Question

1. How to improve the mechanical properties (Hardness) and the physical properties (Conductivity)? How to prevent oxidation in a material`s chemical properties?

2. What is the difference in Cold work and hot work? Explain and give 2 examples of what application are use in each one.

3. How does the dislocations movement behave in metals and ceramics? Explain the difference.

4. Explain the recrystallization phenomenon.

Answer 1

1. To increase the HARDNESS  or we can say hardening the substance. It's a metallurgical process (metal working). Also, hardness is directly proportional to the uniaxial yield stress of the material at the location of imposed strain. Following are some ways to increase the hardness :

a. Work hardening or strain hardening - by cold working , material is strained past its yield point. Ductile material becomes harder and stronger as it physical deformed (formation and grouping of dislocations)

b. Hall petch method / grain boundary strengthening - to obtain small grains which make material harder.

c. Age hardening/ precipitation hardening

d. Martensitic transformation which includes quenching and tempering, specifically for steels.

e. Solid solution strengthening

increase the CONDUCTIVITY,

a electro plating (ALSO IMPROVES STRENGTH OF THE MATERIAL , corrosion resistance ,solder ability)

b. Doping (e.g with oxygen or electrons)

c. Heating

d. By applying high electric fields where super ohmic behavior is observed

To prevent the OXIDATION of a material,

a. Try to keep the area around the material dry.

b. Prophylactic protection (electrolytic process)

c. Making alloy of the metal with atmospheric control furnace

d. By coating a layer of primer.

2. Metal plastically deformed below recrystallization temperature is known as COLD WORKING. It increases strength but decreases ductility and corrosive resistance. Gives better control of dimension and surface finish. Formation of residual stresses. Classification of cold working : shearing, squeezing,  

Bending and drawing.

Metal plastically deformed above recrystallization temperature is known as HOT WORKING . Less energy required but may result in surface oxidation. Formation of new crystals and no residue stresses are there. Classification of hot working : forging, rolling, extrusion.

3. Dislocations move easily in metals, due to the delocalized bonding, but do not move easily in ceramics. This is the reason why we call ceramics as brittle and metals as ductile(mostly). Also dislocation glide is easy in metals fue to metallic bond is non specific, where as it is difficult in ceramics due to specific nature of covalent or ionic bonding, in ionic bonds movement od dislocation disrupts the charge balance around the surrounding atoms . (The attached picture show the slip plane movement.4. Recrystallization- its a primary method for purifying solid compounds obtained from natural resources or reaction mixtures. The impurities may include some combination of insoluble, soluble, and colored impurities. To obtain a
pure compound these impurities must be removed.