DETERMINATION OF THIN FILM'S MECHANICAL PROPERTIES

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CHAPTER THREE
MECHANICAL PROPERTIES OF MATERIALS
3.1 Hardness Test
Indentation tests, in many cases referred to as hardness tests, have for a long time
been a standard method for material characterization. The hardness test consists of
loading an indenter made of diamond or any other hard material (e.g., Tungsten
Carbide) and pressing it into the surface of a softer material to be examined. The
further into the material the indenter sinks (for a given load), the softer the material is
and the lower its yield strength. Hardness is not an intrinsic material property
dictated by precise definitions in terms of fundamental units of mass, length and
time. A hardness property value is the result of a defined measurement procedure.
Hardness tests are the most commonly used non-destructive testing procedures in the
metal industry and in research because they provide an easy, inexpensive and reliable
method of evaluating basic properties of developed or new materials. The hardness
test indenter is so small that it scarcely damages the bulk material; therefore, it can
be used for routine batch tests on small samples of materials to ascertain that they are
up to specifications on yield without damaging them. The usual method to achieve a
hardness value is to measure the depth or area of an indentation left by an indenter of
a specific shape, with a specific force applied for a specific time. There are three
principal standard test methods for expressing the relationship between hardness and
the size of the impression, these being Vickers, Rockwell and Brinell (Ziheng Yao,
2005).
3.1.1 Vickers Hardness Test
The Vickers indenter is a square based pyramid with an angle of 136 degrees
between the faces and a ratio of diagonals of 1:1 (as shown in Figure 3.1). The
Vickers hardness number is one of the most widely used measures of hardness in
engineering and science. The Vickers diamond hardness, VDH, is calculated using