Imperfections in the Atomic and Ionic Arrangements

These flashcards cover key concepts related to imperfections in atomic and ionic arrangements, focusing on types of defects, their significance, and effects on material properties.

What are the four main types of defects in solids?

Vacancies, interstitials, substitutional defects, and dislocations.

What is the significance of vacancies in crystal structures?

Vacancies are vacant atomic sites in a structure that can affect material properties.

Why do FCC structures tend to be more ductile than BCC structures?

FCC structures have more slip systems due to close-packed planes, allowing easier dislocation movement.

What is a substitutional defect?

A defect where different atoms are positioned in normal atomic sites, such as Co in Ni.

What defines a Frenkel defect?

A Frenkel defect is a pair of a vacancy and an interstitial defect.

How does temperature affect the concentration of vacancies in a structure?

The equilibrium concentration of vacancies increases with temperature.

What is meant by solid solution formation?

A solid solution is formed when atoms or ions of a guest element are incorporated into the host material's crystal structure.

What is meant by dislocation motion in materials?

Dislocation motion refers to the movement of dislocations along a slip plane, affecting plastic deformation.

What is the Hall-Petch equation used for?

The Hall-Petch equation is used to relate yield strength to grain size in materials.

What is the importance of grain boundaries in materials?

Grain boundaries are regions between grains that can affect diffusion, mobility, and slip in materials.

What do point defects, line defects, and area defects signify?

Point defects involve atomic sites, line defects involve dislocations, and area defects consist of grain boundaries.

What is strain hardening?

Strain hardening is the process of increasing dislocation density in a material to enhance its strength.

What are some common strengthening mechanisms in materials?

Common mechanisms include strain hardening, solid-solution strengthening, and grain-size strengthening.

Why are dislocations significant in metals and alloys?

Dislocations are significant because plastic deformation is primarily a consequence of their motion.

What happens during the solidification of molten material?

Nuclei form and grow to create crystals, leading to the grain structure of metals.

How does the angle of misorientation affect slip in polycrystalline materials?

Higher angles of misorientation create stronger barriers to slip, affecting the material's mechanical properties.

What is the role of grain refiners in metal processing?

Grain refiners are added to create smaller, more uniform equiaxed grains and improve material properties.

What effect does introducing impurities have on the properties of materials?

Introducing impurities can control mechanical, electrical, optical, and magnetic properties through strategic imperfections.

What are the characteristics of edge and screw dislocations?

Edge dislocations are one-dimensional defects with an extra half-plane, while screw dislocations form a spiral ramp along the dislocation line.