Clas 1

TECNOLOGIAS DE MATERIALES Fall-2009

“Una persona sin vicios, es una persona sin virtudes”

• Dr. Said R. Casolco • [email protected]

• Cubiculo 1508-U http://web.pue.itesm.mx/eia/l

Dr. Said R. Casolco:

Posdoctorado en la UCR, Facultad de Ingeniería Posdoctorado en la UNAM, Facultad de Ingeniería (Centro de Diseño y Manufactura) Doctorado por la UNAM, en el área de Ciencias Químicas (Metalurgia). Maestría por la UNAM, en el área de Diseño Mecánico. Licenciatura por la UAEM, como Ingeniero Mecánico 9 Publicaciones en revistas internacionales 4 Patentes en la unión europea (España) 7 tesis dirigidas a nivel licenciatura 3 publicaciones in extenso de congresos internacionales

10 publicaciones in extenso en congresos nacionales 4 Presentaciones en ponencias internacionales Desde 1998 hasta 2006 en docencia en diversas universidades. http://www.youtube.com/watch?v=kbk5Yq9LgRs&eurl=http%3A%2F%2Fww

POLÍTICAS GENERALES DE COMPORTAMIENTO DENTRO DEL SALÓN DE CLASE:

• Las computadoras deberán estar apagadas durante la sesión de clase, a menos que el profesor indique lo contrario. No se harán advertencias, alumno que sea sorprendido usando su computadora, celular, ipod, etc., se le registrará una falta ese día. Dr. Hugo G. González-Hernández Director del Depto. de Ing. Mecánica y Electrónica

POLÍTICAS DE EVALUACIÓN CALIFICACIÓN FINAL La calificación final del curso se obtendrá de la siguiente manera: Carrera: 3 Exámenes parciales .................................................. 50% Tareas (Problemas del libro) .......................................... 10 % Exposición .............................................................. 10 % Examen final ............................................................ 10 %

Implementacion de la tecnica de CAPACITACIóN BáSICA EN APRENDIZAJE SERVICIO 4

Bibliografía

[1] Introduccióna la Ciencia de Materiales para Ingenieros. J. F. Shackelford.

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PROYECTO

e d s o ñ e s i a D s e t e u g u j e d r i t r a s p e l a i r e t ma lados c i c re

ó i c c u d o Intr n

Crystal Structure of Metals Common crystal structures for metals: • • •

Body-centered cubic (BCC) - alpha iron, chromium, molybdenum, tantalum, tungsten, and vanadium. Face-centered cubic (FCC) - gamma iron, aluminum, copper, nickel, lead, silver, gold and platinum. Hexagonal close-packed - beryllium, cadmium, cobalt, magnesium, alpha titanium, zinc and zirconium.

Body-centered Cubic Crystal Structure

Figure 1.2 The body-centered cubic (bcc) crystal structure: (a) hardball model; (b) unit cell; and (c) single crystal with many unit cells

Face-centered Cubic Crystal Structure

Figure 1.3 The face-centered cubic (fcc) crystal structure: (a) hard-ball model; (b) unit cell; and (c) single crystal with many unit cells

Hexagonal Close-packed Crystal Structure

Figure 1.4 The hexagonal close-packed (hcp) crystal structure: (a) unit cell; and (b) single crystal with many unit cells.

Bravais lattices grouped in seven crystal systems

Aleación de Ni-Ti-V

The lattice parameter in cubic

Boundary grain, atoms not in equilibrium

Enlace iónico • Se da entre metales y no-metales. • Los metales tienen, en general, pocos electrones en su capa de valencia y tienden a perderlos para quedar con la capa anterior completa (estructura de gas noble) convirtiéndose en cationes. • Los no-metales tienen casi completa su capa de valencia y tienden a capturar los electrones que les faltan convirtiéndose en aniones y conseguir

Enlace iónico (cont) • En enlace iónico se da por la atracción electrostática entre cargas de distinto signo, formando una estructura cristalina. • Ejemplo: Na –––––– 1 e–  Cl –––––– –     –               –    e– •        

Propiedades de los compuestos iónicos Duros. Punto de fusión y ebullición altos. Sólo solubles en disolventes polares. Conductores en estado disuelto o fundido. • Frágiles. • • • •

Enlace covalente • Se da entre dos átomos no-metálicos por compartición de e– de valencia. • La pareja de e– (generalmente un e– de cada átomo) pasan a girar alrededor de ambos átomos en un orbital molecular. • Si uno de los átomos pone los 2 e– y el otro ninguno se denomina ”enlace covalente coordinado” o “dativo”.

Enlace covalente. • Puede ser: • Enl. covalente simple: Se comparten una pareja de electrones. • Enl. covalente doble: Se comparten dos parejas de electrones. • Enl. covalente triple: Se comparten tres parejas de electrones. • No es posible un enlace covalente cuádruple entre dos átomos por razones geométricas.

Propiedades de los compuestos covalentes • Moleculares

• Atómicos

• Puntos de fusión y • ebullición bajos. • Los comp.covalentes apolares (puros) son • solubles en disolventes apolares y los polares en • disolventes polares. • Conductividad parcial sólo en compuestos

Puntos de fusión y ebullición muy elevados. Insolubles en todos los disolventes. No conductores (el grafito sí presenta conductividad por la deslocalización de un e– de cada átomo).

Propiedades de los compuestos metálicos. • Punto de fusión y ebullición muy variado (aunque suelen ser más bien alto) • Son muy solubles en estado fundido en otros metales formando aleaciones. • Muy buenos conductores en estado sólido. • Son dúctiles y maleables

presión

Characteristics of Materials

Permanent Deformation

Figure 1.5 Permanent deformation (also called plastic deformation) of a single crystal subjected to a shear stress: (a) structure before deformation; and (b) permanent deformation by slip. The b/a ratio influences the magnitude of the shear stress required to cause slip.

Electron Structure of Multielectron Atom

Periodic Table

• Maximum number of electrons in each atomic shell is given by 2n2. • Atomic size (radius) increases with addition of shells. • Electron Configuration lists the arrangement of electrons inNumber orbitals. of Example :- Orbital letters

Electrons

1s2 2s2 2p6 3s2 Principal Quantum Numbers Ø For Iron, (Z=26), Electronic configuration is 1s2 2s2 sp6 3s2 3p6 3d6

The Scanning Electron Microscope • Electron source generates electrons. • Electrons hit the surface and secondary electrons are produced. • The secondary electrons are collected to produce the signal. • The signal is used to produce TEM of fractured

Figure 4.31

Scanning Probe Microscopy • Scanning Tunneling Microscope (STM) and Atomic Force Microscope (AFM). • Sub-nanometer magnification. • Atomic scale topographic map of surface. • STM uses extremely sharp tip. • Tungsten, nickel, platinum - iridium or carbon nanotubes are used for tips.

• • • • •

Scanning Tunneling Tip placed one atom diameter from Microscope

surface. Voltage applied across tip and surface. Electrons tunnel the gap and produce current. Current produced is proportional to change in gap. Can be used only for conductive materials.

Surface of platinum with defects Constant height and current modes

Atomic Force Microscope • Similar to STM but tip attached to cantilever beam. • When tip interacts with surface, van der waals forces deflect the beam. • Deflection detected by laser and photodetector. • Non-conductive materials can be scanned. • Used in DNA research and polymer coating technique.

Solidificación.

• Tema 3

Las mentes brillantes no están en grandes universidades, se encuentran escribiendo su paso a la historia. SRC

Solidification of Metals •

Metals are melted to produce finished and semi-finished parts. Two steps of solidification Nucleation : Formation of stable nuclei. Growth of nuclei : Formation of grain structure.

•

Thermal

•

grain.

gradients define the shape of each Grains

Nuclei

Liquid

Crystals that will Form grains

Grain Boundaries

Formation of Stable Nucleation • Two main mechanisms: Homogenous and heterogeneous. • Homogenous Nucleation : Ø First and simplest case. Ø Metal itself will provide atoms to form nuclei. Ø Metal, when significantly undercooled, has several slow moving atoms which bond each other to form nuclei. Ø Cluster of atoms below critical size is called embryo. Ø If the cluster of atoms reach critical size, they grow into crystals. Else get dissolved. Ø Cluster of atoms that are grater than critical

Homogenous Nucleation Liquid Solid θ

Nucleating agent

• Nucleation occurs in a liquid on the surfaces of structural material. Eg:- Insoluble impurities. • These structures, called nucleating agents, lower the free energy required to form stable nucleus. • Nucleating agents also lower the critical size. • Smaller amount of undercooling is required to

Growth of Crystals and Formation of Grain Structure • Nucleus grow into crystals in different orientations. • Crystal boundaries are formed when crystals join together at complete solidification. • Crystals in solidified metals are called grains. • Grains are separated by grain boundaries. • More the number of nucleation sites available, more the ofgrains Nucleinumber growing into Forming grain boundaries

Types of Grains • Equiaxed Grains: Ø Crystals, smaller in size, grow equally in all directions. Mold Ø Formed at the sites of high concentration of the nucleation. Ø Example:- Cold mold wall Columnar Grains

• Columnar Grains: Long thin and coarse. Ø Grow predominantly in one direction. Ø Formed at the sites of slow cooling and steep temperature gradient. Ø Example:- Grains that are away from the mold wall. Equiaxed Grains

Solidification of Molten Metal

Figure 1.11 Schematic illustration of the stages during solidification of molten metal; each small square represents a unit cell. (a) Nucleation of crystals at random sites in the molten metal; note that the crystallographic orientation of each site is different. (b) and (c) Growth of crystals as solidification continues. (d) Solidified metal, showing individual grains and grain boundaries; note the different angles at which neighboring grains meet each other.

Grain Sizes ASTM Grain Size:

N= 2n-1 where N=

Grains per square inch at 100x magnification n= ASTM grain size number

Plastic Deformation of Idealized Grains

Figure 1.12 Plastic deformation of idealized (equiaxed) grains in a specimen subjected to compression (such as occurs in the forging or rolling of metals): (a) before deformation; and (b) after deformation. Note the alignment of grain boundaries along a horizontal direction; this effect is known as preferred orientation.

Cracks in Sheet Metal

Figure 1.13 (a) Schematic illustration of a crack in sheet metal that has been subjected to bulging (caused by, for example, pushing a steel ball against the sheet). Note the orientation of the crack with respect to the rolling direction of the sheet; this sheet is anisotropic. (b) Aluminum sheet with a crack (vertical dark line at the center) developed in a bulge test; the rolling direction of the sheet was vertical. Source: Courtesy of J.S. Kallend, Illinois

Recovery, Recrystallization, and Grain Growth Effects

Figure 1.14 Schematic illustration of the effects of recovery, recrystallization, and grain growth on mechanical properties and on the shape and size of grains. Note the formation of small new grains during recrystallization.

Temperature Ranges for Cold, Warm and Hot

Casting in Industries • In industries, molten metal is cast into either semi finished or finished parts.

Continuous casting Of steel ingots

Direct-Chill semicontinuous Casting unit for aluminum

Grain Structure in Industrial castings • To produce cast ingots with fine grain size, grain refiners are added. • Example:- For aluminum alloy, small amount of Titanium, Boron or Zirconium is added.

(a )

(b )

Grain structure of Aluminum cast with (a) and without (b) grain refiners.

Solidification of Single Crystal • For some applications (Eg: Gas turbine bladeshigh temperature environment), single crystals are needed. • Single crystals have high temperature creep resistance. • Latent head of solidification is conducted through solidifying crystal to grow single crystal. • Growth rate is kept slow so that temperature at solid-liquid interface is slightly below melting point. Growth of single crystal for turbine airfoil.

Metallic Solid Solutions • Alloys are used in most engineering applications. • Alloy is an mixture of two or more metals and nonmetals. • Example: Ø Cartridge brass is binary alloy of 70% Cu and 30% Zinc. Ø Iconel is a nickel based superalloy with about 10 elements.

Substitutional Solid Solution • Solute atoms substitute for parent solvent atom in a crystal lattice. • The structure remains unchanged. • Lattice might get slightly distorted due to change in diameter of the atoms. • Solute percentage in solvent can vary from fraction of a percentage to 100% Solvent atoms

Figure 4.14

Solute atoms

Substitutional Solid Solution (Cont..) • The solubility of solids is greater if The diameter of atoms not differ by more than 15% Ø Crystal structures are similar. Ø No much difference in electronegativity (else compounds will be formed). Ø Have some valence.

•

Examples:-

Interstitial Solid Solution • Solute atoms fit in between the voids (interstices) of solvent atoms. • Solvent atoms in this case should be much larger than solute atoms. • Example:- between 912 and 13940C, interstitial solid solution of carbon in γ iron (FCC) is formed. • A maximum of 2.8% of carbon can dissolve interstitially in iron. Iron atoms r00.129nm Carbon atoms r=0.075nm

Crystalline Imperfections • No crystal is perfect. • Imperfections affect mechanical properties, chemical properties and electrical properties. • Imperfections can be classified as Zero dimension point deffects. Ø One dimension / line deffects (dislocations). Ø Two dimension deffects. Ø Three dimension deffects (cracks).

Point Defects – Vacancy • Vacancy is formed due to a missing atom. • Vacancy is formed (one in 10000 atoms) during crystallization or mobility of atoms. • Energy of formation is 1 ev. • Mobility of vacancy results in cluster of vacancies. • Also caused due to plastic defor-mation, rapid cooling or particle bombardment.

Point Defects - Interstitially • Atom in a crystal, sometimes, occupies interstitial site. • This does not occur naturally. • Can be induced by irradiation. • This defects caused structural distortion.

Point Defects in Ionic Crystals • Complex as electric neutrality has to be maintained. • If two appositely charged particles are missing, cation-anion divacancy is created. This is scohttky imperfection. • Frenkel imperfection is created when cation moves to interstitial site. • Impurity atoms are also considered as point defects.

Line Defects – (Dislocations) • Lattice distortions are centered around a line. • Formed during Solidification Ø Permanent Deformation Ø Vacancy condensation Ø

• Different types of line defects are Edge dislocation Ø Screw dislocation Ø Mixed dislocation Ø

Edge Dislocation • Created by insertion of extra half planes of atoms. • •

Positive edge dislocation Burgers vector

Negative edge dislocation

• Burgers vector Shows displacement of atoms (slip).

Figure 4.18

Screw Dislocation • Created due to shear stresses applied to regions of a perfect crystal separated by cutting plane. • Distortion of lattice in form of a spiral ramp. • Burgers vector is parallel to dislocation line.

Mixed Dislocation • Most crystal have components of both edge and screw dislocation.

•

Dislocation, since have irregular atomic arrangement will appear as dark lines when observed in electron microscope.

Dislocation structure of iron deforme 14% at –1950C

Grain Boundaries • Grain boundaries separate grains. • Formed due to simultaneously growing crystals meeting each other. • Width = 2-5 atomic diameters. • Some atoms in grain boundaries have higher energy. • Restrict plastic flow and prevent dislocation 3D view of movement. grains

Grain Boundaries In 1018 steel

Permanent Deformation and Twinning in Crystal Figure 1.6 (a) Permanent deformation of a single crystal under a tensile load. Note that the slip planes tend to align themselves in the direction of the pulling force. This behavior can be simulated using a deck of cards with a rubber band around

Slip Lines and Slip Bands in Crystal Figure 1.7 Schematic illustration of slip lines and slip bands in a single crystal (grain) subjected to a shear stress. A slip band consists of a number of slip planes. The crystal at the center of the upper illustration is an individual grain

Defects in a Single-Crystal Lattice

Figure 1.8 Schematic illustration of types of defects in a single-crystal lattice: self-interstitial, vacancy, interstitial, and substitutional

Dislocations in Crystals

Figure 1.9 Types of dislocations in a single crystal: (a) edge dislocation; and (b) screw dislocation

Edge Dislocation Movement

Figure 1.10 Movement of an edge dislocation across the crystal lattice under a shear stress. Dislocations help explain why the actual strength of metals is much lower than that predicted by theory.