低温超音速火焰喷涂工艺制备轴承钢为基体的WC-12Co厚涂层

Thick WC-12Co coatings on bearing steel fabricated by low-temperature high-velocity fuel spray process

摘要:

采用超音速火焰喷涂工艺(HVOF)制备的WC-12Co涂层能够显著提高系统的硬度和耐磨特性。然而,该工艺中的高温参数会使得涂层在制备过程中产生脱碳现象。本文尝试将WC-12Co涂层引入到滚动副中以提高界面的摩擦学性能和抗磨损特性,例如固体火箭发动机中用于推力矢量控制的滚动轴承,通过温度可控的超音速火焰喷涂工艺在轴承钢基体上制备涂层。详细研究了涂层的相分布、成分组成、微观结构、与基体的结合强度、弹性模量和微观硬度,验证了改进后工艺的可行性和先进性,并阐明了涂层与轴承钢基体之间的结合机制。在WC骨架假设和钴相均匀分布的假设下,根据硬度性能的测试结果,给出了WC-12Co涂层微观硬度的一个经验公式,可用于涂层硬度的理论预估和设计优化。

Abstract:

High-velocity oxygen-fuel (HVOF) sprayed WC-12Co coating can improve system hardness and wear-resistance significantly. However, the coating would suffer decarburization phenomenon due to the high spray temperature and the large cooling rate in the HVOF process. With the application prospect of introducing thick WC-12Co coating into some heavy-load rolling pairs to improve tribological performance and wear-resistance, such as the rolling bearing for thrust vector control in solid rocket engine, this study adopts low-temperature high-velocity liquid fuel spray process to fabricate thick coatings on bearing steel. The modified process with a spray temperature of around 1700 K is realized by the replacement of oxygen by oxygen-nitrogen mixed gas and the introduction of water-cooling system. Phase distribution, elementary composition, microstructure, bonding strength, elastic modulus and microhardness of coatings are investigated to verify the feasibility and advantage of the process. The bonding mechanism between the coating and the substrate is clarified. Based on experimental data and the assumption of WC skeleton structure filled up with cobalt phase, a simple formula of the microhardness of WC-12Co coating is proposed for theoretical predication and coating design.