| At present,the surface coating technology of important parts mainly includes some traditional methods such as thermal spraying,vapor deposition,and electroplating.Most of them have disadvantages such as weak bonding with the substrate,easy fall-off,and large environmental pollution.Laser surface cladding is an emerging advanced surface modification technology,but its efficiency is low.Recently,high-speed laser cladding technology has emerged,which can improve the surface coating preparation efficiency by 2 to 5 times.In this study,a self-developed hollow laser light internal powder cladding nozzle was used to cladding a high-performance alloy coating on the surface of a widely used 304 stainless steel substrate instead of the traditional surface modification technology.This paper establishes a theoretical model of the optical path,analyzes the spot diameter and the spot energy distribution at different defocus amounts;establishes a laser power attenuation model,and obtains that the laser is blocked by metal powder particles at different powder feed rates during positive defocus laser cladding The temperature rise value of the laser power passing through the powder on the surface of the substrate was calculated by ANSYS simulation.The powder temperature rise model was established to study the temperature rise value of the powder particles after passing through the laser beam.It serves as the theoretical basis for high-speed cladding and rapid forming of hollow laser internal powder feed.This paper conducts single factor experiments and orthogonal experiments to optimize the best process parameters,namely:power 1850W,speed 24m/min,defocus amount+2mm,powder feed rate 16.8g/min,overlap rate 80%.Under this optimal process parameter,a high-quality cladding coating with uniform and full,crack-free pores,good metallurgical bonding with the substrate,and flat surface is obtained.The thickness of the coating is 285.71 ?m,the efficiency is 0.51m2/h,and the surface is rough The degree is 6.15?m.From a micro perspective,the phase composition and microstructure characteristics of the cladding layer are analyzed.The cladding layer contains more Fe-Cr solid solutions,(Fe,Ni)solid solutions,and Ni-Cr-Fe than traditional laser cladding layers The solid solution and Fe23(C,B)6 compounds indicate that the high-speed cladding process can promote alloying.The presence of Fe-Cr solid solution helps to improve the friction and corrosion resistance of the coating.Because of the high-speed laser cladding process,the scanning speed is fast,and the liquid metal has a greater degree of subcooling during solidification,which makes the overall composition of the cladding layer a more fine and uniform dendrite composition,indicating that the high-speed cladding process can promote crystal The effect of grain refinement.The microhardness of the coating is further enhanced.The hardness of the cladding layer ranges from 677HV to 515HV,which is 2 to 2.7 times the microhardness of the 304 stainless steel substrate(247HV).At room temperature,the friction and wear properties and corrosion resistance between the Fe55 alloy coating and the 304 stainless steel substrate were analyzed.The friction coefficient and wear rate of the 304 stainless steel substrate and the Fe55 alloy coating were 0.53 and 2.486×10-5(mm3/Nm),0.35,1.322×10-5(mm3/Nm),indicating that the wear resistance of Fe55 alloy coating is better than that of 304 stainless steel substrate.The results of electrochemical corrosion experiments show that the corrosion potential of the 304 stainless steel substrate is-0.004V,which is 0.1505V lower than that of the Fe55 alloy coating,while the corrosion current density of the 304 stainless steel substrate is 7.62×10-7A·cm-2,which is about Fe55 alloy coating.Corrosion current density is 6 times 1.39×10-7A·cm-2,which indicates that Fe55 alloy coating has better corrosion resistance than 304 stainless steel substrate.The results of the three-point bending experiment show that laser high-speed cladding of Fe55 alloy coating can not only enhance the bending and deformation resistance of the substrate,but also under the condition of large deformation,there is no peeling and peeling between the coating and the substrate,indicating that the coating The layer is well combined with the substrate.This study shows that high-speed cladding by laser internal powder feeding has high coating efficiency,good microstructure properties,good interface metallurgy,controllable thickness,and environmental protection without pollution. |
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