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In this course, the educator discusses what is Crystal Structure, Defects in Structure, Heat treatment methods, Creep, Fatigue Fracture, Types of alloys etc. The course will be beneficial for GATE Mechanical Aspirants.

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GATE & ESE

English

Metallurgy and Material Science Engineering (MME )

Basic Crystallography

Engineering Materials

Mechanical Engineering

GATE & ESE - ME & CH

GATE, ESE and IIT-JAM

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In this lesson, gave a detail description of Crystal structures, types of structures etc. There were five types of structures, a) Sub atomic b) Atomic c)Microscopic d) Macro scopic and e) Crystal structure. Orderly arraingements of particles is simply called as crystal structure. Lattice is defined as the array of points each of which has identical surroundings. There were 1D lattice, 2D lattice and 3D lattice. The smallest repeating unit in the lattice which is resulting to produce the crystal is called Unit cell of an atom. So for a unit cell there will lattice parameters,that is magnitude and directions. This will decide the size and shape of the crystal. So by changing that we get 7 crystal systems and 14 Bravais lattices.

Crystal Structure

In this lesson discussed about various defects and gave a detail description of point defects. Otherwise it is called zero dimensional defects. In crystals, particles are arringed in well defined manner, the deviation from this perfection leads to defects. There were point defects, one dimensional defects or line defects, two dimensional defects or surface defects, and three dimensional defects or volume defects. The various point defects are a) vacancy b)self interstitial. But in case of ceramics it is Frenkel defect and Schottky defect. Also said about one additional defect called Non-stochiometric defect.

Defects in Crystal Systems

Described about continuation of point defects that is impurity type defects, it is two types, a) substitutional impurity and b) interstitial impurity. Also discussed about various one dimensional defects or line defects, and described about it's types. Edge dislocation and Screw dislocation are two types of line defects. If one extra half plane is added to the crystal or missed it is called edge dislocation type defect and if the structure of Crystal is slipped or or moved due to shear or something Screw dislocation occurs. Also solidification process, deformation etc are the sources of dislocation.

Continuation of Zero Dimensional Defect, Line Defects Etc

Discussed about various 2D and 3D defects in the crystals. Types of 2D defects are a) External surfaces b) Grain boundaries c) Twin boundaries and d) stacking fault. External surface type defects occur due to free bonds in the material. This is a defect because, basically the atoms doesn't have the type of bonding with its supposed to be where in the bulk. Grain boundary type defects arises due to region of mismatch in Crystal's grain structure. That is if there is change in orientation of the particles, this type of defects arises. It will be of two kinds, low angle and high angle grain boundary defects. The next is the twin boundary defects, occurs due to pair of mismatch in materials. They were exist in pairs. The last one is defect due to missing of stacking sequence,known as stacking fault. Then the volume defects were described, they are Pores, Foreign inclusions, cracks etc.

2D and 3D Defects

Discussed about various Heat treatments, that includes the explanation of annealing processes. Also gave additional information about stress relieving heat treatment method and iso thermal annealing process. Stress relieving heat treatment doesn't have much importance, but it is done to remove internal stresses in the material. And Annealing is the important heat treatment process, which includes heating the material to a certain temperature holding at that temperature and allow to cool it in the furnace itself. Based on temperature it is classified into three a)Full annealing b)Partial annealing and c) Sub-critical Annealing. And based on purpose it is classified as a) Diffusion annealing b)Process annealing and c) Recrystallization annealing. In this lesson deeply discussed only about the types of annealing of temperature kind.

Heat Treatments

Discussed about types of annealing due to purpose. a) Diffusion annealing b) Process annealing and c) Recrystallization annealing. Then the lesson which includes the various other heat treatment methods like Normalising, Hardening, Tempering, Austempering, Martempering and various case hardening methods. In the Normalising heat treatment process, the material is heated to a temperature above upper critical temperature and held at that temperature for a while and allow it to cool slowly. Hardening is one simple method by heating the material to a hardening temperature of the material and it will results in the formation of martensitic structure. Tempering is done after to this hardening and in Austempering process the austenite material is converted to bainitic structure. And Martempering includes converting austenite into martensitic structure.

Annealing Process Continuation and Various Other Heat Treatment Methods

Creep is one important phenomena that occurs in the material and it will result in the failure of material. It is a time dependent phenomena occurs at very low stress limits,for a long period of time at elevated temperatures. Elevated temperature is the temperature that is greater than 0.4 times the melting point of the material. So the creep and failure due to creep occurs even at low temperatures. Next is the stages of creep or creep mechanism. Primary creep, secondary creep and tertiary creep are the various stages of creeps in materials. Among that secondary creep was the longest region comparing to other two stages. Also strain hardening and recovery are two factors which affects the creep rate in materials. Temperature have very good influence on creep rate of materials. I was also discussed it here.

Creep and Mechanism of Creep

Fracture is a phenomena in materials, which occurs due to separation of materials or objects into two or more parts. It occurs initially with a crack and then followed with crack initiation. So this crack propagation decides what type of a fracture it is. That is ductile fracture or brittle fracture. Ductile fracture has plastic deformation in it, and Brittle fracture has no plastic deformation. Described about stages of crack propagation in ductile fracture. Explained about Ductile to Brittle transition. Then Explained the next section that is Fatigue in materials.Simply Failure of materials due to cyclic loads. Cyclic loads be low cyclic and high cyclic. And also repeated stress cycles, reversed stress cycle and random stress cycle. Endurance limit and S-N curve were very important for a material of fatigue strength. Also I gave details about methods to improve fatigue life of material.

Fracture and Fatigue in Materials

This lesson includes the detailed explanation of classification of metal alloys. They are ferrous alloys and non ferrous alloys. Ferrous alloys further classified as, steel and cast iron. This was again classified according to the percentage of carbon in it. For steel they were a) Low carbon steels b) Medium carbon steels and c) High carbon steels. Cast iron was classified as a) Grey cast iron b) White cast iron c) Mottled cast iron d) Malleable cast iron and e) Chilled cast iron. Also there were another type of steels, they are high alloy steels, includes tool steel and stainless steel. Stainless steel is again classified as a) Martensitic stainless steel b) Ferritic stainless steel and c) Austenitic stainless steel. 
Also given all the details about the mechanical properties of this all materials and applications.

Types of Metal alloys

Described and discussed about the various cast iron and it's classification. Also explained about various Non-ferrous alloys. Cast iron have a carbon percentage of greater than 2.1% and it is classified as a) Grey cast iron b) White cast iron c) Mottled cast iron d) Malleable cast iron and e) Chilled cast iron. There is also given the detailed information of its mechanical properties, microstructure and applications. Later gave explanation for various Non-ferrous alloys. They are Copper alloys, Aluminium alloys, Magnesium alloys and Titanium alloys. As same as cast iron described, explained it's all properties and applications. At last given a brief description about Composite materials, that is only a simple introduction to it. The two phases in the composite structure, it's functions, it's classifications etc.

Types of Ferrous Alloys Continuation and Other Non Ferrous Alloys

Pursuing Ph.D. from IIT Patna, an innovator, Music enthusiast, gadget Lover.

Ashish Kumar

In this module crystal structure and defects will be discussed followed by some previous years questions.

(Hindi) Summary of Material Science - Crystal Structure and Defect (Module 3)

Hi, I am Rachit Jain. I am a Final Year Student in Mechanical Engineering, Thapar University. I make courses for GATE aspirants.

Rachit Jain

THIS COURSE IS ABOUT THE DEFECTS IN CRYSTAL AS WELL AS SOLIDIFICATION GROWTH

(Hindi) Physical Metallurgy- Iv Defects in Crystal, Solidification Growth

This course covers Important topics related to Material Science(module 1). About 30-40 % of the syllabus covers almost 90% of the question that comes in exam and rest 10 % questions are very rare and can be asked in exams like ESE.

(Hindi) Mechanical Engineering - Summary on Material Science- Module 1

 Teacher, founder @ GATE Way to ESE (YouTube channel), 3 years of teaching experience 

Aditya Thakur

This Course contains details of iron-carbon diagram and all possible, previous year questions asked in GATE, ESE, ISRO . After watching the course, you are able to draw iron-carbon diagram easily and can remember all the reactions used.

Lessons

10 lessons • 1h 33m