Interfacial Microstructures And Mechanical Properties Of Al/TiC And Al/Al_2.5X_0.5Zr?X=Cu?Zn?Ag? From First-principles Calculations

The comprehensive properties of a composite primarily depend on the nature of interfaces.The interfaces are often influenced by many factors such as interfacial defects and stress,which cause changes in ductility,deformation resistance and wear resistance.Therefore,the interface is a research hotspot in many subject areas such as chemistry,physics,materials science and technology.And the microcosmic mechanism is an important subject to be studied.In this paper,a variety of different Al/TiC and Al/Al_2.5X_0.5Zr?X=Cu,Zn,Ag?interfacial models have been simulated by first-principles methods.The interfaical stability and ductility are analyzed by the interfacial adhesion,generalized stacking fault energy and electronic structure.In addition,the effect of alloying elements on the interface also has been investigated.The research results give a reasonable explanation for the phenomena observed in the experiments,and provide reference for improving the interfacial adhesion and the design of structural materials.The main research contents in this paper are shown as follows:?1?The adhesion of coherent interfaces for Al?100?/TiC?100?and Al?110?/TiC?110?are calculated based on the first principles methods.It is found that the interfaces of Al above the C atoms?C-site?and Al above the C-C bond direction?Bridge-site?are the optimal interfacial structures,respectively.And the generalized stacking fault energies along?100?and?110?directions for Al?100?/TiC?100?interface,and along?100?,?110?and?112?directions for Al?110?/TiC?110?interface are calculated.In order to estimate the influence of the misfit dislocations in the semicoherent interfaces on the interfaces,the Peierls-Nabarro?P-N?model of interfaces is used to obtain the interface energy.It is found that misfit dislocations can increase the interface energy and decrease the adhesion of the interface.And the interface energy increases with the unstable stacking fault energy.The corresponding adhesion of interfaces gets worse.We introduce an energy level diagram to describe the adhesion of interfaces.?2?The effects of Mg,Zn,Cu,Fe and Ti alloying elements on the interfacial adhesion of?100?and?110?Al/TiC have been investigated.Fe and Ti can enhance the adhesion,while Mg and Zn can reduce the adhesion of interfaces.The calculated resultsare in good agreement with other experiments and literatures.To better understand the nature of interfaces,we use density of states?DOS?and difference charge density to analyze the electronic structure of interfaces.The generalized stacking fault energies?_us along?010?and?110?directions for?100?Al/TiC,and along?110?and?112?directions for?110?Al/TiC interfaces are calculated.For the?100?and?110?Al/TiC interfaces,the preferred slip direction is the?110?direction.Furthermore,the effects of Mg,Zn,Cu,Fe and Ti on the ductility have been investigated according to the Rice criterion.The results show that Mg,Fe and Ti can improve the ductility of Al/TiC interfaces.?3?The first principles methods combined with the quasiharmonic approximation are used to study the work of adhesion for the?100?Al/TiC and?110?Al/TiC interfaces at different temperatures?0-800 K?.The results show that the work of adhesion_ad?and interfacial separation₀d are almost unaltered.However,the adhesive energy increases with temperature?>933 K?in the wetting experiments.We conclude that thermal expansion can not result in the improvement of interfacial adhesion with increasing temperature.In order to understand this results,we suspect that other interface structures may exist with increasing temperature.The different?100?Al/TiC and?111?Al/TiC interfacial structures are modeled.For?100?Al/TiC,we have found that the work of adhesion of 5Al/4TiC-C,5Al/4TiC-Ti,4Al/5TiC-C and 4Al/5TiC-Ti interfaces are much smaller than 1Al/1TiC-C.For?111?Al/TiC interfaces,six different structures have been simulated.The calcualted results show that the interfaces of C termination are more stable than Ti termination.And the AlA stacking presents the least adhesion for C and Ti terminations.The interface of AlB stacking is the strongest.In addition,we use density of states and difference charge density to understand the interfacial adhesion.Finally,in order to understand the trend of Al/TiC wetting experiment,we suspect that interfaces may shift from 1Al/1TiC to 5Al/4TiC,4Al/5TiC and Ti-AlA interfaces with the increasing temperature?973-1273 K?.?4?The Al/Al_2.5Cu_0.5Zr coherent interface observed by HRTEM is simulated.Based ontheobservedorientationrelationsbetweenAl_2.5Cu_0.5ZrandAl:?001?_Al2.5Cu0.5Zr//?001?_Al and?27?001?29?_Al2.5Cu0.5Zr//?27?001?29?_Al,six supercell models are established.The interfacial separation of the Al/Al_2.5Cu_0.5Zr interface is 2.015?,which is in good agreement with the experimental value?2.017??.Zn and Ag also can improve the stabilization of L1₂ phase Al₃Zr as well as Cu.Therefore,we also studied the coherent interfaces of Al/Al_2.5Zn_0.5Zr and Al/Al_2.5Ag_0.5Zr.The results show that Al/Al_2.5Cu_0.5Zr interface has the strongest adhesion,and the_ad?is 3.1840 J/m².Model V is the optimal structures for Al/Al_2.5X_0.5Zr?X=Cu,Zn,Ag?interface.According to the calculations of the generalized stacking fault energy,it is found that the preferred slip direction is the?110?direction.According to the Rice criterion,the most ductile interface is Al/Al_2.5Zn_0.5Zr.The segregation of the impurity elements Si,Fe and Ti in the alloy on the interface of Al/Al_2.5X_0.5Zr?X=Cu,Zn,Ag?have been investigated.At the same time,the infulences of Si,Fe and Ti on the adhesion and ductility of interfaces are also estimated.For the Al/Al_2.5Cu_0.5Zr and Al/Al_2.5Zn_0.5Zr interfaces,Si is more likely to segregate at Al_-11 of the interfacial layer.But the interfacial adhesion will be reduced.The ductility along?100?directionis decreasedand along?110?directionis improved.For Al/Al_2.5Ag_0.5Zr interface,Si will segregate at the Ag site and weaken the adhesion of the interface.And the ductility is slightly improved.Fe may segregate at the Zr position in the interface layer of Al/Al_2.5X_0.5Zr,and the adhesion of all interfaces will be improved.However,the ductility of Al/Al_2.5X_0.5Zr?X=Cu,Zn?interface is reduced.For the Al/Al_2.5Ag_0.5Zr interface,there is only a slight increase in the ductilityalong?110?direction.Compared with the positions of Al and X,Ti is more likely to replace Zr in the Al/Al_2.5X_0.5Zr interface.The substitution of Ti will enhance adhesion and reduce ductility.