【作者】 熊云；

【导师】 王勇；

【作者基本信息】 中国石油大学 ， 材料学， 2008， 硕士

【摘要】 催化装置的滑阀一般工作在700℃左右的高温环境下,受到高速的含催化剂固态颗粒气流的冲刷,由于工作环境恶劣,导轨、阀板等内部构件极易腐蚀磨损失效。通常采用热喷涂和堆焊技术强化和修复滑阀内部构件,存在着很大的局限性。本文采用5kW横流CO2激光器,在1Cr18Ni9Ti不锈钢表面分别制备了Stellite6钴基合金以及含有不同比例WC和适量Al的Stellite6/WC钴基金属陶瓷复合层。利用OM、SEM、XRD等手段分析了熔覆层的显微组织结构、相组成,观察了高温冲蚀后的表面形貌;采用电子探针线扫描技术,研究了结合区和熔覆层各合金元素的分布情况;对熔覆层的硬度、抗高温氧化和抗高温冲蚀性能进行了测试,并对高温氧化和冲蚀磨损机理进行了探讨。试验结果表明,激光熔覆层致密均匀,实现了与基体良好的冶金结合,无裂纹、气孔等缺陷。熔覆层的主要组成为γ-Co(面心立方)过饱和固溶体以及碳化物CoCx、Co6W6C、Cr23C6和WC1-x;显微组织为大体上垂直于界面生长的平面晶和胞状晶,向熔池中部过渡为多方向生长的树枝晶区,近表面为平行于激光扫描速度方向生长的细小枝晶区。熔覆层具有很高的硬度,约为基体的2-3倍,而且随WC加入量的增加表面硬度逐渐提高。在700℃高温条件下,钴基合金和添加10%WC(2%Al)钴基合金熔覆层的抗高温氧化性能均比基体优异,其氧化增重约为基体的一半。钴基合金熔覆层具有良好的抗高温氧化性能,在于Co能有效地促进Cr2O3、CoO?Cr2O3的形成,而这一氧化膜致密稳定,并且CoO与Cr2O3间较强的结合键增强了膜的致密性。添加10%WC(2%Al)使熔覆层中Co和Cr元素的含量在一定程度上有所降低,但为消除气孔而加入的Al可以形成一定数量的Al2O3膜,因此其氧化增重速度与钴基合金熔覆层大体相当。700℃、90°攻角下,钴基合金和添加10%WC(2%Al)的钴基合金熔覆层的抗高温冲蚀磨损性能均比基体优异,添加10%WC(2%Al)的熔覆层性能最好,钴基合金熔覆层次之。钴基合金熔覆层的冲蚀机制以犁削脱落为主,伴随挤压后的片屑剥落;添加10%WC(2%Al)的激光熔覆层以挤压后的片屑剥落为主。分析认为,对于钴基合金和添加10%WC(2%Al)熔覆层,由于致密保护膜的存在,有效地降低了底材金属受到的冲击力,使试样具有较低的冲蚀率。添加20%WC(2%Al)熔覆层,由于疏松的氧化膜在磨粒的冲蚀下大面积剥落,保护作用失效,故冲蚀率很高。在Stellite6钴基合金中添加10%WC(2%Al),采用适宜的激光加工工艺参数制备的钴基金属陶瓷复合层具有比Stellite6钴基合金熔覆层更为优异的性能,而且可以减少钴基合金的使用量,具有很大的工业应用价值,为激光熔覆钴基金属陶瓷在滑阀内部构件上的应用提供了理论依据。更多还原

【Abstract】 Slide valves of catalysis fitting were worked in high temperature (about 700℃) flue gas with catalyst particles. Guides and valve plate of which were usually failure in the severe enviroment. The internals were often strengthened or repaired by hot spraying or surfacing technology, which had a lot of advantags and some insurmountable disadvantages.5kW laser with CO2 flow transverse was used for cladding Stellite6/WC powder on 1Cr18Ni9Ti stainless steel surface. The appropriate selection of the process parameters can obtain defect-free fine micro-structures. By means of SEM, TEM and EDAX, the effect of cladding technology on the microstructures of the laser cladding coatings were studied.The result indicated that the microstructures of the laser cladding layers were fine and defect-free and good metallurgical bonding between the coating and the substrate was obtained. The results showed that microstructures of the coating consisted of plane, cellular and dendrite, and the coating has higher hardness which was about 2-3 times of the matrix. When adding appropriate amount of Al with low melting point into the Stellite6/WC powder, the porosities disappeared in argon protecting. The microstructure at the cladding layer bottom was the typical extension growth on plane basis, the morphology of grains changed from planar and cell to dendritic which was coarser. The microstructure at the top and middle was the regular pine-tree crystal and the microstructure at the top was the small pine-tree crystal, respectively. In the guarantee of the forming of the metallurgical combination between coating and substrate, increasing scanning speed or decreasing power density properly would profit the refinement of the coating structure. So the laser cladding process of Co-based composite metal ceramic can improve the performance of stainless steel. High-temperature oxidation tests were researched at 700℃. Oxidation test results at high temperature showed that the high-temperature oxidation resistances of the Stellite6 and the Stellite6 with 10%WC(2%Al) layers were better than the matrix.The erosion-corrosion wastage of coatings and the matrix at 700℃was researched with 90°impact angle. As compared with the matrix, the erosion-corrosion resistances at elevated temperature of Stellite6 and Stellite6 with 10%WC(2%Al) coatings were higher. Especially, the Stellite6 with 10%WC(2%Al) coating presents the best erosion-corrosion resistance.更多还原