UNIT-1
Crystal Structure and Deformation of Materials
Q1) Explain different types of cubic structure?
A1) There are three main varieties of these crystals:
1) Simple cubic (SC) :- Atoms are arranged at the corner of the cell.
Total number of atoms = 8
Number of atoms at each corner 
Edge length a = 2r
Packing efficiency:- volume of spaces occupied by the space
Where z = number of atoms per unit cell
Total space occupied by spares =52.4
Empty space = 100 – 52.4 = 47.6%
2) Body centered cubic (BCC) ;- atoms are arranged at the corners of the cube with another atoms at the cubic centre.
Number of atoms in corner = 8
Number of atoms in each corner 
Number of atoms in middle =1
Total atoms = z = 1 + 1 = 2
According to Pythagoras theorem
In ∆ADC
Where AD = 4r
CD = a
AC = ?
So, ∆ABC
Putting the values in equation (1)
So volume occupied by the space = 68%
Empty space =32%
Example :- Mg, Na, K, Li
(3) FCC ( Face centre of cubic):- Atoms are arranged at the corners of each cube for the cell.
Total number of atoms in corner = 8
Each atom in corner 
Atoms in each face 
So total atoms in cell = 1 + 3 = 4
In ∆ABC
Volume occupied by the space = 7 empty space = 26
Example :- Al, Ag etc.
Q2) What are different types of defects in single atomic crystalline structure?
A2) Different types of defects in single atomic crystalline structure:-
Schotky defect :- A vacancy or vacancies in an ionic crystal structures is called schotky defect.
Interstitial defect:- atoms that occupy a site in The crystal structure at which there is usually not an atom.
Frenkel defect :- nearby peer of vacancy and an interstitial is called as frenkel defect.
Substitutional defect:- if different atoms are occupying the locations of the regular atom then they are called substitutional defect.
Q3) What do you mean by elastic and plastic deformation?
A2) The change in dimensions in form of better under the action of applied force is called deformation.
Types of metal deformation:-
Elastic deformation:- It is the deformations which appears when the load is removed. It happens before the plastic deformation. This information occurs when the stresses applied on a metal
Above figure shows form of the atoms before loading (loading in tension and compression respectively). When a tensile load is applied the piece becomes slightly larger whereas compression load shortens the piece.
For elastic deformation the strain is nearly proportional to the stress.
The ratio between stress and strain and elastic deformation is known as modulus of elasticity or young modulus.
Plastic deformation:- it is the deformation which persist even after the load is removed. Plastic deformation is observed at stresses exceeding the elastic limit which depends primarily on stress in the simplest curves. Plastic deformation is typically a function of stress temperature and rate of straining.
Plastic deformation process is generally applied in metallurgical operation of shaping the operation include rolling of boilerplates, drawing of wire, extrusion of telephone cable etc.
In metal the plastic deformation generally takes place by the process of slipping.
Q4) What is Bauschinger effect? Explain with diagram?
A4) When magnetic material is placed in an external magnetic field, its grains get oriented in the direction of magnetic field which result in the magnetization of material in the direction of external magnetic field. Now, even after removal of external magnetic field some magnetization exists which is called residual magnetism. The property of material is called magnetic retentivity of material.
A hysteresis loop or B.H curve of a typical magnetic material is in below figure. Br in below hysteresis loop represents the residual magnetism of material.
Q5) Define different types of material properties?
A5) Mainly four material properties are discussed here
Magnetic property :- The magnetic properties of a material are those which determines the ability of a material to be suitable for a particular magnetic application.
Some different types of magnetic properties are described below
A) Mechanical properties:- the mechanical properties of materials are those which affect the mechanical strength and ability of a material to be molded in desired shape.
Some of them are as follows :-
1) Strength
2) Hardness
3) Toughness
4) Malleability
5) Hardenability
6) Brittleness
7) Ductility
8) Creep and slip
9) Resilience
10) Fatigue
B) Optical properties :-; Optical property of a material is defined as its interaction with electromagnetic radiation in the visible.
C) Electrical properties :- The electrical properties of a material are those which determine ability of a material to be suitable for a particular electrical engineering.
Some of them are as follows :-
Q6) What is the difference in between brittle and ductile structure?
A6) Differences between ductile and brittle material
Definition
Ductile: A material that can be easy bent or material can be drawn into wires.
Brittle: A material that instantly snaps by external load application.
Deformation
Ductile: Such material will undergo plastic deformation before fracture.
Brittle: These material show zero plastic deformation after stress and instantly break.
Elongation
Ductile: Under tensile stress, percentage elongation before fracture is higher in these materials.
Brittle: They show very less percentage elongation before fracture.
Energy absorption before fracture
Ductile: Under tensile load, they can absorb more energy before fracture.
Brittle: Very small amount of energy is absorbed by such materials before fracture.
Forming operations
Ductile: Metal forming operations like rolling, drawing or bending can be made on such materials.
Brittle: They cannot withstand with any forming operation.
Stress strain curve
Area under curve in stress strain graph denotes the absorbed energy by material.
Factors that can influence properties of materials
Ductile: Ability to draw wires is affected by temperature.
Brittle: Brittleness is dependent on applied stress.
Appearance after fracture
Examples: Ductile: copper, mild steel, rubber, gold, silver and metals.
Brittle: Glass, ceramics, ice, cast iron, concrete and stone.
Q7) Explain creep and how does it occur?
A7) It is a slope permanent deformation which occurs below the yield point. It occurs under steady loading conditions at a function of time.
In creep there are slips along crystallographic direction in individual crystal along with some grain deformation.
Creep behavior can be split into three main stages. In primary, or transient, creep, the strain rate is a function of time. In Class M materials, which include most pure materials, strain rate decreases over time. This can be due to increasing dislocation density, or it can be due to evolving grain size. In class A materials, which have large amounts of solid solution hardening, strain rate increases over time due to a thinning of solute drag atoms as dislocations move.
In the secondary, or steady-state, creep, dislocation structure and grain size have reached equilibrium, and therefore strain rate is constant. Equations that yield a strain rate refer to the steady-state strain rate. Stress dependence of this rate depends on the creep mechanism.
In tertiary creep, the strain rate exponentially increases with stress. This can be due to necking phenomena, internal cracks, or voids, which all decrease the cross-sectional area and increase the true stress on the region, further accelerating deformation and leading to fracture.[5]
Q8. Describe Recovery, Recrystallization and Grain growth?
A8) Recovery, recrystallization, and grain growth are microstructural changes that occur during annealing after cold plastic deformation and during hot working of metals. The structure of the deformed state and describes the changes in the properties and microstructures of a cold-worked metal during recovery stage. It discusses the recrystallization that occurs by the nucleation and growth of grains. The growth behavior of the grains, explaining that the grain growth can be classified into two types: normal or continuous grain growth and abnormal or discontinuous grain growth.
Recovery, recrystallization and grain growth:- If the temperature is raised sufficiently the metal attempts to approach equilibrium through the process name as
1) Recovery
2) Recrystallization
3) Green growth
Recovery:- Recovery is a low temperature phenomenon which result in the Restoration of the physical properties without any observable change in microstructure.
During recovery there is negligible effect on hardness where as electrical resistance decrease rapidly towards the annealed value. The process of recovery is important for releasing internal stress in forging, molded and fabricated equipments without decreasing the strength acquired during cold water.
Recrystallization:- It is a process by which distorted grains of gold worked metal are replaced by new stream free grains during heating above the specific minimum temperature called recrystallization temperature.
Grain growth :- Grain growth is an increase in grain size when the material is held for longest X at temperature above recrystallization temperature or when it is heated to a higher temperature the grain size increases and there is decrease in hardness and strength and gain in ductility.
At a given temperature 't' the grain size D at a given time is given as
Q9) What is the difference in between resistivity and conductivity?
A9) Resistivity and conductivity is an important property for materials. Different materials have different conductivity and resistivity. Electrical conductivity is based on electrical transport properties. These can be measured with multiple techniques by using a variety of instruments. If electricity easily flows through a material, that material has high conductivity. Some materials that have high conductivity include copper and aluminum. Electrical conductivity is the measure of how easily electricity flows through a material.
Conductivity vs Resistivity
Conductivity and resistivity are inversely proportional to each other. When conductivity is low, resistivity is high. When resistivity is low, conductivity is high. The equation is as follows:
ρ = 1/σ
where
Q10) Define different types of mechanical properties of material?
A10) Some of the typical mechanical properties of a material include:
Strength
It is the property of a material which opposes the deformation or breakdown of material in presence of external forces or load. Materials which we finalize for our engineering products, must have suitable mechanical strength to be capable to work under different mechanical forces or loads.
Toughness
It is the ability of a material to absorb the energy and gets plastically deformed without fracturing. Its numerical value is determined by the amount of energy per unit volume. Its unit is Joule/ m3. Value of toughness of a material can be determined by stress-strain characteristics of a material. For good toughness, materials should have good strength as well as ductility.
Hardness
It is the ability of a material to resist to permanent shape change due to external stress. There are various measure of hardness – Scratch Hardness, Indentation Hardness and Rebound Hardness.
Scratch Hardness is the ability of materials to the oppose the scratches to outer surface layer due to external force.
2. Indentation Hardness
It is the ability of materials to oppose the dent due to punch of external hard and sharp objects.
3. Rebound Hardness
Rebound hardness is also called as dynamic hardness. It is determined by the height of “bounce” of a diamond tipped hammer dropped from a fixed height on the material.
Hardenability
It is the ability of a material to attain the hardness by heat treatment processing. It is determined by the depth up to which the material becomes hard. The SI unit of hardenability is meter (similar to length). Hardenability of material is inversely proportional to the weld-ability of material.
Brittleness
Brittleness of a material indicates that how easily it gets fractured when it is subjected to a force or load. When a brittle material is subjected to a stress it observes very less energy and gets fractures without significant strain. Brittleness is converse to ductility of material. Brittleness of material is temperature dependent. Some metals which are ductile at normal temperature become brittle at low temperature.
Malleability
Malleability is a property of solid materials which indicates that how easily a material gets deformed under compressive stress. Malleability is often categorized by the ability of material to be formed in the form of a thin sheet by hammering or rolling. This mechanical property is an aspect of plasticity of material. Malleability of material is temperature dependent. With rise in temperature, the malleability of material increases.
Ductility
Ductility is a property of a solid material which indicates that how easily a material gets deformed under tensile stress. Ductility is often categorized by the ability of material to get stretched into a wire by pulling or drawing. This mechanical property is also an aspect of plasticity of material and is temperature dependent. With rise in temperature, the ductility of material increases.
Creep and Slip
Creep is the property of a material which indicates the tendency of material to move slowly and deform permanently under the influence of external mechanical stress. It results due to long time exposure to large external mechanical stress with in limit of yielding. Creep is more severe in material that are subjected to heat for long time. Slip in material is a plane with high density of atoms.
Resilience
Resilience is the ability of material to absorb the energy when it is deformed elastically by applying stress and release the energy when stress is removed. Proof resilience is defined as the maximum energy that can be absorbed without permanent deformation. The modulus of resilience is defined as the maximum energy that can be absorbed per unit volume without permanent deformation. It can be determined by integrating the stress-strain cure from zero to elastic limit. Its unit is joule/m3.
Fatigue
Fatigue is the weakening of material caused by the repeated loading of the material. When a material is subjected to cyclic loading, and loading greater than certain threshold value but much below the strength of material (ultimate tensile strength limit or yield stress limit), microscopic cracks begin to form at grain boundaries and interfaces. Eventually the crack reaches to a critical size. This crack propagates suddenly and the structure gets fractured. The shape of structure affects the fatigue very much. Square holes and sharp corners lead to elevated stresses where the fatigue crack initiates.
