双重高离化处理增强硬质合金上纳米WN膜附着性机理的研究

Superhard or hard composite coating's preparation methods using in-situ plasma nitriding (PN) and high power impulse magnetron sputtering (HiPIMS) integration technologies (also known as Duplex hybrid technology) with high ionization degrees have a lot of advantages. Traditional WC-Co hardmetals used widely were selected as substrate, high performance composite coatings were firstly prepared with the gradient distribution of N element content and microhardness. The intrinsic relationships between the key technological parameters of Ar-N2 mixed gas plasma nitriding process with a high ionization degree on as-grinded or as-polished cemented carbide surface and compositions, structures, properties of the nitriding layers were investigated, then in-situ several microns thick nanocrystalline WN coatings on the nitriding layer were reactive sputter deposited using pure W target, HiPIMS technology and Ar-N2 mixed gas, the effect laws between the key technological parameters in favour of high ionization degrees for inlet gases and metallic particles sputtered from W target and the nanocrystalline WN coating's compositions, structures, properties were explored. Mainly focusing on: (1) the formation mechanisms and orientation relationships of compound phases (WNx, CoNx) within nitriding layer on cemented carbide surface; (2) the interfacial structures and orientation relationships between the compound layer and the nanocrystalline WN coating. The microstructure evolution laws of cemented carbide surface using plasma nitriding treatment with high ionization degree were ascertained, the growth mechanisms and adhesion enhancement mechanisms of nanocrystalline WN coating magnetron sputter deposited with high ionization degree were revealed, and the basic data and technical support was provided for the industrial applications of a new type of superhard coating system.

基于等离子渗氮（PN）和高功率脉冲磁控溅射（HiPIMS）技术兼具高离化、原位组合制备（超）硬质复合涂层的优势，选择工程应用广泛的钨钴硬质合金为基体，率先制备出氮元素和硬度呈梯度分布的高性能复合涂层（氮化层-纳米WN膜）。首先探讨研磨态/抛光态硬质合金表面Ar-N2混合气高离化等离子渗氮工艺与渗氮层成分-结构-性能的内在关系；然后原位采用纯W靶、HiPIMS技术、Ar-N2混合气在渗氮层上沉积数微米厚的纳米WN膜，研究气体和溅射金属粒子的高离化关键工艺参数对纳米WN膜成分-结构-性能的影响规律。重点研究：（1）硬质合金表面渗氮层中化合物相（WNx、CoNx）的形成机制与位向关系；（2）化合物相层与溅镀纳米WN膜之间的界面结构与位向关系。探明硬质合金表面高离化等离子渗氮处理的组织演变规律，揭示高离化溅镀纳米WN膜的生长机制和附着性增强机理，为新型超硬涂层体系的工业应用提供基础数据和技术支撑。

现代机加工技术不断向高速化、高精化、干切削、硬切削等方向发展，对硬质合金刀具涂层提出了更高的要求。本项目在YG6、YG10x硬质合金上采用直流磁控溅射(DCMS)和高功率脉冲磁控溅射(HiPIMS)技术制备WNx(x=0-0.5)薄膜，重点研究了薄膜的显微结构、附着性能和摩擦学性能，取得了以下创新性试验结果。.（1）采用DCMS技术重点研究W靶溅射功率、N2/Ar流量比、基体偏压、沉积温度等关键工艺参数对WNx薄膜结构和性能的影响。1）不同溅射功率的研究结果表明，WNx薄膜的表面粗糙度Ra值0.062-0.086 μm；随着溅射功率的增加，涂层由单一的fcc-W2N相转变为bcc-W和fcc-W2N的混合相；沉积速率由0.85 μm/h增至2.39 μm/h；平均摩擦系数0.41-0.47，磨损率低至2.11×10-16 m3/Nm；薄膜附着性良好，划痕法载荷100 N时，硬质膜仍未出现失效；TEM分析表明，混合相涂层是由W2N和W纳米晶镶嵌非晶基体组成的纳米复合结构，柱状晶由不连续生长的亚晶构成，亚晶粒尺寸小于100 nm。2）N2/Ar流量比的研究结果表明，随着N2流量升高，薄膜沉积速率下降，薄膜最高硬度为26.44 GPa。3）基体偏压对薄膜的残余应力影响较大；TEM观察表明，薄膜的横截面显微结构为多层膜结构，每层厚度15 nm；摩擦磨损过程中会在薄膜浅表层形成一层几十纳米厚的细晶变形层。4）沉积温度450-550 C范围内，WNx薄膜的结构与性能较稳定。.（2）采用HiPIMS技术沉积W薄膜、低氮掺杂的W(N)薄膜。结果发现，W、W(N)薄膜的表面形貌分别为细长的“杆状”、致密的“韧窝状”。掺氮后的W(N)薄膜硬度由纯W膜的18.12 GPa升至29.39 GPa，磨损率由3.0×10-15降至5.08×10-16 m3/N·m。W(N)薄膜与YG6-YG15系列硬质合金均有优异的附着性。进一步试验结果表明，不同气压下的W(N)薄膜均有着较高硬度(约30 GPa)，与YG6硬质合金的附着性高达171 N。此外，还进一步研究了HiPIMS-DCMS复合技术对薄膜结构与性能的影响规律。.本项目可控制备出具有纳米晶/非晶复合结构的WNx薄膜具有较高的硬度、较低的磨损率以及优异的附着性能，在无中间过渡层的二元单涂层体系中表现优异，具有巨大的工业应用前景。