tailieunhanh - Concise Dictionary of Materials Science Part 8

Tham khảo tài liệu 'concise dictionary of materials science part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | passed through an analyzer with the polarization plane rotated by 90 . If the specimen surface is optically isotropic the image will be dark. If however there are optically anisotropic . having a noncubic lattice crystallites or surface films they will be bright and colored because they rotate the polarization plane of the reflected light. Grains of the same phase can be discriminated because the previously mentioned rotation depends on their orientation. pole In crystallography an intersection of the normal to any lattice plane of a crystal with a reference sphere the crystal is assumed small and placed at the center of the sphere. The position of the pole projected onto the Wulff net characterizes the orientation of the lattice plane. pole figure Stereographic projection displaying the density of certain poles of all the crystallites on the Wulff net definitively oriented with respect to the polycrystalline sample. If the density is inhomogeneous then there is a texture in the sample. The indices of the poles used are commonly included in the pole figure name as . a 002 pole figure. polychromatic x-ray radiation See white radiation. polycrystal Polycrystalline body. polycrystalline Consisting of many crystallites. polygonization Formation and growth of subgrains usually observed at the last stage of recovery. Subgrains form from the dislocation cells see cell structure and their boundaries from geometrically necessary dislocations in the cell walls whereas the other dislocations in the walls rearrange and annihilate. Subgrain growth proceeds in the same manner as grain growth. Commonly polygonization results in the occurrence of recrystallization nuclei. However sometimes it can be the last stage of substructure alterations upon heating deformed materials as . in the case of continuous recrystallization. polygonized Formed by polygonization. polymorphic crystallization Occurrence of a crystalline phase of the same composition as the parent glassy phase.