The Influence of Powder Particle Velocity and Microstructure on the Properties of Cold Sprayed Copper Coatings
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L. Venkatesh, Naveen M. Chavan, and G. Sundararajan (Submitted July 7, 2010; in revised form November 22, 2010) No literature exists on the influence of the velocity of Cu powder particles (during cold spraying) on the properties of the coatings like porosity, hardness, electrical conductivity, residual stress, and microstructure. Similarly, though the occurrence of dynamic recrystallization in the Cu powder particle during its deformation under the cold sprayed process has been well documented, its influence on the properties of the coating has not been studied. In this study, it is shown that while porosity of the coating is determined directly by the powder particle velocity, the other properties like hardness, electrical conductivity, and residual stress are determined not only by the particle velocity which depends on stagnation pressure and preheating temperature of the air (process gas) but also additionally on preheating temperature of air per se. The extent of powder particle fragmentation and dynamic recrystallization as a function of particle velocity has been quantified in terms of the grain boundary area fraction and the influence of the latter parameter on the coating properties has also been presented.
Keywords
cold gas dynamic spraying, copper coatings, dynamic recrystallization, electrical conductivity, hardness, particle velocity, residual stress
1. Introduction Cold Sprayed Copper (CSCu) coatings have been extensively investigated by numerous researchers. The influence of cold spray process parameters on the properties of the CSCu coatings like hardness, porosity, bond strength, electrical conductivity have been the subject of numerous studies (Ref 1-8). Similarly, the influence of heat treatment of CSCu coatings on its microstructure, hardness, and electrical conductivity has been well documented (Ref 1-7). The deformation behavior of the individual Cu particles and the bonding mechanisms during the cold spray process has also been well studied (Ref 911). The influence of cold spray process parameters on powder particle velocity has also been investigated (Ref 12-15). In spite of such extensive studies, few aspects of CSCu have not been investigated till date. The influence of Cu particle velocity (measured in situ during the coating process) on deposition efficiency and bonding has been evaluated (Ref 9, 12, 16). The DeLaval nozzle design has
L. Venkatesh, Naveen M. Chavan, and G. Sundararajan, International Advanced Research Centre for Powder Metallurgy & New Materials (ARCI), Hyderabad 500005, India. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
also been optimized on the basis of maximizing the particle velocity for a given input conditions (Ref 17). However, surprisingly, the influence of powder particle velocity (Vp) on the properties of the as-coated CSCu coatings has not been studied except for our earlier study (Ref 6). It is to be noted that the powder particle velocity (Vp) and temperature (Tp) are the fundamental parameters which determine the coating p
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