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Materials/Processes

Selection of Materials
Specific Metals
  Metal Ores
  Iron and Steel
  Decarburization
  Aluminum/Aluminum Alloys
  Nickel and Nickel Alloys
  Titanium and Titanium Alloys


General Manufacturing Processes

Metallic Components
Ceramic and Glass Components
Polymers/Plastic Components
Composites

Manufacturing Defects
Metals
Polymers
Composites

Service Induced Damage
Metals
Polymers
Composites
Material Specifications

Component Design, Performance and NDE
Strength
Durability
Fracture Mechanics
Nondestructive Evaluation

Diffusion

Diffusion is the migration of atoms from a region of high concentration to a region of low concentration. In a homogeneous material, atoms are routinely moving around but the movement is random (i.e. there is always an equal number of atoms moving in all directions). In an inhomogeneous material, all the atoms are moving near randomly, but there is a migration of atoms to areas where their concentrations are lower. In other words, there is a net diffusion.

Atom diffusion can occur by the motion of host or substitutional atoms to vacancies (vacancy diffusion), or interstitial impurities atoms to different interstitial positions (interstitial diffusion). In order to move, an atom must overcome the bond energy due to nearby atoms. This is more easily achieved at high temperatures when the atoms are vibrating strongly. Carburizing, which will be discussed later, is an example of diffusion is used.