Exam (elaborations) Science and Engineering of Materials The Science and Engineering of Materials

Exam (elaborations) Science and Engineering of Materials The Science and Engineering of Materials, SI Edition Chapter 1: Introduction to Materials Science and Engineering 1-1 Define materials science and engineering (MSE). Solution: Materials science and engineering (MSE) is an interdisciplinary field that studies and manipulates the composition and structure of materials across length scales to control materials properties through synthesis and processing. 1-2 What is the importance of the engineering tetrahedron for materials engineers? Solution: Structure, properties and performance all depend on the route in which a material is processed. We cannot predict the end properties for a material until we have specified a process to produce the component. Using the same material, but changing the way it is processed will result in different structure, properties and performance of that material. This is applicable to all material systems. 1-3 Define the following terms: (a) composition; (b) structure; (c) synthesis; (d) processing; and (e) microstructure. Solution: (a) The chemical make-up of a material. (b) The arrangement of atoms, seen at different levels of detail. (c) How materials are made from naturally occurring or man-made chemicals. (d) How materials are shaped into useful components. (e) The structure of an object at the microscopic scale. 1-4 Explain the difference between the terms materials science and materials engineering. Solution: Materials scientists work on understanding underlying relationships between the synthesis and processing, structure, and properties of materials. Materials engineers focus on how to translate or transform materials into useful devices or structures. 2 © 2016 Cengage Learning. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 1-5 The myriad materials in the world primarily fall into four basic categories; what are they? What are materials called that have one or more different types of material fabricated into one component? Give one example. Solution: Metals, polymers and ceramics. The addition of one or more of these to a single system is called a composite. An example of a composite material is fiberglass. 1-6 What are some of the materials and mechanical properties of metals and alloys? Solution: Metals and alloys have good electrical and thermal conductivity, high strength, ductility and formability, and high stiffness. 1-7 What is a ceramic, and what are some of the properties that you expect from a ceramic? Solution: Ceramics tend to have very high compressive strengths, but behave in a brittle (glass- like) manner. They have very high melting temperatures. Poor thermal conductivity and electrical conductivity make ceramics behave as an insulator instead of a conductor. 1-8 Make comparisons between thermoplastics and thermosetting polymers (a) on the basis of mechanical characteristics upon heating, and (b) according to possible molecular structures. Solution: Thermoplastics tend to soften with elevated temperature exposure with gradually decreasing viscosity. Thermosetting polymers do not soften with elevated temperature exposure; instead they will remain hard and will degrade, possibly charring with prolonged exposure. Thermoplastics consist of long chain molecular arrangements of covalently bonded carbon atoms with various side groups. Thermosetting polymers tend to be a complex 3- D arrangement usually deviating from the clearly defined long-chain molecular arrangement. 1-9 Give three examples of composites that can be fabricated. Solution: Metal matrix composites (MMC) – A metal matrix reinforced with a ceramic material in the form of particles, whiskers or fibers. Example: Cobalt alloy reinforced with tungsten- carbide particulates. Polymer matrix composites (PMC) – A polymer matrix reinforced with a ceramic material in the form of whiskers or fibers. Example: Kevlar or fiberglass. 3 © 2016 Cengage Learning. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Ceramic matrix composites (CMC) – A ceramic matrix reinforced with ceramic or metallic material in the form of whiskers or fibers. Example: Carbon fibers in an alumina (Al2O3) matrix. 1-10 For each of the following classes of materials, give two specific examples that are a regular part of your life: (a) metals; (b) ceramics; (c) polymers; and (d) semiconductors. Specify the object that each material is found in and explain why the material is used in each specific application. Hint: One example answer for part (a) would be that aluminum is a metal used in the base of some pots and pans for even heat distribution. It is also a lightweight metal that makes it useful in kitchen cookware. Note that in this partial answer to part (a), a specific metal is described for a specific application. Solution: (a) Aluminum was described in the problem statement. Stainless steel is used for flatware. It is easily formed and has good corrosion resistance, strength, and hardness. (b) Two specific examples of polymers are polystyrene and polytetrafluoroethylene also known as Teflon. Styrofoam is polystyrene rigid foam insulation that is used for cups that keep hot drinks warm. Teflon is used as a coating on the inside of kitchen cookware such as frying pans because it prevents food from sticking to the pan while cooking. (c) Two examples of semiconductors are silicon doped with phosphorus (n–type) and silicon doped with boron (p–type). Both types of impurities convert silicon from a poor into a useful conductor. Both n and p–type semiconductors are contained in the semiconductor device called a diode, so that at the junction between both types, current is able to flow. A diode blocks current in one direction while allowing current flow in the other direction. A device that uses batteries, e.g. a remote control or a calculator, often contains a diode that protects the device if the batteries are inserted backward. The diode blocks the current from leaving the battery if it is reversed, protecting the sensitive electronics in the device. Another semiconductor is the compound semiconductor AlxGa1-xAs, which is used in lasers. (d) Ceramics are compounds that contain metallic and nonmetallic elements. Two specific examples are tungsten carbide and magnesia. Tungsten carbide is often bonded with cobalt and/or nickel. Tungsten carbide is used mainly in tips for metal cutting tools (knives can be made with this) because of its good wear resistant characteristics. Magnesia is a heat resistant ceramic that is used in liners for ovens. Magnesia can resist high temperatures but is susceptible to thermal stress cracking.