激光熔覆碳化物/钴基涂层的高温氧化性能研究

High Temperature Oxidation Resistance of Carbide/Cobalt Based Coatings by Laser Cladding

为了提高因瓦合金的高温抗氧化性能,课题组利用光纤激光器以添加不同成分纳米粒度的碳化物和钴的复合粉末作为熔覆材料,在因瓦合金表面制备2种不同复合涂层。通过扫描电子显微镜、能谱仪对熔覆层的微观组织及物相组成进行表征;利用箱式电阻炉在800℃温度下循环35 h对母材和熔覆层进行高温氧化实验,对氧化后的母材及涂层利用X射线衍射仪、扫描电子显微镜和能谱仪研究其氧化层成分。研究结果表明:熔覆层与母材实现良好的冶金结合,无气孔等明显缺陷;添加Cr3C2的涂层(C1)主要由胞状晶、柱状晶等组成,而添加VC的涂层(C2)包含更多的鱼骨状枝晶和羽毛状枝晶,并且C1的涂层组织比C2更为细小均匀,界面也更为明显。2种复合涂层的高温抗氧化性相较于母材都有了极大的提升,尤其是试样C1的内氧化层厚度相对母材明显减小,它的内、外氧化层厚度比C2也更小。Cr的加入有利于在界面处形成致密的氧化层Cr2O3,阻碍氧向基体的扩散,极大地提高了因瓦合金的高温抗氧化性。

In order to improve the high temperature oxidation resistance of invar alloy,two different kinds of composite coatings were prepared on invar alloy surface by using fiber laser with different combination of nano-sized carbide and cobalt powder as cladding materials.The microstructure and phase composition of the cladding layer were characterized by SEM and EDS,and the high temperature oxidation experiments of the base metal and the cladding layer were carried out at 800℃for 35 h using a box-type resistance furnace.The oxide layer components of invar alloy and coatings were characterized by XRD,SEM and EDS respectively.The results show that the cladding layers have good metallurgical bonding with the base metal and no obvious defects such as pore.The coating with Cr3C2 is mainly composed of cellular and columnar crystals,while the coating with VC contains more fishbone dendrites and feather dendrites.The coating structure of coating added with Cr3C2 is more fine and uniform than that of VC,and the interface is more obvious.Compared with the invar alloy,the high temperature oxidation resistance of the two composite coatings has been greatly improved,especially the sample added with Cr3C2.The thickness of the internal oxide layer of the coatings is obviously smaller than that of the base metal,and the thickness of both internal oxide layer and external oxide layer of the coating added with Cr3C2 is also smaller than that of the coating with VC.The addition of Cr is beneficial to the formation of a dense oxide layer Cr2O3 at the interface,which hinders the diffusion of oxygen to the matrix and greatly improves the high temperature oxidation resistance of invar alloy.