Polycrystals with grains that are 10 nm indiameter are called Nano crystalline

Polycrystals with grains that are 10 nm indiameter

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Polycrystals with grains that are <10 nm in diameter are called Nano-crystalline . Most engineering materials are polycrystalline . Properties may or may not vary with direction . Example Common steel is polycrystalline. If grains are textured (due to rolling)”, then anisotropic If grains are random , then isotropic (E 210 GPa) Polycrystalline Solid The atoms or molecules are arranged in an irregular manner. No periodic packing. No directional properties - Isotropic substances. Occurs for complex structures, rapid cooling. Example : Glass, Plastic, rubber, etc. Silica Amophous Solid
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06-02-2020 8 ME222a: Nature and Properties of Materials Be Cr Mo Ru Re Ir U Lattice Array of points in space, in which every point has identical environment with respect to all other points. Basis Single atom or group of atoms identical in composition and orientation in space Lattice + Basis = Crystal Structure Lattice / Basis
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06-02-2020 9 3 D Unit Cell A crystalline solid can be constructed from a Unit cell plus Translational operators Unit Cell Translation along X axis Translation along Y axis Translation along Z axis Basic structural unit which forms the crystal structure by its 3D repetition Defined by three vectors a , b , c and the angles α , β , between them a b a = between b and c b = between c and a = between a and b A parallelepiped is generated by the vectors a , b and c 3 D Unit Cell: Lattice Parameters
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