Engineering Materials exam 1 (FAU) 9/27/18 morano

Properties of Ceramic Materials

High Strength. High Fracture Toughness. High Hardness. Excellent Wear Resistance. Good Frictional Behaviour. Anti-Static. Heat-resistant material), and abrasives.

Metallic Crystals

-Densely Packed - Non directional bonding _ have the simplest crystal structures

Properties of polymers

-very unreactive -main carbon chain = usually non-polar -strong covalent bonds within -weak van der waals forces between the chains -Easily formed into thin, flexible, airtight film

How do properties of materials change near grain boundary or a surface?

A grain boundary is the interface between two grains, or crystallites, in a polycrystalline material. Grain boundaries are 2D defects in the crystal structure, and tend to decrease the electrical and thermal conductivity of the material. (twins, low/high angle boundaries, twists and stacking faults) :FROM CANVAS -The smaller the grain size, more are the grain boundaries. •More grain boundaries means higher resistance to slip (plastic deformation occurs due to slip). •More grains means more uniform the mechanical properties are. : FROM CANVAS A change in grain size affects the yield strength due to the dislocations interacting with the grain boundary as they move. Therefore there is an inverse relationship between grain size and yield strength.

Metallic Bond

A primary interatomic bond involving the nondirectional sharing of nonlocalized valence electrons ("sea of electrons") by all the atoms in the metallic solid. -NON Directional(metals)

covalent bond

A primary interatomic bond that is formed by the directional sharing of electrons between neighboring atoms. -Directional (semi conductors, ceramics polymers chains) - chemical bonds

Atomic Packing Factor (APF)

APF = Sum of atomic volumes/Volume of cell

Secondary bonds

Arises from interaction between dipoles Directional Inter-chain(polymer) Inter-molecular

How are Vacancies and Interstitials defined?

Both deal with point deffects/imperfections in solids. Vacancies are empty spaces where an atom should be, but is missing. Interstitials defects are a variety of crystallographic defects where atoms assume a normally unoccupied site in the crystal structure.

valence electrons

Electrons on the outermost energy level of an atom

Allotropy

If the material is an elemental solid, it is called allotropy. An example of allotropy is carbon, which can exist as diamond, graphite, and amorphous carbon

Properties of metals

Lustrous (shiny) Hard. High density (are heavy for their size) High tensile strength (resist being stretched) High melting and boiling points. Good conductors of heat and electricity.

classifications of materials

METALS, CERAMIC, POLYMERS, semiconductors, biomaterials, composites

Ionic bond

Occurs between + and - ions. • Requires electron transfer. • Large difference in electronegativity required. -NON-Directional (Ceramics)

Point (0D) , Line (1D), Surface (2D) and Volume (3D) defects?

Point 0D defects: vacancies, interstitials, Frenkel imperfections are all examples Line 1D defects: edge, screw or mixed dislocations Surface 2D defects: free surface, bonded to atoms on only one side and hence has higher state of energy (highly reactive) Volume 3D defects: cluster of point defects join to form 3D void (extended defects, pores, cracks, etc..)

Properties of electromagnetic materials

Silicon, germanium, and gallium some are large single crystals conductive

Polymorphism

Some materials may exist in more than one crystal structure

Properties of composite materials

These are formed from two or more materials, producing properties not found in any single material. Concrete, plywood, and fiberglass

Coordination number for FCC (face centered)

cord # = 12 contains 4 atoms per unit cell APF=.74

coordination number for SC

cord # = 6 1 atom per unit cell APF=.52

Coordination number for HCP ( Hexagonal close-pack)

cord # of 12 contains 6 atoms per unit cell APF=.74

Coordination number for BCC (body-centered)

cord #=8 Contains 2 atoms per unit cell APF=.68

What happens to the # of vacancies when the temperature is increased/decreased and why?

high temperatures, high vacancies (did not complete flashcard*)