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Polycrystalline, single crystal and Non crystalline Materials

Polycrystalline, single crystal and Non crystalline Materials

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  • Polycrystalline, single crystal and Non crystalline Materials

  • PolycrystallinePolycrystalline material Aggregate of several crystals or grainsThe boundary between the grain is the grain boundary across which the orientation of the crystal changes. The point at which three boundaries meet is called the triple junction.

    Triple junction

  • Line intercept methodThis is one of the most commonly used methods. Number of grains intersecting a given length of a random line is counted. Grain size D = Length of the line/no of grains intersected

    Grain size determination

  • Grain size measurementASTM grain size number, G Number of grains per unit area at a particular magnification

    ASTMNo.

    Grains/mm2 Grains/mm3 Avg. grain size, mm

    -1 3.9 6.1 0.510 7.8 17.3 0.361 15.5 49.0 0.252 31.0 138 0.183 62.0 391 0.1254 124 1105 0.095 248 3126 0.0656 496 8842 0.0457 992 25010 0.0328 1980 70700 0.0229 3970 200000 0.01610 7940 566000 0.011

    G = -2.9542 + 1.4427 ln N where, N is number of grains/mm2

    G is compared in ASTM grain size chart to obtain the grain size.

  • Grain size measurement

    Calculate the grain size from the micrographs using the line intercept method

  • Grain size Property relationshipHall-Petch Relation

    A general relationship between mechanical properties and grain size is given by the Hall-Petch equation

    21/ kdio o is the yield strength, d is the grain size and i and k are material dependent constants.

    Finer grain size means more grain boundaries or higher grain boundary area per unit volume. Deformation in metals takes place by dislocation motion and grain boundaries act as obstacles to dislocation motion. Hence, presence of more grain boundaries (finer grain size) will increase the resistance to deformation and enhance the strength.

  • Single CrystalsSingle crystal only one grain or crystal and hence, no grain boundaries.Useful for applications where grain boundaries are harmful. For example, high temperature deformation or creep resistance (as creep takes place by grain boundary sliding) -single crystal turbine blades (http://blog.makezine.com/2012/01/16/single-crystal-superalloys/)(www.cmse.ed.ac.uk/AdvMat45/SuperEng.pdf)Silicon single crystals for semi conductors

  • Non crystalline or Amorphous materials

    Amorphous random arrangement of atoms: Silicate glass, Polymers

    Metallic amorphous materialsBulk Metallic Glass (BMG)A metallic system can be made amorphous by decreasing the chance of crystallization : Allow less time for crystallization during solidification Rapid solidification processing (RSP)Increase confusion for a particular crystal form by increasing the number of components (alloying elements).

  • Bulk Metallic GlassMulti component elements with different chemical nature and atomic size and number together reduce the chance of crystallization

    Zr41.2Ti13.8Cu12.5Ni10Be22.5 [=(Zr3Ti)55(Be9Cu5Ni4)45], commonly referred to as Vitreloy 1 (Vit1)

    Processing routes:RSP - Melt spinningBall millingSolid-state amorphisation reactionNuclear irradiation

  • Properties of BMGsMechanical properties High strength, low ductility

    Formation of small crystallites in glassy matrix by annealing can improve ductility.

    Magnetic properties excellent soft magnetic properties due to absence of crystalline magnetic anisotropy FINEMET Fe-Si-B-Cu-NbExcellent corrosion resistanceGood acoustic properties

    Elastic strain

    Tensile strength

    Youngs Modulus

    ShearModulus

    Hardness Fracturetoughness

    2% 1.9 GPa 96 GPa 34.3 GPa 534 VHN 55 MPa m1/2

    Some Properties of Vit1 (R D Conner et al. Scripta mater. 1997;37:13738)

  • Applications of BMGs

    Golf heads BMG golf heads can transfer 99% energy compared to 60% for steel heads and 70% for Ti heads

    Thin yet strong electronic casing MP3 player, mobile phones, digital cameras, PDA

    Surgical instruments, Prosthetic implants (Biomaterials)

    Sensors for electronic article surveillance, cores for high frequency transformers

    Self-sharpening tank armor penetrator

  • Nano Materials

  • Nanometer = 10-9 m

    micrometer = 10-6 m

    mm = 10-3 m

  • Nano MaterialsNano Structured Material (NSM) At least one component of the microstructure e.g. grains, particles or dispersoids, is nano meter in size. Nano particles possess very high surface area /unit volume which gives rise to unique physical and chemical properties.In a nano-grained material the grain boundary width is comparable with the grain size.

    Nano particles Nano Ni-ZrO2 composite Nano grains in Al

  • A two-dimensional representation of a nanostructured material. Red circles indicate atoms in the grain while open circles indicate atoms in the grain boundary region

    Nano -Structured Materials (NSM)

  • Classification of NSMs according to their chemical composition and shape

    Classification of NSMs

  • Inert gas condensation Vapour phase condensationWet chemical method High energy mechanical alloying Plasma processing Combustion synthesis Super critical liquid Chemical vapor deposition (CVD) Physical vapor deposition (PVD)

    Processing Routes

  • Properties of NSMs

    Superior functional properties Photoluminescence, Electroluminescence, Electronic and magnetic peoperties

    Enhanced catalytic activity Very high surface area per unit volume

    Structural properties Very high strength Hall-petch equation 0 = i + kd-1/2

    Ultrafine grain size - Superplasticity

    High Hardness Nanocrystalline WC-Co composites

    High stiffness - CNTs

  • ApplicationsSunscreens Lotions - Many sunscreens contain nano particles of zinc oxide or titanium oxide.

    Self-cleaning glass: Activ Glass - uses nanoparticles to make the glass photocatalytic and hydrophilic.

    Clothing: coating fabrics with a thin layer of zinc oxide nanoparticles, better protection from UV radiation. Stain resistant clothes - have nanoparticles in the form of little hairs or whiskers that help repel water and other materials

    Scratch resistant coatings addition of aluminum silicate nanoparticles to scratch-resistant polymer coatings. Scratch-resistant coatings for cars and eye lenses.

    Glossy colors Nano particles of pigments (CoAl2O4). Shiny, better looking colors for cars

  • NSMs in Electronics Better and Smaller

    The advent of the nano technology has immensely helped in miniaturization which is an essential part in many electronic gadgets.The nano technology is already in use in many electronic gadgets like mobile phones, I-pads, cameras, palm tops and so on.Quantum dots - nano-scale semiconductor crystals. Dramatic improvement in digital storage (Flash memory)Less power consumption, better resolution (in visuals), smaller size.

  • Flash memory: Conventional tunneling film must be sufficiently insulating to store the charge. Limits thickness reduction and thus miniaturization. Cannot work with defects in the film.Nano dot or quantum dot flash memory allows for higher defect tolerance, lower thickness (and hence miniaturization). Less power consumptionQuantum dots display - By altering the size of the nano particles, the color they emit can be changed.6 nm red, 2 nm - blue Quantum dot display in place of LCDs or OLEDs less power consumption, better quality pictures.

    Applications of NSMs

  • Applications of NSMs contd.

    IBM has developed Microscopic LED: A thin indium-nitride nanowire that emits infrared light when a current is applied (http://www.technologyreview.in/communications/19129/)

    It is believed that the nanowire LEDs could eventually be used for telecommunications and for faster communications between devices on microchips.

  • Referenceshttp://www.iue.tuwien.ac.at/phd/holzer/node39.htmlhttp://science.howstuffworks.com/nanotechnology3.htmhttp://203.208.166.84/mjrahman/Class%20Note_Jellur.pdfhttp://en.wikipedia.org/wiki/Single_crystalhttp://www.appropedia.org/Single_Crystal_Turbine_Blades

    Processing Techniqueshttp://www2.mmae.ucf.edu/~sury/Online_Pub/Nano-Hyperfine.pdfhttp://library.iyte.edu.tr/tezler/master/kimyamuh/T000294.pdf

    Key words: Polycrystalline; Grain boundary; Amorphous; Bulk Metallic Glass; Single crystal; Nano Materials

  • Quiz1. What aspect of the crystals changes across the grain boundaries?2. How is the gain size measured in a polycrystalline material?3. What is effect of grain boundaries on strength of metals?4. Are grain boundaries desirable for high temperature structural application? Give reasons for your answer.5. What is meant by amorphous material?6. How can a metallic system be made into an amorphous material?7. Why bulk metallic glasses (BMG) are generally multicomponent?8. What is nanostructured material? What imparts unique properties to these materials?9. Classify nanostructured materials.10. What are the processing routes of nano materials?