激光硬化基体对镀铬层组织和结合的影响

Influence of Laser Hardening Substrate on Microstructure and Bonding of Electroplating Chromium Coating

采用激光相变硬化的方法在电镀前对基体表层预先进行处理,以改善镀层与基体的结合强度,提高其承载能力。借助扫描电镜(SEM)分析镀铬层的组织和界面,对镀层、相变硬化区和基体的硬度变化进行分析,对镀层抗高温烧蚀能力进行测试。结果表明,基体经激光相变硬化处理后,既可以促进镀层外延生长,又可以在镀层和基体之间实现硬度的梯度过渡,从而可以改善结合,缓解应力,提高承载能力,镀层的抗剥落能力和使用寿命得到显著提高。激光相变硬化得到细小的淬火马氏体,位错密度显著增加,表面活性增强,是促进镀层外延生长的主要原因。

Under the severe condition of high temperature and heavy load, electroplating chromium coating is extremely easy of premature spallation so that the service lifetime of components is dramatically reduced. Laser phase transformation hardening was used to pretreat the superficial layer of substrate before electroplating in order to improve bonding strength between the electroplating coating and the substrate and enhance the load endurance. The microstructure and interface of electroplating chromium coating were analyzed by scanning electron microscopy （SEM）. The hardness variation of electroplating coating, phase transformation hardening zone, and substrate were analyzed. The ability resisting high temperature ablation was measured. The results showed that laser phase transformation hardening on the substrate could not only effectively promote the epitaxial growth of electroplating chromium coating, but also realize the gradient variation of the hardness from electroplating chromium coating to substrate. Consequently, the bonding was improved, the stress was alleviated, and the load endurance was enhanced. So the spallation resistance and the service lifetime of electroplating chromium coating were evidently enhanced. It was a main reason for the epitaxial growth of electroplating chromium coating that the refined quenching martensite was obtained, the dislocation density was evidently increased, and the surface activity was increased by laser phase transformation hardening.