Part 1 Flashcards
(31 cards)
Q: Can the number and type of defects be varied and controlled?
A: Yes, through processes like alloying, heat treatment, and mechanical working.
Q: How do defects affect material properties?
A: Defects can change properties like strength, ductility, electrical conductivity, and density.
Q: Are defects undesirable?
A: Not always. Some defects improve material properties, like dislocations increasing ductility.
Q: What types of defects arise in solids?
A: Point defects, line defects, planar defects, and volume defects.
Q: What is the solidification mechanism?
A: Solidification involves nucleation, growth, and the formation of grains.
Q: What is solidification?
A: Solidification is the result of casting molten material, involving the formation and growth of nuclei into crystals.
Q: What are the two steps in solidification?
A: 1. Nuclei form.
2. Nuclei grow to form crystals (grain structure).
Q: What happens when crystals grow during solidification?
A: Crystals grow until they meet each other, forming a polycrystalline structure.
Q: What are polycrystalline materials?
A: Materials composed of many small crystals or grains.
Q: What are grain boundaries?
A: Grain boundaries are regions between crystals where the lattice transitions from one region to another.
Q: What are the characteristics of grain boundaries?
A: Grain boundaries are slightly disordered, have lower density, and exhibit high atomic mobility and chemical reactivity.
Q: What is atomic mobility?
A: Atomic mobility refers to the ease with which atoms move within a material, often higher in regions like grain boundaries where the atomic structure is less ordered.
Q: What are point defects (0-dimensional)?
A: Point defects include vacancy atoms, interstitial atoms, and substitutional atoms.
Q: What are line defects (1-dimensional)?
A: Line defects are dislocations, which occur along a line in the crystal structure.
Q: What are area defects (2-dimensional)?
A: Area defects include grain boundaries, external surfaces, phase boundaries, and twin boundaries.
Q: What are vacancies in metals?
A: Vacancies are vacant atomic sites in a crystal structure, which are a point defect in metals.
Q: What are self-interstitials in metals?
A: Self-interstitials are “extra” atoms positioned between atomic sites in a crystal structure, which are a point defect in metals
Q: How does equilibrium concentration of point defects vary?
A: The equilibrium concentration of point defects increases with temperature.
Q: What is the formula for equilibrium concentration of defects?
look at the slides(lecture 7)
Q: How is activation energy (Q v) measured?
- Measure the defect concentration at different temperatures,
- plot the natural log of the defect concentration compared to the total concentration against the inverse of the temperature.
- The slope of the line gives the activation energy.
Q: What happens to the (110) surface of NiAl at increasing temperatures?
A: At higher temperatures, more atoms become vacancies (empty sites) in the crystal. This leads to increased atomic motion, allowing atoms to move from inside the crystal to the surface, where they form islands of atoms.
Q: What are the conditions for a substitutional solid solution (S.S.) according to the Hume Rules?
A: The conditions are:
The difference in atomic radius (Δr) should be less than 15%.
The metals should be close in the periodic table (similar electronegativities).
They should have the same crystal structure.
Valency matters; a metal can dissolve another with higher valency more easily than one with lower valency.
Q: What are dislocations in metals?
A: Dislocations are line defects that cause slip between crystal planes when they move, resulting in permanent (plastic) deformation of the material.
Q: What are linear defects (dislocations)?
A: Linear defects are one-dimensional defects in which atoms are misaligned around the defect.
