Material Science - MCQs from AMIE exams (Summer 2021)

Write notes on the following (2 x 10)

Binary system

Binary phase diagrams are maps that represent the relationships between temperature and the compositions and quantities of phases at equilibrium, which influence the microstructure of an alloy.

Phase diagram

A phase diagram is a graphical representation of all the  equilibrium phases as a function of temperature, pressure,  and composition.  For one component systems, the equilibrium state of the  system is defined by two independent parameters (P and  T), (T and V), or (P and V).

Pressure-temperature phase diagram for H₂O:

Viscoelastic properties

A viscoelastic material has the following properties:
  • hysteresis is seen in the stress–strain curve
  • stress relaxation occurs: step constant strain causes decreasing stress
  • creep occurs: step constant stress causes increasing strain
  • its stiffness depends on the strain rate or the stress rate 

Ductile fracture

Little or no plastic deformation in brittle fracture and large plastic deformation in ductile fracture.
A ductile fracture is a type of fracture characterized by extensive plastic deformation or necking. This usually occurs prior to the actual fracture.
In a ductile fracture, there is absorption of massive amounts of energy and a slower propagation before the fracture occurs, as compared to a brittle fracture.

Bauschinger’s effect

The Bauschinger effect refers to a property of materials where the material's stress-strain characteristics change as a result of the microscopic stress distribution of the material. For example, an increase in tensile yield strength at the expense of compressive yield strength.

Age hardening

  • Age hardening, also known as precipitation hardening, is a type of heat treatment that is used to impart strength to metals and their alloys. 
  • It is called precipitation hardening, as it makes use of solid impurities or precipitates for the strengthening process. 
  • The metal is aged by either heating it or keeping it stored at lower temperatures so that precipitates are formed. 
  • The metals and alloys need to be maintained at high temperatures for many hours for the precipitation to occur; hence, this process is called age hardening. 

Magnetic energy

Each magnetic field contains energy, also called magnetic energy. Because a magnetic field is generated by electric currents, the magnetic energy is an energy form of moving charge carriers (electrons). 
A classic example of the use of magnetic energy is the generator. Simply put, a magnet inside a coil is permanently rotated in a circle, with the magnetic field doing work. Here is the Lorentz force acting on moving electric charges in a magnetic field. As a result, current can be generated and a voltage can be induced when the magnetic field changes.

Define devitrification.

Devitrification, the process by which glassy substances change their structure into crystalline solids. This devitrification process is very slow, but over millions of years, a glass will form a completely crystalline mass; thus, the occurrence of very old glassy rocks is rare.

Vulcanization

Vulcanization, a chemical process by which the physical properties of natural or synthetic rubber are improved; finished rubber has higher tensile strength and resistance to swelling and abrasion, and is elastic over a greater range of temperatures. In its simplest form, vulcanization is brought about by heating rubber with sulphur.

Susceptibility of paramagnetic magnetic material.

Magnetic susceptibility, quantitative measure of the extent to which a material may be magnetized in relation to a given applied magnetic field. The magnetic susceptibility of material, commonly symbolized by Xm, is equal to the ratio of the magnetization M within the material to the applied magnetic field strength H, or Xm = M/H.

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