Titanium alloy has the advantages of low density, high specific strength and rigidity, good corrosion resistance, excellent high-temperature mechanical properties, outstanding fatigue and creep resistance, non-magnetic weldability, etc. It is widely used in aviation, aerospace, the chemical industry, weapons, ships, energy, etc. fields are widely used.
Deformation at lower temperatures below the phase transition point of titanium alloys can inhibit the dynamic recovery and dynamic recrystallization behavior of titanium alloys to a certain extent, improve the microstructure, and improve the comprehensive mechanical properties and strength of materials. However, due to the poor plastic deformation ability of titanium alloys at low temperatures, It is easy to produce processing defects such as cracking, and the research on the behavior of relatively low-temperature materials below the phase transition point of titanium alloys has been less.
The microstructure of titanium alloy metal structure-sensitive materials is closely related to the deformation behavior, and at the same time has a great influence on the macroscopic material properties, so it needs to be studied intensively.
In view of the above problems, this paper explores the material behavior of GR5 titanium alloy at a relatively low temperature below the phase transition point by means of physical simulation, and studies the stress-strain behavior and microstructure evolution characteristics of GR5 titanium alloy during the deformation process through experiments, in order to provide The relative low-temperature plastic forming control of titanium alloy provides theoretical reference.
1. Experimental materials and process
The material used in the experiment is a rolled titanium alloy rod, which is made into a Φ8X12 sample by wire cutting. Using the temperature control system of the Gleeble-1500 experimental machine, experiments were carried out on the thermal compression of GR5 in three different temperature sections. The compression process is a free cooling process. When the termination temperature is reached, the deformation is stopped and quenched in water immediately. Its tissue is frozen to ensure the purity of dynamic crystallization grains.
2. Analysis of experimental results
is the compressive stress-strain curve of GR5 at different temperatures under the same strain rate. When the deformation temperature drops from 700°C to 600°C, the peak flow stress increases by about 100Mpa, and when it drops to 500°C, the peak flow stress increases by about 200Mpa. It is because as the deformation temperature increases, the thermal activation of the alloy is enhanced, and the dynamic recrystallization is easy to proceed. With the increase of the recrystallization volume fraction, the dislocation density decreases, and the flow stress of the alloy decreases, which also shows that GR5 is temperature sensitive. Material. Conversely, the lower the deformation temperature, the more difficult it is to carry out dynamic recrystallization, and the flow stress of the alloy increases.
At the same time, the experimental results also show that the plastic deformation ability of GR5 also decreases with the decrease of temperature. The deformation rate of the 600-500 °C compression test does not reach 50%, but 41.6%, and the deformation rate of the 500-400 °C compression test is only 33.3%.
It is the photo of the microstructure before and after deformation. The grain shape of the original structure is long and narrow, and the average grain length along the rolling direction is about 80 microns. After deformation, the warp grains gradually change from narrow and long to equiaxed, and the grain boundaries gradually decrease, which is mainly caused by dynamic recrystallization. At the same time, it can also be seen from the deformed structure that the grains deformed at 700°C and 600°C are not very different. In addition to the equiaxed grains, there are some original flat and elongated grains, while there are more grains in the deformed structure at 500°C. equiaxed grains. As the lower the temperature, the more difficult the dynamic recrystallization is, which indicates that there may be some other grain refinement mechanism in the deformation of GR5 alloy at low and medium temperatures.
Although GR5 alloy is not easily deformed at low temperatures, it is possible to obtain finer and more uniformly distributed equiaxed grains after deformation than at medium and high-temperature deformation.
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