Polycrystalline Yield
Polycrystalline yields are one of the most important properties of materials. It’s the ability of a material to undergo plastic deformation and remain in a stable state after the external force is removed. Polycrystalline materials are made of many smaller crystal grains that are interconnected and display unique properties depending on the material’s microstructure, which is the arrangement of the crystal grains.
Polycrystalline yield is often measured as the amount of force needed to cause permanent deformation in the material, or the stress needed to cause the material to fail, fracture, or fail in elastic deformation. The most commonly used measure of polycrystalline yield is the yield strength, typically expressed in units of megapascals (MPa).
Factors that can affect a material’s polycrystalline yield include its crystal structure, the amount of impurities present, the amount of strain applied, and the temperature of the environment. Generally, higher temperatures cause greater amounts of strain and more sensitivity to impurities. A material’s polycrystalline yield strength increases as the temperature rises, although at temperatures significantly higher than the materials melting point, the yield strength decreases.
In some cases, the yield strength of a material is also affected by its grain size. Smaller grain sizes increase the yield strength of a material because the boundaries created by the grains are less likely to deform or move than larger grains, which could cause a material to fail. Similarly, a material’s microstructure can also affect its yield strength. A material with a large number of grain boundaries is less likely to fail than one with fewer grain boundaries.
Polycrystalline yields are also affected by other properties, such as creep and fatigue. Creep is the gradual deformation of a material when it is subjected to a certain amount of force, while fatigue is the gradual weakening of a material when subjected to repeated cycles of strain. Both creep and fatigue can reduce the yield strength of a material.
Finally, polycrystalline yield is also affected by surface treatments such as polishing and coating. Polishing can reduce a material’s yield strength by reducing the surface roughness of the material and removing any contaminants. Coating a material can also enhance its properties, such as its corrosion resistance and wear resistance, and also provide protection from abrasion and impact. In addition, coatings can even reduce a material’s polycrystalline yield strength by limiting the deformation of the microstructure.
In summary, polycrystalline yield is an important material property that depends on many different factors, including a material’s crystal structure, impurities, temperature, grain size, microstructure, creep, fatigue, and surface treatments. Understanding and controlling these variables can help ensure a material’s polycrystalline yield strength is optimal for a given application.
