Material Science Test 1
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40 Terms
What is the difference between a single crystal and polycrystal?
A single crystal has continuous lattice with one orientation; a polycrystal is composed of many grains with different orientations.
What is polymorphism (allotropy)?
The ability of a material to exist in more than one crystal structure depending on temperature or pressure.
What are grain boundaries?
Interfaces between crystals of different orientations; they disrupt lattice continuity and impede dislocation motion.
What is the difference between small-angle and high-angle grain boundaries?
Small-angle boundaries (<15° misorientation) consist of dislocation arrays; high-angle boundaries have large misorientation and higher energy.
What is an edge dislocation?
A line defect caused by an extra half-plane of atoms; Burgers vector is perpendicular to the dislocation line.
What is a screw dislocation?
A line defect where atoms spiral around the dislocation line; Burgers vector is parallel to the dislocation line.
What are mixed dislocations?
Dislocations with both edge and screw components.
What are point defects?
Imperfections involving one or a few atoms, such as vacancies, interstitials, and substitutional atoms.
What is a vacancy defect?
A missing atom in the lattice.
What is an interstitial defect?
An extra atom positioned at a non-lattice site.
What is a substitutional defect?
A foreign atom replaces a host atom in the lattice.
What are area defects?
Two-dimensional imperfections such as grain boundaries, tilt boundaries, twin boundaries, and stacking faults.
What is X-ray diffraction used for?
Determining crystal structures by applying Bragg's Law to measure atomic plane spacing.
What is solidification?
The process of nucleation and growth during cooling, forming grains; faster cooling leads to smaller grains.
What is the main difference between metals and ceramics?
Metals have metallic bonding, are ductile, and conductive; ceramics have ionic/covalent bonds, are brittle, and insulating.
Which slip systems are preferred in FCC, BCC, and HCP structures?
FCC: many slip systems (ductile), BCC: less densely packed planes (stronger, less ductile), HCP: few slip systems (brittle).
What is linear density?
The number of atoms per unit length along a crystallographic direction.
What is planar density?
The number of atoms per unit area on a crystallographic plane.
What are the 7 crystal systems?
Cubic, Tetragonal, Orthorhombic, Hexagonal, Trigonal (Rhombohedral), Monoclinic, Triclinic.
What does the net energy vs interatomic distance curve show?
It shows balance between attractive and repulsive forces; the minimum indicates equilibrium bond length and bond energy.
What are the three main categories of crystal defects?
Point defects, line defects (dislocations), and area defects.
What is an edge dislocation?
A line defect caused by an extra half-plane of atoms; Burgers vector is perpendicular to the dislocation line.
What is a screw dislocation?
A line defect where atoms spiral around the dislocation line; Burgers vector is parallel to the dislocation line.
What is a mixed dislocation?
A dislocation that has both edge and screw character.
What is a vacancy defect?
A missing atom from a lattice site.
What is an interstitial defect?
An extra atom squeezed into a site not normally occupied in the lattice.
What is a substitutional defect?
A foreign atom replaces a host atom in the lattice.
What are grain boundaries?
Area defects where crystals of different orientations meet, disrupting lattice continuity.
What is a small-angle grain boundary?
A boundary with misorientation <15°, usually composed of an array of dislocations.
What is a high-angle grain boundary?
A boundary with misorientation >15°, higher energy, more disordered, and more diffusion-prone.
What is a tilt boundary?
A special type of small-angle boundary formed by edge dislocation arrays.
What are stacking faults?
Planar defects where the normal stacking sequence of crystal planes is interrupted.
What are twin boundaries?
Planar defects where the crystal structure on one side is a mirror image of the other.
APF = (Volume of atoms in unit cell) ÷ (Volume of unit cell).
0.52
0.68
0.74 (highest)
0.74 (same as FCC)
FCC and HCP.
Simple Cubic (rare in nature).