JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III Year POWDER METALLURGY Previous Question Paper (March - 2021 - R18)

Powder production methods are categorized into physical, chemical, and mechanical processes. Key methods include: Atomization (gas, water, or centrifugal), Chemical reduction of metal oxides, Electrolysis, Thermal decomposition (e.g., carbonyl process), and Mechanical alloying or milling.

Powder metallurgy differs from traditional manufacturing processes like casting or machining in several ways. Unlike casting, it operates below the melting point of the primary metal, allowing for the fabrication of materials with high melting points or immiscible components. It is a near-net-shape process, significantly reducing material waste compared to machining. Furthermore, it enables the creation of unique microstructures, such as controlled porosity or composite structures, that are impossible to achieve through conventional liquid-state processing.

Ultrasonic gas atomization is a specialized technique where a high-velocity gas stream is modulated at ultrasonic frequencies to disintegrate a molten metal stream into very fine, spherical powder particles. The process uses a gas nozzle design that creates shock waves, which break the liquid metal into smaller droplets than standard gas atomization. This results in a finer particle size distribution and higher cooling rates.

The limitations of this process include:

• High operational costs due to the consumption of inert gases and the complexity of the nozzle design.
• The equipment is sensitive to nozzle clogging if the melt temperature or flow rate is not strictly controlled.
• It is generally limited to lower production volumes compared to water atomization.
• The process requires sophisticated control systems to maintain the stability of the ultrasonic field during atomization.