Mechanisms - Agilent Technologies Nano Indenter G200 User Manual

Scratch Testing E

Mechanisms

During a scratch experiment, several mechanisms can occur at the same
time. Different materials can undergo different damage mechanisms
depending upon the scratch conditions. The following is a short
description of the main kinds of behavior that various types of materials
exhibit. This list is not exhaustive.
Bulk Metals
When scratching metals, mostly plastic deformation occurs. A small
portion of the deformation can be elastic. It is quite difficult to create
fracture in most soft bulk metals. The most widely published behavior
undergone by metals is certainly the cutting and groove formation.
Hard Metal Films
In the process of scratching, much of the deformation occurring is
plastic even for very hard metals. The largest interest in studying hard
metal films is to study the hardening effect of the film over the bare
substrate and to check the strength of the adhesion between the film and
the substrate. The energy released in the delamination of the film is
often hidden in the energy spent in the plastic deformation of both the
film and the substrate, making the estimation of the adhesion strength
very difficult.
However, the hardness of the film can be achieved, and comparative
results can show which film is the strongest in a series of samples and
resists the most to fracture and delamination under equivalent
conditions.
Polymer Materials
The behavior of polymers depends significantly on the scratch
conditions. The indenter geometry will either generate elastic only,
elastic-plastic, or fracture behavior, which all can be time- and
temperature-dependent (scratch velocity, relaxation).
Polymer Thin Films
Studying thin polymer films is always quite complex because it usually
involves several kinds of behavior in both the film and the substrate, as
well as in and around the interface. One always need to keep in mind
that the behavior observed may be due to the substrate properties, the
film being only partially responsible for the scratch resistance.
Agilent Nano Indenter G200 User's Guide E-19