Research On Gas-Liquid-Solid Three-Phase Flow Behavior Coupled During Laser Cladding Of Invar Alloy

Composite is used for civil structure of the large aircraft manufacturing because of high specific strength and specific stiffness compared with traditional structure materials.Composite structure is manufactured by using Invar alloy mold.Whereas Invar alloy mold in the long-term use of the process will be a failure.In this paper,the interaction mechanism among the powder,laser and molten pool is studied in the process of laser cladding repairing(surface strengthening)of the Invar alloy mold used to manufacture the composite structure of large civil aircraft.With the combination of experiment and simulation,the influence of process parameters on the structure size,dilution rate,microstructure and microhardness of Invar alloy during laser cladding were studied systematically.First of all,Invar alloy powders were prepared by powdering and their related performance tests were done.The exploring open experimental study of laser cladding on Invar alloy was carried out.In the meanwhile,the surface roughness,size and defects were analyzed to get the adjustable range of laser power,powder feeding rate and scanning speed,so as to design orthogonal experiment.Secondly,based on the orthogonal experiment,the calculation model of the coupling flow of the powder and the molten pool was established,and the heat source model and the material parameter model were added.The mechanism of Invar alloy during laser cladding experiment was analyzed,and the physical model of the interaction between different phases was deduced.Direct coupling of the interaction between laser,powder and molten pool was achieved with the finite volume method.The physical model was checked according to the experimental results.The temperature field and flow field of powder,temperature field and flow field of the molten pool were obtained by simulating Invar alloy laser cladding with different powder feeding rate and laser power.Finally,the interaction mechanism among of Invar alloy powder,and laser molten pool during laser cladding by analyzing the macro morphology,microstructure and microhardness of the orthogonal experiment results combining simulated settlement.On the basis of this study,the influence of different laser power,powder feeding rate and scanning speed on the size,dilution rate,microhardness and porosity of laser cladding coating for Invar alloy were studied.The results showed that Invar alloy can be repair(surface hardening)by laser cladding in the premise of not changing the material characteristic,getting the cladding structure which was similar to the base material on the microstructure and microhardness,and control the size of cladding structure and defects through the control of process parameters.This paper aimed at the laser cladding repairing(surface strengthening technology)for Invar alloy mold.With the method of combination of experiment and simulation,the influencing mechanism of different process parameters on the cladding structure size,dilution rate,microhardness and porosity was researched on the basis of the interaction mechanism of different phases of the cladding process to lay the foundation for the realization of laser cladding repairing(surface hardening)of Invar alloy mold.