In order to understand the metallurgical properties of the metals, first of all, it is necessary to describe some properties of particles that form all types of matter. These basic particles, which together form solid, liquid and gaseous substances, are called «atoms». One of the main properties of atoms is that in certain temperature ranges they form substances having the ordered structure. This is because certain forces begin to act on atoms that are at the certain distance from each other. These forces attract and at the same time repel atoms from each other. Thus, these opposing forces keep individual atoms at certain «initial» positions with respect to all surrounding atoms. These atoms, each occupying its position, are arranged in rows, layer by layer, within the three-dimensional symmetric crystal structure, or the lattice.
However, the atoms occupying these positions do not remain immobile. In real conditions, they oscillate around the equilibrium position, keeping balanced gaps. At the certain temperature, the atoms remain in equilibrium for a given specific temperature. It is believed that when the equilibrium between the forces of attraction and repulsion is reached, the internal energy state of the metal stabilizes.
The attempts to bring atoms closer to each other are opposed by the repulsive forces, whose influence increases as the atoms come to each other. The presence of this property is confirmed by the fact that metals exhibit extremely high compressive strength. Similarly, the attempts to push the atoms are counteracted by the forces of attraction. However, as the atoms are removed from each other, the action of the attractive forces decreases.
The latter property is manifested when carrying out the tensile tests. Before reaching the yield point of the metal, the load results in stretching the tensile test specimen. The distance between individual atoms increases. After removing the load, the sample exhibits elastic properties, the returns to the original size at the macroscopic level, which indicates the return of atoms to its original equilibrium position.
If the load on the tensile test specimen exceeds the yield strength of the metal, the metal begins to show plastic properties. In this case, it no longer returns to its original size, or interatomic distance, since the atoms are so far apart that the forces of attraction are not enough to keep them in their original position. With the further increase in the interatomic distance, when the forces of attraction are no longer able to hold atoms, the metal is destroyed.
