In this lesson, we will discuss the wide range of commercial applications of ferrous alloys, which includes steel. However, ferrous alloys do have some limitations including having low electrical conductivity compared to other metals, being heavy, and corroding in typical application environments. In addition to the ferrous alloys in this lesson we will look at a range of other (non-ferrous) metal and alloy systems: copper, aluminum, magnesium, and titanium alloys; the refractory metals; the superalloys; the noble metals; and miscellaneous alloys, including those that have lead, tin, zirconium, and zinc as base metals. Many of these non-ferrous metals and alloys have advantages over the ferrous alloys for particular applications.
By the end of this lesson, you should be able to:
Lesson 6 will take us one week to complete. Please refer to Canvas for specific due dates.
To Read | Read pp 136-179 (Ch. 7 & 8) in Introduction to Materials ebook |
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To Watch | The Secrets of the Viking Sword |
To Do | Lesson 6 Quiz |
If you have general questions about the course content or structure, please post them to the General Questions and Discussion forum in Canvas. If your question is of a more personal nature, feel free to send a message to all faculty and TAs through Canvas email. We will check daily to respond.
In this lesson, we are going to take a closer look at metal alloys. First, we will define what an alloy is and how dislocations strengthen alloys. The e-textbook breaks metal alloys into two classes of metal alloys: ferrous and nonferrous alloys. Ferrous is simply the Latin name for iron, so ferrous alloys are simply iron alloys (which means that it is mostly iron mixed with lesser amounts of other metals or nonmetals) and nonferrous alloys are non-iron alloys. In the reading for this lesson, you will see the composition, properties, and applications of a wide variety of metal alloys. The video for this lesson highlights the properties and applications of some of the metal alloys and puts the materials development of the highlighted metal alloys in historical context.
An alloy is a mixture of a metal with another element, either metal or nonmetal. If we start with a base metal and we add impurity atoms there are two possible outcomes if the two mix. The two different cases are highlighted in the figure below. In the substitutional solid case, the impurity atoms replace the host atoms in the lattice. In the interstitial situation, impurity atoms squeeze between the host atoms.
In addition to mixing, it is possible for regions of a new phase to form. An illustration of the formation of a second phase in a solid solution is shown below. The second phase can have a different composition and often a different structure.
Now watch the following video (4:44) on alloys and how dislocations harden alloys:
After watching the video, please proceed to the next section on the development of iron smelting.
Why did it take so long (~2,000 years) for humankind to apply the concepts of smelting copper and bronze to the development of iron? And then another 3000 years to develop steel?
The major issue with the smelting of iron is that with the technology used for smelting of copper and bronze the temperature that is obtainable results in solid iron. So rather than having molten iron, the smelting of iron results in a sponge-like solid mass of impure iron.
As we will see later in the video, impurities could be pounded out of iron by hitting it. So, until the Industrial Revolution, iron could only be produced as a wrought alloy. A wrought alloy is amenable to being mechanically deformed, i.e., pounding it into a desirable shape. Since iron could not be melted it could not be cast in the molds. There were also limits to controlling impurities.
In England in 1709, Abraham Darby started to use coke instead of charcoal as his fuel source to smelt iron ore. Coke, a form of coal, allowed him to build larger and more efficient furnaces than charcoal could support. These furnaces allowed Darby to reach higher temperatures. The temperatures reached were still not high enough to melt pure iron. However, iron that has around 4.3 weight percentage of carbon has a much lower melting temperature than pure iron. Although not pure iron, the iron that he could cast (since it was molten) allowed him to manufacture cast iron pots that could compete successfully with brass.
In the 1850s, Henry Bessemer proposed an incredibly bold idea. Bessemer began using very large blast furnaces (shown below), which could produce 3 to 4 tons of molten iron in a single run. Oxygen was blasted through the furnace, which resulted in higher temperatures and the oxygen combining with carbon to form CO2 gas, which bubbled out of the iron. Initially, Bessemer’s process was not reliable. There were issues with phosphorus and sulfur contamination as well as difficulty producing iron with desired target carbon content. This latter issue was resolved by removing all carbon during the process and adding in desired amounts of carbon after purification of the iron.
Now, proceed to the reading and video assignment for this lesson. We will then explore in more detail aluminum alloy and, one of my favorite alloys, metallic glass.
When you read this chapter, use the following questions to guide your reading. Remember to keep the learning objectives listed on the overview page in mind as you learn from this text.
Read pp 136-179 (Ch. 7 & 8) in Introduction to Materials ebook
Now that you have read the text and thought about the questions I posed, take some time to watch this 53-minute NOVA video about using cutting edge science, old-fashion detective work, and modern craftsmanship to reconstruct a legendary Ulfberht Viking sword. As you watch this video see if you can apply what you know about carbon content in ferrous alloys to the properties of the sword being manufactured in this video.
Go to Lesson 6 in Canvas and watch the Secrets of the Viking Sword video. You will be quizzed on the content of this video.
Aluminum and its alloys were introduced in your e-textbook. The history of the development and applications of aluminum and its alloys were covered in the video for this lesson. Now I am going to expand on this material and highlight the role of aluminum in airplane development.
Aluminum is the third most abundant element in the Earth's crust, after oxygen and silicon, and is the Earth's most abundant metal. It is about 8% of the crust by mass, but it is rarely found as a native metal as it is very chemically active. Its oxide forms more readily than the oxide of iron and, unlike the oxide of iron, once formed it blocks oxygen and water from penetrating the aluminum oxide. This results in aluminum being very corrosion-resistant. Iron, on the other hand, forms rust which does not block oxygen and water, so iron pieces will rust to completion if left long enough in a wet atmospheric environment. Aluminum has a low density, which makes it a candidate for lightweight applications.
Although aluminum is abundant in nature, it occurs chemically bound to other elements, and there is no known way to smelt aluminum using traditional smelting methods. Because of this limitation, before the 19th century, pure aluminum was rarer than gold. In the 19th century, people learned how to use electrolysis to extract aluminum from aluminum oxide, AlO2. As you can see from the figure below aluminum production has continued to increase ever since.
Typically, aluminum oxide is extracted from the mineral bauxite, and then aluminum is further processed from the aluminum oxide. Visit this website to access the list of where aluminum oxide is produced [5]. Although aluminum oxide is used as an abrasive material most of the aluminum oxide is used for the production of aluminum. For more on the electrolysis process for the extraction of aluminum from aluminum oxide, please watch the fuseschool.org video linked below.
Please watch the following short video (3:13), How to Extract Aluminum Using Electrolysis, on the extraction of aluminum using electrolysis before proceeding to the next section on building lighter aircraft.
The lighter that we can build safe aircraft the better. Reducing the operating empty weight of commercial aircraft can allow for an increase in the passengers, baggage, and cargo that the plane can safely transport. Early aircraft were made of wood and fabric. An example of an early aircraft is shown in the figure below. This provided a good combination of lightness and strength but required reinforcing struts, which added weight and drag and resulted in multiple wing designs.
Improved airplane engine designs resulted in more powerful engines and higher airspeeds. As speed increases, drag increases nonlinearly. Single wing (less drag) airplane designs were required to take advantage of the improvements in speed.
The first all metal monoplanes were developed during World War I. These were faster, but it was quickly realized that they did not climb well. Although more powerful than the initial airplane engines, the engines of World War I did not have enough power to lift the all-metal monoplanes quickly enough.
Wood, iron, and aluminum are possible materials for making aircraft wings. How do the densities of these materials compare? The density of water is 1 g/cm3 by definition at standard temperature and pressure. Wood floats in water so its density must be less than 1 g/cm3. Its density ranges from 0.45 to 0.85 g/cm3. Iron and aluminum do not float, so their densities must be greater than 1 g/cm3. Iron's density is equal to 7.9 g/cm3 and aluminum's density is equal to 2.7 g/cm3. So, in theory, it should be possible to reduce the weight of an airplane by utilizing aluminum instead of iron. Aluminum is about 1/3 the density of iron. But there is a problem: aluminum is not strong and alloying does not strengthen the material the way it does in bronze and iron. Aluminum needed to be strengthened, but how?
In 1901, German metallurgist Alfred Wilm was working to harden aluminum-copper alloys. The work was not going well so in frustration he went on holiday (vacation). Upon his return, he found a harder material and after many years of work developed a commercially viable age-hardened aluminum alloy. Age-hardened aluminum, which is about three times lighter than iron, replaced iron in aircraft manufacturing. A photo of an early aluminum-bodied aircraft is shown below.
Age hardened aluminum is not as strong as iron so additional aluminum is needed which does offset some of the weight savings. The video in our later Synthesis, Fabrication, and Processing of Materials lesson has more on the use of aluminum in the construction of a modern commercial jet airliner. In the photo below is a Boeing 787 Dreamliner which utilizes a composite airframe, not aluminum. Boeing claims that this airliner is 20% more fuel-efficient than previous generations of airliners.
Now please proceed to the next section on one of my favorite alloys, a future star, a non-crystalline metal.
Most metals are crystalline. In fact, it is typically very difficult to make a noncrystalline metal. The following short video highlights metals that are noncrystalline, i.e., amorphous. These materials are sometimes referred to as metallic glasses.
After viewing this video please proceed to the summary page of this lesson.
The extremely versatile range of different metals and alloys have produced an incredible range of application for these metals and alloys. In this lesson, we have explored how ferrous metals and the many different non-ferrous metals and alloy systems are historically and currently used. Understanding the strengths and weaknesses of these materials can allow one to properly select the right material for the desired application and the environment in which the application exists. In the next lesson, we will be looking at ceramics and their role as one of the primary materials.
You have reached the end of Lesson 6! Double-check the to-do list on the Overview page to make sure you have completed all of the activities listed there before you begin Lesson 7.
Links
[1] https://www.youtube.com/@fuseschool
[2] https://en.wikipedia.org/wiki/Bessemer_process
[3] https://en.wikipedia.org/wiki/Aluminium
[4] https://upload.wikimedia.org/wikipedia/commons/9/96/Aluminium_-_world_production_trend.svg
[5] https://en.wikipedia.org/wiki/List_of_countries_by_aluminium_oxide_production
[6] https://www.flickr.com/photos/mrsmith075/5001222251/in/photolist-8BWz8R-7UbhKu-imkg7q-au7uqc-9qzVg7-pZbkbf-HB6r-qCnLqT-8oFAuJ-kdQP2i-6d46AW-qBBgAW-oFyogv-ksDJSB-odEQTY-kajiLT-o9Z9PH-pV19o9-qWyjXV-RfTcC1-4CdPzq-6ZKFJm-84fF8F-68pPU7-9qr1Gn-74fKTK-8u7SEC-paYBxb-7LK72U-5Sujtj-pk6RhQ-3P7qbe-8nasuM-4BYwRS-8BK5sH-auGi3y-bAPhPZ-4BTSqN-mD9c5G-ouToJT-oWQwA4-owVw2K-qvHbpm-nwNubY-odG3vk-cyevsC-4G94tV-8kRK7j-6cTuEA-4BTSxh
[7] https://commons.wikimedia.org/wiki/File:Sopwith_F-1_Camel_2_USAF.jpg
[8] https://commons.wikimedia.org/w/index.php?curid=10985391
[9] https://fr.wikipedia.org/wiki/User:Bryan_Fury75
[10] https://fr.wikipedia.org/wiki/
[11] https://commons.wikimedia.org/wiki/File:All_Nippon_Airways_Boeing_787-8_Dreamliner_JA801A_OKJ.jpg