High-Temperature Wettability Of High-Entropy Alloy On Carbide Ceramics Surface

High entropy alloys(HEAs)are a novel alloy material with many excellent properties such as high strength,high hardness,good corrosion resistance,and good high temperature oxidation resistance.It has good prospects as the binder phase of WC-based cemented carbide and Si C ceramic reinforced metal matrix composites.This paper takes Co Cr Fe Ni-based high-entropy alloys(Co Cr Fe Ni,Co Cr Fe Ni Al,Co Cr Fe Ni Al Ti and Co Cr Fe Ni Al Cu)as the object to explore the effects of wetting temperature and alloying elements on high-entropy alloys on the surface of WC and Si C ceramics.The high-entropy alloy type which is suitable for the binder phase of WC-based cemented carbide is selected,WC-HEA cemented carbide is prepared,and its mechanical properties are analyzed.The main conclusions obtained in the thesis are as follows:Firstly,the high-temperature wettability of Co Cr Fe Ni-based high-entropy alloy on the surface of WC was studied.Four Co Cr Fe Ni-based high-entropy alloys and WC substrates were used as experimental materials,and high-temperature wetting experiments were carried out by the sessile drop method,and the wetted samples were characterized by EDS and SEM.The results show that at the test temperature,the wetting process of the Co Cr Fe Ni-based high-entropy alloys on the WC surface can be divided into two stages: the rapid spreading stage and the slow spreading stage.The precursor films are formed on the edge of the high-entropy alloy melt;Co Cr Fe Ni,Co Cr Fe Ni Al,Co Cr Fe Ni Al Ti and Co Cr Fe Ni Al Cu high-entropy alloys have good wettability on the WC surface,and the equilibrium contact angles are 4.10°,7.03°,3.62° and 4.88°,respectively.Secondly,the high-temperature wettability of Co Cr Fe Ni-based high-entropy alloy on the surface of Si C was studied.The results show that,at the test temperature,the wetting process of Co Cr Fe Ni and Co Cr Fe Ni Al Cu alloy melts on the Si C surface is divided into two stages: the rapid spreading stage and the slow spreading stage,while the contact angle of Co Cr Fe Ni Al and Co Cr Fe Ni Al Ti alloy melts has been slowly decreasing during the wetting process;Co Cr Fe Ni and Co Cr Fe Ni Al Cu alloy melts have good wetting properties on the Si C surface(equilibrium contact angles are 25.28° and26.66°,respectively).However,Co Cr Fe Ni Al and Co Cr Fe Ni Al Ti have poor wettability on the Si C surface(the equilibrium contact angles are 61.81° and 68.25°,respectively).Thirdly,the wetting mechanism of Co Cr Fe Ni-based high-entropy alloy melt on the surface of WC and Si C ceramics is analyzed.The results show that the wetting of the Co Cr Fe Ni-based high-entropy alloy melt on the surface of WC and Si C ceramics is a reactive wetting type.Among them,the dissolution of the WC substrate in the Co Cr Fe Ni/WC system plays an important role in the wetting,while the wetting of Co Cr Fe Ni Al/WC,Co Cr Fe Ni Al Ti/WC and Co Cr Fe Ni Al Cu/WC systems mainly depends on the interface reaction.During the wetting process of the four Co Cr Fe Nibased high-entropy alloys on the Si C surface,there is not only the dissolution of the Si C substrate,but also the production of reaction products.The wetting process is jointly affected by two wetting mechanisms,namely,dissolution-driven and reactiondriven,of which the reaction-driven mechanism plays a dominant role.Fourthly,by analyzing the wettability of Co Cr Fe Ni-based high-entropy alloy on WC surface,a high-entropy alloy binder phase(Co Cr Fe Ni Al Ti)suitable for WC-based cemented carbide was selected.The WC-10 Co Cr Fe Ni Al Ti cemented carbide was prepared by mechanical alloying method and vacuum hot pressing sintering process,and its density and mechanical properties were characterized and compared with WC-10 Co.The results show that the density of WC-Co Cr Fe Ni Al Ti decreases first and then increases with the increase of sintering temperature.The hardness and fracture toughness of WC-Co Cr Fe Ni Al Ti prepared at different sintering temperatures are higher than WC-Co.Among them,the WC-Co Cr Fe Ni Al Ti cemented carbide prepared at a sintering temperature of 1420 ? has the highest density,hardness and good fracture toughness,which are respectively increased by 0.19%,8.57% and 9.25% than WC-Co cemented carbide.