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Course Question & Answer0% Engineering Materials & Materials Processing
Purpose of Course
In most engineering classes, you are presented with a set of materials with well-established properties and asked to use the full set of engineering tools at your disposal to design suitable devices and mechanisms for an intended application. In this course, however, we will learn how to produce materials with properties that have been optimized for a set of desired applications.
To form an accessible view of a very complex world, introductory chemistry and physics courses primarily concentrate on materials and structures in chemical and physical equilibrium. The equilibrium form of any material is, roughly, a sphere of atoms whose distribution minimizes the free energy of that material. Because one almost never encounters equilibrium materials, their properties are of little interest in engineering.
Typically, engineering materials are instead highly non-equilibrium assemblages of chemicals that have been carefully combined and distributed in order to constitute a material with a certain set of useful engineering properties. Consider, for example, carbon steel. Prepare a piece of steel by adding about 0.5% of carbon into iron at high temperature. If this material is slowly cooled, it produces a layered structure called pearlite, composed of alternating layers of α-iron and cementite (Fe3C). The resulting steel is soft and ductile. However, if the material is rapidly cooled (quenched), the resulting steel forms a highly strained, highly non-equilibrium, body-centered tetragonal crystal structure that is extremely hard and brittle. These two materials are composed of the same chemical elements in the same proportions; the difference is the material processing.
The theme of obtaining desired engineering properties for a given application through the precise application of processing methods and parameters appears throughout the practice of engineering. The materials with which we carry out engineering projects are a combination of composition, crystal structure, microstructure, and, in some cases, macroscopic structure. Most engineers do not practice this set of arcane arts, but all of engineering depends upon the results of such materials optimization.
Consider swords. For at least 1500 years, the sword was the dominant weapon in most of the world. But how does one make a fine sword? Given a little experience with steel, some of the answers become clear. If you use a low carbon steel, the sword will be tough, but will not take or keep a good edge. If you instead use a high carbon steel, it will sharpen easily to a fine edge, but will tend to be brittle. On the other hand, a katana blade (traditional sword of the Samurai) having the same average atomic composition as the high carbon steel blade will sharpen easily, but will also be tough and flexible.
What is different about the blade of a katana? The katana is composed of thousands of extraordinarily thin layers of steel, generally a few microns in thickness, whose composition alternates between a low carbon steel and an extremely high carbon steel. The high carbon steel allows the katana to take an extremely sharp edge. The cutting edge is also self-sharpening to some extent; it cannot become thicker than the blade’s laminations. In addition, the low carbon steel acts as a strong, tough, and pliable cement between the layers of high carbon steel, thereby giving the blade toughness and flexibility. The result is one of the finest swords ever made.
The difference between the high-carbon steel blade and the katana is not the overall composition; it is possible to take the atoms from the first and rearrange them to form the katana. Rather, there is a difference in the local concentration of carbon in the blade, as alternating laminations have large differences in the amount of carbon in their steel. Does the differing amount of carbon in the laminations result in the superior properties of the katana? Not alone, no. There are at least two levels of additional microstructure that must be created through materials processing in order to yield a fine katana blade. Briefly, the carbon must be convinced to reside in the proper locations in the crystal structure of the iron, and excess carbon that precipitates out of the iron must form a grain structure of the right size. This additional microstructure is generated by a combination of forging and heat-treating the katana steel.
A raw material can be converted into an engineering material with amazing properties through a carefully controlled series of processing steps. Materials engineering pivots on these three points: raw material, amazing properties, and the processing that transforms that raw material into an engineering material having those amazing properties.
In this course, we will discuss a wide range of material types, including metals, ceramics, glasses, crystals, polymers, and composite materials. We will learn about the properties of each of these materials as well as common processing technologies and approaches to optimizing desirable properties. We will also take a look at some novel materials currently on their way to becoming engineering materials.
Note that this is an upper-division course that requires considerable background in the basic studies of materials and mathematics for success. The prerequisites for this course include ME101 and ME102, CHEM 101, MA101 and MA102, and PHYS101 and PHYS102.