Characterization of fracture toughness in amorphous diamond like carbon thin films and coatings

摘要

Any material when under application is subjected to constant loading will fail eventually, sometimes this failure can be slow and sometimes it can be instant. It is very important to know that how long a material can withstand loading without failing after the crack has initiated in the material. This ability of a material to withstand loading after a induced crack is known as fracture toughness. It is observed that ductile materials show highest fracture toughness where as brittle materials fails instantly once the crack has initiated.;Characterization of fracture toughness in ductile materials is very easy but it is difficult when dealing with brittle materials and brittle thin films. As the coating thickness of materials decreases and becomes thinner then ∼1 microm it becomes increasingly difficult to evaluate the fracture toughness using conventional methods, since it is not possible to machine this thin films when attached to substrate material.;Micro and Nano-Indentation technique is proposed for such cases where conventional tension test and impact test fails to evaluate the fracture toughness. Indentation techniques are very well developed for hardness measurement in all types of materials. In this paper we will be focusing towards characterizing of fracture toughness in brittle Single Crystal Silicone and Diamond like carbon films coated on Silicone substrate. Such DLC thin films are designed to enhance thermal, oxidation, corrosion and mechanical resistance of substrate materials, however sometimes service lifetime of such coatings in application are limited by their fracture resistance or fracture toughness of coating material. Indentation is a easy, inexpensive, and non-destructive method for mechanical characterization for small volume of material made using three sided and four sided diamond tip like Vickers and Cube-Corner, where we analyze the radial cracks found around indentation to characterize the fracture toughness.;Presence of DLC coating reduces the radial crack length compared to crack length observed in uncoated Silicone. Different Indentation models are used for characterization of fracture toughness suitable for DLC thin films and Silicon wafer is carried out using those radial crack. Most Challenging part of this research was to understand the effect of substrate on thin film and a way to evaluate the fracture toughness of thin film without influence of substrate.