Grain Boundary Melting
Grain boundary melting has been studied for over one hundred years and, even today, continues to be a topic of growing interest and importance in materials science and engineering. Grain boundary melting usually occurs when two grains of a polycrystalline solid come into contact, form a boundary and consequently melt. The process is also known as grain boundary fusion, grain boundary fusion solidification or grain boundary coalescence solidification.
Grain boundary melting has been studied extensively in order to gain a better understanding of structural properties, properties related to diffusion, embrittlement, fatigue, heat treatment and other issues of technological interest. It has been shown that grain boundary melting affects mechanical properties, such as strength and hardness, as well as thermal properties, such as thermal conductivity, coefficients of thermal expansion, etc. It is also known to play an important role in a number of industrial processes such as welding, forming and casting.
Grain boundary melting occurs when two adjacent grains are brought into contact with each other. As the two grains come closer to each other, the temperature of the grain boundary rises. If the temperature reaches a certain point, the grain boundary will melt, forming a liquid phase, which will result in the formation of a new grain boundary and the reduction of the total grain size.
Furthermore, grain boundary melting can also occur if two adjacent grain boundaries come into contact with each other. This phenomenon is known as intergranular melting and can be caused by the application of thermal or mechanical stresses. The grain boundaries involved in intergranular melting are normally in different sizes.
The melting temperature of grain boundaries depends on several factors, such as grain size and grain orientation. In general, larger grains have higher melting points than smaller grains, and those grains with a low misorientation angle have higher melting points than those with a high misorientation angle.
Understanding the role of grain boundary melting is important due to its influence on the overall structure and properties of materials. It is necessary to consider the characteristics of grain boundary melting, such as the melting temperature, grain boundary surface energy and diffusivity of the material, when designing and/or analyzing materials, in order to ensure the desired properties.
Grain boundary melting is a complex process and is still not fully understood. Despite this, advancements in the field are being made on a regular basis, in particular through theoretical and experimental studies. As a result, grain boundary melting is becoming increasingly understood, leading to improvements in the design and manufacturing of new materials, which in turn will help contribute to the development of new and innovative technologies.
