Simulation Of Molten Pool Evolution And Properties Of Nickel-based Alloy Laser Cladding

The surface of marine equipment has been corroded by seawater for a long time,and the surface of parts is prone to corrosion damage.Improving the corrosion resistance of the surface is an important engineering technology problem that needs to be solved urgently.Nickel-based alloys are widely used in severely corrosive fields such as navigation with their excellent properties of high temperature resistance and corrosion resistance.The cladding layer processed by laser cladding technology is not only a metallurgical bond,but also has a small heat-affected zone.The whole cladding process can realize precise directional machining,which has unique advantages in the processing of Nickel-based high-temperature corrosion-resistant alloys.The distribution of the molten pool during processing is closely related to the quality of the cladding layer.The temperature field and stress field of the molten pool directly affect the formation of the internal structure of the cladding layer and the distribution of elements.However,the existing technology has obvious shortcomings in exploring the internal temperature distribution and flow of the molten pool.It is unable to directly explore the evolution law of the molten pool,which greatly limits the further application of laser cladding technology.Aiming at the above problems,this paper focuses on the evolution process of temperature and stress in the process of Nickel-based alloy cladding for offshore equipment.The relationship between the process parameters and the quality of the cladding layer is studied from three aspects of temperature field,flow field and stress field distribution in the molten pool by combining experiment with simulation.The main research work of this paper is as follows(1)The evolution process of the temperature field of the molten pool was studied,and the relationship between the heat input and the distribution of the cladding layer structure was clarified.The larger the input energy is,the larger the grain size above the bonding line will be,and the more obvious the phenomenon of perpendicular to the bonding line will be.During the processing process,the temperature at the front end of the molten pool will also preheat the surrounding substrate and powder while accumulating,so that the temperature value between the two scanning tracks at the edge of the workpiece can reach 1677 K and 2017 K,both exceeding the powder melting point.Under the influence of secondary heating,the overlapping area of the cladding layer has a denser structure.(2)The evolution of the stress field during the machining process was studied.Combined with the surface quality of the cladding layer,the correlation between the stress distribution and the occurrence of cracks was explored.During the cladding process,the central area of the molten pool shows a low stress distribution,and the stress values at the front and both sides are larger.The stress value in the solidification zone of the molten pool will increase with the increase of the falling temperature,and the maximum stress value can reach 746.11 MPa.It presents a state of tearing to both sides perpendicular to the processing direction.Excessive stress values cause cracks on the surface of the workpiece,which also affects the generation of passivation areas in electrochemical experiments.(3)The influence of process parameters on the flow field distribution of the molten pool was explored,and the influence of the flow field in the molten pool on the heat and mass transfer of the molten pool was clarified.The existence of Marangoni effect makes the temperature in the center of the molten pool decrease,and energy is diffused to the edge of the molten pool,which increases the size of the molten pool.The stirring effect in the flow process will make the element distribution in the cladding layer tend to be uniform and improve the quality of the cladding layer.The flow field in the cladding presents a symmetrical distribution,the flow velocity in the center of the molten pool is low,and the flow velocity is higher in the peripheral area of the molten pool center due to the obvious temperature changes.After processing,due to the stirring effect of the Marangoni effect on the nickel-based cladding layer,the upper grains are fine and Cr compounds are formed,so that the hardness value can reach 450-600 HV.This thesis includes 41 figures,7 tables and 83 references.