Vhp Of Ti - Cu Composites Prepared By The Evolution And Performance Research

The titanium coating electrode is used as anode material in the electrochemical and electrolytic extraction industry. As the electrode material, the main defect of titanium is due to its too large internal resistance. This project, starting from the composition and structure, using Ti plate and Cu plate to prepare Ti/Cu bi-metallic composite plate because of good conductivity of copper, and titanium of superior corrosion resistance, dimensional stability, long life, continuous usage of low loss. These characteristics reduce production costs and achieve energy consumption, and therefore has a broad development prospects. In this thesis, using the vacuum hot pressing diffusion welding (Vacuum Hot Pressing Diffusion Welding), which is called VHP for short, can achieve the bonding of industrially pure titanium and pure copper. The evolution of Ti/Cu diffusion bonding interface in the process is also researched. The evolution mechanism of the Ti/Cu dissimilar materials can provide experimental and theoretical basis for expanding the application of the Ti/Cu dissimilar materials, and also has an important theoretical significance and practical guidance value.Different process parameters, welding joints electrochemical performance and interface morphology, elemental distribution, the resultant phase and its structure are characterized by means of SEM, EDS,XRD, HRTEM, and the electrochemical workstation. We can obtain the impact of the law between welding parameters on welded joints of Ti/Cu and electrochemical properties of the distribution of interfacial composition phase. In addition, we research the mechanism of Ti/Cu solder interface evolution behavior experimentally and theoretically,The experiments show that the welding temperature and holding time is the main factors for the welded joints, while welding pressure is requirement but not sufficient condition. And it points out that the interface diffusion layer thickening with increasing welding temperature, which meet the laws of linear growth. Between holding time and the thickness of diffusion layer belong to exponential growth, the longer the holding time, the thicker the diffusion layer, when the diffusion layer grow to a certain thickness, the rate of increase decreases until remaining stable. In the early stages of the entire welding, welding pressure can heterogeneous metal to plastic deformation to form a flat surface in order to promote a good combination.Due to the different process parameters, the intermetallic compounds which are generated by the Ti/Cu soldered directly will be different. Seven kinds of intermetallic compounds of Ti/Cu composite electrode material in the diffusion zone are generated through vacuum hot pressing diffusion welding, they are CuTi, Cu3Ti2, Cu4Ti3, CuTi3, CuTi2, Cu3Ti and Cu4Ti respectively, CuTi3and Cu3Ti appear at relatively low temperature (600℃,720℃). Too thick intermetallic layer affect electrode conductive properties greatly, because too thick conductor layer can slow the electron transfer rate, which will affect the conductivity.We analyze the evolution mechanism of the Ti/Cu diffusion interface on kinetics and thermodynamics. Due to the properties of the copper itself, more copper than titanium is consumed in the diffusion reaction, so that the intermetallic layer between the copper substrate and the titanium substrate migrate to the copper substrate. When copper is consumed to a certain extent, the interfacial compound is formed of thin CuTi2layer which is adjacent to the titanium substrate, thick CuTi layer and Cu4Ti which is generated on Cu4Ti3+Cu3Ti2matrix, while CuTi is generated firstly.When the welding temperature of600℃, the precipitation sequence of Ti/Cu intermetallic compounds are as follows:CuTi→Cu4Ti3→CuTi3, between720℃～800℃, the order is as:CuTi→Cu3Ti2→Cu4Ti3→CuTi3→CuTi2→Cu3Ti→Cu4Ti.Through MS modeling and analysis, the formation enthalpy of Ti/Cu intermetallic compounds can be obtained. The smaller the formation enthalpy is, the easier the compounds generates thermodynamically. The formation enthalpy of CuTi is the smallest, which is most likely to generate. The formation enthalpy of Cu3Ti2and Cu4Ti3are almost the same, therefore, these two intermatallic compounds may generate at the same time under certain condition. The formation enthalpy of Cu4Ti is the maximum, while Cu3Ti is followed by. The order of size of the formation enthalpy is as follows:CuTi<Cu4Ti3<Cu3Ti2<CuTi2<Cu3Ti<Cu4Ti.The precipitation sequence of Ti/Cu intermetallic compounds is as follows:CuTi→Cu4Ti3→Cu3Ti2→CuTi2→Cu3Ti→Cu4Ti. In industrial production, we control the electrode electrochemical performance through controlling the process parameters, such as selecting appropriate soldering temperature (800℃), shortening the holding time in order to get thin layer of hard and brittle CuTi phase.