04_Metals Summary.pdf

FAMILY OF METALS SUMMARY especially at elevated temperatures. There are two primary diffusion mechanisms: STRESS AND STRAIN CONCEPT V...

FAMILY OF METALS SUMMARY especially at elevated temperatures. There are two primary diffusion mechanisms: STRESS AND STRAIN CONCEPT Vacancy Diffusion: Atoms move to neighboring Stress and strain are fundamental concepts in vacancies; temperature-dependent. mechanics that describe the relationship between Interstitial Diffusion: Smaller atoms move forces applied to a material and the resulting between larger one deformation. Stress is a measure of the internal force per unit area within a material, while strain Failure is a measure of the deformation relative to the The failure of engineering materials is original dimensions. almost always an undesirable event for several The relationship between stress and strain is reasons; these include putting human lives in often depicted by a stress-strain curve, which jeopardy, causing economic losses, and shows how a material deforms under increasing interfering with the availability of products and stress. The slope of the curve represents the services. Even though the causes of failure and material's stiffness or modulus of elasticity. the behavior of materials may be known, Stress and strain are essential in various fields, prevention of failures is difficult to guarantee. such as structural engineering, materials science, and mechanical engineering. Understanding Fracture: these concepts is crucial for designing and - Fracture is a form of failure where the material analyzing structures and components that can separates in pieces due to stress, at withstand loads without failure. temperatures below the melting point. There are Elastic deformation: the material returns to its two types of fracture failures typically identified original shape after the stress is removed. based on the speed of occurrence: brittle and Plastic deformation: permanent deformation ductile. after the yield point is exceeded. The material Fatigue: does not return to its original shape after the - Fatigue failure is the formation and propagation stress is removed. of cracks due to a repetitive or cyclic load. Under these circumstances, it is possible for failure to Imperfections and deformations in solids occur at a stress level considerably lower than the tensile or yield strenth for a static load. Point Defects (small-scale defects in the crystal Creep: lattice of a solid material) - Creep failure is characterized by the permanent Point defects are localized disruptions in deformation of material under constant load and the otherwise perfect atomic arrangement of a temperature. crystal structure. These small imperfections can significantly affect a material's mechanical, Fractology thermal, and electrical properties by altering the Study of fracture surface; Fractographic local environment of atoms and promoting methods are routinely used to determine the deformation processes like diffusion. cause of failure in engineering structures, especially in product failure and the practice of Vacancies: Missing atom/ion in lattice; enhances forensic engineering or failure analysis. atomic diffusion, increases with temperature. Fractographs provide valuable information in the Interstitial Atoms: Extra atom between regular fracture analyses, such as the fracture mode, the lattice sites, causing distortion. stress state, and the site of crack initiation. Substitutional Atoms: A different element replaces an atom, causing lattice strain Principle of Fracture Mechanics. Fracture mechanics is the study of the Dislocations (defects where atoms are initiation, growth, and propagation of cracks in misaligned) materials under stress. It aims to understand the Dislocations are linear or one- underlying mechanisms responsible for failure in dimensional defects in the crystal structure of metals and to predict the conditions under which materials. They play a significant role in the a material will fail. mechanical properties of metals, particularly in plastic deformation. Using fracture mechanical principles, an expression has been developed that relates this Edge Dislocation: Extra half-plane of atoms; critical stress for crack propagation (𝜎c) and motion causes plastic deformation. crack length (a) as: Screw Dislocation: Spiral-shaped; dislocation moves with applied stress. Kc = Y𝜎c√𝜋a Mixed Dislocation: Combination of edge and screw dislocations. where Kc: Fracture Toughness Y: Dimensionless Constant Diffusion in Solids 𝜎: Stress Diffusion refers to the process by which a: Crack Length atoms or molecules move through a solid material. It plays a crucial role in processes such as phase transformations, sintering, and creep,  Fatigue Failure Tertiary Creep - This is the final stage of creep Fatigue is a form of failure that occurs in deformation and culminates in the eventual structures subjected to dynamic and fluctuating rupture of the material. The mechanism of failure stresses (e.g., bridges, aircraft, and machine usually manifests as the development of micro components). Under these circumstances, it is cracks, internal voids, and grain boundary possible for failure to occur at a stress level separation. considerably lower than the tensile or yield strength for a static load. The term fatigue is used How to prevent Creep Failure? because this type of failure normally occurs after a lengthy period of repeated stress or strain Preventing creep failure, especially in cycling. systems exposed to high temperatures and stresses, is crucial to ensuring the reliability and Why does Fatigue Failure occur? longevity of components. Fatigue failure occurs due to the formation and propagation of cracks. Material Selection - Selecting materials with high creep resistance is one of the most effective 3 Stages of Fatigue Failure: methods. Stages 1 - Crack Formation Temperature Control - Reducing the operating Stages 2 - Crack Growth temperature can significantly lower the rate of Stages 3 - Fracture creep. Stress Reduction - Lowering the applied load or 3 Types of Fatigue Failure stress on a component decreases the risk of There are predominantly three types of fatigue creep. failures observed in engineering materials. These Grain Structure Optimization - Materials with include: larger grains tend to have higher creep resistance. The grain boundaries are regions High-cycle fatigue - involves the application of where creep deformation can be concentrated, so low-stress levels over a longer period. reducing grain boundary area by using larger Low-Cycle Fatigue - applies higher stress levels grains reduces the likelihood of creep. but for a shorter duration. Periodic Inspection and Maintenance - Thermal Fatigue - a fatigue failure with Continuously monitor equipment for signs of macroscopic cracks resulting from cyclic thermal creep, such as elongation, cracks, or other stresses and strains due to temperature changes, deformations. Early detection can prevent spatial temperature gradients, and high catastrophic failure. temperatures under constrained thermal deformation. Alloying Elements and Processes Alloying is a process where metals are Fatigue Testing and the S-N Curve combined with one or more other elements to A S-N Curve is a plot of the magnitude of improve their properties, such as strength, an alternating stress versus the number of cycles corrosion resistance, hardness, and durability. to failure for a given material. Typically both the This process is crucial in industries such as stress and number of cycles are displayed on construction, automotive, aerospace, and logarithmic scales. electronics, where enhanced material performance is required. The choice of alloying Creep Failure elements and processes determines the Creep failure refers to the gradual characteristics of the final material. deformation of a material under constant stress, typically occurring at high temperatures over long Common Alloying Elements periods. This type of failure is significant in 1. Titanium (Ti): materials subjected to high stress and ○ Base Metals: Steel, Aluminum temperatures, such as in power plants, jet ○ Effects: Increases strength, corrosion engines, or electrical systems. resistance, and reduces density. Often used in aerospace and medical applications due to its 3 Stages of Creep Failure: light weight and durability. These deformations can occur well below the 2. Nickel (Ni): yield point of the material. Creep typically ○ Base Metals: Steel, Aluminum presents itself in three stages: ○ Effects: Improves corrosion resistance and Primary Creep -Also called transient creep, this is toughness, particularly at low temperatures. the first stage of creep and occurs on the Commonly used in stainless steel and high- instantaneous application of load. This is an temperature alloys. elastic region in which the creep rate will slowly 3. Copper (Cu): reduce as a function of time due to strain ○ Base Metals: Steel, Aluminum hardening in the material. ○ Effects: Enhances corrosion resistance, Secondary Creep - Also called steady-state especially in marine environments. Also improves creep, this stage is characterized by a constant electrical conductivity. creep rate defined by a linear curve, and has the 4. Chromium (Cr): longest duration during creep deformation. ○ Base Metals: Steel, Aluminum ○ Effects: Increases corrosion resistance and Major Processes of Metal Fabrication: hardness. Used in the production of stainless Cutting: steel, where chromium forms a protective oxide - Cutting is the foundational step in metal layer to prevent rust. fabrication, shaping the raw material into manageable pieces. Alloying Processes - Traditional Methods 1. Melting and Mixing: - Modern Methods ○ The most common alloying process involves Bending: melting the base metal and then adding alloying - Bending is crucial for shaping metal without elements. This is typically done in a furnace at removing any material, essential for creating high temperatures, where the metals are angles and complex forms. thoroughly mixed in their molten state. - Techniques Used: Press brakes, folding 2. Casting: machines, and manual hammering are common ○ After mixing, the molten alloy is poured into methods for bending metal sheets and rods. molds to solidify and form the desired shapes. - Result: The bending process achieves desired This is often the first step in shaping the material angles and shapes while maintaining the metal’s for its intended use. inherent strength and integrity. 3. Heat Treatment: Machining: ○ Heat treatment is a process used to alter the - Machining is the process of removing parts of microstructure of the alloy. By heating and metal to achieve a specific shape or design, cooling the alloy under controlled conditions, its crucial for creating components with high properties, such as strength, hardness, and precision. ductility, can be enhanced. - Drilling 4. Powder Metallurgy: - Milling ○ In this process, metals are reduced to powder - Turning and Lathing form, mixed with alloying elements, compacted Punching: into shapes, and heated to bond the particles. - Punching, an efficient method in metal This method allows the creation of alloys without fabrication, involves creating holes or indents in melting, useful for producing high-strength metal using a punch and die. It’s often utilized in materials. high-volume production environments. 5. Mechanical Alloying: Stamping: ○ In mechanical alloying, metal powders are - Stamping is a step beyond punching, not only ground together using mechanical forces, creating holes but also involving additional steps producing alloys that are difficult to make using like bending, embossing, or coining, which add to conventional methods. This technique is useful the metal’s shape and texture. for alloys with very high melting points. Forging: - Forging shapes metal using compressive forces, Alloying is a key process in material a method that dates back centuries. It includes engineering that allows the tailoring of metal techniques like: properties to specific needs. By adding elements - Hammer Forging like titanium, nickel, copper, and chromium, - Press Forging manufacturers can create alloys that are Casting: stronger, more corrosion-resistant, and better - Casting is a fundamental process in metal suited to specific environments. The various fabrication, especially when intricate or complex alloying processes, from melting and mixing to shapes are required. powder metallurgy, ensure that these materials - Process Overview: This involves pouring molten are optimized for use in demanding applications. metal into a mold. Once the metal cools and solidifies, it takes on the shape of the mold. Thermal Properties of Metals Casting is particularly useful for creating It is properties of a material which is related to its components that are challenging to shape conductivity of heat. through other fabrication methods. Shearing: Major Components of Thermal Properties: - Shearing is a straightforward yet vital process, Heat Capacity primarily used for cutting flat sheet metal. It Thermal Expansion involves slicing through metal, typically using a Thermal Conductivity large shear machine. The process is akin to Thermal Stress cutting a piece of paper but on a much more robust scale. Metal Fabrication Forming: Metal fabrication is a manufacturing - Forming is another key process in metal process used to shape metal into parts or end fabrication, involving the shaping of metal under products. It is the art and science of building tension. This can include a range of methods metal structures by cutting, bending, and such as stretching, bending, and spinning. Each assembling processes. This intricate craft technique manipulates the metal into different involves transforming raw metal materials into shapes and forms without removing any material. pre-designed shapes and products, showcasing a blend of technical skills and creativity.  Finishing: components that require high strength-to-weight - The finishing phase in metal fabrication is crucial ratios and durability to harsh climatic conditions. for enhancing both the appearance and functionality of metal products. Welding - Surface Treatments: Common treatments include Welding is a fabrication method in which sandblasting, painting, and powder coating. Each two or more parts are fused together using heat, method serves to not only improve the aesthetic pressure, or both, resulting in a join as the parts appeal but also to provide a protective layer cool. Welding is primarily employed on metals against corrosion, wear, and tear. and thermoplastics, although it can also be used on wood. A weldment is the term used to describe Application of Metal Fabrication a fully welded junction. Metal fabrication, a cornerstone of modern industry, has a wide range of uses. Each Common Joint Configurations: industry uses the adaptability and strength of Butt Joint: metal to meet distinct needs, ranging from - A connection between the ends or edges of two structural frameworks to sophisticated consumer parts making an angle to one another of 135-180° products. inclusive in the region of the joint. T Joint: Construction and Building - A connection between the end or edge of one part Automotive Industry and the face of the other part, the parts making Aerospace Industry an angle to one another of more than 5 up to and Shipbuilding including 90° in the region of the joint. Consumer Products Corner Joint: Electronics and Electrical - A connection between the ends or edges of two parts making an angle to one another of more Heat Treatment than 30 but less than 135° in the region of the Heat treatment is the process of heating joint. and cooling metals using particular Edge Joint: predetermined procedures to get the required - A connection between the edges of two parts characteristics. Both ferrous and non-ferrous making an angle to one another of 0 to 30° metals are heat treated before usage. inclusive in the region of the joint. Cruciform Joint: Types of Heat Treatment Processes: - A connection in which two flat plates or two bars Hardening: are welded to another flat plate at right angles - The fundamental goal of hardening is to increase and on the same axis. the hardness and strength of metal. This Lap Joint: hardening technique includes heating the metal - A connection between two overlapping parts to a high temperature, usually above its making an angle to one another of 0-5° inclusive recrystallization point, and then rapidly cooling it in the region of the weld or welds. in water or oil. Tempering: Different Types of Welding and What are they - Following hardening, metals often become too Used for brittle for practical use. Tempering is employed to Arc reduce this brittleness while retaining much of the Friction increased hardness. Electron Beam Annealing: Laser - Annealing is a heat treatment process that Resistance softens the metal, enhancing its ductility and making it more workable. The metal is heated to Soldering a specific temperature and then cooled slowly, Soldering is a joining process used to join often in the furnace. different types of metals together by melting Normalizing: solder. Solder is a metal alloy usually made of tin - Normalizing is a process similar to annealing but and lead which is melted using a hot iron. involves heating the metal to a higher temperature and then allowing it to cool in the air. Types of Soldering: This treatment refines the grain structure of the Soft Soldering: metal, resulting in a more uniform and desirable - This process has the lowest filler metal melting size of grains point of all the soldering types at less than around 400°C these filler metals are usually alloys, often Application of Heat Treatment containing lead with liquidus temperatures under Heat-treated metals find significant uses 350°C. in a wide range of industries, demonstrating their Hard Soldering: adaptability and relevance. In the automobile - Brass or silver is the bonding metal used in this industry, they are critical for producing durable process, and requires a blowtorch to achieve the and dependable steel parts such as engine parts, temperatures at which the solder metals. gears, and bearings that can endure high stress Brazing: and temperatures. The aerospace industry relies - This type of soldering uses a metal with a much significantly on heat-treated metals for higher melting point than those used in hard and  soft soldering. However, similarly to hard ○ Metals under continuous stress or pressure are soldering, the metal being bonded is heated as more prone to corrosion, especially stress opposed to being melted. corrosion cracking. Corrosion of Metals Prevention Methods Corrosion is the natural process where 1. Protective Coatings: metals deteriorate due to reactions with their ○ Applying paint, varnish, or galvanizing (zinc environment. It commonly occurs when metals coating) can protect metals from exposure to air are exposed to air, moisture, or chemicals, and moisture. leading to the degradation of their mechanical 2. Cathodic Protection: and structural properties. This process is a major ○ A more reactive metal, known as a sacrificial concern in industries like construction, anode, is used to protect the base metal from transportation, and manufacturing, where metal corrosion. For example, zinc is used to protect components are essential to infrastructure and steel. equipment. 3. Alloying: ○ Adding metals like chromium or nickel to create Types of Corrosion alloys, such as stainless steel, enhances 1. Uniform Corrosion: corrosion resistance. ○ This is the most common type, where corrosion 4. Corrosion Inhibitors: occurs evenly across the surface of the metal. It ○ Chemicals are added to the environment (e.g., is predictable and can be managed by applying water or fuel) to slow down the corrosion process protective coatings. by forming a protective layer on the metal. ○ Example: The rusting of iron. 5. Regular Maintenance: 2. Pitting Corrosion: ○ Regular inspections and cleaning help detect and ○ This form of corrosion results in small pits or prevent corrosion before it becomes severe. holes on the metal surface. It is localized and can cause significant damage with minimal material Corrosion is a natural process that can loss. significantly impact the lifespan and safety of ○ Example: Pitting in stainless steel. metal structures. Understanding the types, 3. Galvanic Corrosion: factors, and prevention methods of corrosion is ○ Occurs when two dissimilar metals are in contact essential to managing its effects and ensuring the in the presence of an electrolyte, like water. One long-term durability of metal materials in various metal corrodes faster than usual (anode), while industries. the other corrodes more slowly (cathode). ○ Example: Corrosion between steel and copper in Presentation of Metal Products plumbing. Manufacturing 4. Crevice Corrosion: 1. Iron Bars: ○ Takes place in confined spaces, like joints or Manufacturing Process: bolts, where moisture is trapped and oxygen is - Raw Material: Iron ore (hematite or magnetite). limited. Processing: ○ Example: Corrosion in gaps between metal - Smelting: Iron ore is smelted in a blast furnace to surfaces or under washers. produce pig iron. 5. Stress Corrosion Cracking: - Refining: Pig iron is converted into steel or ○ This type of corrosion happens when metal is wrought iron, depending on the desired under tensile stress and exposed to corrosive properties. environments, leading to the development of - Rolling: The refined metal is heated and rolled cracks. into bars of various dimensions. ○ Example: Stress corrosion cracking in pipelines. Applications: Used extensively in construction, manufacturing, and as structural support. Factors Influencing Corrosion 2. Copper Wire: 1. Environment: Manufacturing Process: ○ The presence of moisture, salts, and chemicals - Raw Material: Copper ore (chalcopyrite, bornite). accelerates corrosion, especially in coastal or Processing: industrial areas. - Smelting and Refining: Copper ore is smelted and 2. Temperature: refined to produce pure copper. ○ Higher temperatures increase the rate of - Drawing: Copper is drawn through dies to create corrosion by speeding up chemical reactions. thin wires. 3. Metal Composition: - Insulation: Wires are coated with insulating ○ The type of metal and its composition influence materials such as PVC or enamel. how easily it corrodes. For example, iron Applications: Used in electrical wiring and corrodes faster than aluminum, while stainless electronics due to its excellent conductivity. steel is more resistant due to its alloying 3. Gold Bars: elements. Manufacturing Process: 4. pH Levels: - Raw Material: Gold ore, extracted through ○ Acidic or basic conditions can significantly affect mining. corrosion rates. Metals in acidic environments Processing: tend to corrode faster. - Refining: Gold ore is refined to remove impurities 5. Mechanical Stress: using processes like cyanidation or electrolysis. - Melting and Casting: Refined gold is melted and cast into bars. - Stamping: Bars are stamped with certification marks for purity and weight. Applications: Used as investment assets, in jewelry, and in various industrial applications. 4. Stainless Steel: Manufacturing Process: - Raw Material: A mix of iron ore, chromium, nickel, and sometimes molybdenum. Processing: - Smelting: The raw materials are smelted in an electric arc furnace. - Alloying: Chromium and other elements are added to produce stainless steel with corrosion resistance. - Forming: The alloyed steel is rolled or forged into various forms such as sheets, plates, or bars. Applications: Used in cutlery, appliances, and construction materials due to its resistance to corrosion and staining. 5. Tin Cans: Manufacturing Process: - Raw Material: Tinplate, which is steel coated with a thin layer of tin. Processing: - Coating: Steel sheets are coated with a layer of tin to prevent corrosion. - Forming: The coated steel is stamped and formed into can bodies, lids, and bottoms. - Sealing: Cans are filled with food or beverages, sealed, and then sterilized. Applications: Used extensively in food and beverage packaging for preservation and safety.