预热温度对灰铸铁表面激光熔覆镍基涂层组织与性能的影响

Effect of Preheating Temperature on Microstructure and Property of Laser Clad Ni-based Alloy Coating on Gray Cast Iron Substrate

采用CO2激光器在HT250基体上分别以不同预热温度制备NiCuFeBSi合金熔覆层,研究基体预热温度对白口组织控制、结合界面元素分布及抗拉强度的影响。结果表明:提高预热温度,有利于降低半熔化区白口化趋势,白口组织呈断续分布,但也导致熔覆层稀释率增大,更多基体Si,P杂质元素稀释进入熔池形成杂质相。拉伸实验表明:熔覆层抗拉强度远大于HT250,熔覆层断裂机制为解理与准解理混合型断裂。观察发现NiCuFeBSi合金激光熔覆层凝固后晶粒内部存在大量位错线并交叉缠结形成亚结构,进一步细化了晶粒,有利于提高熔覆层的强度与性能。最终获得NiCuFeBSi合金熔覆层在HT250基体上的最佳温度为室温30℃。

NiCuFeBSi alloy coatings were fabricated with CO2 laser on gray cast iron substrate HT250 at different preheating temperatures. The effect of preheating temperature on microstructure, elements distribution and tensile strength was investigated. Results show that the chill structures in the semi-molten zone are controlled and distributed discontinuously with increasing of preheating temperatures. Coating dilution rates increase as preheating temperatures increase, which induces the diffusion of more Si, P elements into molten pool and the formation of harmful impurities in the coatings. The tensile tests suggest the strength of NiCuFeBSi coating is superior to HT250, while the butt sample strength is the lowest of all. And the failure types consist of cleavage and quasi-cleavage fractures. Mass of dislocations are observed in the grains after solidification of NiCuFeBSi coating. The tangle- ment between dislocations forms the substructure. Therefore, the grain is further refined, which is beneficial for enhancing the coatings strength. Eventually, the best preheating temperature for laser NiCuFeBSi alloy coating on the substrate of HT250 is considered as 30℃.