NdFeB合金表面Ni-P镀层和激光熔凝层工艺与耐蚀性研究

【作者】 张能；

【导师】 谢发勤；

【作者基本信息】 西北工业大学 ， 材料学， 2004， 硕士

【摘要】 第三代稀土永磁合金NdFeB凭借它优异的磁特性、良好的机械加工性能和相对低廉的价格，被广泛应用于电机、仪器仪表、磁共振成像等领域。但NdFeB合金的化学稳定性差，在日常使用条件下容易发生氧化。并且当处于湿热的气氛中时会发生严重的电化学腐蚀，这都妨碍了它应用范围的扩大。 本文旨在通过表面化学镀Ni-P和激光熔凝，对NdFeB合金进行防腐保护。经过系统地研究NdFeB合金表面化学镀Ni-P的工艺，在合金表面得到了非晶的高磷Ni-P镀层。并借助对非晶Ni-P镀层的晶化热处理，获得了耐蚀性、耐磨性等综合性能优良的纳米级微晶镀层。在实验研究中，针对NdFeB合金的特点，深入地研究了化学镀Ni-P的机理，有目的性地设计了实验方案，确定了实验参数，反复实验不断修正。最终，优选出了在NdFeB合金表面化学镀Ni-P较佳的镀覆工艺。 另外，利用激光熔凝技术对NdFeB合金的表面进行了处理。通过对CO²激光器参数的优化，在NdFeB表面获得了微晶白亮层，白亮层的微结构为定向胞晶凝固组织。并从凝固理论上给出了获得定向胞晶凝固组织的条件，讨论了激光熔化区温度梯度G_TL、固液界面稳定因子G_TL／R和定向凝固、凝固界面胞晶生长之间的关系。 通过盐雾实验和极化曲线，比较了Ni-P非晶镀层和激光熔凝白亮层的耐蚀性，前者明显优于后者。原因是激光熔凝过程中产生了裂纹和气孔等缺陷。在针对NdFeB合金进行防腐保护的表面技术中，化学镀Ni-P是一种比较好的选择。更多还原

【Abstract】 NdFeB alloy, the third era permanent magnet, is widely used in electromotor industry and apparatus industry, etc. It has the advantage of distinguished magnetic properties, being machined easily and comparatively low price. But it is prone to be oxidated in common atmosphere, especially be heavily electrochemical eroded at humidity environment. Corrosion becomes the obstruction to broaden applications of NdFeB.In this thesis, anti-corrosion technology of NdFeB was investigated. Based on the thorough comprehension of the character of sintered NdFeB alloy, surface treatment technology was adopted to protect it against corrosion, including elecroless nickel plating and laser precipitated solidification.By ceaseless aimed experiments, the parameters of elecroless nickel plating were optimized, which led to non-crystal Ni-P coating on NdFeB being obtained. Furthermore, the effect of heat treatment of non-crystal Ni-P coating was studied. With the increase of heat temperature, the non-crystal Ni-P coating began to crystal, and it will entirely transform into micro crystal coating at a proper temperature. Finally, high quality anti-corrosion Ni-P coating was obtained on NdFeB’s surface, whose average grain size was at 10" m as well.What’s more, particular laser precipitated solidification processing was applied to quick melt NdFeB at high heat rate. According to rapid one-dimension conduct of heat by matrix, the melted surface of NdFeB quench to a directional solidification cystiform structure. So an anti-corrosion coating correlated with matrix tightly was made on NdFeB in such a way. The relationship between parameters of laser and the microstructure of laser precipitated solidification coating was discussed either.Compared between Ni-P coating and coating of laser precipitated solidification by corrosion tests, the results show Ni-P coating has excellent corrosion resistances than the latter in various aspects. The key reason causing the difference between those two coating is some micro crevices occurred on NdFeB when utilizing laser surface treatment. In short, elecroless nickel plating is the better choice to prevent NdFeB from corrosion.更多还原