Small-angle Neutron Scattering Of Nickel-based Single Crystal Superalloy DD10 And Nano-strengthened D6A Steel

Due to the excellent thermal mechanical and high temperature properties,single crystal(SC)nickel based superalloys are widely used as turbine blade materials in aircraft engines.With the possibility to achieve both higher strength and better toughness simultaneously,nanostructure steel is of vital importance in industries,such as national defense,aircraft,medicine,natural gas,nuclear industry.During the processing,heat treating or serving proceduces of superalloys and nanostructure steels are processed,the external heat and force affect the precipitation of materials,and these changes will also influence the mechanical properties and safety.Therefore,study the evolution machnisim of the precipitates is in great need,which can be used for the development of new engineering materials,technology and service.Small angle neutron scattering(SANS)is an advanced nondestructive characterization technology,which has some unique advantages in studying the nano-structure.In this thesis,aiming to solve the problems during the analyses of special samples(single crystal nickel based superalloy)and SANS magnetic scattering,the methods of SANS magnetic scattering and anisotropic data analyses are developed.The investigation of precipitation in the creep progress of superalloys and in nanostructure steels by different treatment technics is performed with the help of SANS measurement.1)The specimens of SC superalloy were creeped at different conditions.The SANS investigation was performed.The result shows:Under the creep conditions,the 2D SANS patterns show that the origin cubic symmetry of the precipitate shape becomes elliptical,corresponding to rafting.The direction is perpendicular to[001],With the increase of the a angle between[001]and the stress direction,the raft progress becomes slow.When the a angle is 18°,there are still a few cubic precipitates.During the creep progress,the shape of second ?' precipitate turns to some sort of thin rod-like structure.When the stress direction is parallel to[001],the microstructure arrays with the axis perpendicular to[001],orientative in horizontal y channel.With the increase of a angle,the microstructure with the axis parallel to[001]is formed.The amount of fine particles decreases.With a angle equal to 18°,the microstructure direction is mostly with the axis parallel to[001].During the creep progress,the rate and direction of the breaking of ?' and ?'?' interface correlate with the stress direction.At the direction perpendicular to[001],the rate of breaking decreases with the increase of a angle.It represents the intensity increases first and then decreases.It is helpful to slower the creep progress when the ? angle is not equal to zero,for the stop of the fine second ?' precipitate in y channel.2)The specimens of D6A steels were dealt with different conditions.The SANS investigation was performed.The result shows:The SANS data of D6A steels include the information of nuclear and magnetic scattering.The magnetic microstructures mainly contribute the intensity.The curves of nuclear and magnetic scattering are clearly different.Nuclear scattering and magnetic scattering come from the microstructures in Fe base and the cementite,respectively.When all the magnetic moments are parallel to the direction of magnetic,the trends of intensity of nuclear and magnetic scattering are opposite to that without magnetic field.There are some changes of the microstructure under magnetic field.The curves of nuclear scattering show the reduce of size and the sharper interface,it can benefit the roughness of the materials.The magnetic scattering shows the increasing of surface and sharper interface,it is good for the toughness.3)According to the two kind of materials(DD10 SC superalloys and D6A steels),the methods of SANS magnetic scattering and anisotropic data analysis are developed.In this work,we demonstrate that how to reduce the SANS data,as well as calculate the size and array the microstructures in anisotropic data.The process of how to separate the nuclear and magnetic scattering data is also shown.In order to reduce the intense background at high q region after increasing the flux at sample position,the background suppression experiments were performed by irradiated specimens with existing hardwares and n/y discrimination metnods.The method of optimizing the anode voltage by sample characteristion is displayed,therefore,the data quality at high q region can be improved.