What is the residual stress of titanium alloys? Residual stress refers to the self-balanced internal stress that remains in the object after the external force or uneven temperature field is eliminated. Mechanical processing and strengthening processes such as cold drawing and laser cutting will cause residual stress. The simple explanation is that just like the rubber band we usually use, the stretched rubber band will retract after letting go, and the rubber band will twist after retracting. When the metal material is forced to deform during processing, a kind of resistance force will be generated inside. So even if the external force disappears, this resistance force will still remain inside the material, forming residual stress.
Where does the residual stress come from in the production of titanium alloys? There are three main reasons
1. When the machining tool cuts the metal, the part that is cut off will release stress, but the titanium part left will be forced to twist.
2. The alternating hot and cold during the processing process will also generate stress.
3. When the titanium metal cools, the structure changes and the volume changes are not synchronized, which will also cause deformation.
The destructive power of titanium residual stress is also very large. It will cause changes in the size and shape of objects, shorten the service life of parts, and reduce the corrosion resistance and fatigue strength of metals.
So how can we eliminate the residual stress of titanium alloys? We can deal with this problem from several aspects.
1. We can place metal workpieces in a natural environment to promote the natural release of internal stress through temperature changes and climate effects.
2. We can use annealing, tempering and other methods to eliminate or reduce residual stress by using the thermal relaxation effect of residual stress.
3. Through vibration, when the residual internal stress and additional vibration stress inside the workpiece exceed the yield strength of the material, the material can undergo a slight plastic deformation, thereby reducing the internal stress inside the material.
Residual stress is an inevitable phenomenon in mechanical manufacturing. It will affect the life, plasticity and corrosion resistance of titanium alloy products. Therefore, if we find residual stress during production, we should deal with it and eliminate it in time.
