Deformability of metals | ductility of lattice structures | slip planes | slip systems

This video explains the deformability of metals and the underlying physical mechanisms. Metals are characterized by their relatively high deformability, which is due to their unique metallic bonding. A distinction is made between elastic and plastic deformation. In elastic deformation, atoms shift only slightly and return to their original position after the applied force is removed. In contrast, plastic deformation involves the permanent slipping of atomic layers past each other, meaning the material does not fully regain its original shape. Plastic deformation occurs along so-called slip planes, where atoms are displaced by shear stresses. The number of available slip systems significantly determines a metal’s deformability. Metals with a face-centered cubic (FCC) crystal structure, such as aluminum, copper, or nickel, are particularly deformable, whereas metals with a hexagonal close-packed (HCP) structure, like magnesium or zinc, are much harder to plastically deform. Another crucial factor is the applied force and its division into normal and shear stresses. Only shear stresses can cause atomic layers to shift within the slip planes. A critical resolved shear stress must be exceeded for plastic deformation to begin. Theoretically calculated values are significantly higher than those observed experimentally, indicating additional effects within the crystal lattice. The video also discusses the influence of crystal structure on deformability. The more slip planes and possible slip directions a metal has, the better it can be deformed without damaging its atomic structure. This is particularly important for industrial manufacturing processes such as forging, bending, or deep drawing. Finally, the concept of polymorphism (allotropy) is addressed, referring to the ability of some metals to change their crystal structure depending on temperature or pressure. For example, iron transitions from a body-centered cubic (BCC) to an FCC structure at higher temperatures, which improves its deformability. This is one reason why steel is heated during forging. Overall, the video provides a detailed insight into the fundamental principles of metallic deformation and their technical relevance. 00:00 Ductility of metals 00:34 Elastic deformation 01:06 Plastic deformation 02:08 Slip system 03:48 Normal and shear stresses 05:20 Inducing shear stresses 06:26 Critical resolved shear stress (CRSS) 07:49 Influence of the lattice structure on ductility 08:40 When does a lattice plane become a slip plane? 09:25 Slip direction 10:15 Maintaining stacking sequence 11:33 Metals and their lattice structures 12:40 Body-centered cubic structure (bcc) 13:47 Face-centered cubic structure (fcc) 15:19 Hexagonal closest-packed lattice structure (hcp) 16:26 Polymorphism (allotropy)