First-principles Study Of Interface Characteristics Of Titanium Alloy/Interlayer/Diamond-like Carbon Film

With the development of technology,titanium alloy gradually expands from structural materials to sports materials,such as artificial bone joints,gears and pistons,which puts forward higher requirements for its surface properties(friction and hardness).Diamond-like carbon(DLC)film is a material with high hardness and low friction coefficient.Depositing DLC film on the surface of titanium alloys can effectively improve its surface properties.However,DLC film and titanium alloys are poor adhesion and are easy to fall off,because great differences in mechanical properties.Adding typical interlayers(Si,Ti and Cr)is one of the most effective methods to solve this problem,but the micro mechanism is not clear.In addition,the surface of titanium alloy is easily oxidized,and the effect of surface oxidation on the microscopic characteristics of titanium alloy/interlayer interface has not been reported.In this paper,the interface bonding and failure mechanism of titanium alloy(oxidized and non-oxidized)/typical interlayer(Si,Ti,Cr)/DLC film are studied by using the first principle method.The following conclusions are obtained:(1)The study on the adhesion of non-oxidized titanium alloy(Ti)/(Si,Ti,Cr)interlayer/DLC shows that when the interlayer is Si,the tensile strength of Ti/Si interface is lower than that of Si/DLC interface,and the tensile strength is 19.93 GPa and 23.09 GPa,respectively;when the interlayer is Ti,the tensile strength of Ti/Ti interface is higher than the interface of Ti/DLC,and the tensile strength is 24.49 GPa and 21.61 GPa,respectively;when the interlayer is Cr,the tensile strength of Ti/Cr interface is lower than the interface of Cr/DLC,and the tensile strength is 21.83 GPa and 43.80 GPa,respectively.(2)The study on the adhesion of oxidized titanium alloys(Ti O₂)/(Si,Ti,Cr)interlayer/DLC shows that when the interlayer is Si,the tensile strength of Ti O₂/Si interface is lower than that of Si/DLC interface,and the tensile strength is 18.75 GPa and 23.09 GPa,respectively;when the interlayer is Ti,the tensile strength of Ti O₂/Ti interface is lower than the interface of Ti/DLC,and the tensile strength is 9.32 GPa and 21.61 GPa,respectively;when the interlayer is Cr interlayer,the tensile strength of Ti O₂/Cr interface is lower than the interface of Cr/DLC,and the tensile strength is 12.92 GPa and 43.80 GPa,respectively.(3)The adhesion of the interface between the titanium alloy of non-oxidized and oxidized/(Si,Ti,Cr)interlayer shows that the oxidation of titanium alloy is not conducive to the improvement of the interface adhesion of the titanium alloy and the interlayer.In the whole interface between titanium alloy non-oxidized and oxidized/(Si,Ti,Cr)interlayer/DLC,the bonding strength of titanium alloy/Cr interlayer/DLC is the highest when titanium alloy is non-oxidized;the bonding strength of titanium alloy/Si transition layer/DLC is the strongest when the titanium alloy is oxidized.(4)The electronic structure analysis of the interface between titanium alloy of non-oxidized and oxidized/(Si,Ti,Cr)interlayers shows that the titanium alloy weakened by the interface between the titanium alloy and the interlayer is small,and the interface bonding strength is relatively high,because there have metal bonds in the titanium alloy,and more electrons are distributed among atoms when the titanium alloy is non-oxidized;the titanium alloy of oxidized(Ti O₂)have ionic bonds.When the interface is formed between Ti O₂ and the interlayer,the interface bond is always strong bond(ionic bond or covalent bond which related to O)which would plunder the surrounding electrons,led to the weakening of the chemical bond of Ti O₂and the reduction of the interfacial bonding strength,and then the fracture occurs in Ti O₂ during tension.(5)The atomic and electronic structure analysis of the interface between titanium alloy of on-oxidized and oxidized/(Si,Ti,Cr)interlayer/DLC shows that the Cr interlayer has the best improvement on the interface bonding strength of non-oxidized titanium alloy/interlayer/DLC,because the bond strength of titanium alloy weakens least by the interface bond of Cr/titanium alloy,and the tensile strength of Cr interlayer is greater than that of Ti interlayer;the Si interlayer has the greatest improvement on the interface bonding strength of titanium alloy of oxidized(Ti O₂)/interlayer/DLC,because the stacking mode of Si atoms and O atoms on the surface of Ti O₂ is different from Ti and Cr,and the interface distance is larger,so,the bond of Ti O₂ is weakened smaller.