NAT SCI 1-CHEMISTRY FOR ENGINEERS Lesson 2: Metals and Alloys PDF

NAT SCI 1-CHEMISTRY FOR ENGINEERS Lesson 2: Metals and Alloys Learning Outcomes: Having successfully completed this lesson, you will be able to: ✓ Determine the characteristics of metals and alloys and their applications. Time Frame: 2 hours Introduction...

NAT SCI 1-CHEMISTRY FOR ENGINEERS Lesson 2: Metals and Alloys Learning Outcomes: Having successfully completed this lesson, you will be able to: ✓ Determine the characteristics of metals and alloys and their applications. Time Frame: 2 hours Introduction Engineers are often involved in materials selection decisions, which necessitates that they have some familiarity with the general characteristics of a wide variety of metals and their alloys. Thus, this lesson introduces you to the basic properties of metals and overview of some of the commercial alloys and their general properties and limitations. The properties of metals are the focus of the first discussion followed by the properties of alloys and some of their applications. Activity # 2.2 A: Recalling Recall the mechanical properties of metals and alloys. For the metals, write them in the blue clouds while for the alloys in the green clouds. You may add clouds as many as you desire. 1|Page  CHEMISTRY FOR ENGINEERS Analysis: Checking Insight Instruction: Answer the following questions: a. Define a metal. b. Illustrate the arrangement of metals in the periodic table. c. Describe an alloy. d. Compare and contrast metal and alloy. Give at least two examples for each. In our study of periodicity, we learned that metallic character increases toward the left and toward the bottom of the periodic table and that oxides of most metals are basic. The oxides of some metals (and metalloids) are amphoteric. The discussion below focuses primarily on the mechanical behavior of metals. Description of Metals The term “Metal” is originated from the Greek word “metallon” which means “mine, quarry, metal”. Defined as a material that forms positive ions by losing electrons during chemical reactions. It is a material that is typically hard,opaque, shiny, and has good electrical and thermal conductivity. Metals are characterized by hardness, good heat and thermal conductivity, bright luster, ability to resonate sound, high density, and high melting point. With the exception of mercury, metals are solids at room temperature. Properties of Metals Physical Properties These properties are related to the atomic structure and density of the material. 2|Page  CHEMISTRY FOR ENGINEERS Coefficient Heat and Magnetic Melting Point Reflectivity of Linear Electrical Susceptibility Expansion Conductivity is the is the is the ability temperature ability of a is the is the ability of a material at which a material to increase in of a material to hold a substance reflect length of a to conduct or magnetic field passes from a light or body for a transfer heat when it is solid state to a heat. given rise in or electricity. magnetized. liquid state. temperature. Mechanical Properties Define the behavior of materials under the action of external forces called loads. The mechanical properties of metals are determined by the range of usefulness of the metal and establish the service that is expected. Mechanical properties are also useful for helping to specify and identify metals. Common Mechanical Properties of Metals Strength Strength is the mechanical property that enables a metal to resist deformation load. The strength of a material is its capacity to withstand destruction under the action of external loads. The stronger the materials the greater the load it can withstand. Types of Strength Tensile Strength ✓ Is the ability of a metal to resist being pulled apart by opposing forces acting in a straight line. ✓ Generally, refers to the amount of stress components can tolerate until deforming permanently. o Pure molybdenum has a high tensile strength and is very resistant to heat. o It is used principally as an alloying agent in steel to increase strength, hardness, and resistance to heat. 3|Page  CHEMISTRY FOR ENGINEERS Compression Strength ✓ Refers to the amount of stress a material can withstand while being pushed equally from sides, rather than pulled. Shear Strength ✓ Refers to the ability of a material to resist being fractured by to two opposite forces acting in a straight line on two different tangential areas. Elasticity Elasticity is the ability of an object or material to resume its normal shape after being stretched or compressed. When a material has a load applied to it, the load causes the material to deform. The elasticity of a material is its power of coming back to its original position after deformation when the stress or load is released. Plasticity The plasticity of a material is its ability to undergo some permanent deformation without rupture(brittle). Plastic deformation will take place only after the elastic range has been exceeded. Pieces of evidence of plastic action in structural materials are called yield, plastic flow and creep. Materials such as clay, lead are plastic at room temperature, and steel plastic when at bright red-heat. Hardness The resistance of a material to force penetration or bending is hardness. The hardness is the ability of a material to resist scratching, abrasion, cutting or penetration. Hardness indicates the degree of hardness of a material that can be imparted particularly steel by the process of hardening. 4|Page  CHEMISTRY FOR ENGINEERS Toughness It is the property of a material which enables it to withstand shock or impact. Toughness is the opposite condition of brittleness. The toughness is may be considering the combination of strength and plasticity. For metal to be tough, it must display both strength and ductility. Manganese steel, wrought iron, mild steel are examples of toughness materials. Brittleness The brittleness of a property of a material which enables it to withstand permanent deformation. Cast iron, glass are examples of brittle materials. They will break rather than bend under shock or impact. Generally, the brittle metals have high compressive strength but low in tensile strength. Ductility The ductility is a property of a material which enables it to be drawn out into a thin wire. Mild steel, copper, aluminum are the good examples of a ductile material. Stiffness The stiffness is the resistance of a material to elastic deformation or deflection. In stiffness, a material which suffers light deformation under load has a high degree of stiffness. The stiffness of a structure is important in many engineering applications, so the modulus of elasticity is often one of the primary properties when selecting a material. Malleability The malleability is a property of a material which permits it to be hammered or rolled into sheets of other sizes and shapes. It is also the property of a metal to be deformed or compressed permanently without rupture or fracture. Aluminum, copper, tin, lead are examples of malleable metals. 5|Page  CHEMISTRY FOR ENGINEERS Cohesion The cohesion is a property of a solid body by virtue of which they resist from being broken into a fragment. Impact Strength The impact strength is the ability of a metal to resist suddenly applied loads. Fatigue The fatigue is the long effect of repeated or alternating stresses which causes the strain or break of the material or permanent deformation. It is the term 'fatigue' use to describe the fatigue of material under repeatedly applied forces. Such a repetition of stress may occur, for example, in the shank of a rockdrill. Creep The creep is a slow and progressive deformation of a material with time at a constant force. Some metals are generally exhibiting creep at high temperature, whereas plastic, rubber, and similar amorphous material are very temperature sensitive to creep. The force for a specified rate of strain at constant temperature is called creep strength. Chemical Properties A chemical property is any of a material's properties that becomes evident during, or after, a chemical reaction; that is, any quality that can be established only by changing a substance's chemical identity. Chemical Property of Metals Metals when burned in the presence of oxygen, they combine with oxygen to form metallic oxides which are basic in nature. Metals react differently with water. Sodium reacts violently with waterforming sodium hydroxide and hydrogen. Magnesium reacts mildly with water but vigorously with steam. 6|Page  CHEMISTRY FOR ENGINEERS Zinc and iron react mildly with steam. Copper, gold and silver do not react with water at all. Most metals, on reacting with water produce hydroxide. Metals differ in their reactivity with acids. Most metals react with acids to produce salts and hydrogen. Most metals corrode when they are exposed to atmosphere. Example, the iron gets rusty after sometime if it is not painted. Application of Some Important Metals Metal, Characteristics Uses Chemical Symbol Aluminum, Al Lightweight, soft, low Used as a deoxidizer and alloying agent in strength metal which the manufacture of steel. Castings, pistons, can easilybe cast, torque converter pumphousings, aircraft forged, machined, structures, railway cars, electrical formed, and welded. transmission lines, and kitchen utensils Chromium, Cr Hard, brittle, corrosion Used as an alloying agent in steel and cast resistant, andcan be iron and in nonferrous alloys of nickel, welded, machined, copper, aluminum, and cobalt. and forged. Used in electroplating for appearance and wear, in powder metallurgy, and to make Xray targets, mirrors, and stainless steel. Cobalt, Co Can be welded, Used as an alloying element in permanent limitedly machined, and soft magnetic materials, highspeed and colddrawn tools bits and cutters, high temperature creep resisting alloys, and cemented carbide tool bits and cutters. It is also used in making insoluble paint pigments and blue ceramic glazes. Copper, Cu Can be forged, cast, Used of commercially pure copper is in the welded but its electrical industry where it is made into machinability is only wire and other such conductors. fair Used in the manufacture of nonferrous alloys such as brass, and bronze. Lead, Pb Can be cast, cold Used in the manufacture of electrical worked, welded, and equipment, such as lead sheathed power machined, has low and telephone cables and storage strength with heavy batteries. 7|Page  CHEMISTRY FOR ENGINEERS weight Magnesium, Can be forged, cast Used as a deoxidizer for brass, bronze, Mg welded, and nickel, and silver. It is used in commercial machined weight saving applicationssuch as aircraft parts, as a pyrotechnic for railroad signals and military purposes, and to make magnesium castings used for engine housings, blowers, hose pieces, and aircraft landing wheels. Manganese, Can be welded, Used as an alloying agent in the Mn machined, and manufacture of steel to increase its tensile coldworked. strength. Molybdenum, Can only be welded Used as an alloying agent in steel to Mo in an atomic increase its strength, hardenability, and hydrogen arc, or resistance to heat. Heating elements, butt welded by switches, contacts, thermocouples, resistance heating in welding electrodes, and cathode ray tubes vacuum. are made of molybdenum. Nickel, Ni Readily welded, Used in the production of ferrous and machined, forged, nonferrous alloys. Chemical and food cast, and easily processing equipment, electrical formed. resistance heating elements, ornamental trim. It is used as an alloy agent in the manufacture of stainless steel. Tin, Sn Can be cast, Its major application is in the coating of coldworked, steel, and in the manufacture of containers machined, and for the preservation of perishable food. soldered, not It is used in the form of foil for wrapping weldable food products. It is also used as an alloying agent with copper to produce tin brasses and bronzes, with lead to produce solder, and with antimony and lead to form babbit. Titanium, Ti Can be machined, has Used as an alloy agent for aluminum, low impact strength, copper, magnesium steel, nickel, and and low creep other metals. strength at elevated It is also used in making powder for temperatures (above pyrotechnics and in manufacturing 800° F). It can be cast turbine blades, aircraft firewalls, engine into simple shapes nacelles, frame assemblies, ammunition 8|Page  CHEMISTRY FOR ENGINEERS only. tracks, and mortar base plates. Tungsten, W Hard to machine, Used in the manufacture of incandescent requires high lamp fililaments and phonograph needles; temperatures for and as an alloying agent in the production melting of non-consumable welding electrodes, armor plate, high speed steel, and projectiles. Zinc, Zn Can be cast, cold Use of zinc is in galvanizing such items as worked (extruded), pipe,tubing, sheet metal, and wire nails. It machined,and is also used as an alloying element in welded. producing alloys such as brass, and bronze. What are Metal Alloys? Metal alloys are substances created by mixing metal with another component, either another metal or a nonmetal substance. They are generally made by melting the substances, mixing them together, and then letting them cool to room temperature, resulting in a solid material. Properties of Alloys Have low Hard and less electrical malleable conductivity Have lower Have corrosion melting points resistance and than the chemical component resistance elements 9|Page  CHEMISTRY FOR ENGINEERS Importance of Alloys Types of Metal Alloys Metal alloys, by virtue of composition, are often grouped into two types. Ferrous Alloys Those of which iron is the prime constituent along with C, Al, B, Cr, Co, Cu and Mn to improve the properties of steel. Ferrous alloys are: ✓ Steels are iron–carbon alloys that may contain appreciable concentrations of other alloying elements ✓ Cast Irons are a class of ferrous alloys with carbon contents above 2.14 wt. %; in practice, however, most cast irons contain between 3.0 and 4.5 wt. % C and other alloying elements. 10 | P a g e  CHEMISTRY FOR ENGINEERS Limitations of Ferrous Alloys: # Relatively high density, # Comparatively low electrical conductivity, # Susceptibility to corrosion Widely used in construction materials due to # Iron-containing compounds exist in abundant quantities within the earth’s crust; # Metallic iron and steel alloys may be produced using relatively economical extraction, refining, alloying, and fabrication techniques; # Ferrous alloys are extremely versatile, in that they can be tailored to have a wide range of mechanical and physical properties Nonferrous Alloys Alloys that are not iron-based or those that does not contain iron in appreciable amounts. Common Alloys GOLD ALLOYS Although pure gold is sometimes used in electronics, gold jewelry is always a mixture of gold and other metals. Pure gold is actually quite soft. Adding small amounts of other metals makes the gold hard enough to use in jewelry. Alloying gold with different metals also affects its color. The familiar yellow gold is an alloy of gold with copper and silver. Adding more copper than silver gives redder shades. White gold is an alloy of gold with nickel, platinum or palladium. Around 12% of people may be allergic to the nickel in white gold. Alloys of Gold and Their Composition Color of Gold Alloy Composition Yellow Gold (22K) Gold 91.67%, Silver 5%, Copper 2%, Zinc 1.33% Red Gold (18K) Gold 75%, Copper 25% Rose Gold (18K) Gold 75%, Copper 22.25%, Silver 2.75% 11 | P a g e  CHEMISTRY FOR ENGINEERS Pink Gold (18K) Gold 75%, Copper 20%, Silver 5% White Gold (18K) Gold 75% Platinum or Palladium 25% White Gold (18K) Gold 75%, Palladium 10%, Nickel 10%, Zinc 5% Gray-White Gold (18K) Gold 75%, Iron 17%, Copper 8% Soft Green Gold (18K) Gold 75%, Silver 25% Light Green Gold (18K) Gold 75%, Copper 23%, Cadmium 2% Green Gold (18K) Gold 75%, Silver 20%, Copper 5% Deep Green Gold (18K) Gold 75%, Silver 15%, Copper 6%, Cadmium 4% Blue-White or Blue Gold(18K) Gold 75%, Iron 25% Purple Gold Gold 80%, Aluminum 20% STEEL Steel is an alloy of iron and other elements, including carbon, nickel and chromium. It is stronger than pure iron and can contain up to 2% carbon. Varying the amount of carbon gives steel different properties. For example, a higher carbon content makes a hard steel. Types of Steel Steels are classified by how much carbon they contain. ❖ Low Carbon Steels Contain less than 0.25% carbon. These alloys are relatively soft and weak but have outstanding ductility and toughness; in addition, they are machinable, weldable, and, of all steels, are the least expensive to produce. Typical applications include automobile body components, structural shapes (I- beams, channel and angle iron), and sheets that are used in pipelines, buildings, bridges, and tin cans. ❖ Medium-Carbon Steels Have carbon concentrations between about 0.25 and 0.60 wt. %. These alloys may be heat-treated by austenitizing, quenching, and then tempering to improve their mechanical properties. Applications include railway wheels and tracks, gears, crankshafts, and other machine parts and high-strength structural components calling for a combination of high strength, wear resistance, and toughness. 12 | P a g e  CHEMISTRY FOR ENGINEERS ❖ High Carbon Steels Normally having carbon contents between 0.60 and 1.4 wt. %, are the hardest, strongest, and yet least ductile of the carbon steels. They are almost always used in a hardened and tempered condition and, as such, are especially wear resistant and capable of holding a sharp cutting edge. These steels are utilized as cutting tools and dies for forming and shaping materials, as well as in knives, razors, hacksaw blades, springs, and high- strength wire. ❖ Stainless Steels Highly resistant to corrosion (rusting) in a variety of environments, especially the ambient atmosphere. Their predominant alloying element is chromium; a concentration of at least 11 wt. % Cr is required. Corrosion resistance may also be enhanced by nickel and molybdenum additions. Stainless steels in their solid state have a microscopic crystalline structure. Types of Stainless Steel based on the Crystal Structure of the Metal Ferritic stainless steel ▪ Ferritic stainless steels contain 11–25 % chromium, 0.08 to 0.20 % carbon, 1.0- 1.5 % manganese besides iron and an amount of nickel and titanium. ▪ Made up of ferrite crystals, a form of iron which contains only a very small amount (up to 0.025%) of carbon. Ferrite absorbs such a small amount of carbon because of its body centered cubic crystal structure - one iron atom at each corner, and one in the middle. This central iron atom is what gives ferritic stainless steels their magnetic properties. ▪ Ferritic stainless steels are less widely-used due to their limited corrosion resistance and average durability. ▪ These are magnetic and exhibit a better resistance to corrosion than martensitic grades. ▪ Utilized in automotive exhaust components, tanks for agricultural sprays, valves, glass molds, and combustion chambers. 13 | P a g e  CHEMISTRY FOR ENGINEERS Martensitic stainless steel: ▪ Martensite is a body centred cubic form of crystallized iron which is created when heated austenite is rapidly cooled by quenching. ▪ Martensitic stainless steel is characterized by its extremely high strength, low fracture resistance, and low ductility. ▪ These steels contain 12–18% chromium and 0.15 to 0.70% carbon. ▪ Steels with 12 to 14% chromium and 0.3% carbon are widely used for table cutlery, tools and equipment. Austenitic Stainless Steels: ▪ Austenitic stainless steels contain austenite, a form of iron which can absorb more carbon than ferrite. Austenite is created by heating ferrite to 9120C, at which point it transitions from a body centred cubic crystal structure to a face centred cubic crystal structure. Face centred cubic structures can absorb up to 2% carbon. ▪ Are the most corrosion resistant because of the high chromium contents and also the nickel additions. Nickel is a very strong austenitic stabilizer and therefore the microstructure of these steels is austenitic at room temperature. ▪ Not magnetic ▪ These steels contain 12 to 21% chromium and 8 to 15% nickel and carbon less than 0.2%. ▪ Typical applications are in chemical and food processing equipment, and welding construction. CAST IRONS Cast irons are a class of ferrous alloys with carbon contents above 2.14 wt.%; in practice, however, most cast irons contain between 3.0 and 4.5 wt.% C and, in addition, other alloying elements. Alloying Elements for Cast Iron Nickel: It may be termed as one of the most important alloying elements. It improves tensile strength, ductility, toughness and corrosion resistance. Chromium: Its addition to steel improves toughness, hardness and corrosion resistance. 14 | P a g e  CHEMISTRY FOR ENGINEERS Boron: It increases hardenability and is therefore very useful when alloyed with low carbon steels. Cobalt: It is added to high-speed steels to improve hardness, toughness, tensile strength, thermal resistance and magnetic properties. It acts as a grain purifier. Tungsten: Tungsten improves hardness, toughness, wear resistance, shock resistance, magnetic reluctance and ability to retain hardness at elevated temperatures. It provides hardness and abrasion resistance properties to steel. Molybdenum: It improves wear resistance, hardness, thermal resistance, ability to retain mechanical properties at elevated temperatures and helps to inhibit temper brittleness. Vanadium: It increases tensile strength, elastic limit, ductility, shock resistance and also acts as a degasser when added to molten steel. It provides improvement to hardenability of steel. It is a very good deoxidizer and promotes grain growth. It is the strongest carbide former. Titanium is used to fix carbon in stainless steel and thus prevents the precipitation of chromium-carbide. Niobium: It improves ductility, decreases hardenability and substantially improves the impact strength. It also promotes fine grain growth. Application of Major Metallic Alloys ❖ Steel alloy – Composed of 90 % iron and 10 % carbon. It is hard with high strength. Widely used in ships, buildings, railway lines, reinforced concrete. ❖ Stainless Steel – contains 74 % iron,8 % carbon, 1 % chromium. Shiny, high strength and does not rust. Used in cutlery and surgical instruments. ❖ Aluminum alloys – high specific strength, corrosion resistance, specific conductivity, used in aerospace, packaging, sports equipment, energy, construction Aircraft, food containers, power cables. ❖ Titanium alloys –extremely strong; room-temperature tensile strengths as high as 1400 MPa (200,000 psi) are attainable, yielding remarkable specific strengths. Furthermore, the alloys are highly ductile and easily forged and machined. They are commonly utilized in airplane structures, space vehicles, and surgical implants, and in the petroleum and chemical industries. 15 | P a g e  CHEMISTRY FOR ENGINEERS ❖ Copper alloy – high electrical & thermal conductivity, easy to form/cast, corrosion resistance, used in electronics, coins, wiring, circuit boards, electronic components. ❖ Nickel alloy – high temperature strength and creep resistance (super alloys), used in Aerospace, Aircraft engines. ❖ Bronze, an alloy of 90 % copper and 10 % tin. It is hard and strong, does not corrode easily and has shiny surface. Commonly used to build statues and monuments, in the making of medals, swords and artistic materials.by civilizations before iron extraction methods were developed. ❖ Brass: Is composed of 70 % copper and 30 % zinc. It is harder than copper and does not tarnish. It is used for door knobs, buttons and musical instruments and kitchenware. ❖ Solder: an alloy of zinc and lead. It is used in electronics to attachcomponents to circuit boards. ❖ Amalgam: an alloy of mercury and silver or tin. It is used for dental fillings because it can be shaped when warm and resists corrosion. ❖ Duralumin – contains 93 % aluminum, 3 % copper, 3 % magnesium, 1 % manganese. Light and strong. Used to make the body of aero planes and bullet trains. ❖ Pewter – composed of 96 %tin, 3 % copper and 1 % antimony. Its properties are shiny and strong. Used in making of souvenirs Checking your understanding! Construct a vis-à-vis comparison of different alloyed materials. Cite the advantages, disadvantages, and its best application. Congratulations! Well done! You finish module 2 lesson 2. 16 | P a g e  CHEMISTRY FOR ENGINEERS References: Gaffney, J., & Marley, N. (2018). General chemistry for engineers. Elsevier Inc. Holleman, A.F.; Wiberg, E. (2001). Inorganic Chemistry. Academic Press: San Diego, Callister, W. D. Jr., & Rethwisch, D.G. (2010). Materials Science and Engineering An Introduction, 8th Edition, John Wiley & sons, Inc. 17 | P a g e