Bruce J. Pletka
B.S. (Metallurgical Engineering), Cleveland State
University; M.S. (Ceramics) and Ph.D.
(Ceramics), Case Western Reserve University
Research Interests: Fracture of brittle materials;
high temperature deformation; solidification of
ceramics; plasma spray processing.
Fracture of ceramics at high strain rates
An understanding of the influence of
microstructure on the high strain rate behavior of
ceramic materials is currently not available. High
strain rate experiments are being conducted on
ceramics fabricated in our laboratories so that
control over the microstructural features is
maintained. For example, initial work has
focused on high purity aluminum oxide which was
densified without the aid of sintering additives
while still maintaining a fine grain size of 1-2 xb5m.
Variations in grain size and porosity are achieved
using additional heat treatment. Damage in shock
loaded specimens is evaluated using a variety of
techniques. The information from these
systematic investigations is being used to
develop models which will include the effects of
microstructure as well as the loading conditions
on deformation and fracture behavior.
Plasma deposition
Plasma deposition may be used to apply coatings
for a wide range of applications. However, the
complexity of the process has led to primarily
empirical advances in system design and coating
development. The goal of the work being carried
out in our laboratory is to develop a more
fundamental understanding of processing-
structure-property relationships in plasma
sprayed coatings and splats (the `building blocks'
of coatings). These studies should lead to more
rapid coating development and to the tailoring of
coating characteristics. Systematic variations in
plasma temperature and velocity as well as the
powder particle size are used to assess their
influence on splat and coating structure and
properties.
Solidification of ceramics
We have been studying the solidification of
ceramics as an alternative processing route and
as a means of providing ancillary data for our
plasma spraying program (since we can control
the solidification rate). An example of the former
involves our work on the unidirectional
solidification of ceramic superconductors. The
commercialization of these materials depends on
the ability to achieve high critical current densities
(Jc), but the necessary Jc values have not been
achieved in sintered material. Our approach is to
eliminate as much nonsuperconducting grain
boundary as possible by aligning the grain
boundaries so that applied supercurrents could
run parallel to the boundaries with the eventual
goal of producing single crystals.