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Materials and Metallurgy Viva Questions
Module 1
1.Engineering Material Classification
Ans:
2.What is crystalline and noncrystalline material?
Ans:
I. A crystalline material is one in which the atoms are situated in a repeating or periodic array over
large atomic distances; that is, long-range order exists, such that upon solidification, the atoms
will position them- selves in a repetitive three-dimensional pattern, in which each atom is
bonded to its nearest-neighbor atoms. All metals, many ceramic materials, and certain polymers
form crystalline structures under normal solidification conditions
II. Amorphous solid, any noncrystalline solid in which the atoms and molecules are not organized
in a definite lattice pattern. Such solids include glass, plastic, and gel. Solids and liquids are both
forms of condensed matter; both are composed of atoms in close proximity to each other.
3.What do you mean by unit cell?
Ans:The atomic order in crystalline solids indicates that small groups of atoms form a repetitive pattern. Thus, in describing crystal structures, it is often convenient to sub- divide the structure into small repeat entities called unit cells.
4.Define FCC BCC AND HCC
Ans:Types of Environments:
FCC
FCC (face centered cubic): Atoms are arranged at the corners and center of each cube face of
the cell.
BCC
Atoms are arranged at the corners of the cube with another atom at the cube center.
HCC
Cell of an HCP lattice is visualized as a top and bottom plane of 7 atoms, forming a regular
hexagon around a central atom. In between these planes is a half hexagon of 3 atoms
5.What is crystallographic directions and crystallographic plane
Ans:
crystallographic directions
directions in the various crystal systems that correspond with the growth of the mineral and
often with the direction of one of the faces of the original crystal itself.
crystallographic plane
Any set of parallel and equally spaced planes that may be supposed to pass through the centers
of atoms in crystals. As every plane must pass through atomic centers and no centers must be
situated between planes, the distance between successive planes in a set depends on their
direction in relation to the arrangement of atomic centers.
6.What is line Dislocations and its types
Ans:
Dislocations are linear defects and represent a line around which atoms in the crystalline lattice
are misaligned.
Types of Dislocations:
EDGE DISLOCATION: A dislocation introduced into
the crystal by adding an โโextra half planeโโ of atoms.
SCREW DISLOCATION: A dislocation produced by skewing a crystal so that one atomic plane
produces a spiral ramp about the dislocation.
MIXEDโ DISLOCATION: A dislocation that contains partly edge components and partly screw
components
7.Recrystallization, Recrystallization temperature
Ans:
Recrystallization - A medium-temperature annealing heat treatment designed to eliminate all of
the effects of the strain hardening produced during cold working. Nucleation and growth of a
new stress-free microstructure occurs. Recrystallization must be accomplished above the
Recrystallization temperature. - The temperature above which the effects of strain hardening
are eliminated during annealing. The recrystallization temperature is not a constant for a
material but depends on the amount of cold work, the annealing time, and other factors. At this
temperature atomic mobility becomes high enough to allow recrystallization. This temperature
is usually one-third to one half the melting temperature (in degrees Kelvin)
8.What are types of point defects?
Ans:
Vacancy
Impurity
Frankel defect
Schottky defect
9.What is Annealing, cold Working
Ans:Annealing -Annealing is a heat treatment process which alters the microstructure of a material to change its mechanical or electrical properties. Typically, in steels, annealing is used to reduce hardness, increase ductility and help eliminate internal stresses Cold working - Deformation of a metal below the recrystallization temperature. During cold working, the number of dislocations increases, causing the metal to be strengthened as its shape is changed.
10. Factors affecting Recrystallization temperature
Ans:
I. Melting point: Higher the melting point of metal higher the recrystallization
temperature
II. Degree of cold work: Higher the degree of cold work lower the recrystallization
temperature
III. Grain size: Finer the grain size lower the recrystallization temperature
IV. Purity of metal: Presence of impurities increases recrystallization temperature
V. Heating time: Longer the heating time, lower the recrystallization temperature
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