Bruce J. Pletka

(906) 487-2639

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.