specimens, and ‘CS repair’ specimens. For both specimen types, tests were carried out in four conditions: (i) as-deposited (AD), and after three different thermal treatments, i.e., (ii) solution treatment and ageing (STA), (iii) hot isostatic pressing (HIP), and (iv) HIP followed by STA (HIP + STA). Complementary to tensile testing, characterisation of CS deposited material was also carried out in terms of microstructure and hardness. The STA process resulted in the highest improvement in ultimate tensile strength by more than 200%, reaching 868 MPa for ‘fully CS’ and 951 MPa for ‘CS repair’ specimens. However, no appreciable improvement in elongation at failure was achieved, highest being 1.2% for ‘fully CS’ after STA, and 4.3% for ‘CS repair’ after HIP. In addition to experimental investigation, a comprehensive collection of data from the open literature on the effect of various thermal treatments on improving the tensile properties of CS Ti6Al4V deposits is reported and discussed.

Cold spray (CS) is a rapidly growing solid-state additive material deposition technique often used for repair of high-value metallic components. This study aims at evaluating the interfacial adhesion strength of cold sprayed Ti-6Al-4V (Ti-64) coatings deposited onto Ti-64 substrates for repair applications. An adhesive-free test method, referred as modified Collar-Pin Pull-off Test was developed based on Sharivker's (1967) original design, in order to overcome the limitations of existing test approaches (both adhesive-based and adhesive-free). This method was designed to allow measurement of adhesion strength of high strength coatings such as CS Ti-64, where adhesion strength is higher than 70-90 MPa. A parametric study was performed to assess the effect of coating thickness, scanning speed, track spacing, toolpath pattern, and substrate surface preparation on the coating adhesion strength. A finite element model was also used to evaluate the stress distribution during the pull-off test, and to check the validity of the proposed test method. The proposed adhesive-free test method was found to be capable of measuring coatings with adhesion strengths beyond the upper limit of conventional adhesive-based methods such as ASTM C633. Among the investigated cases, the highest value of coating adhesion strength was measured around 122 MPa, in the case of CS Ti-64 deposited on ground Ti-64 substrates.

The deformation behaviour of particles and substrate in cold spray is dictated by the intrinsic properties of both materials, and their bonding directly affects the resulting properties of the deposited coating. The processing through heat treatment of aluminium alloy powders has only recently been developed for both cold spray and additive manufacturing, hence the necessity to evaluate and further understand the evolution of their properties. In this study, an Al 7075 gas-atomised powder was solution heat treated, quenched and subsequently aged. The powder in its as-quenched, T4 (natural ageing at room temperature for 21 days) and T6 (artificial ageing at 120 C for 24 h) condition was characterised through differential scanning calorimetry and scanning electron microscopy to evaluate the precipitation kinetics. Powders were cold sprayed using heated N-2 at 500 C and 6.0 MPa and the resulting deposits were evaluated using tubular coating tensile and pull-off bond strength tests. The precipitation development in the gas atomised powder was found to be similar to the bulk alloys, with development eta' precipitates during artificial ageing and Guinier-Preston zone formation and development during natural ageing. A relationship between the deposition efficiency of the powders and the coating properties was discovered and explained through an adapted densification mechanism based on powder tamping.

Cold spray (CS) is a solid-state additive material deposition technique, which has gained attention in the aerospace industry as a potentially viable technology for structural repair of high-value parts made of high-strength alloys such as Ti-6Al-4V (Ti-64). Residual stresses build up in the substrate and deposited materials resulting from the CS process can influence the integrity of a coating or repair. However, the nature, magnitude and distribution of residual stresses in Ti-64/Ti-64 CS repairs are currently unknown. This study aims to evaluate the effects of geometrical variables (i.e. the number of CS layers, CS layer thickness, and substrate thickness) and track pattern on the magnitude and distribution of residual stresses in CS deposit-substrate assemblies. Through-thickness stress distributions were measured experimentally by neutron diffraction and contour method. Furthermore, a comparison among different residual stress build-up mechanisms induced by CS processes has been discussed for different combinations of substrate and deposit assemblies. An analytical model based on the force and moment equilibrium requirements was used to interpret the experimental stress profiles and to predict the residual stress distribution. It was found that residual stresses are highly tensile near the free surface of the Ti-64 deposits as well as towards the bottom of the substrate, and compressive near the interface region. Although all the specimens showed similar stress distribution, the magnitudes were found to be higher in one or more of the following cases: specimens with a higher number of CS layers, lower substrate thickness, higher layer thickness (i.e. at lower scanning speed), and deposited with a horizontal track pattern.

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This study forms an initial investigation into the development of SprayStir, an innovative processing technique for generating erosion resistant surface layers on a chosen substrate material. Tungsten carbide - cobalt chromium, chromium carbide - nickel chromium and aluminium oxide coatings were successfully cold spray deposited on AA5083 grade aluminium. In order to improve the deposition efficiency of the cold spray process, coatings were co-deposited with powdered AA5083 using a twin powder feed system that resulted in thick (>300 mu m) composite coatings. The deposited coatings were subsequently friction stir processed to embed the particles in the substrate in order to generate a metal matrix composite (MMC) surface layer. The primary aim of this investigation was to examine the erosion performance of the SprayStirred surfaces and demonstrate the benefits of this novel process as a surface engineering technique. Volumetric analysis of the SprayStirred surfaces highlighted a drop of approx. 40% in the level of material loss when compared with the cold spray deposited coating prior to friction stir processing. Micro-hardness testing revealed that in the case of WC-CoCr reinforced coating, the hardness of the SprayStirred material exhibits an increase of approx. 540% over the unaltered substrate and 120% over the as-deposited composite coating. Microstructural examination demonstrated that the increase in the hardness of the MMC aligns with the improved dispersion of reinforcing particles throughout the aluminium matrix. (C) 2016 Elsevier B.V. All rights reserved.

This work reports on the erosion performance of three particle reinforced metal matrix composite coatings, co-deposited with an aluminium binder via cold-gas dynamic spraying. The deposition of ceramic particles is difficult to achieve with typical cold spray techniques due to the absence of particle deformation. This issue has been overcome in the present study by simultaneously spraying the reinforcing particles with a ductile metallic binder which has led to an increased level of ceramic/cermet particles deposited on the substrate with thick (>400 mu m) coatings produced. The aim of this investigation was to evaluate the erosion performance of the co-deposited coatings within a slurry environment. The study also incorporated standard metallographic characterisation techniques to evaluate the distribution of reinforcing particles within the aluminium matrix. All coatings exhibited poorer erosion performance than the uncoated material, both in terms of volume loss and mass loss. The Al2O3 reinforced coating sustained the greatest amount of damage following exposure to the slurry and recorded the greatest volume loss (approx. 2.8 mm(3)) out of all of the examined coatings. Despite the poor erosion performance, the WC-CoCr reinforced coating demonstrated a considerable hardness increase over the as-received AA5083 (approx. 400%) and also exhibited the smallest free space length between adjacent particles. The findings of this study reveal that the removal of the AA5083 matrix by the impinging silicon carbide particles acts as the primary wear mechanism leading to the degradation of the coating. Analysis of the wear scar has demonstrated that the damage to the soft matrix alloy takes the form of ploughing and scoring which subsequently exposes carbide/oxide particles to the impinging slurry. (C) 2016 Elsevier B.V. All rights reserved.