Changes that occur in wire because of manipulation
Explain the
changes that occur to the different types of orthodontic wires when subjected to
strain hardening as well as annealing processes. (where applicable)
Deformation of metals When the stress is below the proportional limit it is assumed that the atoms in the crystal lattice are displaced a small amount that when the stress is relieved, they can return to their original position. However once the proportional limit is exceeded permanent deformation takes place and the structures does not return to its original dimension when the load is released. With the increase of load the atoms separate completely and fracture results.
.Strain hardening Strain hardening is when greater stress is required to produce further slip during cold working and the metal becomes stronger and harder.
Annealing The effect of cold working can be reversed by making use of heat treatment that is called annealing. The greater extend of cold working the readily does annealing occur. Annealing goes through tree stages that are the recovery, recrystallization and the grain growth stage.
Recovery This stage is when the cold working properties start to disappear before any changes are visible under the microscope.
Recrystalization When severly cold work metal is annealed, then recrystalization occurs after some recovery. This involves a radical change in the microstructure of the material.
Grain growth The recrystalization structure have a serten grain size, depending upon the number of nuclei.the more sever the cold working the greater are the number of such nuclei. This the grain size for the completely recrystalization material can range from rather fine to fairly coarse.if now the fine grain form are further more anneald ,the grains begin to grow.The larger the grains structure is detrimental to strength properties of a metal.
1) Stain hardening The increase in strength and hardness and decrease in ductility of a metal that is cause by plastic deformation below its rerystallisation temperature is known as strain hardening or work hardening. During strain hardening a wire fracture by being bend back and forth repeatedly, during each bend, the wire is cold worked; which requires greater stress to achieve subsequent bending deformation. This result in decreases ductility, eventually the wire fractures after extensive permanent deformation.
2) Annealing process The effect associated with plastic deformation e.g. stain hardening, decrease ductility, distorted grains and increase dislocation density, can be reversed by simply heating the metal to an appropriate elevated temperature without melting it. This process is known a Annealing and it take place in three successive stages; recovery, recrystallization and grain growth
When a block of material is subjected to tensile stress, it temporarily increases in length, this temporal increase in length is the strain
Annealing is when a relatively low- temperature heat treatment for removing residual stress is applied to the wire.as described above annealing has three stages: recovery, recrystalization and grain growth.
Annealing- this controlled heating and cooling process softens the wire, increases its plastic deformation potential, stabilizes shape and helps in increasing the machinability of the wire.
Strain hardening- also known as work hardening, increases the strength and hardness and decreases ductility of the wire and is caused by plastic deformation below recrystallization temperature.
When working with orthodontic wire, it is subjected to pressing and drawing. This cold working caused phase transformation to occur and distorts the atoms into long fibrous shapes and elongates the wire. Thus cold working increases the strength of the wire and its hardness. This can lead to brittleness and failure. After bending, the wire can be heated up to release the stresses created inside. The heating of the wire to release the stresses is known as annealing. The heating of the wire can have an adverse effect and increase the elasticity of the wire. The applied heat reduces the corrosion resistance and causes the release of metallic ions which can have an adverse effect on the human body.
Strain hardening/ work hardening/ cold working is all the same thing. It is the increasing of the wire's hardness by bending. The hardness can be increased to such an extent that the wire break due to brittleness.
Deformation of metals
ReplyDeleteWhen the stress is below the proportional limit it is assumed that the atoms in the crystal lattice are displaced a small amount that when the stress is relieved, they can return to their original position. However once the proportional limit is exceeded permanent deformation takes place and the structures does not return to its original dimension when the load is released. With the increase of load the atoms separate completely and fracture results.
.Strain hardening
Strain hardening is when greater stress is required to produce further slip during cold working and the metal becomes stronger and harder.
Annealing
The effect of cold working can be reversed by making use of heat treatment that is called annealing. The greater extend of cold working the readily does annealing occur. Annealing goes through tree stages that are the recovery, recrystallization and the grain growth stage.
Recovery
This stage is when the cold working properties start to disappear before any changes are visible under the microscope.
Recrystalization
When severly cold work metal is annealed, then recrystalization occurs after some recovery. This involves a radical change in the microstructure of the material.
Grain growth
The recrystalization structure have a serten grain size, depending upon the number of nuclei.the more sever the cold working the greater are the number of such nuclei. This the grain size for the completely recrystalization material can range from rather fine to fairly coarse.if now the fine grain form are further more anneald ,the grains begin to grow.The larger the grains structure is detrimental to strength properties of a metal.
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ReplyDelete1) Stain hardening
ReplyDeleteThe increase in strength and hardness and decrease in ductility of a metal that is cause by plastic deformation below its rerystallisation temperature is known as strain hardening or work hardening. During strain hardening a wire fracture by being bend back and forth repeatedly, during each bend, the wire is cold worked; which requires greater stress to achieve subsequent bending deformation. This result in decreases ductility, eventually the wire fractures after extensive permanent deformation.
2) Annealing process
The effect associated with plastic deformation e.g. stain hardening, decrease ductility, distorted grains and increase dislocation density, can be reversed by simply heating the metal to an appropriate elevated temperature without melting it. This process is known a Annealing and it take place in three successive stages; recovery, recrystallization and grain growth
When a block of material is subjected to tensile stress, it temporarily increases in length, this temporal increase in length is the strain
ReplyDeleteAnnealing is when a relatively low- temperature heat treatment for removing residual stress is applied to the wire.as described above annealing has three stages: recovery, recrystalization and grain growth.
Annealing- this controlled heating and cooling process softens the wire, increases its plastic deformation potential, stabilizes shape and helps in increasing the machinability of the wire.
ReplyDeleteStrain hardening- also known as work hardening, increases the strength and hardness and decreases ductility of the wire and is caused by plastic deformation below recrystallization temperature.
When working with orthodontic wire, it is subjected to pressing and drawing. This cold working caused phase transformation to occur and distorts the atoms into long fibrous shapes and elongates the wire. Thus cold working increases the strength of the wire and its hardness. This can lead to brittleness and failure. After bending, the wire can be heated up to release the stresses created inside. The heating of the wire to release the stresses is known as annealing. The heating of the wire can have an adverse effect and increase the elasticity of the wire. The applied heat reduces the corrosion resistance and causes the release of metallic ions which can have an adverse effect on the human body.
ReplyDeleteStrain hardening/ work hardening/ cold working is all the same thing. It is the increasing of the wire's hardness by bending. The hardness can be increased to such an extent that the wire break due to brittleness.
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ReplyDelete