Influence of Nickel Powders on Corrosion Resistance of Cold Sprayed Coatings on Al7075 Substrate

Mieczyslaw Scendo,Wojciech Zorawski,Anna Goral

doi:10.3390/met9080890

Abstract

The influence of the size and structure of nickel powder grains on the corrosion resistance of nickel coatings on an Al7075 substrate in an acidic chloride solution was investigated. The Ni coating was produced by the cold spraying (CS) method. The surface and microstructure of specimens were observed by a scanning electron microscope (SEM). The corrosion test of the materials was carried out by using the electrochemical method. It has been found that the size of Ni powders has a significant effect on the corrosion resistance of nickel coatings. The porosity of nickel coatings on the Al7075 alloy increases with the increasing size of nickel powders. The corrosion rate of nickel coatings in the chloride environment decreases as the diameter of the nickel powders decreases. On the other hand, the highest corrosion resistance of nickel coatings was obtained using the Ni powders of the irregular spherical or dendritic structure. Moreover, the large particles of nickel powder cause strong residual stress (compared to small grains) in the depth of the nickel coatings.

Highlights

Cold spraying (CS), an emerging coating technique, has been developed to deposit high-quality metallic coatings
The inter-granular interspace is clear between the branches of the dendrites on the cross-section of the powder, which means that its porosity is considerable (Figure 2b)
Nickel coatings adhere well on the Al7075 alloy, and the most smooth surface structure was obtained for Ni powders of irregular spherical and dendritic morphology

Summary

Introduction

Cold spraying (CS), an emerging coating technique, has been developed to deposit high-quality metallic coatings In this process, high-pressure gas is introduced into a de-Laval type nozzle and produces a high-speed gas flow, and spray particles are fed axially into the gas flow and accelerated to a high velocity ranging between 300 and 1200 m s−1. High-pressure gas is introduced into a de-Laval type nozzle and produces a high-speed gas flow, and spray particles are fed axially into the gas flow and accelerated to a high velocity ranging between 300 and 1200 m s−1 They are deposited through an intensive plastic deformation upon impact on a substrate in a solid-state at a temperature well below the melting point of the spray material, i.e.,

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Conclusion