,Unit1 Advanced Engineering Materials,Types of materials By state：solid, liquid, or gas By living：organic, inorganic By industrial purposes： engineering materials. nonengineering materials.,Engineering materials used in manufacture and become parts of products. Nonengineering materials chemicals, fuels, lubricants, and other materials used in the manufacturing process, which do not become part of the product.,Engineering materials may be further subdivided into: Metals Ceramics (陶瓷) Composite (复合材料) Polymers (聚合体) others,Metals and Metal Alloys,Metals are elements that generally have good electrical and thermal conductivity. Many metals have high strength, high stiffness, and have good ductility. Some metals, such as iron, cobalt and nickel are magnetic （adj. 有磁性的）. At extremely low temperatures, some metals and intermetallic compounds (金属间化合物) become superconductors .,Differences between a metal alloy and a pure metal,Pure metals are elements which come from a particular area of the periodic table. Examples ： 1. copper in electrical wires 2. aluminum in cooking foil and beverage cans.,Metal Alloys contain more than one metallic element. Their properties can be changed by changing the elements present in the alloy. Examples ： 1. stainless steel which is an alloy of iron, nickel, and chromium; 2. gold jewelry which usually contains an alloy of gold and nickel.,Some important properties of metals,Density is defined as a materials mass divided by its volume. Most metals have relatively high densities, especially compared to polymers. Materials with high densities often contain atoms with high atomic numbers, such as gold or lead. However, some metals such as aluminum or magnesium have low densities, and are used in applications that require other metallic properties but also require low weight.,Fracture Toughness can be described as a materials ability to avoid fracture, especially when a flaw is introduced. Plastic deformation is the ability of a material to bend or deform before breaking. As engineers, we usually design materials so that they dont deform under normal conditions. You dont want your car to lean to the east after a strong west wind. However, sometimes we can take advantage of (利用) plastic deformation.,Alloys are compounds consisting of more than one metal. Adding other metals can affect the density, strength, fracture toughness, plastic deformation, electrical conductivity and environmental degradation. For example, adding a small amount of iron to aluminum will make it stronger. Also, adding some chromium to steel will slow the rusting process, but will make it more brittle.,The atomic bonding of metals,In metals, the outer valence electrons are shared among all atoms, and are free to travel everywhere. Since electrons conduct heat and electricity, metals make good cooking pans and electrical wires. It is impossible to see through metals, since these valence electrons absorb any photons of light which reach the metal .2 No photons pass through.,Ceramics and Glasses,A ceramic is often broadly defined as any inorganic nonmetallic material. By this definition, ceramic materials would also include glasses; however, many materials scientists add the stipulation (n.约定, 约束, 契约) that “ceramics“ must also be crystalline. A glass is an inorganic nonmetallic material that does not have a crystalline (晶体) structure. Such materials are said to be amorphous (非晶体).,Properties of Ceramics and Glasses,usual properties : high melting temperature, low density, high strength, stiffness, hardness, wear resistance, and corrosion resistance. special properties: electrical and thermal insulators; magnetic materials; piezoelectric materials; superconductors at very low temperatures. Ceramics and glasses have one major drawback : they are brittle.,Ceramics Forming,Ceramics are not typically formed from the melt. This is because most ceramics will crack extensively (i.e. form a powder) upon cooling from the liquid state. Hence, all the simple and efficient manufacturing techniques used for glass production such as casting and blowing, which involve the molten state, cannot be used for the production of crystalline ceramics.,Sinteringceramic powders are processed into compacted shapes and then heated to temperatures just below the melting point. At such temperatures, the powders react internally to remove porosity and fully dense articles can be obtained. Application An optical fiber,An optical fiber contains three layers:a core made of highly pure glass with a high refractive index for the light to travel,a middle layer of glass with a lower refractive index known as the cladding which protects the core glass from scratches and other surface imperfections,and an outer polymer jacket to protect the fiber from damage.4 In order for the core glass to have a higher refractive index than the cladding,the core glass is doped with a small,controlled amount of an impurity,or