WC/Co-Cr复合涂层激光熔覆工艺优化与表征

Process Optimization for Laser Cladding Operation of WC / Co-Cr and Its Characterization

目的优化复合涂层的熔覆工艺参数,获得综合性能优异的WC/Co-Cr复合涂层。揭示复合涂层的相结构、组织构成及界面特性。方法采用YAG固体激光器在45钢上熔覆WC/Co-Cr复合涂层,以电流、频率、脉宽、扫描速度作为变量,设计四因素三水平正交试验,对熔覆效果进行评分,获得最佳参数组合。通过XRD,XRF,OM,EMPA等分析手段对复合涂层进行表征。结果电流对熔覆效果的影响最显著,其次为频率,再次之为激光扫描速度,脉宽的影响显著性最小。随WC含量增加,激光脉宽应增加,而激光扫描速度应该适当减小。复合涂层的显微组织形貌主要为固溶体上分布着共晶组织以及金属间化合物、碳化物,还有由成分过冷导致的胞状组织。复合涂层的物相组成包括Cr Co,WC,Cr7C3,Cr3C2等。结论采用WC质量分数10%的熔覆粉末,最佳熔覆工艺组合为:电流380 A,频率40 Hz,脉宽1 ms,扫描速度8 mm/s。采用WC质量分数20%的熔覆粉末,最佳熔覆工艺组合为:电流380 A,频率40 Hz,脉宽1.5 ms,扫描速度6 mm/s。复合涂层与混合粉末相比,相组成发生了变化,有金属间化合物、碳化物等强化相产生,且元素在界面的分布呈现过渡式变化,这对涂层的综合性能有利。

Objective To optimize the laser cladding operation of excellent WC/Co-Cr composite coating, and to figure out the phase, microstructure and distribution of chemical elements of composite coating. Methods YAG Laser was utilized to carry out WC/Co-Cr composite coating on 45 carbon steel. Orthogonal experiments were performed which contains four factors at three differ-ent levels. Four factors were current, frequency, pulse width and scanning speed. Several characterization techniques, such as XRD, XRF, OM and EMPA, were employed to characterize the phases, structure and interface of WC/Co-Cr Composite coating. Results The influence of the Electric current to the cladding effect was the most significant, followed with the frequency, the laser scanning speed, and then the Pulse-width. Laser pulse width should be increased, conversely, laser scanning speed should be re-duced with the increase of WC content. The microstructure of composite coating are eutectic, carbide and intermetallic distributingon solid solution. In addition, cell structure caused by composition undercooling was observed on the micro-graph. The phases of coating are CrCo, WC, Cr7 C3 and Cr3 C2 . Conclusion Current is the main influence factor for Laser cladding. Two optimum tech-nological parameters combinations are respectively 380 A, 40 Hz, 1 ms, 8 mm/s for coating which contains 10wt%WC, and 380 A, 40 Hz, 1. 5 ms, 6 mm/s for coating which contains 20wt%WC. Several new phases were observed after laser cladding, such as carbide and intermetallic. The distribution of chemical element along with the cross section are transitional. Our results suggest there is a transition region between the coating and substrate.