Molecular Dynamics Simulation Of Grain Boundary Segregation Behavior Of Elements In Ni-alloys And Its Effect On Grain Boundary Properties

With the development of the times and the progress of science and technology,people's demand for high-precision materials is also increasing.However,what nature can give us is limited.Therefore,realizing the sustainable development of materials has become a focus topic that has been widely concerned in today's scientific research work.In order to realize the sustainable development of materials,improve material performance,reduce material development costs,and increase material recycling rate,scientists have proposed the making materials plain theory based on "grain boundary segregation engineering".Nickel-based alloy is currently the most widely used superalloy system.From aerospace to deep-sea drilling,the use of nickel-based superalloys has penetrated into all aspects of human production and life,and its performance requirements are increasing day by day.Therefore,this paper takes the making materials plain as the core guiding ideology,and uses the molecular dynamics method to conduct theoretical research on the Ni ?5[001](210)twin boundary.By doping pure Ni ?5[001](210)grain boundaries with different properties of solute elements(Ti and Fe)to calculate the grain boundary energy and segregation energy at different temperatures and different concentrations,as well as the stress and strain under tensile load Curve,in-depth study of the effect of grain boundary segregation on the mechanical properties of materials,in-depth analysis of dislocations and structural transformations generated during the stretching process,study of its micro-mechanism,and finding evidence that grain boundary segregation can strengthen the material,as well as the material Demonstration and verification of the vignette theory.The main results of the research in this paper are as follows:(1)Ti,as a solute element,exhibits different segregation properties and segregation capabilities in different grain boundaries with Ni as the matrix.For example,by calculating the segregation of twelve kinds of twins of Ti in Ni,it can be found that in ?3[110](111),?3[110](112),?5[001](210),?5[001](310),?9[110](221),?17[100](223),?17[100](410),?43[110](335)all have segregation ability in the grain boundaries,but in ?11[110](113),?13[001](320),?19[110](331),?27[110](335)have no segregation ability in the grain boundaries.At the same time,the calculation of the grain boundary energy of Ti doping in the above-mentioned twelve kinds of twins of Ni and Fe in the ?5[001](210)grain boundary of Ni found that the influence of doping elements on the grain boundary energy has nothing to do with element segregation.(2)The solute elements with segregation ability will be affected by the segregation energy,move directionally to the grain boundary region,and gather in the grain boundary region under the interaction between atoms,so as to strengthen the material performance stably for a long time.This makes the material's service life and service cycle longer;and for solute elements that do not have segregation ability,they recover the attraction from other directions in the grain boundary to leave the grain boundary area and enter the interior of the crystal.Not only does it not have the function of stabilizing grain boundaries,but it also causes lattice distortion inside the crystal,which makes the material more prone to dislocations and stacking faults under the action of external forces.This is the phenomenon mentioned in the "making materials plain" theory that the more the element,the stronger the element.(3)Grain boundary segregation,by doping and segregating Ti in the Ni?5[001](210)grain boundary and applying 150 K,300 K,450 K,600 K,750 K,900 K,1050 K and 1200 K The temperature field calculation shows that the segregation behavior of Ti in the Ni ?5[001](210)grain boundary is affected by different temperatures.The higher the temperature,the stronger the segregation ability of Ti element,but when the temperature rises to a certain degree,The kinetic energy of the matrix atoms will also increase in response,and even homogenization will occur within the system,which will reduce the segregation energy of solute elements and weaken the segregation ability.(4)By calculating Ti in the Ni ?5[001](210)grain boundary with 5 at.%,8 at.%,9at.%,10 at.% and other different doping concentrations,the segregated solute The concentration of atoms itself has little effect on segregation,but the entry of a large number of solute atoms will change the original neatly arranged lattice structure and cause a large amount of lattice distortion.The main manifestation is that the thickness of the grain boundary is to a certain extent.It will increase as the concentration of segregation increases.