激光熔覆Cr_3C_2/Co基合金复合涂层组织与摩擦磨损性能研究

Microstructure and Wear Performance of Laser Cladding Cr_3C_2/Co Alloy Composite Coating

在低碳钢表面激光熔覆制备了添加质量分数40%Cr3C2的钴基合金复合涂层(Cr3C2/Co),研究了激光熔覆Cr3C2/Co涂层的显微组织、相结构、显微硬度及其摩擦磨损性能,并与激光熔覆钴基合金涂层(Co60)进行了相同工艺条件下的对比试验.结果表明,激光熔覆Co60涂层以亚共晶方式结晶,涂层组织主要由大量初生γ-Co枝晶固溶体及其间的共晶组织γ-Co+Cr23C6组成;激光熔覆Cr3C2/Co涂层以过共晶方式结晶,组织主要由未熔Cr3C2粒子、大量杆状和块状的富Cr碳化物(M7C3及M23C6型碳化物)以及其间的细小枝晶与共晶组织组成.添加Cr3C2改变了Co60涂层的凝固特征,未熔Cr3C2粒子起到了非自发形核作用,在其周围形成了许多富Cr碳化物,细化了涂层枝晶组织.激光熔覆Cr3C2/Co涂层的显微硬度及其耐磨性比Co60涂层明显提高.Co60涂层主要磨损机理为脆性剥落和犁削,Cr3C2/Co涂层的磨损机理主要为轻微犁削.

Laser cladding Cobalt-based alloy coating （Co60） and Cobalt-based composite coating doped with 40% Cr3C2 particles （Cr3C2/Co） were prepared on the low carbon steel substrate by 5 kW CO2 laser. Microstructures of the coatings were analyzed by optical microscopy and scanning electron microscopy, and the phase composition and elemental composition of the coatings were determined by X-ray diffraction and energy dispersive X-ray analysis. Moreover, microhardness of the coatings were measured, and friction and wear behaviors of the coatings sliding against H13 alloy with laser cladding WC/Ni coating in a block-on-ring configuration were evaluated on an MM-200 test rig. Worn surface morphologies of the coatings were also observed by scanning electron microscopy. It was found that the Co60 coating was crystallized in hypo-eutectic crystal mode, and consisted of many T-Co dendritic solid solution and eutectic structure （T-Co and Cr23C6） between the dendrites. Cr3C2/Co coating was crystallized in hyper-eutectic crystal mode and consisted of undissolved Cr3C2 particles, rich-chromium carbides （M7C3 and M23 C6 ） with different shapes and fine dendrite and eutectic structure between the carbides. Addition of Cr3C2 particles altered the solidification characteristic of the Co60 coating. Undissolved Cr3C2 particles played a role in non-spontaneous nucleation, and rich-chromium carbides were formed around Cr3C2 particles, and dendrite microstructure was refined. Cr3C2/Co coatings has higher micro-hardness and it exhibited better wear resistance than that of the Co60 coatings. Wear of the Co60 coating was dominated by brittle spalling and ploughing, while the Cr3C2/Co coatings was dominated by ploughing.