Jawaharlal Nehru Technological University Hyderabad B.Tech III FUNDAMENTALS OF ENGINEERING MATERIALS Previous Question Paper (March - 2021 - R16)

A substitutional solid solution occurs when solute atoms replace solvent atoms in the crystal lattice. This is favored when the atomic radii of the solute and solvent are similar. Sketch description: A regular grid of solvent atoms with some positions occupied by slightly larger or smaller solute atoms.

An interstitial solid solution occurs when smaller solute atoms occupy the empty spaces (interstices) between the larger solvent atoms in the lattice. This is possible only when the solute atom is significantly smaller than the solvent atom. Sketch description: A grid of large solvent atoms with small solute atoms placed in the gaps between them.

The Hume-Rothery rules define the conditions for extensive solid solubility in metallic alloys:

• Atomic Size Factor: The difference in atomic radii between solute and solvent must be less than 15% for substitutional solid solutions.
• Crystal Structure: For complete solid solubility, both metals must have the same crystal structure (e.g., both BCC or both FCC).
• Electronegativity: The more electropositive one element is and the more electronegative the other, the greater the likelihood they will form intermetallic compounds rather than solid solutions.
• Valency: A metal with a higher valency is more likely to dissolve in a metal with a lower valency than vice versa.