FEATURE Nanomechanical Characterization of Materials by Nanoindentation Series

I nstrumented indentation testing (IIT) is a technique for measuring the mechanical properties of materials. It is a development of traditional hardness tests such as Brinell, Rockwell, Vickers, and Knoop. IIT is similar to traditional hardness testing in that a hard indenter, usually diamond, is pressed into contact with the test material. However, traditional hardness testing yields only one measure of deformation at one applied force, whereas during an IIT test, force and penetration are measured for the entire time that the indenter is in contact with the material. All of the advantages of IIT derive from this continuous measurement of force and displacement. IIT is particularly well suited for testing small volumes of material such as thin films, particles, or other small features. It is most commonly used to measure Young’s modulus (E) and hardness (H).1–2 The Young’s modulus for a material is the relationship between stress and strain when deformation is elastic. If an engineer knows the Young’s modulus for his design material, then he can predict strain for a known stress, and vice versa. In metals, hardness depends directly on the flow stress of the material at the strain caused by the indentation. In other words, hardness is an indirect but simple measure of flow stress; within a class of metals, the metal with the higher hardness will also have the higher flow stress.