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Lecture+3a+-+Structure+of+Materials

Lecture+3a+-+Structure+of+Materials - Structure Structure...

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Structure and Manufacturing Properties of Materials Lecture 3.a ISE 2204 – Introduction to Manufacturing Processes Dr. Jaime Camelio February 2 nd , 2010 Material Structure Importance Crystal Structure Plastic Deformation Grain Boundaries Effect of Temperature Fracture Material Properties ISE 2204 – Introduction to Manufacturing Processes – Spring 2010 Outline
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Manufacturing properties are determined largely by the material’s mechanical and physical properties Mechanical and physical properties are largely determined by the material’s: Crystal structure Grain boundaries Grain size Texture Imperfections ISE 2204 – Introduction to Manufacturing Processes – Spring 2010 Relevance of Material Properties Turbine blades for jet engines, manufactured by three different methods: (a) conventionally cast; (b) directionally solidified with columnar grains ISE 2204 – Introduction to Manufacturing Processes – Spring 2010 Motivation Motivation – Turbine Blades Turbine Blades (a) conventionally cast; (b) directionally solidified, with columnar grains, as can be seen from the vertical streaks; and (c) single crystal. Although more expensive, single-crystal blades have properties at high temperatures that are superior to those of other blades. Source: Courtesy of United Technologies Pratt and Whitney.
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When metals solidify, atoms arrange themselves into various orderly configuration, called crystals. The arrangement of the atoms in the crystal is called crystalline structure . The smallest group of atoms showing the characteristic lattice structure of a particular metal is known as a unit cell . Three basic patterns of atomic arrangement Body-centered cubic (bcc) Face centered cubic (fcc) ISE 2204 – Introduction to Manufacturing Processes – Spring 2010 Crystal Structure Face-centered cubic (fcc) Hexagonal close packed (hcp) The body-centered cubic (bcc) crystal structure: (a) hard-ball model; (b) unit cell; and (c) single crystal with many unit cells. Common bcc metals include chromium, titanium, and tungsten. The face-centered cubic (fcc) crystal structure: (a) hard-ball model; (b) unit cell; and (c) single crystal with many unit cells. Common fcc metals include aluminum, copper, gold and silver. Th h l l k d (h ) t l ISE 2204 – Introduction to Manufacturing Processes – Spring 2010 Common Crystal Structures The hexagonal close-packed (hcp) crystal structure: (a) unit cell; and (b) single crystal with many unit cells. Common hcp metals include zinc, magnesium and cobalt. Source: After W.G. Moffatt.
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Different crystal structures form due to the differences in the energy required to form these structures Ex. temperature Crystal structures can be altered by adding atoms of other metal(s) Alloying More than one crystal structure is polymorphism ISE 2204 – Introduction to Manufacturing Processes – Spring 2010 Crystal Structures If a crystal is subjected to external force, and it returns to shape = “elastic deformation”
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