Study On Machinability Of High Chromium Alloys Based On Molecular Dynamics

The performance of the main pump thrust bearing affects the reliability,life span,and economic and technical cost of the entire unit directly.The requirement of thrust bearing bush is stringent for the material.It can be solved by adding a coating on the surface.But the coating has some disadvantages such as non-uniformity,micro-cracks,and high maintenance costs.high-chromium alloy can be used to solve this problem and it becomes the material of thrust bearing pad because of its excellent performance of high hardness and wear-resistant property.However,the high-chromium alloy is a new alloy,the physical and processing properties of the alloy are not known completely.It is difficult to explore the processing mechanism through experiments.It is an effective way to explore the processing mechanism of high-chromium alloy by computer simulation.In this paper,molecular dynamics(MD)simulation was used to explore the processing mechanism of high-chromium alloy,and the results of nanoindentation experiments verified the simulation.According to the composition and element content of high-chromium alloy.Fe,Cr,Ni,and C were selected.The MD model of high-chromium alloy was established by mixing the replacement unit cell and the interstitial unit cell.Potential functions are the basis of molecular dynamics simulation.At present,there is no an exact potential function for the high-chromium alloy simply.In this paper,the potential of high-chromium alloy was established through the coupling and superposition of three potential functions(L-J potential,Tersoff potential,and EAM potential).The accuracy of the potential function was verified by calculation.Nano-indentation simulation of high-chromium alloy was performed.The influence of cylindrical and spherical indenters on the force and elastic moduli was studied.It was found that the spherical indenter simulation was more in line with the actual situation.The spherical indenter was selected according to the calculation accuracy,simulation time and actual conditions for subsequent indentation simulation.Indentation simulations were performed in different depths.Simulation results show that dislocations in a small range occur in high-chromium alloy at the beginning of plastic deformation.As the depth of indentation increases,the elastic recovery decreases and tends to be stable;plastic work becomes the main work method,and elastic recovery work is reduced.Scratch simulations were also performed to simulate grinding process.The average cutting force of the scratches increased with the scratch speed and scratch depth.The greater the scratch depth,the thicker the damage layer.The depth of the nanoscratches increased from 5 ? to 20 ? and the thickness of the damage layer increased from 3.68 ? to 11.7 ?.The bond angle between the damage layer atoms is smaller than the crystal bond angle,the longitudinal distance between the atoms becomes smaller,and work hardening occurred.Tensile simulations of high chromium alloy were carried out.When the strain was at ? = 0.025,the shear bands formed gradually.The shear band and the force direction are 45.1 degrees angle.The shear band breaks and the high chrome alloy necks down until it breaks during the tensile process.The yield stress of high-chromium alloys was 4.52 Gpa obtained by tensile simulation.The residual stress of high-chromium alloy scratched by 40? grains was calculated according to the Swadener I calculative model,and the residual stress was 0.99 GPa.Finally,nano-indentation experiments were performed.The influence of indentation depth on normal stress,hardness,and elastic modulus was analyzed.The variation tendency of these physical properties in experiments were the same as it obtained by molecular dynamics simulation.MD simulation can predict the variation trend of the experiment and provide theoretical support for the precision machining of high-chromium alloy in a micro perspective.