Effect Of Current On Microstructure Of Directionally Solidified Ti-48Al-2Cr-2Nb Alloy

As the TiAl alloy has a high specific strength,high temperature performance and other advantages,so its use in aerospace field is very extensively.However,the poor plasticity at room temperature hinders its promotion and application in various fields.AS an advanced solidification process,current solidification technology is usually used to improve structure and performance of materials.In this paper,the microstructures of TiAl-based alloys under different current are studied emphatically.In this paper,the alloy composition Ti-48Al-2Cr-2Nb was used as the research object,and the directional solidification experiment was carried out by directional solidification technique of electromagnetic crucible.In the process of directional solidification,DC current and pulse current with different densities were applied respectively,and the influence of current on Ti-48Al-2Cr-2Nb alloy was analyzed.Firstly,the electromagnetic field distribution of TiAl-based alloy was simulated by ANSYS under the action of current.It is found that the magnetic induction intensity and Lorentz force decrease from outside to inside under the action of DC current.And the internal value is the lowest.Under the action of pulsed current,the magnetic induction intensity and Lorentz force are mainly distributed in the vicinity of the surface skin layer.And the internal influence is very small.From the macroscopic view of the specimen,under the action of current,the angle between the growth direction of the columnar crystal and the direction of the drawing is smaller,and the effect of the DC current is more obvious than the pulse current.Under the action of DC current,when the current density increases to 74 m A/mm2,some of the columnar crystals in the stable growth zone are converted to equiaxed grains.Under the action of DC current,the columnar crystal width decreases with the increase of current density.Under the action of pulsed current,the columnar crystal width becomes smaller and then becomes larger as the current density increases.Under the action of DC current,the lamellar spacing decreases first and then increases with the increase of the current density.Under the action of pulsed current,the lamellar spacing decreases with the increase of current.With the increase of the current density,the angle between the lamellar group and the drawing direction in the tissue increases in the range of 30-60°,the vertical angle is less,and the angle fluctuation range becomes smaller.Under the action of current,the content of B2 phase in the structure decreases with the increase of current density,the Al content of the gamma single phase tissue is also reduced.The current action makes the solute distribution even more uniform and reduces microsegregation.The current action can make the directional solidification start interface more flattened.Moreover,as the current density increases,the equiaxed grains in the as-cast zone gradually increase,and the trend of directional columnar transformation is favorable for the growth of columnar crystals.Under the action of current,there are both ? dendrites and ? dendrites at the solid-liquid interface.The increase of the current density is beneficial to reduce the component supercooling at the front of the solid –liquid interface.The performance test of the directional samples with different current parameters shows that the results are shown.Under the action of DC current,the hardness of the alloy increases with the increase of the current density,Under the action of pulse current,the hardness of the alloy increases with the current density increases.Since the effect of current on the solid phase transition process is small,the hardness of the original cast zone is basically no significant change.Under the influence of DC current,the compressive strength increases and then decreases with the increase of the current density.Under the action of pulsed current,the compressive strength increases with the increase of current density.With the increase of current density,the room temperature compression plasticity has been improved.The fracture toughness of the alloy under the action of current is improved.Under the action of DC current,the fracture toughness increases and then decreases with the increase of current density.When the current density is 49.7 m A/mm2,the fracture toughness is 22.91 MPa·m^1/2.Under the action of pulsed current,the fracture toughness of the alloy increases with the current increases.When the current density is 49.7 m A/mm2,the fracture toughness is 20.09 MPa·m^1/2,which is slightly lower than that of the DC current.