Topic 4 - Metals

Metals : 

Metals

Metallic Bonding : 

Metallic Bonding Metallic bonds are strong bonds made between metals that are held together by a sea of electrons flowing around the outer shells of the atoms. Metallic bonds do not have specific electrons for each atom, but all the electrons, in the metal, flow around to hold the atoms together.

Electrical and Thermal Conductivity : 

Electrical and Thermal Conductivity In science, a conductor is a material which contains movable electric charges. In metals, such as copper or aluminum, the movable charged particles are electrons. Thermal conductivity is the ability of a material to transfer heat. The heat is moved through the metal by the flow of electrons. Electrical conductivity is the ability of a material to transfer electricity. Just like in thermal conduction; the electricity moves through the metal via the flow of electrons.

Metals as Crystals : 

Metals as Crystals Crystals are particles made out of regular, repeating patterns of atoms, molecules and ions arranged together. Grain size The size of the diameter of a sediment, is what is meant by grain size. (One single grain can be made from several types of crystals.) This picture shows different kinds of arrangements in grains. If the sizes are somewhat equal in the grain, the arrangement is very good, but if the sizes are too different from each other the arrangement is very poor.

Controlling Grain Size : 

Controlling Grain Size The size of the grains in a metal can be changed by heating or cooling it. For example, if you heat a metal to above its melting point, and wait for some time; a homogeneous structure is created in the metal and grain growth will occur inside it. Controlling the size of grains is used during the production of steel when aluminium is added to the mixture. (The fact that steel is created by humans and that it has a very controlled grain size; is also one of the reasons why it is a very strong compound.)

Plastic Deformation : 

Plastic Deformation When some materials are overloaded they will bend into a temporary deform shape. But when the force is taken away from the material it bends back into its original shape. This is called “Elastic Deformation” Sometimes, the same thing happens, except when the force is removed; the material stays in this deform shape permanently. This is what is meant by “Plastic Deformation”

Plastic Deformation : 

Plastic Deformation Plastics are split into 2 groups: Thermoplastics and Thermosetting plastics. These 2 kinds of plastics are very different from each other when looking at their deformation properties. Soft thermoplastics can be deformed into a big variety of shapes because of their wide range Ductile metals work the same way (f.ex. copper, silver and gold) Hard thermosetting plastics have a small range of deformation This works the same way for some metals (f.ex. Iron)

Work-Harden : 

Work-Harden Work-hardening is when a piece of material plastic deforms /stretches beyond its (apparent) maximum point. This is used to create very curved shapes in materials, and to strengthen it . The Material has been bend so much that it cannot return to its original position again and as a result; this makes it stronger.

Work-Harden Example : 

Work-Harden Example

A Work-Hardened Metal : 

A Work-Hardened Metal

Tensile strength : 

Tensile strength Tensile strength measures the force required to pull something such as rope, wire, or a structural beam to the point where it breaks. The tensile strength of a material is the maximum amount of tensile stress that it can be subjected to before failure.

Effects Of Alloying. : 

Effects Of Alloying. Research and development have shown that alloying can raise the tensile strength of titanium metal while still maintaining useful ductility. The presence of interstitial elements, mainly carbon and the reactive gases of the atmosphere, also add strength to the metal but at the expense of severe loss in ductility.

SUPERALLOY : 

SUPERALLOY Superalloys are metallic materials for service at high temperatures, particularly in the hot zones of gas turbines. Materials like such allow the turbine to operate more efficiently by withstanding higher temperatures. One of the most important superalloy properties is high temperature creep resistance. Other crucial material properties are fatigue life, phase stability, as well as oxidation and corrosion resistance.

Applications For alloy : 

Applications For alloy Superalloys are used in places where there is a need for high temperature strength and corrosion/oxidation resistance. The largest applications of superalloys are aircraft engines, industrial gas turbines, rocket engines, space vehicles, submarines, nuclear reactors, military electric motors etc.

Bibliography : 

Bibliography http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Structure/deformation.htm www.wikipedia.org http://www.engineersedge.com/material_science/work_strain_hardening.htm http://metals.about.com/library/bldef-Grain-Size-Control.htm