Nanoindentation evaluation of brittle films on metals

The present study addresses two cases of brittle ceramic films on metals. With the assistance of AE as a supplementary technique, yield initiation phenomena have been evaluated for W single crystal surfaces under several nm thick native oxide film. An AE sensor coupled to an indenter tip allowed an increasing sensitivity to localized fracture and plasticity events in the vicinity of an indentation contact. A good correlation between AE signals and indentation induced plasticity and fracture has been accomplished for contacts below 100 μN. Second, mechanical behavior of porous nanocrystalline SiC films on Mo substrates was examined. An analysis was based on the P-δ² approach. With this method, both loading and unloading parts of indentation curves obtained with sharp pyramidal indenters may be represented as P=Kδ² where P, and δ denote indentation load and displacement respectively. The parameter K includes a material's hardness/modulus ratio and indenter geometry.