Research On Corrosion Resistance Of Brazed Joints Of Cemented Carbide And Stainless Steel

Cemented carbide materials have a wide range of applications in exploration engineering,but due to the poor toughness and workability of cemented carbide,it is necessary to braze and connect with stainless steel to prepare complex components.During the service process,the complex components formed by cemented carbide and stainless steel will corrode at the welds.It is of great significance to study the corrosion resistance of the brazed joints of cemented carbide and stainless steel to provide service stability guarantees for exploration projects.The current research on the corrosion mechanism and protection strategies of brazed joints is mainly focused on optimizing process parameters.The influence of the microstructure of brazing alloys and brazed joints on the corrosion behavior and corrosion mechanism has not been fully studied.In view of the above problems,this article first studied the influence of alloying elements Ti and In on the corrosion performance of AgCu brazing filler metal,and then brazed cemented carbide and stainless steel under vacuum conditions,and studied the effect of Ti and In on the joint structure from the interface structure and theoretical calculations.Finally,through the quantitative analysis of corrosion,the location of joint corrosion is studied,which reveals the corrosion mechanism of dissimilar metal brazed joints,and further provides guidance for joint corrosion protection strategies.The AgCu-based solder alloy has excellent weldability,so it is selected as the solder used for the connection of cemented carbide and stainless steel in this article.This paper uses classic electrochemical testing technology to study the corrosion resistance of AgCu brazing filler metal alloys.The electrochemical test results show that the relative size of the corrosion tendency of the AgCu brazing filler metal alloy changes during the corrosion process.The corrosion product of the AgCu brazing filler metal alloy is Cu₂O,which indicates that the Cu element in the AgCu brazing filler metal alloy is corroded preferentially.The morphology and element distribution of AgCu solder alloys after corrosion show that the introduction of Ti element reduces the corrosion resistance of silver-copper solder alloys,and the introduction of In element enhances the corrosion resistance of silver-copper solder alloys.AgCu In solder sheet has the best corrosion resistance and can be used as the brazing filler metal for hard alloy and stainless steel brazing.After selecting the brazing filler metal for hard alloy and stainless steel brazing,vacuum brazing,AgCu and AgCu Ti filler metal were used as a comparison.In order to maximize the strength of brazing joints,the best brazing temperature for AgCu,AgCu Ti,AgCu In is 850?,and the best holding time is 15min,5min,and 15min.The microstructure of the joint interface shows that the weld structure of AgCu brazing joints is a eutectic phase structure of silver-based solid solution and copper-based solid solution.The introduction of alloying elements Ti and In will change the typical eutectic structure of the weld structure.In order to reveal the influence of the introduction of alloying elements Ti and In on the joint structure from the atomic level,first-principles calculations are used.The calculation results of interface electron cloud distribution,weld tissue separation work and weld tissue local density of states show that the introduction of In element will increase the shear strength of brazed joints.After optimizing the brazing process parameters,classical electrochemical testing techniques are used to analyze the corrosion resistance of the brazed joints under the best process parameters.Corrosion experiments show that AgCu In brazed joints have the best corrosion resistance,and the corroded structure of the brazed joints is copper-based solid solution,and the copper-based solid solution containing Ti in the AgCu Ti brazed joints does not corrode.This shows that the alloying element Ti entering the copper-based solid solution can improve the corrosion resistance of the copper-based solid solution,which points out the direction for improving the corrosion resistance of the brazed joint.In order to study the difference in corrosion resistance of different areas of brazed joints,scanning electrochemical microscope and first-principles calculations were used.Scanning electrochemical microscopy results show that there is a significant difference between the resistance values of the base material and the weld of AgCu and AgCu Ti brazing joints.The joints are prone to galvanic corrosion,and the galvanic corrosion tendency of AgCu Ti joints is greater.The base material and welds of AgCu In brazing joints The difference in impedance value is small,and the corrosion resistance of the joint is better.The work function simulation results of cemented carbide base metal,stainless steel base metal,weld copper-based solid solution and weld silver-based solid solution show that the work function of weld copper-based solid solution is the lowest,and it loses electrons preferentially in corrosive environments and causes corrosion.