激光熔覆NbC 颗粒复合镍基非晶涂层结构调控及其强韧化机理

The relatively low microhardness and high cracks sensitivity are two important factors gauging the performance of Ni-based amorphous coating. In this study, NbC particles are introduced to deposit high mechanical and wear resistance properties Ni-based amorphous composite coating on mild steel substrate by laser cladding process. The study details and aims are: The calculated mixing enthalpy and mismatch entropy, deep eutectic theory and experimental results are used to design and optimize the Ni-based alloy system composition. Then, the powders are fabricated by high pressure atomization process. With the helping of numerical simulation and melted pool real time observation, the effects of process parameters on flow characteristics, solidification behavior and NbC particles distribution are studied to accurately control the coating microstructure. In order to design and build a synergistic strengthened amorphous composite coating with micro, nano-wear effect. The interaction between shear-bands and NbC particles are studied to learn the rule of particle/matrix compatible deformation and meso-damage evolution. Then the strengthening and toughening model of the coating is build. Finally, the correlation among phase, microstructure and wear resistance tests is conducted to study the wear resistance mechanisms and its physical model. The findings of the project can provide theory evidence and technical guidance for the fabrication of particles strengthened amorphous composite coating using laser processing and its application in key mechanical components.

针对镍基非晶涂层硬度相对较低、裂纹敏感性高等问题，提出通过激光熔覆技术制备具有优异力学和摩擦学性能的NbC颗粒相增强镍基非晶复合表面涂层。研究内容和目标为：利用混合焓、归一化错配熵及深共晶等非晶形成理论并结合激光熔覆技术特点设计和优化镍基合金体系的成分比例范围，并进行高压氩气雾化粉末制备；借助数值模拟和熔池动态实时观测，重点突破激光熔覆参数对瞬时微区熔体流动特性、凝固行为对NbC颗粒相分布的影响，实现涂层微结构的有效调控，设计和构筑出具有协同增强微、纳摩擦效应的非晶复合涂层；以非晶剪切带与NbC颗粒相之间的交互作用行为为切入点，揭示颗粒/基体协调变形与细观损伤演化之间的规律，探讨非晶复合涂层的强韧化机制；研究涂层相组成、微结构与摩擦学性能之间的关联，建立颗粒复合非晶涂层的抗磨机制和物理模型。预期成果将为颗粒增强非晶涂层的激光制备及其在关键机械部件上的应用提供理论依据和技术储备。

激光非晶化技术是用连续激光对待加工零部件表面进行均匀扫描，使零部件表面形成一定厚度的非晶组织，可大大提高其表面硬度、耐蚀及耐磨性能，在材料表面改性领域具有十分巨大的潜在应用价值，目前受到国内外学者的广泛重视，是表面工程技术领域研究的热点之一。本项目首先利用混合焓、归一化错配熵及深共晶等非晶形成理论并结合激光熔覆技术特点设计和优化了镍基合金体系的成分比例范围，将合金体系的成分确定为B含量为18%，Si元素的含量为10%，Nb元素的含量为4～8%，C元素的含量为1～3%，其余为Ni和Fe（Ni/Fe=60:40）并进行高压氩气雾化粉末制备；涂层组织观察分析表明随激光熔覆扫描速度的增加涂层非晶相的含量逐渐增加涂层中NbC颗粒相的体积含量随Nb、C含量的增加而增加，并且NbC颗粒相的体积含量还会随激光熔覆参数的变化而变化，当激光熔覆热输入降低时，NbC颗粒相的数量较多。结合高速摄像和截面SEM组织观察，发现在激光快速熔覆过程中，熔池内部流动剧烈，且存在较大的不均匀性，导致在熔覆层内不同位置NbC颗粒的分布呈现严重不均匀的宏观偏析现象。并且发现当激光热输入较大时，由于熔池高温停留时间较长，激光导致的流体流动也更加充分，涂层内部的NbC颗粒分布较为均匀。涂层力学测试结果表明NbC颗粒相能够提高涂层的硬度，其理论计算所得硬度贡献值为92.5 HV，与试验所得的测量贡献值（96.7 HV）相近，且在涂层裂纹扩展中具有阻碍作用和增殖效应。激光热输入较低时，涂层硬度值较高，NbC颗粒相能够阻止Al2O3磨球对涂层表面的切削，阻碍了涂层的塑性形变，提高涂层耐磨性能；激光热输入较高时，涂层硬度值较低，NbC颗粒容易在摩擦过程中与涂层材料一起发生脱落，协同Al2O3磨球对涂层表面进行磨损，降低涂层耐磨性能。研究成果将为颗粒增强非晶涂层的激光制备及其在关键机械部件上的应用提供强有力的理论依据和技术储备。