Structural Analysis of Cold-Sprayed Nickel-Based Metallic and Metallic-Ceramic Coatings
- PDF / 1,300,703 Bytes
- 15 Pages / 593.972 x 792 pts Page_size
- 45 Downloads / 195 Views
eli Koivuluoto and Petri Vuoristo (Submitted October 31, 2009; in revised form December 29, 2009) In cold spraying, many factors, e.g., powder characteristics and compositions, spraying parameters, and post-treatments affect coating formation. Cold spraying is the optimal technique to produce highly dense coatings. Furthermore, denseness and impermeability are the criterions for the corrosion resistance of anodically protective coatings. Therefore, this study focuses on denseness improvement of cold-sprayed (CS) metallic coatings. The aim of this study was to characterize structural details of CS Ni, Ni-20Cu, Ni-20Cr, Ni-20Cr + Al2O3, and Ni-20Cr + WC-10Co-4Cr coatings in order to produce dense coatings by optimizing the affecting factors. Denseness of Ni coating was improved with optimized spraying parameters whereas denseness of Ni-20Cr coatings was increased with added hard particles in the powder mixture. In addition, denseness of Ni-20Cu coatings was improved by heat treatments. Denseness of the coatings is evaluated by corrosion tests. In addition, fracture behavior, microstructures, and hardness studies of the coatings are performed.
Keywords
coating structure, cold spraying, denseness, heat treatment of coatings, Ni alloy coatings
1. Introduction Cold spraying is a solid-state process wherein the coating is formed by powder particle impacts with a high kinetic energy and thus, with a high particle velocity (Ref 1, 2). In addition, ceramic particles with a metallic matrix can be sprayed using the cold spray system. At least one component of the sprayed powder needs to be ductile (Ref 3). During impacts, powder particles deform plastically and adhere to the substrate surface or to other particles and form the coating (Ref 4, 5). Formation of bonds between particles requires critical impact velocities of particles in order to obtain adequate bonding and adhesion (Ref 1). Furthermore, successful particle-substrate and particle-particle bonding requires a high level of plastic deformation and adiabatic shear instability. In addition, strong adhesion between particles requires the formation of material jets due to the thermal softening. Higher particle velocity leads stronger bonding and thus, affects the denseness of coatings (Ref 2). Cold spraying is a potential method of spraying dense (very low porosity) coatings for applications where corrosion protection is needed. Denseness and impermeability depend strongly
Heli Koivuluoto and Petri Vuoristo, Department of Materials Science, Tampere University of Technology, Tampere, Finland. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
on spraying process conditions, powder characteristics, and coating material, and moreover, the combination of these affecting factors (Ref 6). Additionally, coating quality relies on spraying conditions, higher velocity leads to stronger plastic deformation and furthermore, coating structure become denser and mechanical properties are improved (Ref 7, 8). The preheating temperature of process gas reporte
Data Loading...
