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BCC structure. The primitive unit cell for the body-centered cubic crystal structure contains several fractions taken from nine atoms (if the particles in the crystal are atoms): one on each corner of the cube and one atom in the center. Because the volume of each of the eight corner atoms is shared between eight adjacent cells, each BCC cell ...
The structure can also be described as an HCP lattice of arsenic with nickel occupying each octahedral void. Compounds adopting the NiAs structure are generally the chalcogenides, arsenides, antimonides and bismuthides of transition metals. [citation needed] The unit cell of nickeline. The following are the members of the nickeline group: [16]
Conversely, materials with a hexagonal close packed (HCP) structure and a high c/a ratio, such as cobalt-based alloys, are extremely resistant to galling. [4] Galling occurs initially with material transfer from individual grains on a microscopic scale, which become stuck or even diffusion welded to the adjacent surface.
The choice of structure and the value of the axial ratio ... The "d-weight" calculates out to 0.5, 0.7 and 0.9 for the fcc, hcp and bcc structures respectively. The ...
Slip in hexagonal close packed (hcp) metals is much more limited than in bcc and fcc crystal structures. Usually, hcp crystal structures allow slip on the densely packed basal {0001} planes along the <11 2 0> directions. The activation of other slip planes depends on various parameters, e.g. the c/a ratio.
However, in real materials there are deviations from this in some metals where the unit cell is distorted in one direction but the structure still retains the hcp space group—remarkable all the elements have a ratio of lattice parameters c/a < 1.633 (best are Mg and Co and worst Be with c/a ~ 1.568).
Comparison between HCP and FCC Figure 1 – The HCP lattice (left) and the FCC lattice (right). The outline of each respective Bravais lattice is shown in red. The letters indicate which layers are the same. There are two "A" layers in the HCP matrix, where all the spheres are in the same position. All three layers in the FCC stack are different.
Understanding such properties is essential to making quality zirconium hydride. At room temperature, the most stable form of zirconium is the hexagonal close-packed (HCP) structure α-zirconium. It is a fairly soft metallic material that can dissolve only a small concentration of hydrogen, no more than 0.069 wt% at 550 °C.