In this talk, we will examine methods to measure and understand both plastic and elastic deformations in an every growing family of ultra-hard materials based on transition metal borides. We will specifically focus on the use of non-hydrostatic high pressure X-ray diffraction methods to directly probe both elastic lattice deformations and the onset of plastic deformation in a wide range of materials in a lattice specific manner. Ultra-hard transition metal borides are exciting because, unlike diamond, they can be synthesized at atmospheric pressure. The materials were initially constructed using three very simple design rules: 1) use late transition metals to create high electron density so that the materials are incompressible; 2) add boron to build strong covalent bond to prevent slip and generate hard materials; 3) use solid-solution effects to further tune materials properties. While these ideas is incredibly simple, they have also proven to be very effective. In this talk, we will thus use a combination of materials synthesis, indentation measurements, and pressure dependent studies to gain an understanding of how the hardness in this family of materials can be tuned based on chemical composition and bonding motifs. To gain a global understanding of the family of materials we will move from metal (M) rich MB phases, to more conventional MB2 and MB4 type materials, and finally to very high boron content MB12 type materials. In all cases, the goal will be to correlate structure and bonding with hardness. Finally, we will end with some new studies on nanoscale versions of these materials, where nanoscale architecture is combined with bonding constraints to further improve hardness.

Exploring plastic and elastic deformations in ultra-hard transition metal borides using high pressure diffraction

256th National Meeting (2018)

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