24 Questions
What two elements comprise a crystal structure?
Lattice and basis
Which term refers to the unique minimal spacings between lattice points?
Crystal parameters
What type of materials do not have a crystal structure at all?
Amorphous materials
What do organic polymers form that greatly increases density, opaqueness, and strength?
Spherulites
How are crystals usually described in terms of repeat elements?
Tessellated in space
What determines the yield strength of a material?
Critical resolved shear stress
What do crystallographic planes use to determine their indices?
Coordinate axes
Which type of crystallographic defect is a location where the periodicity in a crystal is disrupted?
Point defects
In an FCC crystal, how many unique close-packed {111}-type planes exist?
4
What are defects that involve impurity atoms called?
Extrinsic defects
What type of directions link the lattice sites along slip planes in FCC crystals?
<110>-type directions
What type of forces can arise due to stress fields around dislocations?
Both attractive and repulsive forces
Which type of doping is used to increase the number of free charge carriers in semiconductors?
N-type doping
What happens when an edge dislocation is created in a crystal?
Compression above and tension below the dislocation line
What happens when unloading the material after yielding?
Recovery of elastic strain
What is the main consequence of strengthening a material through retained dislocations?
Increase in yield strength
What characterizes the incoherent inter-phase interface between dissimilar crystals?
Comprises a dense network of dislocations
How does solute strengthening impact the movement of dislocations?
Generates a stress field that interacts with dislocation stress field
What is the main effect of planar defects on the material?
Retained dislocations strengthen the material further
What factor contributes to the increase in strength of aluminium when alloyed with magnesium?
Solute concentration
Why does the presence of chemically ordered crystals in aluminium increase its strength?
Creation of energetically unfavorable 'wrong' bonds opposes dislocation motion
In precipitation hardening, what role do fine particles with a stronger crystal structure play?
Act as obstacles to dislocation glide
What is the factor that determines whether dislocations must cut through particles or bypass them in precipitation hardening?
Particle size and volume fraction
What is the critical resolved shear stress increased by in the presence of chemically ordered crystals in aluminium?
Energy per unit area of APB
Study Notes
- The critical resolved shear stress due to a dissolved impurity is determined by factors such as the shear strength of the solute, the square of the atom/particle radius, solute concentration, and the shear modulus of the solute.
- Solution strengthening in aluminum alloys can be achieved by alloying aluminum with 5 weight % magnesium, significantly enhancing its strength compared to pure aluminum.
- Order strengthening can occur in a crystal with chemically ordered structures, creating antiphase boundaries that impede dislocation motion and increase material strength.
- Precipitation hardening involves forming fine particles within a crystal structure, which act as obstacles to dislocation glide, ultimately increasing material strength.
- A crystal consists of a lattice and a basis, where atoms or molecules are placed on lattice points, with unique lattice parameters defining the crystal structure.
- Polymer crystallites like spherulites in organic polymers increase density, opaqueness, and strength within the material.
- Crystallographic defects such as point defects, line defects, and planar defects can significantly impact material properties, both functionally and structurally.
- Solute strengthening occurs when a dissolved impurity atom with a different size from the host lattice atoms creates a stress field that inhibits dislocation glide, contributing to increased material strength.
This quiz covers the concepts of crystals, defects, and interfaces discussed in Lecture 2 of the course DM308 Production Techniques 2 by Dr. Vassili Vorontsov. Topics include crystal lattice, basis, crystal structure, and more.
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