Grain size and grain boundary diffusion

In summary, larger grains "absorb" smaller grains during cross-boundary diffusion in solid state diffusion in order to minimize the system's free energy. This is achieved by reducing the surface energy through the growth of one grain at the expense of another. This phenomenon is known as Ostwald Ripening and can be further explored in literature on the subject.
  • #1
krahl
1
0
Hi all,

I was wondering if anyone knows of any literature that explains why larger grains "absorb" smaller grains during cross-boundary diffusion in solid state diffusion. I read a book that explains it analogously in terms of pressure differences and boundary tension but I'm not quite happy with that explanation.

Thanks
 
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  • #2
Assuming the concentration of solute is constant in the solid solution, the growing of one grain is at the expense of the other grain. This is to reduce the surface energy of the whole system because in equilibrium, a system will choose to 'react' in a way to minimize its free energy. The total interfacial area of large, fewer particles will be smaller than total interfacial area in the system with many small particles. Note that interfacial energy will increase the free energy of the system hence it is preferable to have smallest interfacial energy as possible.
 
  • #3
qazxswedc said:
Assuming the concentration of solute is constant in the solid solution, the growing of one grain is at the expense of the other grain. This is to reduce the surface energy of the whole system because in equilibrium, a system will choose to 'react' in a way to minimize its free energy. The total interfacial area of large, fewer particles will be smaller than total interfacial area in the system with many small particles. Note that interfacial energy will increase the free energy of the system hence it is preferable to have smallest interfacial energy as possible.

Yeah, minimising the total free energy is what drives this.

Look at Ostwald Ripening for literature on this.
 

FAQ: Grain size and grain boundary diffusion

What is grain size and why is it important in materials science?

Grain size refers to the size of the individual crystals, or grains, in a material. It is an important aspect of materials science because it can greatly affect the mechanical, electrical, and thermal properties of a material. Smaller grain sizes often result in increased strength and hardness, while larger grain sizes can lead to improved ductility and toughness.

How does grain size affect diffusion in materials?

The smaller the grain size, the smaller the distance between grain boundaries. This means that the atoms have less distance to travel when diffusing from one grain to another. As a result, smaller grain sizes typically have a higher diffusion rate than larger grain sizes.

What is grain boundary diffusion and how does it differ from bulk diffusion?

Grain boundary diffusion refers to the movement of atoms along the boundaries between individual grains in a material. It differs from bulk diffusion, which involves the movement of atoms within the grains themselves. Grain boundary diffusion typically occurs at a faster rate than bulk diffusion due to the shorter distances involved.

How can grain size be controlled in materials?

Grain size can be controlled through various methods, including alloying, heat treatment, and mechanical deformation. Alloying is the process of adding elements to a material to control its microstructure and grain size. Heat treatment involves heating and cooling the material to specific temperatures to manipulate the grain size. Mechanical deformation, such as rolling or forging, can also refine the grain size of a material.

Why is grain boundary diffusion important in materials processing?

Grain boundary diffusion plays a crucial role in materials processing as it can greatly influence the properties of a material. It can be used to control the distribution of impurities, enhance the homogenization of alloys, and improve the strength and ductility of materials. Understanding and controlling grain boundary diffusion is essential for producing high-quality materials with desirable properties.

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