First-principles Study Of The Strengthening And Toughening In Medical Magnesium Alloy

Magnesium is an essential element in biological systems,and magnesium usually appears in the human body as the form of Mg2+ ions,as one of the necessary elements for the human body,widely found in various cellular structures.The appropriate amount of magnesium can not only promote the absorption of calcium in human bones,but also play a certain role in the regulation of the human nervous system.In the implanted medical devices field,magnesium is expected to become an ideal alternative for the traditional medical alloys such as iron and titanium.However,due to the poor toughness of pure magnesium and low strength to match the requirements of the device,this has become a widely problem.At present,alloying is one of the effective ways to improve the toughness and strength.In this paper,10 kinds of medical alloying elements,such as Al,Ca,Ce,Gd,Li,Nd,Sc,Y,Zn and Zr were added.Firstly,the surface energy of pure magnesium and its alloy {0001} basal slip is calculated by using the first principle method,and the surface energy of the system is used to characterize the material strength.Secondly,by simulating the generation and expansion of cracks in the crystal,the resistance ability of different alloying elements in the crack propagation is investigated by the condition of {0001} basal slip and {1010} prismatic slip,and the strength of the material is characterized by comparing the increase and increase of the total energy of the system.The change of system energy in the crack propagation of magnesium and its alloy{1122} conical slip is calculated,and measuring the difficulty of sliding system of conical surface to characterize the toughness of the alloy system.(1)In the {0001} basal slip system,the steps of optimization of the calculation model are added,the total internal energy of the optimized system decreases,and the difference between the power before and after optimization is the energy generated by the local lattice distortion caused by the addition of atoms with different atomic sizes in the system.The differential charge graph shows that there is an electron hole in the direction of the atomic crystal axis of the alloying element,while the magnesium atom is not present around it.This can be inferred that after the model optimization,the nuclear electrons of each atom are rearranged,so that the system reaches a more stable state,the optimization of the calculation model can not only eliminate the internal stress of the system,but also make the structure composition more reasonable.(2)In the {0001} basal slip system,the surface energy of each system after the addition of alloying elements is calculated,the results surface,Al,Ce,Gd,Li,Nd,Sc,Y,Zn,Zr and other elements can increase the surface energy of the system,improve the strength of the system,and the Zn atom will reduce the surface energy of the system.For the sensitivity of crack size change,the addition of Al,Ca,Gd,Li,Nd,Y and other elements will make the energy growth of the system become larger,the expansion of cracks in the crystal becomes more sensitive,the addition of these elements will reduce the shear strength of magnesium alloys,add Ce,Sc,Zn,Zr elements,The increase of energy in system crack propagation shows a decreasing trend compared with that of pure Mg,and the system can maintain the state of low energy when the crack expands in the crystal,and the addition of these elements can improve the shear strength of magnesium alloy.(3)In the {10(?)0} prismatic slip system,the energy growth of different systems in the system and crack propagation is calculated,and the results show that the total energy of the system decreases compared with the {0001} basal slip system,and the addition of Zn elements can reduce the internal ability of the system,Al,Ca,Ce,Gd,Li,Nd,Sc,Y,The Zr element improves the energy of the system.For the sensitivity of different element composition systems of crack propagation,the addition of Al,Ca,Gd,Li,Nd and Y elements will make the system increase the energy growth greatly and reduce the shear strength of magnesium alloys.Ce,Sc,Zn and Zr elements will reduce the sensitivity of the system to crack propagation the calculated results are consistent with the state of the basal surface,which will increase the shear strength of magnesium alloys.Compared with the increase of system energy when the surface-layer crack propagation of {0001} substrate,the increase of energy under cylindrical orientation generally increases.The growth of the total energy and crack size of the system is exponential growth,and with the increase of crack size,the increase of system energy is also increasing.(4)The start of the {11(?)2} conical sliding system plays an important role during the process of improving the toughness of magnesium alloys,and the ability of crack propagation in the conical conditions can reflect the plastic forming capacity of materials.The addition of Al,Ca,Gd,Li,Nd,Y and other elements will make the system increase the energy of the system in the crack propagation,in the process of plastic deformation,the system will increase greatly with the increase of deformation,the addition of these elements will reduce the toughness of magnesium alloy.The addition of Ce,Sc,Zn,Zr and other elements can reduce the energy growth amplitude,thus improving the plastic molding ability of the material.The growth of the total energy and crack size of the conical system changes exponentially,and when the crack size inereases,the growth rate of accelerates.size increases,the growth rate of the system energy accelerates.