Deposition of copper by cold gas dynamic spraying has attracted much interest in recent years because of the capability to deposit low porosity oxide free coatings. However, it is generally found that as-deposited copper has a significantly greater hardness, and potentially lower ductility, than bulk material. This paper will describe work undertaken to investigate the effect of annealing heat treatments on the structure and mechanical properties of freestanding cold sprayed copper. After de-bonding from substrates these tracks were annealed for one hour at a range of temperatures up to 600 °C. Optical microscopy, scanning electron microscopy and X-ray diffraction were all employed to examine the microstructure. The peak widths in XRD were analysed according to the Hall – Williamson method so that changes in grain size and microstrain (i.e. dislocation content) could be quantified. Mechanical behaviour of the deposits was studied by microhardness measurements and tensile testing. The influences of annealing on mechanical properties are rationalised in terms of microstructure evolution and its effect on strengthening and recrystallization mechanisms in metals. The softening behaviour of cold sprayed Cu is explained considering the low stacking fault energy of Cu and the possibility of dynamic recystallization occurring during spraying.

In the Cold Gas Dynamic Spray (CGDS) process, coatings are deposited by the virtue of the high particle velocity achieved by the use of converging-diverging (de Laval) nozzle along with suitable particle characteristics and process parameters. In this study copper coatings were deposited on aluminium substrates using helium as the accelerating gas. The influence of the CGDS conditions, primarily driving gas temperature and pressure, on the nature of the deposited coatings and the deposition efficiency of the process were investigated. The results indicate that it is possible to deposit copper coatings at a wide range of process conditions, with successful deposition being observed with the driving gas at room temperature and 11 bar pressure (a condition where the nozzle is still choked). However, the nature of the coatings is strongly dependent upon the processing conditions. With room temperature driving gas, an increase in pressure lead to an increase in deposition efficiency, and increase in substrate deformation and an increase in microhardness in the deposit due to higher levels of work hardening. The use of driving gas at temperatures as low as 473 K resulted in recrystallisation in the deposit and a decrease in tendency to debond due to stress relief during recrystallisation. Recrystallisation also manifested itself in reduced hardness. The sensitivity of the recrystallisation conditions to the traverse speed of the jet over the substrate indicated that these processes are initiated by the impingement of the hot gas jet onto the deposit following deposition and not by changes in velocity or temperature of the particles upon impact.

NiCrBSi spray and fuse types of coatings are routinely applied on various jobs where metallurgical bond of the coating to the substrate is desired. These coatings require a subsequent fusing operation at temperature of about 1050°C. In the present study NiCrBSi coatings were formed by the HVOF process and by the conventional spray and fuse route. The coatings were characterized for their microstructure, hardness and porosity. The aim of this study was to see whether HVOF spraying NiCrBSi spray and fuse powder could cause instant fusing of the coating without the need for additional fusing operation. XRD study of the coatings was also carried out to find out the difference between the spray and fused NiCrBSi coatings and the HVOF sprayed coatings. The HVOF spraying of NiCrBSi was carried under different set of parameters to determine the effect of spraying parameters on the properties of coating.

The high velocity combustion wire (HVCW) sprayed coatings have unique structures and properties which are different from the conventional wire / powder HVOF coatings. This paper studies the coatings of 0.8% C Steel formed by the HVCW system. 0.8% C Steel coatings formed by the HVCW system were studied for their wear resistance (pin on desk wear test) and phase composition. Methods like SEM with Wavelength Dispersion Spectroscopy (WDS) attachment were utilized for determining the composition of the coatings. Microhardness and tensile bond strength of the coatings were also ascertained. A set of conventional oxy-acetylene wire flame spray coatings of 0.8% C Steel were also prepared and these coatings were then compared with the HVCW coatings. Possible applications of the HVCW coatings are discussed based upon the properties of the coatings.

This paper assesses the performance of a supersonic flame spraying gun along with the quality of molybdenum coatings produced with it. The hardness of the wire sprayed molybdenum was compared to coatings made using conventional flame spraying methods. The coatings were also evaluated for porosity, bond strength, and phase distribution by X-ray diffraction. The results indicate that the supersonic gun performs better than conventional flame spray equipment when depositing refractory metals such as molybdenum.