Process of Plastic Deformation
When material is subjected to different forms of pressures and stresses beyond which it cannot yield, it is normally forced to undergo a process of distortion that is best referred to as deformation. The stress that can cause this kind of deformation can either be compressive, tensile, torsion or may involve the bending of the material. The stress can easily result in the material being forced to become longer than it usually is, to stretch, to bend, buckle or even twist. For a process to be considered as plastic deformation, there ought to be a non-reversible change in the shape of material. Many materials undergo the process of plastic deformation. A good example of these are rocks, metals, soils, concrete and foams. During the process of plastic deformation, one can witness changes in the shape and size of material whereas changes can also be witnessed in the atomic level in the interior of the same material.
Whereas the process of deformation can take place through dislocations in some materials, it can also take place through slips, especially relating to micro-cracks in rocks. The process of deformation is characterized by the individual atoms in a piece of material slipping on crystal planes. Dislocations are usually responsible for the slipping and as a result, they are usually responsible for the deformation process. As the process continues, materials become stronger because of the accumulation of dislocations in a crystal. Materials that have acquired a stronger structure as a result of the process of deformation are normally referred to as work hardened materials. They normally revert to their previous softer shapes when the accumulation of dislocations is scattered.
Delegate your assignment to our experts and they will do the rest.
Plastic deformation is instrumental in the modern age because of the different benefits that are likely to be enjoyed from it. For instance, it is easier to come up with different shapes and samples of materials. Through plastic deformation, materials can be shaped into bulk, tube and sheet. Plastic deformation also helps to refine crystallized structures. They also ensure that crystal grains are enhanced through saturation and refinement. Through plastic deformation, it is also relatively easier to enhance the microstructure of metals.
Example of Plastic Deformation
A good example of a plastic deformation process is chewing gum. Chewing gum has the ability to be stretched to a dozen times its original length because it has a large plastic deformation range. When tensile stress is applied to chewing gum, strain hardening region and necking region are usually formed, thus, resulting to a final fracture in the end. Strain hardening makes the material harder than it was initially as a result of the movement of atomic dislocations. When the cross-sectional area of a material reduces during the process of deformation, necking is said to have started. After the material has reached its position of ultimate strength, it cannot withstand the stress applied anymore, and thus, usually ends up fracturing.
Cold deformation and Thermal Deformation
For instance, subjecting a work hardened material to heat brings about the disappearance of atoms through diffusion. Such disappearance is usually responsible for the soft appearance of the material during heating since the process of heat annealing and work hardening takes place at the same time. This is referred to as hot rolling. On the contrary, cold rolling refers to the process of work hardening that only takes place as a result of absence of heat annealing. While heat rolling results in materials that are softer and elastic, cold rolling leads to materials that are hard and brittle.
Experiment
This section will highlight the findings of an experiment whose focus was on the effect of deformation temperature on a particular type of austenitic steel. The temperature range used was from −40°C to 200°C with the main goal being to study the effects of these changes in temperature on the microstructure evolution of the aforementioned metal. The study reveals that the tensile strength and the yield strength of the metal under experiment reduced considerably after the addition of more temperature. This experiment implied that thermal deformation is responsible for softening metals. At higher temperatures, there are more dislocations, thus, meaning that metal is much softer. The experiment focuses on stacking fault energy. It highlights that there is an effect on SFE when temperatures are increased, which eventually causes the softening of metal. The study does not focus on cold deformation, but based on the above evidence it is safe to conclude that colder temperatures will result in more brittle metals.
Crystallization and Crystal Gains
Crystals are subjected to rotation during the process of plastic deformation. Crystal rotation is an exclusive process, which occurs only when a certain set of conditions have been fulfilled. In this instance, rotation occurs once the process of deformation has taken place on a specific plane and slipping direction. Through the process of rotation, a texture is formed that characterizes the orientation of crystal gains in the mechanical working direction. When cold rolling with a large deformation takes place, crystals grains are likely to adapt longer shapes than they had before. Materials with elongated crystal grains can be made to return to their previous softer states upon the application of heat. This normally happens to materials that have been deformed beyond their critical value. The heat usually results in newly equiaxed crystal grains possessing fewer dislocations. The grains then undergo the process of nucleation and growth, thus, forcing the material to revert their prior softer state. The process is usually referred to as re-crystallization and its purpose is to aid in the process of making crystal grains more refined and softer.
