Creep

Question 1

Dislocation Creep

Answer 1

This is creep of a missing half plane of atoms, it occurs because dislocations there were previously locked by precipitates are unlocked due to the diffusion of atoms. This weakens the material as precipitates are used to block the movement of dislocations, making it stronger. In the structure, the atoms diffuse away from the bottom of the half plane of atoms, in dislocation climb. Under the applied load. the dislocations want to move and climb around the precipitate in order to move. the precipitate therefore doesn’t block it any more and allows it to move. This follows the Arrhenius Creep law.

Question 2

Diffusional Creep

Answer 2

Involves instead the diffusion of atoms. At lower temperatures, there is diffusion from one grain boundary to another. However, at higher temperatures, there is bulk diffusion within the crystal. This method also follows the Arrhenius creep law.

Question 3

Creep Curve Stage 1

Answer 3

Starts with a very steep slope, which decreases its gradient as strain hardening takes place and deformation becomes more difficult.

Question 4

Creep Curve Stage 2

Answer 4

This part has a constant slope due to the trade off between strain hardening and recovery. Recovery si the softening of a material due to the natural heating which occurs under an applied load. This stage has the longest duration.

Question 5

Creep Curve Stage 3

Answer 5

The strain rate increases as failure/rupture occurs. there is grain boundary seperation with formation of cavities, voids and cracks.