激光熔覆铁基合金梯度涂层的组织性能及应用

Microstructure,Properties and Applications of Laser Cladding Fe-based Alloy Gradient Coatings

辊轴是高速线材轧机的重要部件,轴颈表面易磨损,为了延长辊轴的服役寿命,可以对磨损后的轴颈表面进行激光熔覆再制造。但是辊轴表面硬度较高,激光熔覆高硬度粉末易产生大量裂纹,而梯度熔覆则可在一定程度上解决此问题。前人关于梯度熔覆的研究多集中于理论及工艺阶段,鲜见应用于实际修复中。本工作利用4 kW光纤激光器在辊轴材料45^#钢基体表面逐层熔覆了Fe1合金粉末和Fe5合金粉末,前者为过渡层,后者为强化层。利用渗透探伤检测了涂层表面的缺陷情况,运用OM、SEM和EDS等手段分析了熔覆层的显微组织及元素含量变化,采用XRD技术分别分析了各层的物相组成,利用显微硬度计测试了涂层的显微硬度。结果表明,梯度熔覆层表面形貌良好,无宏观裂纹,内部组织致密无缺陷。各层之间呈现良好的冶金结合,过渡层与强化层结合处的晶粒出现了细化,上层晶粒比下层晶粒细小。XRD分析表明,过渡层主要由奥氏体组成,强化层由奥氏体和马氏体两相组成。熔覆层硬度呈典型的梯度分布,强化层平均硬度为566.12HV 0.2,达到了辊轴的硬度要求,过渡层平均硬度为385.98HV 0.2,起到了很好的缓冲作用。最后,推导出了激光熔覆时机械臂与轴颈转速之间的关系模型,取得了较好的修复效果。

Roller shaft is an important part of high speed wire mill, and the shaft journal is easy to wear. In order to extend the service life of the roller shaft, the worn shaft journal can be remanufactured by laser cladding. However, the hardness of the roller shaft is high. And there will be large number of cracks when laser cladding high hardness powder. But gradient cladding can be used to solve this problem. Previous researches of gradient cladding mainly focus on theory and technology, but few works touch the practical repairing. In this paper, Fe1 alloy powder and Fe5 alloy powder were coated on the surface of 45^# steel by 4 kW fiber laser. The former was transition la-yer, and the latter was strengthened layer. The defects on the surface of the coating were detected by penetrant inspection. Furthermore, the microstructure and element content of the coating were analyzed by means of OM, SEM and EDS. And the phase composition of each layer was investigated by XRD. Meanwhile, the microhardness of the coating was measured by microhardness tester. The results showed that the sample presented good surface morphologies. No macroscopic cracks formed on its surface. And the coating was compact and free of defects. Moreover, metallurgical combinations were achieved between the layers. And the grains at the junction of the transition layer and the strengthened layer were refined. In general, the upper grains are smaller than the lower ones. XRD analysis showed that the transition layer was mainly composed of austenite and the reinforcement layer was made up of austenite and martensite. The hardness of the cladding layer presented a typical gradient distribution. And the average hardness of the strengthened layer was 566.12HV 0.2 , which met the hardness requirement of the mill roll shaft. Furthermore, the average hardness of the transition layer was 385.98HV 0.2 , which played a good role in buffering. The relationship between the speed of mechanical arm and the rotating speed of journal during laser cladding were deduced. Meanwhile, a good repair effect has been achieved.