Characterization of the Local Mechanical Properties of Interfaces in Heteregeneous Materials

The notion of “interface” is a universal topic of research in material sciences. Interfaces are responsible for many of the magnetic, electrical, optical and mechanical properties of materials and therefore need to be characterize. The focus of this work is to bring a new understanding of the interfacial mechanical properties of materials by characterizing two industrial components which properties are governed by their interfaces. First, we address the notion of coating and adhesion by characterizing the hardness and microstructure of a 17-4PH steel substrate subjected to a grit blasting surface treatment followed by the deposition of a cermet coating by high velocity oxy-fuel (HVOF). The hardness was characterized using nanoindentation and the microstructure was imaged by optical and electron microscopy. The results showed a strong impact of the surface treatment on the interfacial microstructure and hardness of the substrate revealing a potential weakening of the interfacial adhesion because of it. Then, in light of the results gathered, a similar method was applied to the characterization of an aluminum foam. However, the aluminum foam is a much more complex material and requires a multiscale approach. The structure and microstructures were characterized by several techniques to account for the multiscale nature of the material. Similarly, the mechanical properties were determined by diverse procedures. The results unveil a particularly inhomogeneous material at all scales resulting in non-uniform mechanical properties. The strong interdependence of the macroscopic and microscopic properties is highlighted and gives a better understanding of the mechanical behavior of the foam.