JNTU B.Tech II METALLURGY AND MATERIAL SCIENCE Previous Question Paper (May/June - 2019 - R16)

A metal is a pure elemental substance characterized by high electrical and thermal conductivity, ductility, and a lustrous appearance, consisting of atoms of a single chemical element. An alloy is a metallic substance composed of two or more elements, where at least one is a metal, combined to enhance specific mechanical or chemical properties such as strength, hardness, or corrosion resistance.

For an FCC crystal, the atomic density (planar density) is calculated as the number of atoms centered on the plane divided by the area of the plane. Given the lattice parameter a = 3.61 Å, the atomic density is calculated as follows:

1. (100) plane: The plane contains 4 corner atoms (each contributing 1/4) and 1 center atom, totaling 2 atoms. The area is a². Atomic density = 2 / (3.61)² = 0.153 atoms/Ų.
2. (110) plane: The plane contains 4 corner atoms (each contributing 1/4) and 2 face-centered atoms (each contributing 1/2), totaling 2 atoms. The area is a × (a√2) = a²√2. Atomic density = 2 / ((3.61)² × 1.414) = 0.108 atoms/Ų.
3. (111) plane: The plane contains 3 corner atoms (each contributing 1/6) and 3 face-centered atoms (each contributing 1/2), totaling 2 atoms. The area is (√3/4) × (a√2)² = (√3/2)a². Atomic density = 2 / (0.866 × (3.61)²) = 0.177 atoms/Ų.