Hardness is a critical mechanical property required for a range of materials’ applications. Hardness is defined as the resistance to plastic deformation, and is mostly commonly measured through indentation. Even though these indentation measurements are very common, they probe the bulk properties of a material leading to knowledge of the average, polycrystalline response. However, most materials have an anisotropic crystal structure and mechanical properties, adding complexity to our current understanding of hardness. Here, we study the anisotropic hardness of NiP2 using indentation measurements which are supported by electronic structure calculations. Large (≈1 mm) single crystals of NiP2 were grown via tin flux and characterized through single crystal X-ray diffraction and electron microscopy. Nanoindentations were then made normal to various crystallographic planes to examine the mechanical anisotropy of NiP2 in relation to specific chemical bonds. To better understand our experimental data, first principle density functional theory methods are employed to obtain orientation-dependent stress-strain curves, which are known to correlate with hardness. Furthermore, the chemical bonding was interpreted based on the crystal orbital Hamilton population (COHP) curves and the electron localization function (ELF). Combining the theoretical and experimental data provides insight into the link between NiP2 crystal structure and its mechanical behavior.

Experimental and computational studies of anisotropic hardness in NiP2

255th National Meeting (2018)

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