高膜基结合力驱动的TiAlN基PVD涂层硬质合金基体与界面研究

The realization of “Made in China 2025” national strategy is strongly affected by the core technology localization level of coated cemented carbide tools. This project is aimed to conquer the key core technology of coated cemented carbides, i.e., the design, regulation and control of the microstructures of the film-substrate interfaces, and hence to achieve high film adhesion and high stability of film adhesion. TiAlN based PVD coatings, with typically anisotropic nucleation characteristic are chosen for the investigations. To solve the key scientific issue, i.e., the microscopic characteristics of each phase in cemented carbide substrates and their synergistic effects on the mechanism of film adhesion, and hence to achieve the above-mentioned targets, a series of investigations are proposed. A new concept of the microscopic structure design and regulation for the coated cemented carbide substrates is proposed, including the crystallographic orientation relationships of film nucleation, the main channels for atomic diffusion and the micro-channels for stress relaxation at the interfaces. Regulation and control methods of the characteristic-matching degrees among the phases of the cemented carbide substrates and the films will be developed. For the substrates, WC crystal factor, phase composition factor and interface factor are the representative characteristics. A finite element simulation method on the micro thermal stresses at the film-substrate interfaces is proposed based on a unit cell model containing WC (0001) with strong adhesion and other crystallographic planes with weak adhesion, the average grain size of WC and the mean free path of the β phase. A FIB sample preparation technique, image-corrected Titan3™ G2 60–300 S/TEM and 3DAP key equipment will be employed to carry out the atomic scale investigations of the film-substrate interfaces and film structures. The intrinsic connections among the microstructures of the substrates, interfaces and films, the physical, mechanical, electrochemical, microscopic stress parameters of the coatings will be fully excavated.

以“中国制造2025”目标为导向，以攻克膜基界面微观结构设计与调控这一关键核心技术，实现涂层高膜基结合力与高膜基结合力稳定性为目标，围绕硬质合金基体中各物相微观特性及其协同效应对膜基结合力作用机制这一关键科学问题，以具有典型形核各向异性的TiAlN基PVD涂层为切入点，提出基于薄膜形核晶体学位向关系、界面原子扩散主通道与应力松弛微通道设计的涂层硬质合金专用基体微观结构设计与调控新概念；研究以WC晶面因子、物相成分因子与界面因子为代表的硬质合金微观组织中物相特性对薄膜特性匹配度的调控方法；建立含WC(0001)强结合面和弱结合面、硬质相晶粒度和β相平均自由程的单胞模型，开展膜基界面微观热应力有限元模拟；采用FIB制样技术、图像球差校正FETEM和3DAP关键设备，系统开展原子尺度膜基界面与薄膜内部结构研究，充分挖掘基体、膜基、薄膜微观结构与涂层物理、力学、电化学、微观应力等参数间本征关联。

以实现PVD涂层高膜基结合力与高膜基结合力稳定性为目标，围绕硬质合金基体中各物相微观特性及其协同效应对膜基结合力作用机制这一关键科学问题，开展相关研究的主要结果如下： .1）硬质相与Co基粘结相（β相）分别通过形成共格/半共格膜基相界面和耗散薄膜生长应力，实现对膜基结合力（LC2）和涂层内聚失效抗力（LC1）的改善。提高WC(0001)晶面比例或通过固溶原子降低WC晶格常数，均有利于形成共格/半共格膜基相界面。 .2）薄膜生长过程中，界面处β相中因拉应力超过其极限强度而产生塑性变形和马氏体相变，耗散薄膜应力，形成强适配性无序原子层。β相中W原子向膜基界面迁移，形成bcc-W原子层与涂层间半共格界面，实现膜基界面硬度和弹性模量梯度适恰。基体Co含量为10~12%时，涂层可获得最高的LC1和LC2。.3）增加β相中W/Cr/V/Ta/Ti/Mo固溶量，改善硬质相和β相分布均匀性，降低硬质相晶粒度和邻接度，降低基体表面粗糙度，均能有效降低涂层中残余应力波动，有利于膜基结合力及其稳定性提高。 .4）高分辨透射电镜分析表明，采用新开发的高WC(0001)晶面比例的细小纯板状晶硬质合金作基体的PVD-AlTiN/TiN纳米复合涂层合金（新型涂层合金）中，存在TiN(-11-1)/WC(0001)共格界面和TiN(200)/WC(01-11)半共格界面，验证了新型涂层合金LC2＞100 N高膜基结合力作用机理。由于PVD-AlTiN/TiN纳米复合涂层的超晶格强化效应，铣削受力时内部原位形成的微纳尺度裂纹能释放不均匀塑性变形所导致的残余应力，从而有效延缓铣削刀具表面裂纹的萌生和扩展。 .5）采用相同涂层工艺和铣削工艺，在316L不锈钢干、湿式铣削条件下，因涂层超晶格强化效应和高比例共格/半共格膜基相界面强化效应的协同作用，新型涂层合金铣削刀具较商业化参比对象寿命分别提高55%和42%。