X-RAY ANALYSIS OF SUBSTRUCTURE - PROPERTY INTERRELATIONS IN ELECTRODEPOSITED Cu - COATINGS

G. Lange, P. Klimanek

For a long time it is well known ([1], for instance) that microstructure and mechanical properties of Cu coatings depend strongly on the special deposition conditions (i.e. electrolyte composition and temperature, current density, kind and structural state of the substrate material etc.). But up to now the knowledge of microstructure - property interrelations is, essentially, only qualitative. To get more defined information, the substructures of Cu coatings deposited from various (i.e. acid, cyanitic, and pyrophosphatic) electrolytes were studied by analysis of X - ray diffraction line broadening and related to measurements of the microhardness HV$_{0.01}$ carried out at the cross-section of the coatings. The results may be summarized as follows:

• Microhardness values of electrodeposited Cu coatings can often be significantly higher than those of a bulk material after strong plastic deformation.
• The microstructures of coatings with high microhardness are always characterized by very small grain sizes (d$_{c} < 1\mu m$ [2]) with high dislocation densities (N$_{d} > 10^{11}$ cm$^{-2}$) and numerous microtwins leading to a significant apparent particle-size broadening of the diffraction peaks.
• The hardening effect of the grain boundaries estimated from the Hall-Petch relationship for microcrystalline Cu [3] is much smaller than the observed hardness values. That means, the mechanical properties of the coatings must, obviously, be related preferrently to the dislocation content of the crystallites.
• X-ray analysis based on the Krivoglaz-Wilkens theory of dis location-induced diffraction line broadening [4] leads, independently of the special deposition conditions, to the relationship HV$^{2} - HV^{2}_{O} = K_{Cu} \surd N_{d}$ between the microhardness HV$_{0.01}$ and the mean total dislocation density N$_{d}$, where HV$_{O}$ is the microhardness of completely recrystallized copper and K$_{Cu}$ a constant.