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热喷涂技术:2021,13(1):1-12
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大气等离子喷涂工艺参数与粉末成分对 NiCrCuB 涂层成分、 组织结构及性能的影响
(西安交通大学 材料科学与工程学院金属材料强度国家重点实验室)
Influences of Spray Parameters and Powder Composition on the Coating Composition, Microstructure and Properties during Atmospheric Plasma Spraying of NiCrCuB
(State Key Laboratory for Strength of Metal Materials, School of Materials Science and Engineering Xi'an Jiaotong Univeristy)
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中文摘要: 针对如何降低 NiCrCu 涂层氧化物含量以改善涂层内粒子层间结合的问题, 本研究设计了含 B 的 NiCrCu 粉末, 以期通过 B 在高温熔滴飞行中的牺牲氧化并蒸发去除氧化物机制, 在大气等离子喷涂条件下获得无氧化 物的熔滴制备高致密的金属涂层。 为此, 采用粒度 30~50 μm 的 NiCrCu1.5B 和 NiCrCu4B 喷涂粉末, 研究了粉末 成分与大气等离子喷涂工艺参数对涂层成分、 组织结构及力学性能的影响。 结果表明, 等离子喷涂制备 NiCrCuB 涂层时, 基体在等离子射流中的受热程度对涂层氧化物含量影响显著, 随喷枪移动速率和喷涂距离的增加, 等离 子射流对基体加热效果减弱, 涂层氧化物含量显著降低。 采用 NiCrCu4B 粉末制备涂层时, 涂层氧含量随喷涂距 离的增加而显著减小, 这与迄今等离子喷涂金属合金涂层的氧含量随距离的增加而增加的规律完全相反, 该结果 表明 NiCrCuB 熔融粒子中的硼在粒子飞行中具有优先氧化的去氧化效应。 采用含硼量为 1.2 wt.% 的 NiCrCu1.5B 粉末喷涂涂层时, 涂层内氧元素含量呈先降低后增加趋势, 表明 B 含量低于约 0.6 wt.% 的临界值时, 无法实现 完全的氧化保护, 致使其他元素随飞行距离的增加逐步氧化所致。 针对等离子喷涂中金属熔滴飞行中的氧化与碰 撞基体沉积后的氧化两种机制, 采用较高 B 含量粒子可使飞行中氧化得到抑制, 通过强化熔滴沉积后的冷却过程, 可显著降低涂层氧含量, 达到最低氧含量值, 约 0.6 wt.%。 研究表明涂层的结合强度约为 40MPa, 受喷涂参数的 影响有限。 涂层中的 B 以硼化物弥散分布使得涂层的硬度显著增加, 当 B 含量从 0.2 wt.% 增加至 3.2 wt.% 时, 涂层的硬度呈线性相关, 从 280HV0.3 增加至 700HV0.3。
Abstract:The oxidation during plasma spraying of metal coatings in the ambient atmosphere always occurs. The resultant oxide inclusion not only reduces the wettability of molten droplets to splat surface and subsequently inhibits the lamellar bonding formation, but also degrades the performance of the coatings. It is still great challenge to effectively reduce the oxide contents in atmospheric plasma sprayed metal coatings by exploring novel approaches. Accordingly, we revently proposed a novel approach to achieve oxide-free molten metal droplets in atmospheric plasma spraying by utilizing sacrificial oxidation of boron in the in-flight molten droplet following by subsequent evaporation for high performance metal coating deposition. Therefore, in this study, boron containing NiCrCu spray powders were designed to examine the effect of powder composition and spray parameters on the oxide inclusion in the NiCrCu coatings and to clarify the sacrifical oxidation effect of boron during in-flight of molten droplet. Two powders with nominal compositions of NiCrCu1.5B and NiCrCu4B were used for atmospheric plasma spraying (APS) in a particle size range of 30~50 μm. The in-flight particle temperature during plasma spraying was measured by commercial particle velocity and temperature diagnosis system DPV-2000. The microstructure of the coating was characterized by scanning electron microscopy and X-ray diffraction. The contents of oxygen and boron in the coating were measured by chemical approach using Nitrogen and Oxygen Determinator and Ion Coupled Plasma Mass Spectropy, respectively. The porosity of the coatings was estimated by image analyzing. The microVickers hardness and adhesive strength of the coatings were measured. The measurement of spraying molten particle temperature yielded the values higher than 2000℃ , which fulfilled the requirement to evaporate boron oxide. The results showed that the porosity of the coatings decreased with the increase of the arc power and the oxygen content in the coatings decreased with the increase of the torch traverse speed. However, the change of the oxygen content in the NiCrCu4B coatings plasma-sprayed with higher boron content in spray powder against the spray distance presented the trend that always decreased with the increase of the spray distance. This trend was opposite to those observed for thermal spraying of metal coatings. Taking the fact that the boron content in the coating always decreased with the increase of spray distance, the results confirmed that the oxidation of boron and subsequently the evaporation continuously occurred and the inflight oxidation of alloying elements was suppressed by the preferential sacrificial oxidation of boron in the molten droplets. Thus, the oxide inclusion in the NiCrCu4B coatings was mainly introduced by post-deposition oxidation. On the other hand, the results showed that the oxygen content in the NiCrCu1.5B coatings decreased with the increase of the spray distance up to spray distance of 110 mm and then turned to increase with the further increase of the spray distance. Taking account of boron content in the in-flight NiCrCu particle, it could be concluded that there existed a critical boron content of about 0.6 wt.% in the in-flight particle below which the boron could not provide sufficient protection of other alloying elements from oxidation. When the oxide inclusion was mainly resulted from post-deposition oxidation, the oxygen content in the coating was dependent on cooling condition of coating during deposition. It was confirmed that the oxygen content in the NiCrCu4B coating samples was significantly reduced through enhancing the cooling effect from the back of the substrate. As a result, NiCrCuB coating with an oxygen content of 0.6 wt.% was deposited. The measurement yielded the adhesive strength of about 40 MPa for NiCrCu coating which was influenced little by spray conditions. It was also found that the boron content changed with spray conditions which influenced the consume of boron during in-flight. The residual boron was present in the coating as dispersed borides by which the NiCrCu coating is strengthened. As a result, it was found that with the increase of boron content in the coating from 0.2 wt.% to 3.5 wt.% the hardness of NiCrCu coating was increased linearly from 280 HV0.3 to 700 HV0.3.
文章编号:     中图分类号:TG174.4    文献标志码:
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引用文本:
孙浩,董昕远,任媛,雒晓涛,李成新,Mahrukh M.,朱永胜,李长久.大气等离子喷涂工艺参数与粉末成分对 NiCrCuB 涂层成分、 组织结构及性能的影响[J].热喷涂技术,2021,13(1):1-12.
Sun Hao,Dong Xinyuan,RenYuan,Luo Xiaotao,Li Chengxin,Mahrukh M.,ZhuYongsheng,Li Changjiu.Influences of Spray Parameters and Powder Composition on the Coating Composition, Microstructure and Properties during Atmospheric Plasma Spraying of NiCrCuB[J].Thermal Spray Technology,202113(1):1-12.

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