Text

theses

ETD doctoral

Boron carbide is a ceramic material known for its high hardness and low density. These properties make it an ideal material to be used in armor materials. However, when subjected to shock-loading experiments, boron carbide does not perform as expected. Rather than undergo a work-hardening mechanism past a critical shock-loading point, as is the case in similar ceramic materials like silicon carbide, boron carbide suddenly fails. This abrupt failure under dynamic loading has been attributed to “amorphization,” the appearance of nanometer-sized amorphous bands that limit the boron carbides ballistic performance.

Much work has been done to understand amorphization and elucidate its atomistic mechanism. These attempts to identify the peak point in boron carbide lead to several suggestions to fix boron carbides amorphous behavior as a means to improve its ballistic performance. One such alternative theorized doping the boron carbide structure with boron and silicon. Much work has been done already in understanding silicon-doped boron carbide mitigating amorphization, but little has been done in understanding boron-rich boron carbides effect on amorphous behavior. While several studies have been carried out to process boron-rich boron carbides and study their mechanical properties, no work has been experimentally carried out in understanding amorphization in these materials.

In this dissertation, boron-rich boron carbides are studied with respect to amorphization, something previously overlooked in the literature. This work is done with the intention of supporting and validating models that suggest boron-rich boron carbides can mitigate amorphization. Methods will be developed to accurately assess and quantify the degree of amorphization in boron carbides that span the materials homogeneity range. Indentation was used as a means to activate stress-induced amorphization in samples. Raman spectroscopy will be heavily utilized in this work as a means to quickly probe samples for amorphization in a non-destructive manner.

Additionally, the use of Raman spectroscopy allows for various in situ measurements to be carried out at elevated temperatures and large pressures. These factors are critical in simulating ballistic impact parameters in the laboratory and studying these in situ can help determine the evolution of the amorphous phase as these parameters are varied.

Amorphization mitigation in boron-rich boron carbides was determined through Raman spectroscopy quantification methods developed in this thesis and were also validated through TEM imaging. Further, in situ experiments were carried out at large pressures that determined critical onset pressure conditions to induce amorphization in doped samples. This allowed for comparison between amorphization mechanisms between samples of differing compositions.

ETD_11120

Ph.D.

Includes bibliographical references

doi:10.7282/t3-qb1g-em73

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