The Structure And Properties Of Laser Alloying Layers Coated With Sub-micron Ceramics

In this study, Nd: CW CO₂ laser were used in LSA experiment on ductile iron with new coating materials. Appropriate process parameters and influencing factors were discussed, and new LSA coatings were developed to get an ideal reinforcing result. The microstructures of laser alloyed coatings were detected by SEM, EDS,XRD and TEM. The microhardness and wear-resistance of the coatings were also investigated.Using HG0₃ paints for laser alloying experiments on ductile iron, through changing laser scanning speed to study the influence of laser scanning spped upon microstructure and properties of alloyed layers. The results show that, with the laser scanning speed increased, the microstructure of alloyed layers gradually refined, the spacing between dendrites decreased, so the hardness and wear resisitance of alloyed layers also improved. In this experimental condition, when the laser power P = 3kw, spot diameter D = 5mm, the better laser scanning speed is 1000 mm / min, under this process parameters , the laser alloying layer can obtained better performance.Using HG0₃, HG0₁, TH₂A, AY paints for laser alloying experiments under the same process parameters, alloyed layers of HG series and TH₂A appear to be with good surface smoothness, but alloyed layer of AY with bad surfce smoothness. The hardness and wear resistance of alloyed layers of HG series are better than that of TH2A and AY. The friction coefficient and abrasion loss of alloyed layer of HG03 is the smallest , HG03 paint is created on the basis of HG01, the alloyed layer of HG03 showed excellent friction and wear properties, the wear rate was only one-nineth of ductile cast iron.The addition of new type carbides obviously improved the microhardness and wear resisitance of alloyed layers. The abrasion loss of the alloyed layer which alloying paints with ceramic hard phase content of 0% was significantly greater than alloyed layers which alloying paints with ceramic hard phase content of 20%, 30%, 40%. But with the ceramic hard phase content increased, the abrasion loss did not change significantly, the wear rates of the alloyed layers which alloying paints with ceramic hard phase content of 20%, 30%, 40% are almost one-tenth of ductile cast iron.The new coatings of HG series are applied in Shuicheng steel enterprise and Tangshan machining station. Treated with HG03, the service lives of primary roller and medium roller are both enhanced 120%. In Tangshan machining station, LSA was processed on H-shape steel with HG03 and the service life of finish roller is enhanced 110%.