Biomedical Engineering Reference
In-Depth Information
result in permanent bonding of the material and substrate (Klinkov, Kosarev,
and Rein, 2005). Still, many combinations remain unexplored.
To develop a pneumatic gun for the purpose of exploring impacts with the
substrate material, it is practical to have a basic understanding of the bonding
mechanisms that contribute to this phenomenon. Several theories attempt to
find the reasons behind this. Klinkov (2005) suggests four possible
mechanisms to explain the bonding from a particle to a substrate:
Mechanical interlocking: Due to high kinetic energies, a high rate of
plastic strain occurs. This causes both work hardening and thermal
softening.
Repeated Impacts: A particle strikes another particle already
undergoing plastic deformation, creating more suitable conditions for
attachment.
Sticking: Assumes particles initially stick to a substrate due to Van
der Waals or electrostatic forces. Stronger adhesion occurs only after
repeated particle impacts.
Topochemical reactions: Bonding energy of particle is compared to
elastic energy stored in particle. The particle will bond to the substrate
if the bonding energy is greater than the elastic energy.
M. Grujicic (2003) suggests the possibility of atomic diffusion, surface
adhesion, and plastic deformation. Assadi (2003) refers primarily to adiabatic
shear instabilities, similar to the mechanical interlocking described by Klinkov
(2005). Although the mechanisms at work to result in this bonding are not
completely understood at the present time, it has been shown by many sources,
including the ones cited, that impact velocity is the most critical variable in
determining the possibility of materials bonding to substrates.
2.3. Findings on the Methodology
There are numerous existing methods to fire particles at supersonic
speeds. Some of these methods are used with the intention of bonding particles
with for a variety of different applications. Figures 2-6 show devices used for
different types of thermal spray processes, and Figure 7 illustrates a cold spray
device (Hermanek 2002).
