A comparative study of interface characteristics and properties of bronze coatings on steel by plasma arc and cold metal transition deposition

A comparative study of bronze coatings on steel produced by plasma and cold metal transfer wire-arc depositing was carried out. The microstructure, interface characteristics, hardness, and shear bond strength of bronze deposits were investigated. Cold metal transition (CMT) deposition presented lesser penetration cracks and lower dilution than that of plasma arc deposition (PAD). The interfacial bonding of CMT deposits appeared as diffusion bonding characteristics, whereas PAD achieved a good metallurgical bond. Plasma arc deposited specimens showed more severe penetrating cracks and less CMT due to the difference of dilution rate. As heat input increased, microstructure of CMT and PAD deposited layer transformed from α-Cu + spherical or dendritic Fe-rich phase to massive Fe-rich phase + ε-Cu. The volume percentage of α-Cu +γ₁ in CMT deposits was observed higher than that of PAD, and Fe-rich phase in the PAD was significantly higher than that of CMT, leading in a significant increase of microhardness of PAD. Interfacial bonding strength of PAD under high heat input was much higher than that of CMT.