Research On Grain Refinement Of Superalloy K4169 With Pulsed Magnetic Field And Mechanical Vibration Treatment

Superalloy is used for manufacturing such parts as low pressure turbine blade, turbine disk and guide apparatus of aero-engine and industrial gas turbine, whose working temperatures is usually under medium temperature(760℃). Therefore, the whole solidified structure of superalloy should be uniform and fine equiaxed grains, in order to improve the low cycle fatigue property and operational reliability of superalloy. Both pulsed magnetic field(PMF) and mechanical vibration belong to dynamic refining technology, which have advantages of good refining effect, easy operation, no pollution and so on. In recent years, with the rapid development of modern solidification technology, a single physical field could not meet the requirement of solidification technology. In order to give a better control on solidification structure of metals, compound field treatment technology has appeared. Devices of superalloy solidification by low-voltage pulsed magnetic field(LVPMF), mechanical vibration and combination action of PMF and mechanical vibration were designed and made by ourselves. Superalloy K4169 and H62 brass were used as research object. Effects of LVPMF, mechanical vibration and compound treatment on solidified structure and mechanical properties of the alloy were studied, by using optical microscope, tensile testing machine, scanning electron microscope and so on, and the related mechanism was also discussed. The research shows the results as follows:1) Self-designed device of superalloy solidification by LVPMF can not only produce high energy in a single discharge and good grain refinement effect, but also be operated safely. The device of compound treatment were designed on the basis of LVPMF device, which has the advantages of LVPMF and mechanical vibration, and a better grain refinement effect.2) Solidified structure of superalloy K4169 can be refined greatly by LVPMF or mechanical vibration during the course of solidification. Meanwhile, primary dendrites of alloy are fractured from coarse and well-developed dendrites into fine equiaxed grains or non-dendritic structures. When the pulse voltage is at 0~300 V or the pulse frequency is at 0~5 Hz, the increase of pulse voltage or frequency enhances the refinement effect of LVPMF processing. With the increase of vibration amplitudes in the range of 0~2 mm, solidified structures of superalloy K4169 are refined gradually and the microstructure is changed from well-developed dendrites to disintegrated dendrites or rosette crystals. When the vibration frequency increases in the range of 50~75 Hz, morphology of primary phase of the alloy degrades gradually and some dendrites are fractured, but the change of frequency has less influence on morphology of primary phase. Primary phase of the alloy is coarsened, when the frequency reaches 100 Hz. When the pouring temperature is at 1380~1530 ℃ or the mold temperature is at 1000~1300 ℃, the increase of pouring temperature or mold temperature enhances the refinement effect of LVPMF or mechanical vibration processing.3) Contrasting with the single treatment process, the better refinement effect and mechanical properties of H62 brass are achieved with the compound treatment, and primary α phase is changed from coarse and well-developed dendrites to short and rod-shaped dendrites. Meanwhile, hardness, tensile strength and elongation of the alloy under compound treatment compared with the alloy in traditional condition is increased by 8.52%、9.7% and 14.6%, respectively. When the pulse voltage is at 0~300 V or the pulse frequency is at 0~5 Hz, the increase of pulse voltage or pulse frequency enhances the refinement effect and improves the mechanical properties of H62 brass. When pouring temperature increases from 950 ℃to 1100 ℃ or mold temperature increases from 700℃ to 1000 ℃, the refinement effect of brass is enhanced and mechanical properties can be improved under the action of compound treatment, but the refinement effect of compound treatment will be weakened when the mold temperature reaches 1000 ℃.4) Grain of superalloy K4169 can be refined by LVPMF, mechanical vibration and compound treatment. Among these processes, compound treatment has the best effect. Average grain size of the alloy can be refined from 4.5 mm to 0.98 mm and the fraction of equixed grains of the alloy can be increased from 36% to 96% by compound treatment. Meanwhile, tensile strength and elongation of the alloy with compound treatment compared with the alloy in traditional condition is increased by up to 49.2% and 37.3%, respectively. In the range of 0~300 V or 0~5 Hz, with the increase of magnetic field parameters, primary phase of the alloy degrades gradually from well-developed dendrites into fine equiaxed grains or rosette crystals, and mechanical properties of the alloy can be improved obviously. When the compound treatment is applied, the refining effect enhances gradually and mechanical properties of the alloy improves remarkably with the increase of the pouring temperature within 1380~1530 ℃ or mold temperature within 1000~1300 ℃.