Summary of Understanding Metals

00:00:00 - 00:15:00

The YouTube video "Understanding Metals" discusses the properties of metals and how they are classified. Metals are crystalline materials with a regular, repeating unit cell, and they have high densities because of the close packing of the atoms. Lattices also contain linear and point defects. Elastic deformation is caused by the stretching of atomic bonds, and plastic deformation is caused by the motion of dislocations. Grain boundary strengthening is just one of many strengthening techniques. Alloys are materials that are created by combining different elements. The main alloying elements in iron-carbon alloys are carbon, copper, manganese, silicon, zinc, and magnesium.

• 00:00:00 Metals are crystalline materials with a regular, repeating unit cell. The three most common crystal structures in metals are the FCC, HCP, and BCC structures, which have a packing factor of 74%, 68%, and 54%, respectively. Metals have high densities because of the close packing of the atoms. Lattices also contain linear and point defects.
• 00:05:00 Metals are materials that have an ability to resist deformation. The underlying mechanism behind plastic deformation in metals is the motion of a large number of dislocations at the atomic level. Elastic deformation is caused by the stretching of atomic bonds. When a shear stress is applied, the atoms rearrange into a new stable configuration. Most real dislocations will actually be a combination of edge and screw dislocations. Because dislocations move through the lattice by the breaking and re-forming of atomic bonds, the process is irreversible - a dislocation does not return to its original position when the applied shear stress is removed. This is the underlying mechanism behind plastic deformation in metals. Grain boundary strengthening is just one of many strengthening techniques. We can also strengthen a metal by plastically deforming it, using techniques like cold rolling or forging. Alloys are materials that are created by combining different elements in this way. Ferrous and non-ferrous metals are typically divided into categories based on the base metal of the alloy.
• 00:10:00 The main alloying elements in iron-carbon alloys are carbon, copper, manganese, silicon, zinc, and magnesium. Steel is a type of alloy that is made of iron and carbon, and it has many useful properties. The main phases that iron-carbon alloys undergo with changes in temperature are ferrite, austenite, and FCC. Ferrite can only hold a very small amount of carbon, and when the solubility of ferrite is exceeded, extra carbon atoms have to go somewhere, and so a new phase called cementite forms. Cementite is a hard, brittle compound made up of one carbon atom for every three iron atoms.
• 00:15:00 Metals are made up of atoms that are joined together by metal oxides. Ferrite and cementite are two of the most common oxides, and their structures depend on the amount of carbon present. When more carbon is added, we get a two-phase material with austenite and cementite phases. The presence of a cementite phase can have a significant strengthening effect, which is part of the reason steel is much stronger than pure iron.