Experimental and Computational Investigations of Deformation Behavior of Icosahedral Boron-Rich Ceramics
Abstract
Among superhard materials, boron-based ceramics (e.g., boron carbide, boron nitride) are popularly used in numerous military (body and vehicular armor), automotive (engine valves), refractory (high temperature crucibles and furnace walls) and civilian (polishing media and wear-resistant parts) applications. While a majority of these applications are fueled by the high melting point, high hardness and strength, moderate fracture toughness, and low mass density of these materials, many icosahedral boron-rich ceramics (e.g., boron carbide and boron suboxide) exhibit a unique deleterious deformation mechanism, often referred to as ÔamorphizationÕ, where crystalline order collapses under high pressure loads (such as ballistic impact). This deformation behavior has been shown to be responsible for reduced ballistic resistance of boron carbide at higher threat levels and is theorized to intrinsically lower hardness well below its theoretical capacity. These ceramics are classified based on their atomic structure where their unit cell consists of a boron-rich icosahedron and few chain atoms. Ceramics such as boron carbide, boron suboxide, and other boron-based ceramics fall into this category. Among these, boron carbide has been extensively investigated in the past two decades due to its relevance to armor applications. In recent years, the attention has shifted to boron suboxide because in addition to its low mass density (2.6 g/cm3), high hardness (>30 GPa), and high compressive strength (>5 GPa), it has been theorized to have nanotwinned microstructure in the ground state. Recent literature has shown that nanotwinned structures in copper exhibited more than nine times the tensile strength compared to its untwinned counterpart, and nanotwinned cubic boron nitride (c-BN) and diamond have exhibited double the hardness compared to their traditional untwinned structures. With this motivation, the current proposal aims to conduct a systematic study to investigate high pressure-induced deformation and propensity for amorphization of untwinned and nanotwinned boron suboxide. A coordinated experimental and computational study will be conducted to understand the Raman spectral signature of the nanotwinned boron suboxide and decipher the mechanism for enhanced properties and its propensity for amorphization. To understand the behavior under impact loads, its deformation behavior under a range of indentation loads (both static and dynamic) and low-velocity spherical impact will be studied using transmission electron microscopy, and experimental and computational spectroscopy. The induced amorphization zone size and shape will be experimentally mapped and the zone size will be estimated using dynamic expanding cavity models. These mechanistic models are expected to capture the ballistic response and target resistance of such ceramics. The proposed investigations are expected to lay a foundation for the development of a comprehensive methodology for analysis of boron-rich icosahedral ceramics under ultrahigh pressure loads. The ultimate goal of this work is to provide a predictive tool for understanding the high-pressure deformation response of boron-rich solids so as to identify promising compositions for further development. The proposed three year research effort will partially support a post-doctoral researcher, a graduate student and an undergraduate student. The PI will make sincere efforts to recruit talented minority students and provide state-of-the-art research experience in experimental and computational methods. In a previously funded ARO grant, the PI supported an African American graduate student and an undergraduate Hispanic student. The proposed fundamental study will actively involve ARL researchers both in experimental and theoretical model development stages. The deformation patterns and the Raman maps under the various stress states will be shared for further input.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 07, 2018
- Source ID
- W911NF1810040
Entities
People
- Ghatu Subhash
Organizations
- Army Contracting Command
- United States Army
- University of Florida