Magnesium/Carbon Interface Control Through Rare Earth Oxides:First-Principles Calculations

Magnesium-based composites are considered to be an effective way to improve the comprehensive mechanical properties of magnesium alloys due to their advantages of high specific stiffness and specific modulus.Nano-carbon materials(graphene,carbon nanotubes)are effective reinforcements for magnesium-based composites,which can significantly improve its mechanical properties.In the nano-carbon materials reinforced magnesium-based composites,the non-coherent interface between magnesium and carbon makes the interface bond weaker,which severely limits the further improvement of its mechanical properties.By introducing the idea of "transition bridge" to control the magnesium/carbon interface,a magnesium/"transition bridge"/carbon interface is formed in the composite material,thereby improving the interface bonding between the magnesium matrix and the carbon.Researches have found that rare earth oxides(La2O3,Ce2O3)are expected to become a "transition bridge" for nano-carbon materials to strengthen magnesium-based composites.Based on this,this paper adopts the method of first-principles calculation to study the interface bonding performance of the composites after introducing La2O3 and Ce2O3 "transition bridge",so as to verify the effectiveness of the "transition bridge".By constructing Mg/La2O3/graphene and Mg/Ce2O3/graphene interfaces,calculating and analyzing the interface work of separation and electronic structure,to exploring its interface strengthening mechanism from the atomic scale.The research results can provide a reliable theoretical basis for the design and development of nano-carbon materials reinforced magnesium-based composites.The main contents are summarized as follows:(1)First,the bulk properties of Mg,La2Oand Ce2O3 are calculated,and the results are close to the experimental and theoretical calculated values reported in the literature,which verifies the reliability of our calculation method.Next,the interlayer distance and surface energy Mg(0001),La2O3(0001)and Ce2O3(0001)were calculated to test the convergence of the surface.Finally,we selected 7-layer atoms Mg(0001),6-layer atoms O1-La2O3(0001)and O1-Ce2O(0001),7-layer atoms O1-La2O3(0001)and Ce-Ce2O(0001)and 9-layer atoms of O2-La2O3(0001)and O2-Ce2O3(0001)for subsequent modeling and calculation.(2)Secondly,according to the interface atomic chemical ratio and the interface coordination relationship,there are 6 different types of Mg(0001)/La2O3(0001),La2O3(0001)/graphene,Mg(0001)/Ce2O(0001)and Ce2O3(0001)/graphene interfaces are constructed.The work of separation of the above-mentioned interfaces is calculated,and it is found that the work of separation values of these four interfaces are far greater than that of Mg(0001)/graphene.Among them,the maximum work of separation of Mg(0001)/La2O3(0001)is 9.462 J/m2;the maximum work of separation of La2O3(0001)/graphene is 10.898 J/m2;the maximum work of separation of Mg(0001)/Ce2O(0001)is 12.849 J/m2;the maximum work of separation of Ce2O3(0001)/graphene is 2.285 J/m2.The bonding strength of the above four interfaces formed by introducing La2O3 and Ce2O3 "transition bridges" are all greater than the bonding strength of the Mg(0001)/graphene interface.Therefore,both La2O3 and Ce2O3 can be used as"transition bridges" for nano-carbon materials reinforced magnesium-based composites.(3)Then,through the calculation of the electronic structure of the interface,the strengthening mechanism of the interface is further revealed.The charge density,differential charge density and density of states of the Mg(0001)/La2O3(0001),La2O3(0001)/graphene,Mg(0001)/Ce2O(0001)and Ce2O3(0001)/graphene interfaces is calculated.The results show that the bonds of Mg(0001)/La2O3(0001)and Mg(0001)/Ce2O(0001)interfaces are mainly formed by metal bonds and ionic bonds.There are a large number of atomic orbital hybridization at the interface,which makes the interface bond stronger.The La2O3(0001)/graphene interface has a large amount of charge accumulation,and the C atoms and O atoms have a strong atomic orbital hybridization and form a covalent bond,which makes the interface bond stronger.The Ce2O3(0001)/graphene interface has less charge distribution,weaker atomic orbital hybridization,and weaker interface reaction,which leads to lower interface bonding strength.The overall evaluation of the effects of the three "transition bridges" of MgO,La2O3 and Ce2O3 is carried out,and it is found that the enhancement effect of La2O3"transition bridges" is the best,and the order of the enhancement effects of the three"transition bridges" is La2O3>MgO>Ce2O3.(4)Finally,the basic requirements of "transition bridge" interface design is summarize as follows:1)The interfaces of magnesium/"transition bridge" and"transition bridge'/carbon are coherent/semi-coherent interfaces;2)The "transition bridge" is a metal oxide,which is combined with the magnesium matrix through metal bonds and ionic bonds;3)The "transition bridge" can react with carbon to form a C-O covalent bond.The research in this paper shows that the introduction of La2O3 and Ce2O3"transition bridges" into nano-carbon materials reinforced magnesium-based composites can effectively enhance the bonding strength of the interface,thus solving the problem of weak bonding between the magnesium matrix and carbon.The research results provide theoretical support for the screening of "transition bridges" of nanocarbon materials reinforced magnesium-based composites.