A First-principles Study Of The Effect Of Temperature And Pressure On The Phase Transition Of Carbon Nanotube-reinforced Titanium Matrix Composites

Titanium(Ti)-based composite materials have the characteristics of corrosion resistance,high strength and high specific gravity,and are indispensable key materials in the aerospace field.With the development of modern science and technology,the demand for new high-performance titanium-based composite materials is more urgent.Carbon nanotube-reinforced titanium-based(CNTs/Ti)composite materials are one of the important research directions.In this study,a large plastic deformation method was used to prepare CNTs/Ti composites at low temperature.The results show that in addition to the evacuation,structural integrity,and the interface between the CNTs and the matrix,the mechanical properties are greatly affected,and the phase transformation behavior of the matrix causes The strengthening effect cannot be ignored.This study focuses on the influence of the matrix transformation behavior of the CNTs/Ti composite on the composite mechanical properties:using spherical aberration transmission electron microscopy and other experimental methods and first-principles calculation methods to study the matrix transformation of the CNTs/Ti composite Behavior,exploring ways to control the phase transition behavior is of great significance for optimizing the microstructure of the material and improving the comprehensive mechanical properties of the material.The mechanical properties of CNTs/Ti composites prepared by the high-pressure torsion method have been significantly improved.The grain orientations of fcc-Ti and hcp-Ti found in the matrix are:(?).This phenomenon is mainly caused by the hcp-Ti?fcc-Ti solid phase transition caused by stress.The first-principles calculation method was used to study the possibility and process conditions of the structural transition of hcp-Ti and fcc-Ti under the pressure of 0?15 Gpa,and the calculation results were in good agreement with the experimental results.The results show that the formation enthalpy(?H_Ti),bulk modulus(B),shear modulus(G)and Young's modulus(E)of fcc-Ti and hcp-Ti structures gradually increase with the increase of external pressure.The hybridization between atomic orbitals becomes more complicated.The E of the cubic fcc-Ti structure shows strong anisotropy along the[0 1 0]and(?)directions,while the E of the hcp-Ti structure shows obvious differences on the(1 0 0)plane Anisotropy.The thermodynamic stability of hcp-Ti and fcc-Ti structures will decrease under high pressure.However,the decreasing trend of the stability of the two structures is different,indicating that hcp-Ti has a greater tendency to change to the fcc-Ti structure under high pressure.The calculation results of the fcc-Ti/hcp-Ti interface relaxation phenomenon indicate that the minimum stable thickness of 3 atomic layers is required for the nucleation of the fcc-Ti structure.As the external force increases from 0 Gpa to 15Gpa,the hcp-Ti(0002)/fcc-Ti((?) )interface adhesion work(W_ad)gradually decreases,the surface energy gradually increases,and the fcc-Ti/hcp-Ti interface bonding strength reduce.The stability of hcp-Ti(0002)/fcc-Ti(?)interface decreases under high pressure,which will promote the nucleation and growth of fcc-Ti phase at the interface.The results of this study help to better understand the nucleation and growth process of the fcc-Ti phase,and the properties of the fcc-Ti/hcp-Ti interface,and provide a theoretical basis for improving the mechanical properties of CNTs/Ti composites.