| Compared with traditional chemical propulsion,space electric propulsion has the advantages of high specific impulse,accurate and controllable thrust,smaller engine volume and longer service life.It is the most rapidly developing advanced propulsion technology in the field of space propulsion.As the critical factor of the arc heating engine,the cathode is responsible for heating the working medium gas to produce thrust.Due to the long service cycle and frequent ignition times of the satellite,high requirements are put forward for the service life and burning loss resistance of cathode materials.Based on this background,the composition of two electrode compositions with excellent ablation resistance under TIG welding conditions was optimized.Four electrode materials W-La-Ce-Y,W-La-Y-Zr,W-La-Ce-Y-Re and W-La-Y-Zr-Re were prepared by solid doping and medium frequency sintering.The performance test is carried out under the simulated working condition of DC welding.At the same time,in order to simulate the actual application conditions of the electric propulsion system,an arc heating engine is designed and installed,and the supporting vacuum system is built.The working environment of the arc propeller is simulated under different working currents,and the anti ablation performance and ablation morphology of the electrode are studied to further improve the anti ablation performance of the electrode.The test results of DC welding simulation conditions show that under the working current of 250 A,the two rhenium doped electrodes have less mass loss,less change of tip morphology,stronger electron emission ability and better burning loss resistance.The microstructure analysis of the electrode shows that the doping of rhenium increases the recrystallization temperature of W-La-Ce-Y-Re and W-La-Y-Zr-Re electrodes,inhibits the coarsening of the recovery structure and the nucleation and growth of recrystallized grains at high temperature,which is more conducive to the supplement of rare earth elements to the tip in the matrix,so as to reduce the electron escape work of the material and alleviate the surface ablation.The ablation morphology of the electrode shows that the doping of rhenium inhibits the growth of grains and the oxidation of the matrix,which alleviates the heat concentration caused by the local sharp structure on the surface and aggravates the ablation of the electrode.In addition,due to the difference of ablation degree of materials,the migration path and surface distribution of rare earth elements in the matrix are also different.The test results of the quasi in-situ working condition of the arc thruster show that the ablation resistance of the four electrodes is improved due to the small working current of the electrode,among which the ablation resistance of the rhenium doped electrode is particularly outstanding and the arc burning stability is better.On the one hand,the electron emission capacity of W-La-Ce-Y-Re and W-La-Y-Zr-Re electrodes is stronger,on the other hand,the deposition of tungsten oxide is more significant under this test condition,The formation of a ring-shaped structure at the tip of the electrode is not conducive to the formation of a ring-shaped structure of rhenium,which can alleviate the formation of electron emission at the tip of the electrode.In addition,the ablation quality of rhenium doped electrode is less than 0.1mg after one hour of arc burning,which is an order of magnitude lower than that of non rhenium doped electrode,and the stability of tip morphology is better.Rhenium doping can also reduce electrode ablation,inhibit matrix grain coarsening and reduce the loss of rare earth second phase under quasi in-situ conditions. |
