Disadvantages Of Powder Metallurgy

Powder metallurgy is defined as the process of mixing of powder materials in some desired ratio, compacting the powder mixture to some higher pressures in a compaction die so that the bond formation would takes place followed by the sintering process at higher temperatures (nearly around melting temperatures) so as to achieve sufficient strength. The resulting parts are solid bodies of material with sufficient strength and density for use in diverse fields. Highly porous parts, precise high performance components and composite materials can be produced by P/M route. P/M offers compositional flexibility, minimized segregation and ability to produce graded microstructures with varying physical and mechanical properties. P/M also offers advantages

Compacting: In this step, the blended mixture is compacted to bring the finely divided particles or powders into close proximity while imparting the desired part configuration and providing green strength to the part.

4. Sintering: In this step, the compacts obtained are heated at elevated temperature to establish permanent strong bonds between adjacent particles and thereby to impart strength to the compacts.

Each of the step defined above in discussed in brief later on. 1.2 Advantages of powder metallurgy

Powder metallurgy is one of the popular manufacturing process now a days due to some fabulous advantages, these are described as below,

1. The powder metallurgy eliminates or minimize machining i.e. very little or no scarp is produced during P/M process.

2. P/M enables close dimensional tolerances- near- net shape possible.

3. Provides good surface finish.

4. Facilitates manufacturing of complex shapes, which would be impractical with other metal working processes.

5. Components of hard materials which are difficult to machine can be readily manufactured e.g. tungsten wires.

6. Powders with uniform chemical composition with the desired characteristics, resulting from the absence of segregation during solidification. These characteristics will be reflected in the finished

Environment friendly.

1.3. Limitations of powder metallurgy

1) Die and equipment cost is quiet high. Therefore, the process is feasible for mass production.

2) A surface pollution (oxidation or adsorption) introduces the foreign and detrimental matter in the metal powders this can be avoided if all the processes undergone are made in a clean environment i.e. free of contaminants. This is very difficult to achieve in all cases of industrial practice.

3) The compaction techniques such as die pressing or isostatic pressing are highly technically inefficient.

4) Sintering has three stages namely, slow heating during burn off, a constant temperature period, and cooling after sintering. The non-uniform and non- steady heating and cooling can results into formation of non- equilibrium structures and composites.

5) The porosity in the die pressed mechanical induces structural heterogeneity hence the properties like ultimate tensile strength, and elongation are inferior to wrought materials.

6) Some thermal difficulties are experienced with low melting point metals such as Sn, Pb, Zn and Cd. During sintering the atmosphere in the furnace should be controlled to avoid the formation of oxides as oxide will have adverse effects on the sintering process and results in inferior quality