Creep Mechanism and Heat Treatment Processes in Materials

SOLUTION 1:
a) The creep mechanism Bulk Diffusion is weakly dependent upon the stress. As the creep
is the tendency of a material to change its shape when it is subjected to a particular load
in a prolonged period. (Frost, et.al 1982)
Fig1. Creep and time dependency
b) In the bulk diffusion creep mechanism, which is also known as Nebarro herring creep.
The creep formation mechanism is highly dependent upon the size of the grain. with the
increase in the Grain size the creep decreases.

Fig2. Creep vs grain size
c) With the help of Ni-based single crystal, the Creep mechanism in superalloys can be
controlled. The static magnetic field will be introduced in the material during
solidification process.
d) Bulk deformation creeps mechanism or Nebarroheriing Creep is the most noticed type of
creep in the case of Alloying elements. As the element is strengthened for increasing one
its physical properties the creep will prominently be at the second stage as the metal is
stronger. (Fatemi-Varzaneh, S.M. et.al 2009)
SOLUTION 2:
a) TTT Diagram for Plain Carbon Steel of eutectoid composition
Fig3. TTT diagram of plain carbon steel

The method of accelerated cooling of a heated material is known as the quenching
process. The heat treatment processed metal will be cooled by the exposure of quenching
medium like water, gas, air, etc. Rapid cooling is achieved by the application of liquid
quenching mediums. (Rahaman, M.S.A et.al 2007)
There are various commercially available types of quench mediums are:
 water
 vegetable oil
 animal oil
 gas
 cold water
 brine
 Caustic soda
b) Due to the hardening process, martensitic material properties change and it will be brittle,
lose its ductile and toughness. In order to improve these properties, the heat treatment
process is carried out which is known as tempering process. The tempering is generally
done after the hardening process. The tempering process is done by heating the material
to be tempered below its martensitic temperature and then allowing to cool down itself in
a slow and steady process.
c) The results of Martensitic transformation is theSME (shape memory effect). The process
in which the deformed material returns to its initialshapewhen heat treatment is done is
known as shape memory effect.There are some specific alloys known as shape memory
Alloys which exhibit pure properties of shape memory effect (Pichkaleva, M., et.al 2017)
d) The measurement of the capacity of the material to withstanding scratches and
indentation is called the hardness of the material. Material with high hardness tends to
exhibit very low ductility and machinability properties. The machining process of the
hard material is challenging so the geometry or the dimensions of the hard material

should be simple and easy to machine no complex curves shall be implemented in the
design (Taufik, A., et.al 2018)
e) The alloying of the carbon in steel found to increase its hardness to a greater extent. The
carbon decreases the ferrite and pearlite formation and increases the hardness of the
material. The hardness of a material is directly proportional to the percentage of carbon
content in it. There are many processes to improve the hardness such as Carburizing,
nitriding, carbonitriding, flame hardening, induction hardening, etc.
The solution for Question3:
Function a) Suspension of Truck
Constraints a) Fixed length
b) Max displacement is given
c) Stiffness is given
Objective a) Mass reduction or minimization
Free variables a) The width of the leaf spring
b) The thickness of the leaf spring
c) The required material selection
Objective: Mass reduction
Total mass,
m=b Ltρ
Here,