Engineering Materials Module II PDF

Module II: Engineering Materials and Metal Joining Processes Content: Metals-Ferrous: Tool steels and stainless steels. Non-ferrous /metals: aluminum alloys. Ceramics- Glass, optical fiber glass, cermets. Composites- Fiber reinforced composites, Metal matrix Composites. Smart materials- Piezoe...

Module II: Engineering Materials and Metal Joining Processes Content: Metals-Ferrous: Tool steels and stainless steels. Non-ferrous /metals: aluminum alloys. Ceramics- Glass, optical fiber glass, cermets. Composites- Fiber reinforced composites, Metal matrix Composites. Smart materials- Piezoelectric materials, shape memory alloys, semiconductors, and super-insulators. Metal Joining Processes: Fitting, Sheet metal, Soldering, brazing and Welding: Definitions. Classification and methods of soldering, brazing, and welding. Brief description of arc welding, Oxy-acetylene welding, Introduction to TIG welding and MIG welding. Ferrous and Non-Ferrous Metals/Alloys  Tool Steel Tool steel is any of various carbon steels and alloy steels that are particularly well-suited to be made into tools and tooling, including cutting tools, dies, hand tools, knives, and others. Their suitability comes from their distinctive hardness, resistance to abrasion and deformation, and their ability to hold a cutting edge at elevated temperatures. As a result, tool steels are suited for use in the shaping of other materials, as for example in cutting, machining, stamping, or forging. With a carbon content between 0.5 % and 1.5 %, tool steels are manufactured under carefully controlled conditions to produce the required quality. The presence of carbides in their matrix plays the dominant role in the qualities of tool steel. The four major alloying elements that form carbides in tool steel are: tungsten, chromium, vanadium and molybdenum.  Types of Tool steels There are several classes of tools steels available which will be selected based on the specific environment, particularly allowing for temperature. Among those are Cold-work, Hot-work, and High-speed. Cold-work tool steels feature strength, impact toughness and wear resistance. They are typically used in temperatures that do not exceed 400°F / 200°C. Hot-work tool steels combine the strength, impact toughness and wear resistance with the ability to perform at higher temperature. High-speed tool steels, likewise, deliver strength, impact toughness and wear resistance, and are able to retain those properties in environments of 1000°F / 540°C.  Aluminium Alloys An aluminium alloy is an alloy in which aluminium (Al) is the predominant metal. The typical alloying elements are copper, magnesium, manganese, silicon, tin, nickel and zinc. There are two principal classifications, namely casting alloys and wrought alloys, both of which are further subdivided into the categories heat-treatable and non-heat-treatable. About 85% of aluminium is used for wrought products, for example rolled plate, foils and extrusions. Cast aluminium alloys yield cost-effective products due to the low melting point, although they generally have lower tensile strengths than wrought alloys. WROUGHT ALUMINUM ALLOY DESIGNATION SYSTEM CAST ALUMINUM ALLOY DESIGNATION SYSTEM  Ceramics A ceramic is a solid material comprising an inorganic compound of metal or metalloid and non-metal with ionic or covalent bonds. Common examples are earthenware, porcelain, and brick. A ceramic material is an inorganic, non-metallic, often crystalline oxide, nitride or carbide material. Ceramic materials are brittle, hard, strong in compression, and weak in shearing and tension. They can withstand chemical erosion that occurs in other materials subjected to acidic or caustic environments. Ceramics generally can withstand very high temperatures, ranging from 1,000 °C to 1,650 °C. Classification of ceramic materials on the basis of application  Glasses The glasses are a familiar group of ceramics; containers, windows, lenses, and fiberglass represent typical applications. They are non-crystalline silicates containing other oxides, notably CaO, Na2O, K2O, and Al2O3 , which influence the glass properties. A typical soda–lime glass consists of approximately 70 wt. % SiO2 , the balance being mainly Na2O (soda) and CaO (lime). Compositions and Characteristics of Some of the Common Commercial Glasses  Glass ceramics Most inorganic glasses can be made to transform from a non-crystalline state to on that is crystalline by the proper high-temperature heat treatment. This process is called devitrification, and the product is a fine-grained polycrystalline material which is called a glass–ceramic. A nucleating agent (frequently titanium dioxide) is added to induce the crystallization or devitrification process. Desirable characteristics of glass–ceramics include a low coefficient of thermal expansion, such that the glass–ceramic ware will not experience thermal shock; relatively high mechanical strengths and thermal conductivities.  Glass ceramics Some glass–ceramics may be made optically transparent; others are opaque. Possibly the most attractive attribute of this class of materials is the ease with which they may be fabricated. Glass–ceramics are manufactured commercially under the trade names of Pyroceram, Corning ware, Cercor, and Vision. The most common uses for these materials are as ovenware and tableware, primarily because of their strength, excellent resistance to thermal shock, and their high thermal conductivity. They also serve as electrical insulators and as substrates for printed circuit boards, and are utilized for architectural cladding, and for heat exchangers and regenerators.  Clay products One of the most widely used ceramic raw materials is clay. This inexpensive ingredient, found naturally in great abundance, often is used as mined without any upgrading of quality. Another reason for its popularity lies in the ease with which clay products may be formed; when mixed in the proper proportions, clay and water form a plastic mass that is very amenable to shaping. The formed piece is dried to remove some of the moisture, after which it is fired at an elevated temperature to improve its mechanical strength.  Clay products Most of the clay-based products fall within two broad classifications: the structural clay products and the white-wares. Structural clay products include building bricks, tiles, and sewer pipes-applications in which structural integrity is important. The white-ware ceramics become white after the high-temperature firing. Included in this group are porcelain, pottery, tableware, china clay, and plumbing fixtures.  Refractories The salient properties of these materials include the capacity to withstand high temperatures without melting or decomposing, and the capacity to remain unreactive and inert when exposed to severe environments. Refractory materials are marketed in a variety of forms, but bricks are the most common. Typical applications include furnace linings for metal refining, glass manufacturing, metallurgical heat treatment, and power generation.  Abrasives Abrasive ceramics are used to wear, grind, or cut away other material, which necessarily is softer. Therefore, the prime requisite for this group of materials is hardness or wear resistance; in addition, a high degree of toughness is essential to ensure that the abrasive particles do not easily fracture. Diamonds, both natural and synthetic, are utilized as abrasives; however, they are relatively expensive. The more common ceramic abrasives include silicon carbide, tungsten carbide (WC), aluminium oxide (or corundum), and silica sand. Abrasives are used in several forms-bonded to grinding wheels, as coated abrasives and as loose grains.  Cements The another important class of ceramic materials are inorganic cements classified as: Cement, plaster of Paris, and lime, which, as a group, are produced in extremely large quantities. The characteristic feature of these materials is that when mixed with water, they form a paste that subsequently sets and hardens.  Cements Of this group of materials, Portland cement is consumed in the largest tonnages. It is produced by grinding and intimately mixing clay and lime-bearing minerals in the proper proportions, and then heating the mixture to about 1400°C in a rotary kiln; this process, sometimes called calcination, produces physical and chemical changes in the raw materials. The resulting ‘‘clinker’’ product is then ground into a very fine powder to which is added a small amount of gypsum (CaSO4–2H2O) to retard the setting process. Several different constituents are found in Portland cement, the principal ones being tri-calcium silicate (3CaO–SiO2) and di-calcium silicate (2CaO–SiO2).  Advanced Ceramics Advanced ceramics are utilized in optical fibre communications systems, in micro-electromechanical systems, as ball bearings and in applications that exploit the piezoelectric behaviour of a number of ceramic materials. Advanced ceramics can be defined as the substances possessing exceptional properties that makes them highly resistant to bending, stretching, melting or corrosion. Few examples of advanced ceramics are silicon nitride, silicon carbide, etc. Advanced ceramics are mostly non oxides while conventional ceramics are oxides. COMPOS ITES  Introduction Many of our modern technologies require materials with unusual combinations of properties that cannot be met by the conventional metal alloys, ceramics, and polymeric materials. This is especially true for materials that are needed for aerospace, underwater, and transportation applications. Material property combinations and ranges have been, and are yet being, extended by the development of composite materials. A composite is considered to be any multiphase material that exhibits a significant proportion of the properties of both constituent phases such that a better combination of properties is realized.  Introduction Composite materials are composed of two phases; one is termed the matrix, which is continuous and surrounds the other phase, often called the dispersed phase. The properties of composites are a function of the properties of the constituent phases, their relative amounts, and the geometry of the dispersed phase. ‘‘Dispersed phase geometry’’ means the shape of the particles and the particle size, distribution, and orientation;  Metal Matrix composites A metal matrix composite (MMC) is a composite material with fibers or particles dispersed in a metallic matrix, such as copper, aluminum, or steel. The secondary phase is typically a ceramic (such as alumina or silicon carbide) or another metal (such as steel). They are typically classified according to the type of reinforcement: short discontinuous fibers (whiskers), continuous fibers, or particulates. MMCs are made by dispersing a reinforcing material into a metal matrix. The reinforcement surface can be coated to prevent a chemical reaction with the matrix. For example, carbon fibers are commonly used in aluminum matrix to synthesize composites showing low density and high strength.  In the area of the matrix, most metallic systems have been explored for use in metal matrix composites, including Al, Be, Mg, Ti, Fe, Ni, Co, and Ag. By far the largest usage is in aluminum matrix composites. From a reinforcement perspective, the materials used are typically ceramics since they provide a very desirable combination of stiffness, strength, and relatively low density. The potential reinforcement materials include SiC, Al2O3, B4C, TiC, TiB2, graphite, and a number of other ceramics.  Overview of Smart Materials Features: These materials are a part of a group of materials These materials are a part of a group of materials broadly known as Functional Materials. The basic energy forms that gets interchanged are: thermal energy, electric energy, magnetic energy, sound energy & mechanical energy. Analogous to Biological Materials: Analogous to Biological Materials: adaptivity, cellular, self sensing, actuation & control.  Smart Materials Materials which can think on their own & have Mental alertness, quick perception, speedy activity, effectiveness, spirited liveliness intelligence … Smart materials can respond to a change & are able to receive information (sensing the problem) able to analyze & decide (processing the information) able to act on the decision (actuating the process)  Super Insulators A super-insulator is a material that at low temperatures does not conduct electricity, i.e. has an infinite resistance so that no electric current passes through it. Super insulators are the materials that exhibit the reverse property of super-conductor. The super insulators will hold a charge forever, whereas a superconductor will pass a current forever. The super-insulating state is the exact dual to the superconducting state and can be destroyed by increasing the temperature and applying an external magnetic field and voltage.  Super Insulators At temperature close to absolute zero, super insulators have a resistance 100,000 times higher than that at room temperature. Scientists/Researchers prepared the super-insulator on a very thin film of Titanium Nitride. The film can act as superconductor or super-insulator depending on the thickness of the film. The film which just on the side of insulating side of transition stage when undergone a decrease in temperature or magnetic field suddenly transformed into a super-insulator. The super-insulators store charge forever, so that they can be employed to make more efficient electric circuits in conjunction with superconductors.  Semiconductors A semiconductor is a material, which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises. Its conducting properties may be altered in useful ways by introducing impurities ("doping") into the crystal structure. When two differently doped regions exist in the same crystal, a semiconductor junction is created. The behaviour of charge carriers, which include electrons, ions, and electron holes, at these junctions is the basis of diodes, transistors, and most modern electronics. Some examples of semiconductors are silicon, germanium, gallium arsenide etc.  Semiconductors After silicon, gallium arsenide is the second-most common semiconductor and is used in laser diodes, solar cells, microwave-frequency integrated circuits, and others. Silicon is a critical element for fabricating most electronic circuits. Semiconductor devices can display a range of useful properties, such as passing current more easily in one direction than the other, showing variable resistance, and having sensitivity to light or heat. Because the electrical properties of a semiconductor material can be modified by doping and by the application of electrical fields or light, devices made from semiconductors can be used for amplification, switching, and energy conversion.