Effect Of Vacuum Heat Treatment On The Interface Of TC4/Cu Plating Layer And The Tribological Properties

Titanium alloy has many advantages of high specific strength and stiffness and excellent biocompatibility.It plays important roles in many fields such as aerospace,marine engineering,national defense and biomedical.However,its application is restricted because of insufficient rear resistance.The surface engineering technology can effectively improve the wear resistance of titanium alloy,so as to unlock its application potential.In this thesis,TC4 titanium alloy was used as the substrate material.Firstly,the pure Cu layer was deposited on the surface of the substrate by electroplating.Then,it was subjected to vacuum heat treatment.Finally,the wear resistance of the TC4titanium alloy which was covered by Cu coating were tested.The effect of vacuum heat treatment on the diffusion structure of interface between TC4 titanium alloy and Cu electroplated layer was studied.What's more,the formation mechanism of Cu-Ti intermetallic compounds was analyzed in combination with thermodynamics and kinetics.Besides,the wear resistance of TC4 titanium alloy/Cu electroplated layer was analyzed.The main results are as follow:(1)The initial interface of the TC4 titanium alloy surface and the electroplated Cu layer is mechanically bonded.After vacuum heat treatment,the solid phase transformation produces Cu-Ti intermetallic compounds with the Cu atoms and Ti atoms interdiffusion at the interface.The interface of TC4 titanium alloy/Cu coating transforms into TC4 titanium alloy/Cu-Ti intermetallic compounds/Cu coating or TC4titanium alloy/Cu-Ti intermetallic compounds,which means metallurgical bonding between the TC4 titanium alloy surface and the electroplated Cu layer.(2)Four kinds of Cu-Ti intermetallic compounds appeared after the vacuum heat treatment.From the side of TC4 titanium alloy to the electroplated Cu layer,they were CuTi₂,CuTi,Cu₄Ti₃ and?Cu₄Ti,which was consistent with the order of Cu-Ti phase diagram from the Ti end to the Cu end.(3)The relative size relationship of the formation enthalpy of Cu-Ti intermetallic compounds calculated by Miedema model is:?H_?Cu4Ti>?H_CuTi2>?H_Cu4Ti3>?H_CuTi.The CuTi phase has the smallest enthalpy of formation,and this phase is most stable.The thickness of the Cu-Ti atomic diffusion layer and the diffusion time follow a parabolic relationship.The growth activation energy of the intermetallic compounds in the diffusion zone is Q_K=126.0 k Jmol^-1.(4)After vacuum heat treatment,the intermetallic compounds formed between the TC4 titanium alloy matrix and the Cu coating,which improved the wear resistance of the TC4 titanium alloy.(5)The wear mechanism of Cu plating layer electroplated on the surface of TC4titanium alloy is mainly peeling wear,the wear mechanism of Cu-Ti intermetallic compound is mainly fatigue wear,and the wear mechanism of TC4 titanium alloy matrix is mainly adhesive wear.