MEASUREMENT METHODS AND CALCULATIONS TO DETERMINE INTERNAL DEPOSIT STRESS IN APPLIED METALLIC COATINGS

摘要

Internal stress exists as an inherent force within electroplated and chemically applied metallic deposits. This induced stress can be tensile or compressive in nature, causing the deposit to contract or expand in relation to the base material. High levels of stress in deposits produce micro-cracking and macro-cracking, and in severe cases produce a lack of deposit adhesion in the form of blistering, peeling, and flaking. In extreme cases, wave-like ripples in electroforms, accelerated corrosion and deposit wear failure can also occur. This paper reviews test methods, procedures and formulas used to determine the internal stress in applied metallic coatings. A comparative study for the determination of internal tensile deposit stress as plated from a semi-bright sulfamate nickel plating electrolyte was completed for the Spiral Contractometer Method and for the Deposit Stress Analyzer Bent Strip Method. Spirals were used in this study to compare the former style conractometer design and the recently designed style with and without a masked surface on the spiral inside diameter. Also, the formulas that are frequently used to calculate deposit stress values in applied metallic layers were evaluated. Limitations of these formulations, accuracy of the results and frequent errors in their use are also reported.