Chapter 3-CLASSES OF MATERIALS AND PROPERTIES PDF

 Types of Materials Metals: – Strong, ductile – high thermal & electrical conductivity – opaque, reflective. Ceramics: ionic bonding (refractory) – compounds of metallic & non-metallic elements (oxides, carbides, nitrides, sulfides) – Brittle, glassy, elastic...

 Types of Materials Metals: – Strong, ductile – high thermal & electrical conductivity – opaque, reflective. Ceramics: ionic bonding (refractory) – compounds of metallic & non-metallic elements (oxides, carbides, nitrides, sulfides) – Brittle, glassy, elastic – non-conducting (insulators) Polymers/plastics: Covalent bonding  sharing of e’s – Soft, ductile, low strength, low density – thermal & electrical insulators – Optically translucent or transparent. METALS Properties: Metals have relatively high moduli. Pure metals are soft, weak (have low strength) and have high ductility. They can be made strong by alloying, mechanical treatment and heat treatment. When strength is increased ductility is reduced. Their strength is the same in tension and compression. They are not resistant to corrosion (except the noble metals) They conduct electricity. Some metals and alloys: Iron and steels Copper and its alloys Nickel and its alloys Aluminium and its alloys Magnesium and its alloys Titanium and its alloys CERAMICS Properties: Ceramics and glasses have high moduli. But, unlike metals, they are brittle. They are weak in tension, but strong in compression. They are resistant to corrosion. They have high melting temperatures, so they can be used at high temperatures. They do not conduct electricity. Some Ceramics and Glasses: Alumina (AI2O3, emery, sapphire) Magnesia (MgO) Silica (SiO2) glasses and silicates Silicon carbide (SiC) Silicon nitride (Si3N4) Cement and concrete POLYMERS Properties: Polymers (or Plastics) are generally organic compounds based upon carbon and hydrogen. They are very large molecular structures. They have low density and low melting point, therefore they are not usable at high temperatures. They are weak and easy to form. They have high corrosion resistance. They do not conduct electricity, they are electrical insulators. Some polymers are elastic, they are elastomers. POLYMERS Some Polymers: Polyethylene (PE) Polymethylmethacrylate (Acrylic and PMMA) Nylon (Polyamide) (PA) Polystyrene (PS) Polyurethane (PU) Polyvinylchloride (WC) Polyethylene tetraphthalate (PET) Polyethylether Ketone (PEEK) Epoxies (EP) Elastomers, such as natural rubber (NR) COMPOSITES Properties: Composites consist of more than one material type. Mud brick is the earliest composite material. Fiberglas, a combination of glass fibbers and a polymer, is an example. Concrete and plywood are other familiar composites. Many new combinations include ceramic fibbers in metal or polymer matrix. Composites have varying properties depending on the properties of the matrix and the added material (reinforcement).  Some Composites: Fibreglass (GFRP) Carbon-fibre reinforced polymers (CFRP) Filled polymers Cermets Advanced Materials Materials that are utilized in high-technology applications are sometimes termed advanced materials. By high technology we mean a device or product that operates or functions using relatively intricate and sophisticated principles; examples include electronic equipment (camcorders, CD/DVD players, etc.), computers, fiber-optic systems, spacecraft, aircraft, and military rocketry. These advanced materials are typically traditional materials, whose properties have been enhanced, and, also newly developed, high-performance materials. Furthermore, they may be of all material types (e.g., metals, ceramics, polymers), and are normally expensive. Advanced materials include semiconductors, biomaterials, and what we may term “materials of the future” (that is, smart materials and nanoengineered materials). The properties and applications of a number of these advanced materials-for example, materials that are used for lasers, integrated circuits, magnetic information storage, liquid crystal displays (LCDs), and fiber. Semiconductors Semiconductors Semiconductors have electrical properties that are intermediate between the electrical conductors and insulators. Furthermore, the electrical characteristics of these materials are extremely sensitive to the presence of minute concentrations of impurity atoms, for which the concentrations may be controlled over very small spatial regions. Semiconductors have made possible the advent of integrated circuitry that has totally revolutionized the electronics and computer industries (not to mention our lives) over the past three decades. Semiconductors Biomaterials Biomaterials are employed in components implanted into the human body for replacement of diseased or damaged body parts. These materials must not produce toxic substances and must be compatible with body tissues (i.e., must not cause adverse biological reactions). All of the above materials-metals, ceramics, polymers, composites, and semiconductors-may be used as biomaterials. Smart Materials Smart (or intelligent) materials are a group of new and state-of-the-art materials now being developed that will have a significant influence on many of our technologies. The adjective “smart” implies that these materials are able to sense changes in their environments and then respond to these changes in predetermined manners-traits that are also found in living organisms. In addition, this “smart” concept is being extended to rather sophisticated systems that consist of both smart and traditional materials. Components of a smart material (or system) include some type of sensor (that detects an input signal), and an actuator (that performs a responsive and adaptive function). Smart Materials Four types of materials are commonly used for actuators: shape memory alloys, piezoelectric ceramics, magnetostrictive materials, and electrorheological/magnetorheological fluids. Shape memory alloys are metals that, after having been deformed, revert back to their original shapes when temperature is changed. Piezoelectric ceramics expand and contract in response to an applied electric field (or voltage); conversely, they also generate an electric field when their dimensions are altered. The behavior of magnetostrictive materials is analogous to that of the piezoelectric, except that they are responsive to magnetic fields. Also, electrorheological and magnetorheological fluids are liquids that experience dramatic changes in viscosity upon the application of electric and magnetic fields, respectively. Materials/devices employed as sensors include optical fibers, piezoelectric materials (including some polymers), and microelectromechanical devices (MEMS).  Crystalline, amorphous and molecular structure Metals are crystalline. Ceramics are crystalline, inorganic, non-metals. Glasses are non-crystalline (or amorphous) solids. Most engineering glasses are non-metals, but a range of metallic glasses with useful properties is now available. Polymers are very large molecular structures  Crystalline and Amorphous Materials Crystalline materials... atoms pack in periodic, 3D arrays long range order over large atomic distances typical of: -metals, -many ceramics -some polymers and crystalline SiO2 Adapted from Fig. 3.18(a), organic molecules Callister 6e. Noncrystalline materials... atoms have no periodic packing occurs for: -complex structures -rapid cooling "Amorphous" = Noncrystalline noncrystalline SiO2 Adapted from Fig. 3.18(b), Callister 6e. 3  Molecular Structure The arrangement of C and H atoms in chain molecules of polyethylene Bar-chart of room temperature strength (i.e., tensile strength) values for various metals, ceramics, polymers, and composite materials. Bar-chart of room temperature stiffness (i.e., elastic modulus) values for various metals, ceramics, polymers, and composite materials. Bar-chart of room-temperature resistance to fracture (i.e., fracture toughness) for various metals, ceramics, polymers, and composite materials Bar-chart of room temperature electrical conductivity ranges for metals, ceramics, polymers, and semiconducting materials.