Abstract
The commercially available software package Elastica has been used to calculate the von Mises stresses in steel as well as in titanium nitride (TiN) and nickel coated aluminium subjected to spherical indentation. Uncoated steel of three different yield strengths was used as reference material, and indenters of different radii were utilised. The critical loads for plastic deformation arrived at were then applied to an Al alloy coated with 5 μ m TiN, and any yield was detected. In cases where the TiN coating could not protect the Al alloy from plastic flow, the required thickness of an intermediate nickel layer was calculated. It was found that with sharp indenters, it is possible to obtain the same critical load for onset of plastic deformation for TiN coated aluminium as for uncoated hardened steels. When the radius of the indenter is large, however, this is not possible owing to the limited thickness of the TiN coating. With the introduction of an intermediate load carrying nickel layer between the aluminium base material and the thin TiN coating the critical load for onset of plastic deformation can be increased.
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