Strengthening Mechanisms

Question 1

Define Hardening of Metals

Answer 1

Hardening is increasing the strength of a material. it requires the movement of dislocations to be restricted.,

Question 2

Grain size hardening

Answer 2

Adjacent grains have different crystallographic orientations. Grain boundaries act as barriers for dislocations because of grain disorientation and discontinuity of the slip planes. If the disorientation is large, the grain boundaries have a build of dislocations. Pile ups increase concentration at grain boundaries and generate new dislocations in adjacent grain boundaries.

Question 3

Solid solution hardening

Answer 3

Atoms of alloying elements distort the lattice and creates lattice strain fields. these strain fields interact with strain fields of the dislocations. This leads to pinning. to move the pinned dislocations requires a high=er stress, thus, increasing yield stress.

Question 4

Substitutional solid solution

Answer 4

requires atoms of similar size.

Question 5

Interstitial solid solution.

Answer 5

requires much smaller atoms.

Question 6

Work/Strain hardening

Answer 6

a ductile metal becomes harder and stronger as it plastically deforms. Plastic deformation causes dislocations to move and multiply. Eventually, the dislocations become progressively hindered from moving because they become blocked by other dislocations. Thus, increasing yield stress.

Question 7

Precipitation Hardening

Answer 7

Fine particles, precipitates, increase the strength and hardness of metallic alloys. they obstruct dislocation motion, increasing the strength. Fine precipitates are more effective that course precipitates. this is different to solid solution as done by changing phase when heating.