Influnce of indenter angle on the mechanical/physical responses of materials during sharp indentation

Abstract

Over the past 2 decades, instrumented indentation techniques (especially, nanoindentation) have been extensively used to measure mechanical behavior of materials at small-scale. Possible application fields of instrumented indentation can be roughly divided into three groups: (1) Measurement of small-scale mechanical properties such as hardness and elastic modulus; (2) investigation of fundamental materials physics (e.g. phase transformation, plastic instability, and dislocation activity) by analyzing the material`s response during indentation; (3) development of new processes for nano-imprinting/patterning and nano-machining/precision by applying indentation equipments. For any type of application, to define appropriate testing conditions (including indenter geometry, loading/unloading rate, and maximum load) is very important since mechanical response of material under indenter is significantly affected by controlling the contact conditions. While there have been many studies on the effect of the indentation peak load (so-called indentation size effect), relatively less efforts have been given for systematically examining the influences of other testing parameters. Nevertheless, some research experimentally proved that the change in indenter geometry and indentation rate can also produce very interesting results. For example, it was reported in recent studies that to use various three-sided pyramidal indenters having different angle might be very helpful not only for estimating some important mechanical properties in addition to hardness and elastic modulus (e.g., flow properties and fracture toughness of brittle materials at very small scale) but for better understanding of materials physics (e.g. phase transformation of semiconducting materials, inhomogeneous plastic flow of amorphous alloys). This is due to the fact that the stresses and strains developed under the geometrically self-similar indenter can vary seriously with indenter sharpness. Here, both classic and recent researches on the influences of indenter sharpness are critically reviewed and discussed in terms of providing information which might be somewhat valuable when determining the most appropriate indentation testing conditions for the purpose of each indentation experiment.