Dear Ziyauddin Seikh,

What you mentioned is exactly right..!!

Sintering is applied for the densification of the powder compact.

During sintering, the heated material becomes softer and it exerts plastic deformation under the uniaxial force. Simultaneously, heat increases the diffusion of the atoms/molecules.

Thus, plastic deformation combined with diffusion results in the densification of the powder compact to over 99% of its theoretical density.

Thank you.

In general, there are two phenomena that explain the behaviour of contacting particles during sintering process leading to coarsening. In the first place, mass diffusion across the particles contacting boundaries followed by particles contacting boundaries migration which requires higher activation energy. It is shown that the driving force for interparticle mass diffusion is highly depends on the rate mass transport between two contacting particles, their surface energy, atomic volume, and the radius of each two contacting particles with different sizes. This coarsening process will not stop practically until the size ratio between each two particles reaches a critical value for contacting boundary migration. I suggest for you to go through my published article on the attached RG link. it may covering more explanations and details specially with reference 9 .

Best regards

Article Investigating the effects of calcination temperatures on the...

Sintering occurs well above recrystallisation temperature and below melting point by the process of mass diffusion across grain boundaries till the overall free energy decreases to a minimum in metals and composites having high melting points. The process of grain boundary diffusion and volume diffusion occurs rapidly forming a new grain structure. Temperature control is very important in sintering process. Grain-boundary diffusion and volume diffusion depend on temperature variation, size and distribution of grains in the material, its composition and the environmental conditions.

Sintering is a effective heat treatment applied to a powder compact in order to improvement of strength and integrity. After compaction, neighboring powder particles are held together by cold welds, which give the compact sufficient “green strength” to be handled.

The consolidation of powders and densification of porous solids is possible by pressing and subsequent pressureless heat-treatment (solid-state sintering), by simultaneous application of pressure and heat (hot-pressing or pressure-sintering) or with the aid of a limited amount of melt (liquid-phase sintering).

During the sintering process the temperature must be kept below the melting point of the constituent materials

Dear Ziyauddin Seikh,

Powder sintering has found wide application in the production of metallic and non-metallic materials. The advantage of the method is that better homogeneity of the material can be achieved along the entire thickness (uniform grain structure). Uniform mechanical characteristics throughout the volume of the part. Guaranteed chemical composition due to the possibility of good mixing of the mixture of materials. Better technological properties.

Sintering is done to improve the strength of the compacts and during sintering process the particle bonding strength is improved.

• Sintering is one of the essential steps in powder Metallurg.
• After compaction, Component do not have enough strength for specific applications. So to impart strength and to densify the component sintering is done above recrystallisation and below melting point of used materials.

Hello,

read the books written by Geguzin (Yakov Evseevich). One of them is Fyzika spekania (Physics of Sintering, Moscow 1971) available in english at Amazon. It is several decades I read this book. What I still remember is that sintering of amorphous materials (like glass balls) can be described as viscous flow. Agreement between theory and experiment is excelent. It is not true for crystalline bodies. Here is sintering far to complicated process. Agreement between theories and experiment is often poor or fair for some region of parameters. Surface energy, surface faults, surface contamination, surface curvature, grain boundaries, vacancies, dislocations, etc. and their synergy makes it difficult to describe sintering mathematically.

Diffusion takes place at a contacts of two individual bodies. Even evaporation at curved surface (small radius or capillary like effects) is considered in some cases.

Some other interesting books by Geguzin: Bubbles, Migration of Macroscopic Inclusions in Solids, Live Crystals, Droplet, Why and How Disappears Emptiness, ...

In sintering process, metal powders and other alloying elements are added and then heated in a furnace at required temperature.

The green compact obtained after powder compaction has very less strength, hence the heat treatment (sintering) is done to provide strength to it. Sintering is done at around 0.8 times the melting temperature of the base material. At that temperature, diffusion in the material takes place that leads to the diffusion bounding of particles.