Wetting And Interfacial Behavior Of Cu(Ni)-Ti Alloys On Three High-Temperature Structural Materials

High temperature alloys,high temperature structural ceramics and ceramic reinforced metal-matrix composites are the three kinds of high-temperature structural materials,which are widely applied in the fileds of aerospace and so on.Among them,solid-phase sintered SiC,GH3030superalloy and Ti?B,C?/TC4 composite are their respective representatives.In the applications of these high-temperature structural materials,they often need to be brazed with themselves or other high-temperature structural materials,while the wettability and interfacial behavior between brazing alloy and substrate directly affect joint quality,thus determining the service performance of the brazed components.This dissertation focuses on the wettability and interfacial behavior of Cu-50Ti and Ni-71Ti alloys on the three high-temperature structural materials on the basis of preparation of Ti?B,C?/TC4 composite.The main results and conclusions obtained are as follows:The wettability of Cu-50Ti and Ni-71Ti aollys on solid-phase sintered SiC at 960?1000°C and 1090?1170°C is positively correlated with experimental temperature,respectively.All the contact angles of Cu-50Ti on SiC at three temperatures are less than 30°,and the contact angle of Ni-71Ti/SiC system varies from 75°to 24°with the temperature increasing,indicating that increasing temperature can markedly improve the wettability of Ni-71Ti alloy on SiC substrate.The Cu element can react with the SiC substrate to produce silicide and graphite,which leads to poor wettability of Cu-50Ti/SiC system,while the Ti element from Cu-50Ti alloy can react with SiC to form silicide and carbide,that improves the wettability of Cu-50Ti/SiC system.Ti₂Ni is a low melting point solid solution from Ni-71Ti alloy,and its liquid-solid mass transfer plays a driving role in the wetting process.Ni from Ni-71Ti alloy reacts with SiC to produce silicide and graphite,and the thickness of graphite layer increases with temperature,while Ti can decrease this graphitization.Due to the difference of thermal expansion coefficient between alloys and SiC ceramic,microcracks are easy to generate at the drop/substrate interface during cooling process,and even the interface can be peeled off.Both the wettability of Cu-50Ti and Ni-71Ti alloys on GH3030 superalloy at 960?1000°C and 1090?1170°C are quite good,and all the contact angles are less than 20°.Layered phenomenon appears at the Cu-50Ti/GH3030 interface,which is attributed to serious interfacial interactions among Cu,Ti from Cu-Ti drop and Ni from GH3030 substarte to form a reaction layer containg Cu,Ti and Ni,and the thickness of reaction layer increases with experimental temperature increasing.In particular,the intermetallic compounds and solid solution formed in the reaction layer can contribute to interfacial bonding.The Ni-71Ti/GH3030 system are typically wetting and dissolution,and the alloy"embedded"in the superalloy substrate forming an arc-shaped interface,while the diffusion depth of Ni and Ti elements increases with the increase of temperature.Both the wettability of Cu-50Ti and Ni-71Ti alloys on Ti?B,C?/TC4 composite at 960?1000°C and 1090?1170°C are excellent,and all the contact angles are less than 15°.However,the effect of temperature on wettability is quite limited.Cu exists in the main form of Cu_xTi_y phase at the interface while wetting of Cu-50Ti alloy on Ti?B,C?/TC4 composite,while Ni mainly exists in the forms of Ni-Ti and Ni-C compounds while wetting of Ni-71Ti alloy on Ti?B,C?/TC4 composite.The strong interfacial reactions not only promotes the spreading of Cu?Ni?-Ti alloys on Ti?B,C?/TC4 composite,but also enhances the interfacial bonding.