Metri Zughbi

Student: Metri Zughbi

Project: Quantitative Analysis of Crack Propagation in Doped Magnesium Aluminate Spinel

Poster: Horizontal (PDF) | Vertical (PDF)

Institution: Lehigh University

Major: Material Science & Engineering

Advisor: Masashi Watanabe

Abstract

Polycrystalline magnesium aluminate spinel is a transparent ceramic material with high strength. It’s expected uses range from lenses to high-strength, high temperature windows to even transparent armor. However, tradition processing methods utilize LiF as a sintering aid to achieve transparency, but these methods cause grain boundary embrittlement. In this study, Ca and Y are studied as alternative dopants to achieve grain boundary strengthening while maintaining transparency. These elements were selected due to their larger ionic size and relatively low cost.

Doped samples are fabricated using a hot press and following heat-treatment, and then microhardness testing was examined. Since ceramics like spinel undergo brittle fracture, cracks are formed during hardness testing. The crack propagation though grains or grain-boundaries informs the strength of grain boundaries, i.e. grain-boundary embrittlement. We hypothesize that doping elements modify grain-boundary strength significantly as high as that of grains. To study this, we analyzed the ratio of intergranular to transannular fraction along the cracks and comparing it to the hardness of samples. There is a difference in crack patterns with 500 ppm of a given dopant, which implies these dopants improve the grain-boundary strength.