07-07-2012, 12:30 PM
Methods of wear testing for advanced surface coatings and bulk
materials
methods of wear testing for advanced surface coatings and bulk materials.pdf (Size: 281.55 KB / Downloads: 338)
Introduction
Wear occurs to the hardest of materials, including
diamond, wear studies having focused on surface damage
in terms of material-removal mechanisms, including
transfer film, plastic deformation, brittle fracture and
tribochemistry [1]. With the development of surface
engineering design, the need to evaluate the properties
of new raw materials and substrate-coating combinations
is important. In many research works to date, the
authors have investigated the effects of contact abrasion,
erosion and impact effects on uncoated components,
mainly as separate problems [2]. More recently,
experiments and testing on coated materials have occurred
and some standardised, and experimental test
equipment has been produced to meet specifications on
wear resistance. Standard test methods such as pin-ondisc
are used extensively to simulate rubbing action in
which plastic yielding occurs at the tip of individual
asperities. This testing is mainly carried out on a microscopic
scale and in thin films technology [3].
Wear test criteria
In selecting a suitable wear test, the following points
should be considered: (i) ensure that the test selected is
measuring the desired properties of a material; (ii)
whether the material is in bulk form or is a thick or
thin coating; (iii) whether the forces and stress limited
are suitable for the test; (iv) whether abrasives be
present, considering the abrasive size, form and velocity;
(v) whether the contact between the components is
rolling, sliding, impact or erosion only, or a combination
of these, bearing in mind that the surface finish of
the test samples should be similar to that of the actual
components;
Wear test methods
Tests are used for quality control functions such as
thickness, porosity, adhesion, strength, hardness, ductility,
chemical composition, stress and wear resistance.
Non-destructive tests include visual, penetrant dies,
magnetic particle and acoustic techniques. Many tests
for coated and uncoated cutting tools are conducted on
machine tools, including lathes, mills, drills, punches
and saws [13,14].
Experimental analysis
As most engineering components experience complicated
wear conditions in practice, a means of testing
combined-wear effects seems a logical and necessary
process at this time. A test rig was designed and
developed by the author to examine coated samples
under dynamic wear tests of combined impact abrasion.
The impact actions combines shock loading, fatigue,
gouging and spalling, whilst the sliding action combines
abrasion, adhesion, and fretting wear. Unlike most test
equipment described in the literature, this rig uses a
reciprocating stylus, the velocity of which is changing
continually over the test surface.
Conclusions
If wear tests are carried out with a high degree of
simulation of the service situation, then the results can
be used with considerable confidence in selecting the
best wear-resistant coating system. Every wear test,
whether for bulk material or coatings, can be complicated
by equipment problems, test procedures, sample
preparation, inconsistency in abrasive materials and the
wrong interpretation, of the test information.