Weakening effect of plastic yielding inception in thin hard coating systems

Hard coatings have been widely applied to enhance tribological performance of mechanical components. However,it was predicted that thin hard coatings may have a weakening effect which could reduce the coating/substrate system's resistance to plastic yielding compared with the uncoated substrate material. In this paper, analytical simulation is utilized to investigate the origin of weakening effect. The functions of material mechanical properties and coating thickness on the weakening effect are theoretically investigated. Partial-unloading spherical nanoindentation tests are performed on tungsten coated single crystalline silicon and copper to acquire the stress-strain curves and compared with the uncoated cases. The experimental results are in consistence with the analytical solutions, demonstrating the presence of weakening effect.