Coating Failures - The Eggshell Effect

Enlighten Coatings Team
28.06.21 04:43 PM Comment(s)

The ​Costly Mistake of Applying Hard Coatings to an Unhardened Surface

Many engineered surfaces exist for lightweight metals. However, none of them can completely solve the current wear and corrosion (tribo-corrosion) issues facing many applications.

Applying hard coatings onto an unhardened surface of a lightweight metal leads to the potential of cracks and delamination caused by inadequate support of the coating. This inadequate support is caused by the large difference in hardness between the surface and the hard coating [1,2]. This is also known as the "eggshell" effect.

Applying hard coatings onto an unhardened surface of a lightweight metal leads to the potential of cracks and delamination caused by inadequate support of the coating. This inadequate support is caused by the large difference in hardness between the surface and the hard coating [1,2]. This is also known as the "eggshell" effect.


Finite element modeling analysis has shown that in most coating systems, plastic deformation initiates at the interface under high normal loads and plastic deformation does not occur in the coating until a substantial, plastically-deformed region has developed in the substrate, underneath the coating [3].

Surface Engineering

Surface engineering is not about simply selecting existing treatments to alleviate problems from poor material selection or poor material performance. The focus of surface engineering is to design a surface that can provide a cost-effective solution that can produce the desired surface properties [4]. One possibility of solving these obstacles that must be overcome is the use of duplex surface treatments. A properly selected duplex surface treatment will enable the material to withstand high contact loads and resist scuffing and wear. Creating a duplex surface treatment by nitriding titanium and then applying a Diamond-Like Carbon (DLC) coating has shown favorable results [5].

Duplex Treatment

A duplex treatment is necessary to achieve a high load-bearing capacity in lightweight metals . However, in a duplex coating system, a synergy between two processes occurs. Improper synergies could result in degradation of properties rather than an improvement. Proper selection of duplex treatments can provide a simultaneous increase in load-bearing capacity and sliding tolerance .

Enlighten Coatings specializes in design and selection of engineered surfaces to help you get the right coating for your application the first time. If you're experiencing the eggshell effect on your components, contact us to schedule a free consultation.
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Surface Engineering References