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Do you know how to increase strength by changing the material structure?
In today's engineering world, the mechanical properties of materials are of paramount importance. From construction to aerospace, strength, ductility and toughness are integral factors in design and applications. Changing the material's structure can effectively enhance these properties and provide customized solutions for various applications. By tweaking the structure of crystalline and amorphous materials, engineers can increase their yield strength, ductility and toughness, according to new research.
Strength improvement can be achieved through a variety of mechanisms, such as solid solution strengthening, precipitation hardening and grain boundary strengthening.
Steel's properties are primarily formed by the interstitial solid solution of carbon into the iron lattice, which in turn enhances its mechanical properties. Brass, an alloy of copper and zinc, exhibits superior mechanical properties compared to its constituent metals due to solid solution strengthening. Process changes, such as forging red-hot metal, are an ancient and effective method used by black iron workers. This work hardening can introduce dislocations, further increasing the material's yield strength.
Material strengthening mechanism
There are currently five known mechanisms for material strengthening. These mechanisms are designed to hinder the motion of dislocations, thereby increasing the strength of the material. The hindrance of dislocation motion helps to increase the material's resistance to deformation. These mechanisms include:
Work Hardening
Dislocations are the main cause of work hardening. When a large number of dislocations appear on the surface of a material, they interact with each other, generating a stress field that in turn hinders the movement of the dislocations. In this case, the relationship between dislocation density and shear strength is very close, so work hardening is reflected in the growth of dislocation density.
Solid solution strengthening and alloying
Solid solution strengthening is achieved by adding solute atoms of one element to another material. These atoms can cause deformation of the crystal lattice, thereby hindering the movement of dislocations. The higher the concentration of the solute, the higher the yield strength of the material, but at the same time its strengthening effect has a limit.
Precipitation hardening
In most binary systems, excess alloying leads to the formation of a second phase. These second phase precipitates will act like solute atoms in a solid solution, hindering the motion of dislocations.
Dispersion Enhancement
Similar to precipitation hardening, dispersion strengthening involves the attraction and fixation of dislocations by incoherent precipitates. This method is particularly effective at high temperatures and can be used to create high-strength materials.
Grain boundary strengthening
In polycrystalline metals, grain size has a dramatic effect on mechanical properties. Grain boundaries hinder the movement of dislocations, so the yield strength of the material increases as the grain size decreases.
Strengthening mechanism of amorphous materials
For amorphous materials, such as polymers and ceramics, strengthening methods are very different from those for metals. The strengthening of these materials mainly depends on the changes in their chemical structure and the way they are processed.
The increase in polymer strength comes primarily from the increase in cross-linking between chains. This cross-linking makes the material more rigid and crack-resistant.
For example, in thermosetting polymers, disulfide bridges and other covalent crosslinks enable them to maintain good structural stability at high temperatures. Therefore, the reinforcement of various polymers can be carried out by introducing additives such as fibers and particles.
Challenges and opportunities
However, improving material strength does not come without a price. Each strengthening mechanism may affect other physical and chemical properties. In addition, the strength of a material cannot be increased infinitely, and excessive strengthening may lead to a decrease in certain properties, such as toughness or ductility. Therefore, when designing materials, engineers must consider improving strength while taking into account other desired performance characteristics.
With the continuous advancement of science and technology, our understanding of material properties is becoming more and more in-depth, and materials with both high strength and good ductility may appear in the future. Whether it is possible to find the best balance between strength and other properties will be a major challenge and opportunity for the future development of materials science.
