JNTU B.Tech III POWDER METALLURGY Previous Question Paper (September - 2021 - R18)

The powder metallurgy manufacturing process consists of four fundamental stages:

1. Powder Manufacture: Production of metallic powders through methods such as atomization, chemical reduction, or electrolysis to achieve desired particle size, shape, and purity.
2. Mixing and Blending: Combining elemental or alloy powders with lubricants, binders, or additives to ensure chemical homogeneity and improve flowability and compressibility.
3. Compaction: Pressing the powder mixture into a rigid die at high pressure to form a 'green compact'. This shape has sufficient strength for handling but lacks final mechanical properties.
4. Sintering: Heating the green compact in a controlled atmosphere furnace at temperatures typically 70-90% of the melting point. This promotes atomic diffusion, leading to bonding between particles, densification, and improved mechanical properties.

The electrolysis process is primarily used to produce high-purity metallic powders with specific dendritic or needle-like morphologies, which are advantageous for mechanical interlocking during compaction. Key powders produced via this method include:

• Copper Powder: The most common application. Electrolytic copper powder is highly pure and exhibits excellent electrical and thermal conductivity, making it ideal for electrical contacts and carbon brushes.
• Iron Powder: Electrolytic iron is produced for high-performance applications where extreme purity and specific magnetic properties are required, often used in specialized electromagnetic components.
• Silver and Gold Powders: Used in high-end electronic and decorative applications where the high purity attainable through electrolytic deposition is critical for performance.

The process involves dissolving a metal anode in an electrolyte and depositing the metal as a loose, brittle powder on the cathode. The resulting powder is then scraped off, washed, dried, and annealed to reduce oxides and improve ductility.