Study On The Influence Of Electrothermal Effect On Microstructure And Tensile Response Of Nickel-based Alloys

As an indispensable metal material in the development of national frontier science and technology and national defense construction,superalloys have an irreplaceable position in the fields of aviation,aerospace,and nuclear power.With the continuous improvement of alloying,the difficulty of processing has gradually increased,thus limiting the processing and application of superalloys.Therefore,this paper took the effect of current on the structure of Inconel 718 alloy and the change of tensile response as the starting point,and discussed the law of the influence of current on Inconel 718 alloy through the method of combining experiments and numerical simulations,so as to provide a theoretical guidance for the structure regulation and performance improvement of Inconel 718 alloy.In this paper,a DC current was first used to carry out an electrification treatment test on Inconel 718 alloy.The tissue regulation was realized by the electrothermal effect generated by the current and a remarkable effect was obtained.The results showed that the content of δ phase in Inconel 718 alloy increased with the increase of current intensity,and it mainly concentrated in the grain boundary and existed in the form of lotus-shaped,granular and needle-shaped precipitation.When the current was 130 A,and the content of δ phase reached the highest.With the increase of δ phase content,the tensile strength of Inconel 718 alloy showed a trend of first increasing and then decreasing,and the tensile strength was the highest at 105 A.When the current intensity is greater than 105 A,the tensile strength decreased with the increase of the current intensity.High-intensity current lead to a decrease in the dislocation density(that was recovery),which reduced the interaction between dislocations and δ phase particles,resulting in a decrease in the strength of the Inconel 718 alloy and softening.Compared with holding at 780°C for 30 minutes,static recrystallization of the structure occured,the grains were refined,and the rotation of the grains was promoted at the same time,resulting in similar levels of <111> and <001> oriented grains under the action of1010°C generated by 130 A current.Then,tensile tests were conducted using the method of pulse current assisted tensile to analyze the influence of pulse current on the microstructure evolution and tensile properties of Inconel 718 alloy.The results showed that the tensile strength decreased with the increase of pulse voltage and pulse frequency,and the elongation increased first and then decreased with the increase of pulse voltage.Under the condition of different pulse frequency,the elongation was basically the same at 200 Hz and 400 Hz,and the elongation gradually decreased when the pulse frequency exceeded400 Hz.As the sample deformed,the cross-sectional area decreased and the current density increased.The Joule heat generated by the pulse current caused the sample to be overheated and caused premature failure and fracture,thereby reducing the elongation.With the occurrence of necking,the crystal grains were deformed and had a large storage energy,and dynamic recrystallization occured under the action of pulse current.As the pulse frequency increased,the electron wind force increased the migration ability of atoms and vacancies.At the same time,the annihilation of dislocations was promoted,so that the driving force on the grain boundaries was reduced,resulting in finer recrystallized grains.Dynamic recrystallization was accompanied by the migration of grain boundaries,and the migration of grain boundaries leaded to a decrease in flow stress.Therefore,dynamic recrystallization was also an important factor that leads to the decrease in tensile properties of Inconel718 alloy.For the precipitation of δ phase,there was no obvious promoting or inhibiting effect during the pulse current assisted tensile process.The finite element analysis software ABAQUS was used to numerically simulate the temperature field and stress-strain field of the direct current electrothermal effect and pulse current assisted tensile Inconel 718 alloy.The temperature of the electrothermal effect was mainly distributed in the middle area of the sample.The numerical simulation temperature was basically consistent with the experimental temperature,the temperature increased gradually with the increase of current,and the residual stress under all parameters was lower than the yield strength.In numerical simulation of current assisted tensile,the numerically simulated tensile curve obtained by the J-C model was basically consistent with the experimental tensile curve.With the necking of the model,the distribution of current and temperature was extremely uneven,the current density and temperature near the necking area increased,and the numerical simulation temperature was basically consistent with the temperature measured by the thermocouple.Under the condition of not considering the non-Joule heating effect of current,the tensile strength was higher than the test tensile strength,and the elongation was lower than the test result.