Coating Bonding and Its Influencing Factors-Characteristics of Coating Bonding

       3 Combination of coating and its influencing factors

 

3.1 Characteristics of coating combination



    The bonding of the coating depends mainly on the thermodynamics of the crystal structure of the base metal and the electrocrystallization kinetics of the coating. Under thermodynamic equilibrium conditions, metal atoms can solidify into metal crystals with the lowest energy state. This lowest energy state is the state in which the average metal bond force between the lattice lattice groups is the largest, that is, the state in which the metal cohesion is the largest. But the actual metal materials are obtained in a non-ideal equilibrium state and are always in a lower energy state under certain kinetic preparation conditions. Electroplating is a dynamic process that deviates far from the thermal equilibrium state, and the growth of the coating can only tend to the lowest possible energy state, so that the coating can obtain the bonding force suitable for the surface layer of the base metal and the cohesion of the coating. This bonding force mainly depends on the bonding mode between the lattice atoms on the bonding surface and the influence of the electroplating process.

 

    The main characteristics of the plated metal bond are as follows.

 

    1) The bonding thin layer of the coating is a tight bonding layer that is lattice-matched or epitaxially grown with the substrate. In crystallography, it belongs to the form of intercrystalline, intracrystalline or their mixed combination.

 

    2) The physical and chemical nature of the binding force is the metal bond force between the lattice groups at the binding interface. Therefore, the ideal bonding strength is high, which is of the same order of magnitude as the cohesive strength of metals.

 

    3) Most of the metal substrates to be plated are polycrystalline, and most of the metal coatings obtained are of fine crystal structure. Therefore, the macroscopic bonding strength of metal bonding is generally the comprehensive performance of intragranular and intergranular bonding.

 

    4) Defects formed by electroplating and internal stress environment inevitably exist at the metal bonding interface. Therefore, the actual bonding strength of the coating is not easy to achieve the same ideal bonding strength as the cohesive force, which is generally lower than the bonding strength of the metallurgical coating.