Question

This question is from the material science class.

Briefly describe

1. Grain refinement

2.Solid-solution formation

3. strain hardening(cold work)

4. Precipitation Strengthening

Answer 1

1. Grain refinement  

To understand this first we should know what grains are? Grains are regions of the material and in these regions, atoms have a particular orientation.Grain refinement is the process of reduction in the size of the grains inside a material.

With grain refinement, new more and more grains starts forming and replace the original grain structure. Newly formed small grains have a different orientation. Due to the different orientation, it is difficult for a dislocation to travel and accumulate. Accumulation of dislocations are precursors to crack initiation and failure. Grain refinement is used to introduces more and more grains boundaries and due to this, movement of dislocations stops and thereby it takes a longer time to fail the material and it improves the strength of a material. So, generally, grain refinement is used to strengthen the material.

2.Solid-solution formation

Solid solution formation occurs when two metals are mixed together and there will be a formation of an alloy if one metal is in solid state and other metal is soluble. Therefore, an alloy is also known as a solid solution of two or more metals.

Formation of solid solutions between two metals is governed by a set of rules known as Hume-Rothery rules

Hume-Rothery rules

1. The electronegativity difference between the metals should be small. metals should have the minimum chemical affinity to each other.
2. Size difference between the atoms of solute and the parent metal should be less than 15%.
3. The solubility of a metal with higher valence in a solvent of lower valence should be more. for e.g. Zn (higher valence) is much more soluble in Cu (lower valence).
4. The crystal structures of the solute and the solvent must be the same for complete solubility.

3. strain hardening

Strain Hardening is the process when a metal is strained beyond the yield point. For strain hardening, we need an increasing stress to produce additional plastic deformation and the metal becomes stronger after that it will be more difficult to deform the metal. Strain hardening is somewhere related to fatigue. Strain hardening reduces ductility, as a result of this there will increase in the brittle failure property of a material.

4. Precipitation Strengthening

Precipitation strengthening is also known as age or particle hardening. It is a heat treatment process that enhances the strength and hardness of some metal alloys by the formation of uniformly dispersed particles within a metal's grain structure. It is called precipitation hardening because the small particles of the new phase are termed as precipitates. These particles hinder dislocation motion and thereby strengthen the metal, particularly those that are malleable.