Boron carbide (nominally B4C) is an important technological material because of its high hardness and low density. These properties make it a material of potential interest for wear resistant coatings as well as security, safety and ballistic applications (i.e. personnel and vehicular armor). Surprisingly, given these properties, it has been found that boron carbide is not particularly good at withstanding high velocity impacts. The aim of the proposed research is to initially thoroughly understand the structure of B4C and then modify it by adding a small amount of silicon in order to enhance its performance at high velocity impacts. The basis of the proposed comes from the fact that we have preliminary results based on calculations that the weak link in B4C can be eliminated by adding 1 - 5% silicon. The successful outcome of this project should lead to the realization of a material that has hardness values only second to those of diamond. Such a material will be useful in wide ranging applications but especially as an armor material against high velocity threats. The project will involve collaboration with several industrial partners who are ceramic armor providers. In addition, the project will involve training of undergraduate female or minority students. We also intend to invite an elementary or high school teacher over the summer in order to translate our research activity from the laboratory to the classroom.
TECHNICAL DETAILS: Ab-initio calculations have shown that B4C is unique in that numerous polytypes can co-exist simultaneously due to similar lattice parameters and stability energies. One of these polytypes [B12(CCC)], however, has a very low impact resistance, failing at much lower pressure (~ 7 GPa) compared to other polytypes (40 GPa). Thus, the B12(CCC) polytype is the weak link in B4C which leads to its premature failure at high impact velocities. Calculations have recently revealed that it is possible to eliminate the B12(CCC) polytype from B4C by addition of 1 - 5% Si. The incorporation is possible, without separation in to SiC and B4C, through far-for-equilibrium processing using sputtering or plasma melting. It is anticipate that such a fundamental investigation of Si containing boron carbide will provide insights into how to improve its mechanical properties in order to minimize damage from high-pressure impacts. The project also provides training in latest materials processing and characterization techniques to graduate students.
