Study On The Mechanisms Of The Influence Of Alloying Atoms And Temperature On The Shear-strain Induced Relaxation Of Copper Grain Boundary

At present,the over alloying phenomenon and the difficulty or high cost of rare precious elements recovery have become the prominent bottleneck to restrict the sustainable development of alloy materials.Therefore,how to improve the properties of alloys without(less)reliance on alloying elements is in urgent need of new solutions.Grain boundaries(GBs)relaxation is a promising and effective strategy to improving GB stability or stabilizing nanocrystalline metals,it can transform the original GB into a lower energy state GB to achieve the effect of stabilizing nanocrystalline metal materials.The previous studies mainly focused on nanocrystalline pure metals and GB behaviors therein,which rarely considering the role of foreign atoms such as impurity or alloying atoms in GB relaxation.In this work,the energy changes and structural relaxation under shear load of Cu ?3[110](112)and ?17 [110](223)two kinds symmetric tilt GBs(STGBs),and the effects of impurity elements(Fe,Ni and Ag)and temperature on the GB relaxation were investigated in systematic by molecular dynamics method.The microscopic mechanism of the effect of impurity atoms and temperature on GB relaxation were revealed by observing the GB structure and dislocation changes under different shear strains and temperatures.Our work can not only provide theoretical guidance for Cu GB control and performance improvement,but also provide useful reference for alloy composition design.The main results obtained are as follows:(1)The structural units(SUs)of the high-energy Cu ?17 [110](223)GBs and low-energy Cu ?3 [110](112)GBs dissociate spontaneously into two GBs that are made up of SUs of ?11(113)and ?3(111)GBs in the process of energy minimization.Compared with the optimized Cu ?3 [110](112)GBs,there are also Hirth,Lomer-Cottrell and other unidentified dislocations in the optimized ?17 [110](223)GBs,besides the Shockley partial dislocations.(2)The shear strain can trigger the structural transformation of pure Cu ?3[110](112)GB and Fe-,Ni-and Ag-containing Cu GBs by the emission of Shockley partial dislocations from the optimized Cu GBs.However,Fe,Ni and Ag,all three have impediment effects on the shear-strain induced GB relaxation,though the content of Fe,Ni or Ag atom(0.00165 at.%)is quite low in the GB model.The temperature cannot trigger GB relaxation independently within the considered temperature range(50 K-100 K)in this paper,but play a positive role in the shear-strain induced structural relaxations of pure,Fe-,Ni-and Ag-containing Cu GBs,the shear strains required to start and finish the SU transformation become smaller with the increase of temperature.(3)Because of the Hirth dislocation lock and lomer-cottrel dislocation lock at the optimized Cu ?17 [110](223)GBs,the SUs of the GB would not change with the increase of shear strain.In addition,at 50 K,the presence of Ni atoms at the GB can promote the energy relaxation of atoms in the disordered GB region,but this promotion would weaken or even disappear with the increase of temperature.The existence of Ag atoms at the GB can hinder the energy relaxation of atoms in the disordered GB region,and this inhibition is not affected by the temperature.The existence of Fe atoms at the GB does not have any promote or inhibit effect the energy relaxation of atoms in the disordered GB region.