Study on the detailed micro-structural characteristics of Laser Cladding in terms of porosity distribution, dilution of alloying elements and stresses in the laser melted zone using focused ion beam tomography

在过去的1-20年里，人们一直在使用激光进行表面改性。已经有几个出版物研究了不同的表面性质改性。这主要包括腐蚀、氧化、磨损、摩擦和硬度。从这些研究中获得的有用信息也有助于各行业采用这项技术作为替代工艺。例如，激光淬火已被许多行业采用，以取代传统的渗碳、离子渗氮和离子渗氮。激光合金化和熔覆已经扩展到几个复杂和昂贵的部件的修复，如船舶部件、曲轴和航空发动机涡轮叶片。我们一直在进行激光表面合金化和熔覆方面的工作，并在钢、不锈钢、钛等表面的腐蚀、氧化和磨损行为方面做出了贡献。详细的研究证实了表面改性是根据氧化和腐蚀的机理进行的。我们也利用这一技术制作了激光成形的近净形状零件，但感觉激光熔化区或熔覆层内的微观机制仍不清楚。无论是激光处理致密化的作用，还是显微组织(非晶态或微晶态)的变化，以及合金元素稀释的作用还不是很清楚。在我们最近的互动和我在萨尔兰大学担任功能材料教授(F·穆克利希教授)的短暂停留期间，我发现了对这类研究的浓厚兴趣。该研究所拥有基本的激光设备，并在使用聚焦离子束断层扫描和X射线衍射术等尖端技术和其他表面分析工具进行微观结构评估方面能力很强。因此，建议在这一领域共同努力--利用我们在激光合金化和熔覆方面的强大专业知识以及他们在微观结构评估方面的强大专业知识。

Surface modifications by laser are being practiced now for the last 1-2 decades. There have been several publications, where different surface property modifications have been studied. This includes mainly, corrosion, oxidation, wear, friction and hardness. Useful information obtained from these siudies has also helped in adaption of this technique by various industries, as an alternative process. For example, laser hardening has been adopted by many industries in place of conventional case-carburizing, ion-nitriding and plasma nitriding. Laser alloying and cladding have been extended to the repair of several complicated and expensive components such as ship parts, crank shafts and aero-engine turbine blades. We have been carrying oul work on laser surface alloying and cladding and contributed towards the modification of surfaces, such as steel, stainless steels, titanium in terms of their corrosion, oxidation and wear behavior. Detailed studies confirm the surface modification as per the mechanism of oxidation and corrosion. We have also used this technique to fabricate near-net shaped components using laser forming.It is however, felt that the micro-mechanisms within the laser melted zone or cladding are still not clear. Whether it is the role of densification due to laser treatment or it is the change in microstructure (amorphous or micro-crystalline) and also the role of dilution of the alloying elements is not very clear. During our recent interactions and my short stay at the chair of functional materials (Prof. Dr. F. Mücklich) at Saarland University, I found a dedicated interest towards this kind of study. The instituie has basic laser facilities and is very strong in micro-structural evaluations using sophisticated techniques such as focused ion beam tomography and XRD and other surface analytical tools. It was therefore proposed to work together on this field - with our strong expertise in laser alloying and cladding and their strong expertise in micro-structural evaluations.