Strengthening Effect And Segregation Behavior Of P In Ni-based Deformed Superalloy

Phosphorus is a common residual element in superalloys,and its element content is inextricably linked with alloy properties.Phosphorus is mainly present in the raw materials of smelting alloys,so it is usually considered a harmful element by scientists.Until the hightemperature alloy smelting process has been gradually developed and the purity increased,it was found that trace amount of phosphorus was beneficial to the performance of superalloys.In the IN718 alloy,phosphorus increased the durability by as much as 7 times.Due to the wide variety of superalloys,the role of phosphorus in alloys of different systems is not the same.Therefore,this article is divided according to the types of matrix elements,and compared whether phosphorus has a differential effect on nickel-based and nickel-iron-based alloys.Based on the IN718 alloy,the main elements Ni,Cr,Fe,Al are retained,and Fe element is removed at the same time as a control group to observe the effect of different phosphorus content on the two types of alloys.By comparing the role of phosphorus in the two types of alloys,the interaction of P and Fe elements can be grasped more clearly.The results show below: in the as-cast structure of the two types of alloys,the addition of phosphorus inhibits the formation of equiaxed crystals,at the same time refines columnar crystals and promotes the regular growth of columnar crystals.The dendrite spacing is gradually reduced,dendrites are refined,and the formation of tertiary dendrites and the lateral growth of secondary dendrites in Ni-Cr and Ni-Cr-Fe alloys are promoted respectively.Phosphorus in the as-cast state is mainly distributed in the form of regular spherical phases among the dendrites.According to the literature,the phosphorus-rich phase seems as MNP-? eutectic,and the melting point of the phase is 980?-990?.The addition of trace phosphorus in the smelting process increases the solute concentration gradient in front of the interface and accelerates the solidification rate of the liquid phase.And using EPMA to analyze the elements between the dendrite and the dendrite area,it is found that the addition of P element in the as-cast structure increases the segregation behavior of the solidified structure.The rolled microstructures of the two types of simplified alloys are both single-phase ?-phase microstructures,indicating that the solid solubility of phosphorus in Ni-based and Ni-Febased superalloys is higher than 0.09%.The grain size of the rolled structure is 6?m-8?m.Through XRD diffraction,it is found that P can shift the diffraction peak of Ni-Cr-Fe alloy to the right,which proves that P is dissolved in a large amount of solid solution and intragranular in the form of substituted atoms,and the diffraction peak data of Ni-Cr alloy shows the solid solubility of P in it.Lower.The effect of P on the tensile properties of the two types of alloys is different,and it shows a harmful effect on the yield strength of Ni-Cr alloys,but a beneficial effect on Ni-Cr-Fe series alloys.The analysis shows that Fe element can increase the lattice distortion of Ni-based alloy and form a large number of vacancies.The addition of P weakens this phenomenon.However,due to the high orderness of Ni in the matrix itself,the Ni content in the Ni-Cr simplified alloy is as high as 81%.At this time,when P is dissolved in a small amount of Ni-Cr alloy,this order is broken,and instead The introduction of excessive intragranular defects leads to the generation of strained micropores.This also results in that even after P improves the mechanical properties,the performance of the Ni-Cr-Fe alloy is still lower than that of the Ni-Cr alloy..P can affect the part where the grains grow during the recrystallization process.The effect of P during grain growth is also different in the two types of alloys.For Ni-Cr alloys,due to the small solid solubility of P in the grains,a large amount of P tends to be enriched at grain boundaries.However,during the cooling process of hot forging and rolling,P will form a composite atomic group structure with vacancies and segregate toward the grain boundary,which makes P promote the further growth of grains.The promotion effect is strongest at 950°C for 10 minutes,which makes the crystal grain grow from 22.19?m to 31.50?m.Compared with P-free,the size of P-0.09% increases by 42%.The effect of phosphorus on the grain growth of Ni-Cr-Fe alloys is more complicated.Due to the increase of Fe content,the saturated solid solubility of P in the crystal is increased.In addition to the mechanism by which P and vacancies form atomic groups to diffuse into the grain boundary,there is also the non-equilibrium segregation of P atoms at the grain boundary into the grain.This makes the promoting effect of P on Ni-Cr-Fe alloys determined by two mechanisms,and presents three trends with the increase of solid solution temperature: promoting grain growth,first inhibiting and then promoting grain growth,and completely inhibiting The grains grow up.After the sample was solid-dissolved at 1050?,the enrichment effect of P element in the crystal was significantly reduced.At this time,the X-ray diffraction peak was observed and no deviation was found.Experiments on the mechanical properties of the alloy at this time show that the beneficial effect of P on the Ni-Cr-Fe series alloy disappeared,and the difference in the mechanical properties of different phosphorus contents is mainly determined by the Holpage relationship caused by the grain size.