AE2354 High Temperature Materials B.E Question Bank : sriengg.com

Name of the College : Srinivasan Engineering College
University : Anna University
Department : Aeronautical Engineering
Degree : B.E
Subject Code/Name : AE2354 High Temperature Materials
Year : 3rd
Semester : 6th
Document Type : Question Bank
Website : sriengg.com

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SRI Engg High Temperature Materials Question Paper

Unit-1

Creep :
1. Define creep :

Related : Srinivasan Engineering College AE2202 Aero Engineering Thermodynamics B.E Question Bank : www.pdfquestion.in/3208.html

Creep is large plastic deformation of material on application of stress or elevated temperature or a combination of both applied for a prolonged time. A material subjected to a constant stress may fail well below its yield stress if load is applied for prolonged time.

2. Define creep formation :
It involves time-dependent deformation and high temperature creep cracking generally develops in an intercrystalline manner in components of engineering importance that fail over an extended time.

3. What is meant by diffusion process? :
At low stress and high temperature atoms diffuse from sides to the top and bottom. The grain becomes longer as the applied stress does work. Atomic diffusion in one direction is same as vacancy diffusion in opposite direction.

4. Why the rate of creep is more at elevated temperature? :
Creep is one of the most serious high temperature damage mechanisms. As temperature increases mobility of atom increases, frequently increasing the diffusion mechanism and has significantly influence on high temperature mechanical properties like creep and fracture. So the rate of creep is more at elevated temperature.

5. What are the problems associated with materials used at elevated temperature? :
Generally a material subjected to high temperature reduces the strength of the material and failure mechanisms affecting the functional life of components are totally different. At high temperature the strength of material has strong dependence on time.

6. What are the factors influencing functional life of components at elevated temp? :
1) Creep
2) Corrosion
3) High temperature fracture
4) Thermo mechanical Fatigue
5) Interaction of all above with each other
6) Metallurgical ageing and metallurgical stability
7) Micro structural changes

7. Which types of materials are preferred for creep application? :
A material which posses the following features to avoid creep formation and get creep resistant at high temperatures.
1. Higher creep resistance is observed with metals having high melting point. Creep becomes significant above 0.4 Tm .
2. A coarse grain metal has high creep resistance than fine grained metals.
3. Single crystal have excellent creep resistance because they have no grain boundary.

8. What are the deformation modes? :
1. Dislocation climb and glide
2. Vancancy diffusion
3. Dislocation Creep
4. Diffusion Creep
5. Grain Boundary Sliding

9. Draw typical creep curve, mark the various stages and mention the factors influencing each stage :
1. Primary Or Transient Creep – Strain or work hardening
2. Secondary Or Steady State Or Recovery Creep- Thermal Softening or Annealing
3. Tertiary Creep – Void Propagation and Grain boundary sliding

10. Define super plasticity :
Super plasticity is the ability to withstand very large deformation in without necking.

11. What are effects of stress and temperature on the creep curve? :

12. Write any two high creep resistance materials :
1. Tungsten
2. Nickel based super alloys
3. Iron based super alloys
4. Cobalt based super alloys,
5. Molybdenum

13. Name two metallurgical factors that affect creep rate :
1. Work hardening
2. Thermal Softening
3. Grain boundary sliding
4. Diffusion and cavitation

Unit – 2

Design For Creep Resistance
1. What are Material aspects for creep resistance? :
** Creep resistance improved if diffusion rates are decrease.
** An increased modulus improves resistance to dislocation creep

** When creep is controlled by dislocation climb and glide process, similarly material having high shear modulus display a better creep resistance.
** Stress raises such as sharp corners are avoided so that the stress concentration diminish or vanish considerably and materials with finer grain size are utilized.

** Surface irregularities and cracks are removed by polishing surface.
** Compressive stresses are introduced at the surface by process such as short sand blasting.
** Nitriding and carburising operations are performed to create strong surface layers.

2. Define rupture life of creep? :
Rupture life of creep is defined as the maximum stress that will allow the member to withstand creep without failure at the specified period of time. In creep testing the main goal is to determine the minimum creep rate in stage II.

Once a designer knows the materials will creep and has accounted for this deformation a primary goal is to avoid failure of the component.