Engineering Alloys - Intermediate Mechanics of Materials - Lecture Slides, Slides of Classical Mechanics

Download Engineering Alloys - Intermediate Mechanics of Materials - Lecture Slides and more Slides Classical Mechanics in PDF only on Docsity! CHAPTER 9 Engineering Alloys 9-1 Docsity.com Production of Iron and Steel • Production of pig iron Fe2O3 + 3CO 2Fe + 3CO2 Ore Coke Blast Furnace Pig iron (Liquid) Figure 9.1 After A. G. Guy,”Elements of Physical Metallurgy,”2nd ed., !959, Addision-Wesley, Fig. 2-5, p.21. 9-2 Docsity.com Invariant reactions • Peritectic reaction: Liquid (0.53%C) + δ (0.09% C) γ (0.17% C) • Eutectic reaction: Liquid (4.3% C) γ austenite (2.08%C) + Fe3C ( 6.67%C) • Eutectoid reaction: γ Austenite (0.8%C) α Ferrite(0.02%C) + Fe3C ( 6.67%C) 14950C 11480C 7230C 0.8% C Eutectoid Steel Hypoeutectoid Steel Hypereutectoid Steel Less than 0.8% More than 0.8% 9-5 Docsity.com Slow Cooling of Plain Carbon Steel • Eutectoid plain carbon steel: If a sample is heated up to 7500C and held for sufficient time, structure will become homogeneous austenite. • Below eutectoid temperature, layers of ferrite and cementite are formed. Pearlite. Figure 9.7 Figure 9.8 After W. F. Smith, “The Structure and Properties of Engineering Alloys,” 2nd ed.,McGraw-Hill, 1981, p.8 9-6 Docsity.com Slow Cooling of Plain Carbon Steel (Cont..) • Hypoeutectoid plain carbon steel: If a sample of 0.4% C is heated up to 9000C, it gets austenitized. • Further cooling gives rise to α and pearlite. Figure 9.9 Figure 9.10 Pearlite After W. F. Smith, “The Structure and Properties of Engineering Alloys,” 2nd ed.,McGraw-Hill, 1981, p.10 9-7 Docsity.com Microstructure of Fe – C Martensites • Lath martensite: Less than 0.6% C and consists of domains of lathe of different orientation. • Plate martensite: More than 0.6% C and have fine structure of parallel twins. Lath type Plate type Figure 9.13 Figure 9.14 After A. R. Marder and G. Krauss, as presented in “Hardenebility Concepts with Applications to Steel,” AIME, 1978, p. 238. 9-10 Docsity.com Martensite (Cont..) • Transfer to martensite is diffusionless. • No change of relative position of carbon atoms after transformation. • Strength and hardness increases with carbon content. • Strength is due to high dislocation concentration and interstitial solid solution strengthening. Figure 9.17 Figure 9.19 After E. R. Parker and V. F. Zackay Strong and Ductile Steels, Sci.Am.,November 1968, p.36; Copyright by Scientific American Inc; all rights reserved 9-11 Docsity.com Isothermal decomposition of Austenite. • Several samples are first austenitized above eutectoid temperature and rapidly cooled in sand bath to desired temperature in a salt bath and then quenched in water at various time intervals. Repeat procedure at progressive lower temperatures Figure 9.20 Figure 9.21 Figure 9.22 After W. F. Smith, “The Structure and Properties of Engineering Alloys,” McGraw-Hill, 1981, p.14 9-12 Docsity.com Continuous Cooling-Transformation Diagram • In continuous cooling transformation from martensite to pearlite takes place at a range of temperature. • Start and finish lines shifted to longer time. • No transformation below 4500C. Figure 9.26 Figure 9.27 After R. A. Grange and J. M. Kiefer, “Alloying Elements in Steel,” ASM 2nd ed., 1966, p.254. 9-15 Docsity.com Annealing and Normalizing • Full annealing: Sample heated to 400C above austenite ferrite boundary, held for necessary time and cooled slowly. • Process annealing: Used for stress relief. Applied to hypoeutectoid steel at eutectoid temperature. • Normalizing: Steel heated in austenite region and cooled in still air. • Makes grain structure uniform • Increases strength Figure 9.28 After T. G. Diggers et al., “ Heat Treatment and Properties of Iron and Steel,” NBS Monograph 88, 1966, p. 10 9-16 Docsity.com Tempering of Plain Carbon Steel • Martensitic steel is heated at a temperature below eutectic temperature. • Makes steel softer and ductile. • Carbon atoms, in low carbon steels, segregate themselves on tempering. Tempering Temperature Below 2000C 200 – 7000C 400 – 7000C Structure Epsilon Carbide Cementite (rod-like) Cementite (Spheroidite) Figure 9.29 Figure 9.31 From “ Suiting the heat Treatment to the job,” United States Steel Corp., 1968, p.34. 9-17 Docsity.com Calssification of Plain Carbon Steel • Four digit AISI-SAE code. • First two digits, 10, indicate plain carbon steel. • Last two digits indicate carbon content in 100th wt%. • Example: 1030 steel indicate plain carbon steel containing 0.30 wt% carbon. • As carbon content increase, steel becomes stronger and ductile. 9-20 Docsity.com Low Alloy Steels • Limitations of plain carbon steels:  Cannot be strengthened beyond 690 MPa without loosing ductility and impact strength.  Not deep hardenable.  Low corrosion resistance  Rapid quenching leads to crack and distortion.  Poor impact resistance at low temperature. • Alloy steels: Up to 50% alloying elements like manganese, nickel, chromium, molybdenum and tungsten. 9-21 Docsity.com Distribution of Alloying Elements • Distribution depends upon compound and carbide forming tendency of each element. Table 9.5 After JE. C. Bain, and H. W. Paxton, “Alloying Elements in Steel, “ 2nd ed., American Society for Metals, 1996 9-23 Docsity.com Hardenability (cont..) • For 1080 plain carbon steel, the hardness value at quenched end is 65 HRC while it is 50 HRC at 3/16 inch from quenched end. • Alloy steel 4340 has high hardenability and has hardness of 40 HRC 2 inches from quenched end. • In alloy steel, decomposition of austenite to ferrite is delayed. • Cooling rate depends on bar dia, quenching media and bar cross section. Figure 9.37 Figure 9.38 After H. E. McGannon(ed.), “The Making Shaping and Treating of Steel,” United States Steel Corp., 1971, p.1139. 9-26 Docsity com Mechanical Properties of Low Alloy Steels 4820 Table 9.6 9-27 Docsity.com Aluminum Alloys • Precipitation Strengthening : Creates fine dispersion of precipitated particles in the metal and hinder dislocation movement. • Basic steps :  Solution heat treatment: Alloy sample heated to a temperature between solvus and solidus and soaked at that temperature.  Quenching: Sample then quenched to room temperature in water.  Aging: Solutionized and quenched sample is then aged to form finely dispersed particles. 9-28 Docsity.com Example - Al 4% Cu Alloy • Al -4% Cu is solutionized at about 5150C • Alloy is rapidly cooled in water. • Alloy is artificially aged in 130 – 1900C • Structures formed :  GP1 Zone: At lower aging temperature, copper atom is segregated in supersaturated solid solution.  GP2 Zone: Tetragonal structure, 10-100 nm diameter.  θ’ Phase: Nucleates heterogeneously on dislocation.  θ Phase: Equilibrium phase, incoherent (CuAl2). 9-31 Docsity.com Correlation of Structure and Hardness • GP1 and GP2 Zones increases hardness by stopping dislocation movement. • At 1300C when θ’ forms, hardness is maximum. • After θ’ forms, GP2 zones are dissolved and θ’ gets coarsened reducing hardness. Figure 9.47 After J. M. Silcock, T. J. Heal, and H. K. Hardy “Alluminium,” 1, American society of Metals, 1967,p.123. 9-32 Docsity.com General Properties of Aluminum • Low density, corrosion resistance. • High alloy strength (about 690 MPa) • Nontoxic and good electrical properties. • Production: • Aluminum hydroxide is precipitated from aluminum solution. • Aluminum hydroxide is thickened and calcined to Al2O3 which is dissolve in cryolite and electrolyzed. • Metallic aluminum sinks to bottom and is tapped out. Aluminum Ore (Bauxite) Hot NaOH Sodium Aluminate + Figure 9.48 Courtesy of Aluminium Company of America 9-33 Docsity.com Non Heat Treatable Aluminum Alloys • 1xxx alloys : 99% Al + Fe + Si + 0.12% Cu Tensile strength = 90 MPa Used for sheet metals • 3xxx alloys : Manganese is principle alloying element. Al 3003 = Al 1100 + 1.25% Mn Tensile strength = 110 MPa General purpose alloy • 5xxx alloys: Al + up to 5% Mg Al5052 = Al + 25%Mg + 0.2% Cr Tensile strength = 193 MPa Used in bus, truck and marine sheet metals. 9-36 Docsity.com Heat Treatable Aluminum Alloys • 2xxx alloys : Al + Cu + Mg Al2024 = Al + 4.5% Cu + 1.5% Mg +0.6%Mn Strength = 442 MPa Used for aircraft structures. • 6xxx alloys: Al + Mg + Si Al6061 = Al + 1% Mg + 0.6%Si + 0.3% Cu + 0.2% Cr Strength = 290 MPa Used for general purpose structure. • 7xxx alloys: A + Zn + Mg + Cu Al7075 = Al + 5.6% Zn + 2.5% Mg + 1.6% Cu + 0.25% Cr Strength = 504 MPa Used for aircraft structures. 9-37 Docsity.com Aluminum Casting • Sand Casting: Simple and used for small quantities and complex jobs. • Permanent mold casting: Molten metal is poured into permanent metal mold.  Finer grain structure and strength due to fast cooling.  Less shrinkage and porosity.  More shrinkage and simple parts only. • Die casting: Molten metal forced into molds under pressure.  Almost finished parts, automatic.  Good tolerance and surface finish.  Fine grain structure. 9-38 Docsity.com Unalloyed Copper • Electrolytic tough pitch copper is least expensive and used in production of wire, rod, and strip. • Has 0.04% oxygen. • Cu2O + H2 2Cu + H2O • H2O causes inner holes and blisters. • Copper cast in controlled reducing atmosphere Heated 4000C Oxygen free high conductive Copper (Alloy C10200) Figure 9.51 Courtesy of Amax Base Metals Research, Inc. 9-42 Docsity.com Copper Zinc Alloys • Copper forms substitutional solid solution with Zn till 35% Zn. • Cartridge brass 70% Cu & 30% Zn single phase • Muntz brass 60% Cu & 40% Zn two phase. • Zinc (0.5 to 3%) is always added to copper to increase machinability. Alpha Beta Figure 9.53 Courtesy of Anaconda American Brass Co 9-43 Docsity.com Other Copper Alloys • Copper-Tin Bronzes: 1 to 10% tin with Cu to form solid solution strengthened alloys.  Stronger and less corrosive than Cu-Zn bronzes.  Up to 16% Sn is added to alloys that are used for high strength bearings. • Copper beryllium alloys: 0.6 to 2% Be and 0.2 – 2.5 % Cobalt with copper.  Can be heat treated and cold worked to produce very strong (1463 MPa) bronzes.  Excellent corrosion resistance and fatigue properties.  Used in springs, diaphragms, valves etc. 9-44 Docsity.com Austenitic Region • Iron-Chromium (16-25%) – Nickel (7-20%) ternary alloy. • Austenitic structure (FCC γ ) remains austenitic at all temperature due to nickel. • Better corrosion resistance than other steels. • Tensile strength 559-759 MPa. • Used for chemical equipment, pressure vessels etc. • Alloying element, columbium, prevents intergranular corrosion if the alloy is to be used for welding. 9-47 Docsity.com Cast Iron • General Properties: Contains 2-4% Carbon and 1-3% Si. • Easily melted, very fluid, low shrinkage, easily machinable. • Low impact resistance and ductility. • Types of Cast Iron:  White cast iron  Gray cast iron  Malleable cast iron  Ductile cast iron 9-48 Docsity.com White Cast iron • Much of Carbon forms Iron Carbide instead of graphite up on solidification. • Fractured surface appears white and crystalline. • Low carbon (2.5 – 3%) and silicon (0.5 – 1.5%) content. • Excellent wear resistance. Iron Carbide Pearlite Figure 9.59 Courtesy of central Foundry 9-49 Docsity.com Malleable Cast Iron • 2-2.6 % C and 1.1 – 1.6% Si. • White cast iron is heated in malleablizing furnace to dislocate carbide into graphite. • Irregular nodules of graphite are formed. • Good castability, machinability, moderate strength, toughness and uniformity. Figure 9.65 After “Metals Handbook,” vol. 7, 8th ed., American Society for Metals, 1972, p.95. 9-52 Docsity.com Heat Treatment • Heat treatment of white irons to produce malleable irons are  Graphitization: Castings heated above the eutectoid temperature (9400C) and held for 3 to 20h depending on the composition and structure. white iron graphite and austenite.  Cooling : • Ferritic malleable iron: Fast cooled from 740-7600C and then slowly cooled. • Pearlitic malleable iron: Slowly cooled up to 8700C and then air cooled. • Tempered martensitic malleable iron: Casting cooled in furnace to a quenching temperature and homogenized and then quenched in agitated oil. 9-53 Docsity.com Magnesium, Titanium and Nickel Alloys • Magnesium Alloys:  Low density metal, high cost, low castability, low strength, poor creep, fatigue and wear resistance.  Two types: wrought alloys (sheet, plate, extrusion) and casting alloys (casting).  Designated by two capital letters and two or three numbers.  First two letters indicate two major alloying elements.  The numbers indicate wt% of alloying elements. 9-54 Docsity.com Nickel Alloys • Expensive, good corrosion resistance and high formability. • Commercial Nickel and Monel alloys: good weldability, electrical conductivity and corrosion resistance. • Nickel + 32% Cu Monel alloy (strengthens nickel). • Nickel based super alloys: High temperature creep resistance and oxidizing resistance for gas turbine parts. • 50 -60 % Ni + 15-20% Cr + 15-20% Co + 1-4% Al + 2-4% Ti. • 3 phases – Gamma austenite, gamma prime, carbide particles. 9-57 Docsity.com Intermetallics • Unique combination of properties • Examples: Nickel aluminide Iron aluminide Titanium aluminide • Low density, good high temperature strength, less corrosion but brittle. • 0.1 % Boron and 6-9 % Cr added to reduce embrittlement and to increase ductility. • Applications : Jet engine, pistons, furnace parts, magnetic applications (Fe3Si) and electronic applications (MoSi2) High temperature applications Docsity.com Shape Memory Alloys (SMA) • SMA recover predefined shape when subjected to appropriate heat treatment. • Recovers strain and exerts forces • Examples: AuCd, Cu-Zn-Al, Cu-Al-Ni, Ni-Ti • Processed using hot and cold forming techniques and heat treated at 500-800 0C at desired shape. • At high temperature ---Regular cubic microstructure (Austenite) • After cooling – Highly twinned platelets (Martensite) Docsity.com Amorphous Metals • Atoms arranged in random manner in metals under special circumstances • Produced by rapid quenching (10 5 K/s) – No time to form crystals. • Till now only small pieces could be produced • No dislocation activity : Very hard, perfectly plastic, high dimensional accuracy (no shrinkage) • Applications:  surgical knives  Golf clubs crystalline Amorphous Docsity.com Biomedical Applications: Biometals • Biometals come in direct contact with human body fluids.  Used to replace tissue  Support damaged tissue while heeling  Filler material • Biocompatibility : Internal environment of human body is highly corrosive  Metals degrade and release harmful ions  Chemical stability, corrosion resistance, non-carcinogenity and non- toxicity is called biocompatibility. • High fatigue strength is desired. • Pt, Ti, Zr have good biocompatibility. • Co, Cu, Ni are toxic Docsity.com Stainless Steels as Biometals • 316 L stainless steel (cold worked, grain size of minimum 5) is used most often  18Cr-14Ni-2.5Mo---F138 • Inexpensive, easily shaped • limited corrosion resistance inside the body  removed after healing  Used as bone screws Intermedullary nail Fibula Bone plate Spine plate Docsity.com