B 元素对大气等离子喷涂 CuNi 涂层微观组织及微动磨损性能的影响

Atmospheric plasma-sprayed (APS) CuNiIn coatings have been widely used for fretting wear protection in aerospace and automotive components due to their excellent anti-fretting performance. However, the toxicity of indium (In) and its limited supply have prompted the exploration of alternative materials. In addition, the fretting wear performance of the APS CuNiIn coatings is compromised by the weak inter-splats bonding quality, which can be attributed to high content of oxide inclusions resulting from the in-flight oxidation of metal droplets during the spray process. In this study, APS CuNi4B coatings were investigated as a potential replacement for conventional CuNiIn coatings in fretting wear applications. It was expected that the incorporation of B into CuNi powder would suppress the in-flight oxidation of CuNi molten droplets during APS, thereby improving the bonding quality of the deposited CuNi4B coatings. The effect of B addition on the microstructure of the CuNi coatings was analyzed through SEM. Fretting wear tests were performed to assess the effect of B addition on the fretting wear resistance of coatings. Research findings demonstrate that the addition of B effectively suppresses the in-flight oxidation of CuNi droplets during atmospheric plasma spraying, enabling the deposition of CuNi4B coatings with dense microstructure and excellent intersplat bonding quality. The residual boron element in the CuNi coating can significantly enhance its microhardness. The traditional atmospheric plasma-sprayed CuNiIn coating exhibits a microhardness of 171HV0.2, whereas the CuNi4B coating demonstrates a markedly higher hardness of 512HV0.2. Fretting wear test results show that the CuNiB coating exhibits a friction coefficient evolution trend similar to that of the CuNiIn coating throughout the cyclic loading process. However, the friction coefficient of the CuNi4B coating is significantly lower than that of both the CuNiIn coating and the bulk CuNi material. The average friction coefficient of the CuNi4B coating is approximately 0.65, representing a 34% reduction relative to the CuNiIn coating. After 10 000 fretting cycles, the wear volume of the CuNiIn coating reaches 6 μm³, with wear mechanisms characterized by adhesive wear, oxidative wear, and inter-splat fatigue delamination. In contrast, the CuNi4B coating exhibits a significantly reduced wear volume of only 0.83 μm³, dominated by mild adhesive wear accompanied by limited oxidative wear. The volume loss of the CuNi4B coating at 10 000 fretting wear cycles is approximately one-sixth of that of the conventional APS CuNiIn coating. The improvement in the fretting wear resistance of the CuNi4B coating is primarily attributed to the effective suppression of in-flight oxidation during atmospheric plasma spraying by boron addition, which results in a dense coating microstructure characterized by low oxygen content and low porosity. During fretting wear, this dense structure significantly reduces material loss rates. Furthermore, the residual borides within the coating substantially enhance its microhardness, effectively mitigating adhesive phenomena in the initial wear stage. Meanwhile, the relatively high microhardness of the CuNi4B coating can also suppress the spallation behavior of the surface material under stress, further reducing material loss. These results demonstrate the feasibility of preparing Indium-free coatings with excellent fretting wear resistance by APS.