喷距对低温超音速火焰喷涂WC-10Co4Cr涂层性能的影响

Influence of different spray distance on properties of WC-10Co4Cr coating by low temperature high velocity oxygen flame

以粒度为5--15μm的WC-10Co4Cr为热喷涂粉末,采用低温超音速火焰喷涂（LT-HVOF）技术制备WC-10Co4Cr涂层,并利用粒子收集技术研究喷距对涂层显微结构和性能的影响。采用扫描电子显微镜（SEM）、粗糙度测试仪和显微硬度仪分别对涂层的显微结构、粗糙度、硬度和韧性进行测试分析。实验结果表明：WC-10Co4Cr涂层的显微硬度（HV0.3）和致密度随着喷距的增大而降低,分别由喷距100 mm时的1 484.19和0.5%降低至喷距310 mm时的930.50和2.2%;涂层的结构和性能与粉末在焰流中的熔融状态和飞行速度相关,喷距在100~190 mm范围内粉末呈未熔化状态,220~310 mm范围内呈微熔化状态,粉末的飞行速度随喷距的增加呈下降趋势;粉末呈微熔化状态时断裂韧性与HVOF涂层相当且明显高于粉末呈未熔化状态的断裂韧性;优化的喷涂距离为220~280 mm,该段距离内可以获得涂层粗糙度约为2μm、孔隙率小于1%、显微硬度大于1 018（HV0.3）、断裂韧性大于3.323 1 MPa·m1/2的涂层。

WC-10Co4Cr coatings were prepared via LT-HVOF process with 5-15 tam WC-10Co4Cr powder as feedstock, and the effects of spray distance on coating microstructure and properties were discussed by means of splat analysis. Mierostructure, surface roughness, micro-hardness and fracture toughness for WC-10Co4Cr coatings were characterized by SEM, roughness tester and micro-hardness tester. The results show that micro-hardness and density for WC-10Co4Cr coating decrease with the increase of spraying distance. When spray distance is 100 mm, the microhardness （HV0.3） and porosity are 1 484.19, 0.5% respectively. And when spray distance increases to 310 ram, the microhardness and porosity are 930.50, 2.2% correspondingly. Coating structure and properties for WC-10Co4Cr coating are related to the molten state and velocity of particles in LT-HVOF plume. The powders is in un-melted state when spray distance ranges from 100 to 190 mm. And the powders change into light-melted state when spray distance ranges from 220 mm to 310 ram. The velocity of particle decreases with the increase of spray distance. The fracture toughness of coating prepared by LT-HVOF is similar to that of the coating fabricated by HVOF with light-melted powders, which is obviously higher than the coating by LT-HVOF with un-melted powders. WC-10Co4Cr coating sprayed at the spraying distance of 220-280 mm owns surface roughness about 2 μm, porosity is as low as 1%, micro-hardness （HV0.3） over 1 018, and fracture toughness over 3.323 1 MPa.m1/2.