Contribution of nanoindentation and tribology to investigation of welds
The quality of welds depends on the materials used and welding parameters. To help optimizing the welding process, it is necessary to perform very local mechanical characterization of the weld. Nanoindentation and tribology are useful tools for analyzing the effects of the welding process on hardness, elastic-plastic properties and wear resistance.
Welding is an important metallurgical process used to
join two or more components together, usually for the
creation of more complex structures that cannot be
molded directly (tubular frames or structures), for
attaching functional parts to a larger component
(hinges, etc.) or for surface protection. The most
commonly welded materials are metals and
thermoplastics. There are many welding processes
with the most widely used being arc and gas welding.
Other methods such as friction stir welding,
electron/laser beam welding or ultrasonic welding exist
and are employed in cases of welding special materials
or in special environments. During welding, two
parts are heated or melted at the joining surfaces and
fused together using a filler material. Crucial process
parameters for arc welding are arc voltage, passing
current, welding speed, weld geometry, shield gas
composition, and electrode feed speed. These
parameters determine the extent of the thermally
affected material around the weld, the so-called “heat
affected zone” (HAZ). The HAZ is a part of material
close to the weld that has been heated during the
welding process below the melting point but high
enough to undergo microstructural changes. These
changes can lead to changes in mechanical properties
such as increased hardness and decreased yield
strength. Due to the microstructural changes the HAZ
is more prone to cracking and corroding and therefore
the HAZ usually acts as the weakest structural point of
the component. Therefore, it is crucial to understand
and minimize the undesired thermal effects of welding.
The typical dimensions of the weld and the HAZ are
hundreds of micrometers up to several millimeters. To
study the local changes due to the welding process, the
methods of instrumented indentation are preferred
because they offer suitable spatial resolution. For
example, the Anton Paar Micro Combi Tester (MCT3)
or Nano Hardness tester (NHT3) can measure
hardness and elastic modulus or local indentation
stress-strain characteristics in different areas of the
weld or HAZ. To study the causes of weld cracking,
measurements of representative stress-strain curves
around the crack tip can be performed. For cases when
the weld is in frictional contact with another component
or the environment, its tribological and wear properties
are also important. The wear and friction properties can
easily by measured by a tribometer which measures
the coefficient of friction and can be used for wear rate
estimation.
Get the document
To receive this document please enter your email below.