Grain Boundary Strengthening

Grain Boundary Strengthening in Strenghtening Process
Decreasing/Finer grain size will increase the yield stress.

The grain size indicates two conditions: The distance for the dislocations have to move to form grain boundary pile-ups and the number of dislocations involved. Having finer grain size, the mobility of the dislocations is harder to move from one grain to another for plastic deformation. In other words, finer grain will impede the dislocations. This will give rise to the strength of the material. However, the grain size cannot be too small (around below 10 nm). This will lead to grain-boundary sliding. The grain boundaries tend to slide and difficult to fit the dislocations in the grain. Thus, less stress required to move them. The equation to this mechanism is The Hall-Petch Equation which states an increase in yield stress is related to a decrease in diameter of the average grain.


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Definition of Precipitation Hardening

What is Precipitation Hardening?
It is a strengthening Process. it is Heat Treatment Process.
"Changes in solid solubility with temperature to produce fine particles of an impurity phase will increase the strength."

now, lets find out the process detailly........
This heat treatment process involves the changes in solid solubility with respect to temperature to produce fine particles of an impurity phase. This condition will obstruct the dislocation and the crystalline lattice and thus, increase the strength of the material. This heat treatment involves precipitation of impurity particles to have a strengthen material. These impurity particles are considered as second phase particles. The presence of these precipitates of second phase particles will cause lattice distortion because of the different is size comparable to the host particles. This distortion will then impede the dislocation which leads to the hardening of materials.

Solid Solution Strengthening or Alloying

what is Solid Solution Strengthening?
It is a strengthening Process.
Adding alloying element will increase the strength of the material.

Adding atoms of alloying element into the crystalline lattice of base metal, the alloying element will diffuse to a matrix solid solution. These solute atoms will cause lattice distortions which then will obstruct dislocation motion, and thus will increase the yield stress of the material. There are two types of this mechanism: Substitutional Solid Solution and Interstitial Solid Solution. The former type involves the solute (alloy) atoms which are larger compared to the solvent (base) atoms being added into crystalline lattice of base metal. They must be the same crystal structure. The instance is Copper-Nickel in FCC structure. While, the latter type involves the solute atoms are smaller than the solvent atoms. The example is the carbon in iron.

Definition of Work Hardening

What is Work Hardening
Increasing the dislocation density will increase the yield strength.

Work Hardening is a difficult process to understand. but, once you understand the process, you will never forget.

Work hardening is a process when the metal is strained beyond its original yield point. As the material is filled up with more dislocations (increasing dislocation density), more dislocations are prevented to develop more dislocation-formation. This resistance is called nucleating and thus, the resistance to plastic deformation. Therefore, the material has been strengthened. However, the dislocation density cannot be increased to an infinitely high value as the crystalline structure will disappear. Usually, work hardening is done to a reasonably high melting point material by using cold rolling or cold drawing.

Strengthening Process for Metals and Alloys

Strengthening is a process to improve or reduce the mechanical properties of a material inclusive of yield strength and hardness to suit the needs of our application. The main principle of the strengthening mechanism is by reducing the mobility of dislocations; it will reduce the occurrence of plastic deformation and thus will strengthen the material. There are four main strengthening mechanisms applicable to metals and alloys
1. Work Hardening
2. Solid Solution Strengthening
3. Precipitation Hardening
4. Grain Boundary Strengthening

Why do we need Material Science and Metallurgy in Mechanical Engineering

Most of us has got a question that Why do we need Material Science and Metallurgy in Mechanical Engineering?

But there is a big need to know the material properties of any Project. These properties will decide the capabilities of our Project.

List of Material Properties
Tensile Strength
Compressive Strength
Shear Strength
Yield Strength
Ductility
Poisson's Ratio
Youngs Modulus
Specific Weight
Specific Modulus
We all know that what these are all