Cold gas dynamic spray has significant potential for load-bearing repairs of high-value metallic components, as it is capable of producing pore and oxide-free deposits of significant thickness and with good levels of adhesion and mechanical strength. However, recently published research has shown that the rapid solidification experienced by gas atomised powders during manufacture can lead to a non-equilibrium powder microstructure, including clusters of dislocations as well as significant localised segregation of alloying elements within each particle. This paper reports on an investigation into the solution heat treatment of a precipitation hardenable aluminium alloy powder. The objective was to create a consistent and homogeneous powder phase composition and microstructure before cold spraying, with the expectation that this would also result in a more favorable heat treatment response of the cold spray deposits. Aluminium alloy 7075 gas atomized powders were solution heat treated at 450 °C for 5 hours in a sealed glass vial under vacuum and quenched in water. The powder particle microstructures were investigated using scanning electron microscopy with electron back scatter diffraction (SEM/BSE) and optical microscopy. The dendritic microstructure and solute segregation in the gas atomized powders was altered, with the heat-treated powder particles exhibiting a homogeneous distribution of solute atoms. The influence on the mechanical properties of the powder particles was studied using micro-indentation. The heat-treated powders exhibited a hardness decrease of nearly 25% compared to the as-received powders. This paper relates the behavior and the deformation of both as-received and heat-treated powders during spraying (single particle impacts), comparing the measured hardness with the deformation effect and the material jetting occurring upon impact.

Despite much research effort and many application development studies, corrosion resistant alloy (CRA) coatings, prepared by thermal spraying still provide greatly inferior corrosion resistance when compared to parent material of the same composition, due to a network of oxides and pores in the coatings. However, the recent development of Cold Gas Dynamic Spray (CGDS) technology has made possible the deposition of low porosity and oxide-free CRA coatings. This paper describes the corrosion performance of Ni-based Alloy 625 following cold spraying onto steel substrates both as-sprayed and following heat treatment. Microstructures and oxygen content of powders and coatings were investigated, and coating microhardness and strength were determined in both as-sprayed and post treated conditions. Mercury intrusion was used to measure the interconnected porosity in the as-deposited and post-treated coatings. Finally, the corrosion behaviour of the sprayed and post-treated coatings was measured using a standard test (ASTM B117-07a).

An iron aluminide (Fe 3 Al) intermetallic coating was deposited onto F22 (2.25Cr-1Mo) steel substrate using a JP-5000 high velocity oxy-fuel (HVOF) thermal spray system. The as-sprayed coating was characterized by electron microscopy, X-ray diffraction, oxidation, and adhesion. Fe 3 Al coated steel specimens were exposed to a mixed oxidizing/sulfidizing environment of N 2 -10%CO-5%CO 2 -2%H 2 O-0.12%H 2 S (by volume) at 500, 600, 700, and 800°C for approximately seven days. All specimens gained mass after exposure, inversely proportional to temperature increases. Representative cross-sectioned specimens from each temperature underwent scanning electron microscopy (SEM) and X-ray mapping examination. Results are presented in terms of corrosion weight gain and product formation. The research evaluated the effectiveness of an HVOF-sprayed Fe 3 Al coating in protecting a steel substrate exposed to a fossil energy environment.

Coatings have been prepared using the Diamond Jet hybrid and JP5000 high velocity oxyfuel (HVOF) systems with the objectives of improving corrosion resistance and reducing costs through increasing deposition efficiency. Models relating deposition efficiency, coating oxygen content and corrosion resistance to process parameters including fuel flow rate, oxygen flow rate and stand-off distance have been developed. A corrosion test cell has been designed and a procedure determined for studying the corrosion behaviour of large numbers of thermally sprayed coatings in an efficient manner. A significant improvement to the corrosion resistance of HVOF sprayed coatings has been achieved by spraying parameter optimisation and investigation of powder size and distribution. The project has also investigated the influence of spray angle on coating performance with a view to future onsite application. Coating materials tested and compared include nickel alloys Hastelloy C276 and 59, cobalt alloy Ultimet, duplex stainless steel S32750 and an experimental iron-based spray-fuse composition.