In cold spraying, several theories have been presented to explain the bonding between the substrate and coatings. In this work, finite element simulations were performed to obtain the minimal bonding strength to overcome rebounding at different initial velocities. The correlation with critical deposition velocity is also discussed.

Aluminum-titanium powder mixtures were deposited on γ-TiAl alloy substrates by cold spraying then heat treated for 5 h at 600, 650, and 700 °C. SEM and XRD examination showed that the treatment caused Al to diffuse into the substrate where it reacted with Ti, resulting in changes in microstructure. The diffusion of Al left pores in the fringes of the TiAl 3 phase, increasing the porosity of the coatings. A surplus of Al remained in the coatings after heat treatment at 600-650 °C, but at 700 °C, all Al was consumed, contributing to the formation of a continuous TiAl 3 layer.

This study investigates the microstructure, thermal conductivity, hardness, and strength of Cu-Cr-Zr coatings produced by cold gas spraying. The elements in the powders were found to have a significant influence on microstructure, particle morphology, and strengthening mechanisms. The strengthening mechanisms of copper alloy coatings include fine crystal reinforcing, solution strengthening, work hardening, and dispersal reinforcing. Different mechanisms are shown to be more or less effective depending on powder composition and the presence of impurities. By filtering impurities before gas atomization, the thermal conductivity of as-sprayed Cu-Cr-Zr coatings can be improved by a factor of two.

TiAl 3 -Al composite coating on γ-TiAl alloy was prepared by cold spray and subsequent heat-treatment. The Oxidation test, which was carried out at 950 °C in air, indicated that the bare alloy exhibited poor oxidation resistance, significant weight loss was observed after oxidation for 70 h. The oxides formed were the mixture of TiO 2 /Al 2 O 3 . For the specimen with the TiAl 3 –Al coating, great improvement in oxidation resistance was observed. Approximate parabolic oxidation kinetics was observed for the oxidation period. The microstructure analysis showed a dense TiAl 2 interlayer and a reticular Cr rich phase formed between the composite coating and the substrate. The oxides in the oxidized coating were mainly alumina, with only trace of titanium dioxide and titanium nitrides after oxidation up to 1000 h. A certain amount of TiAl 3 phase in the coating remained unoxidized and unconsumed. The EPMA analyses of the coated samples showed that no trend of oxygen or nitride diffusion into the substrate and no oxide formed beneath the TiAl 2 interlayer.

A composite coating using mixed powders of pure Al and α-Al 2 O 3 as feedstock was deposited on AZ91D alloy substrate by cold spraying. The content of α-Al 2 O 3 in mixed powders was 50wt%. Electrochemical experiments were carried out using 3.5wt.% NaCl solution as electrolyte. Because of dense structure, the composite coating could separate substrate from electrolyte thoroughly for long time immersion. The corrosion behavior of the composite coating was evaluated by using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements. It is found that the composite coating presented much better corrosion resistance than bare AZ91D alloy, even than bulk 1050 aluminum by electrochemical studies in 3.5wt.% NaCl solution.

Cold gas dynamic spraying is a promising technology and successfully applied to a wide range of materials. In this paper, orthogonal experimental method was introduced to seek out the optimal parameters for cold spraying copper coating. According to the results, standoff distance influenced the coating’s quality the most significantly as well as the carrier gas temperature had a remarkable impact either, but the carrier gas pressure and controlling voltage which influenced feeding speed subsequently had little influence on the coating’s quality. The coating’s porosity, bonding strength, microhardness and the coating’s conductivity were determined respectively. More over, optical and scanning electron microscopies were introduced to study the coating’s surface morphology and its internal structure. Also the effect of subsequent heat treatment on coating’s microhardness was investigated.