【作者】 岳建岭；

【导师】 李戈扬； 高唯；

【作者基本信息】 上海交通大学 ， 材料学， 2008， 博士

【摘要】 以TiN为代表的陶瓷硬质薄膜在包括切削工具涂层在内的表面改性和防护领域得到广泛应用。制造业中高速切削和干式切削等先进技术的发展对刀具提出了更高的要求,需要作为刀具涂层的薄膜材料不仅具有更高的硬度,还应具有优良的高温稳定性。纳米多层膜因超硬效应具有高硬度,特别是它们材料组合的多样性而获得的性能可剪裁性展示了在刀具涂层上的广阔应用前景。而这类材料通过人工微结构设计获得高硬度的强化机制更具理论研究价值。然而,目前尚不能仅从理论上设计出具有超硬效应的纳米多层膜,实验探索仍是获得高硬度纳米多层膜的主要研究方法。本论文采用磁控溅射技术制备了VN/SiO₂、VN/AlON、ZrO₂/TiN和TiAlN/Si₃N₄等体系的纳米多层膜,采用XRD、TEM、EDX、SEM和微力学探针等先进测试方法表征了薄膜的微结构和力学性能。研究了通过溅射方法获得含氧化物纳米多层膜的制备技术;研究了纳米多层膜中不同晶体结构模板层对另一调制层晶体生长作用的模板效应;研究了纳米多层膜的高温稳定性;讨论了纳米多层膜的超硬机制。并基于所得研究结果对现有高硬度纳米多层膜的设计准则提出了修正和补充。论文的主要研究结果如下:1.对VN/SiO₂和VN/AlON纳米多层膜的研究表明,采用金属靶和氧化物陶瓷靶,通过在Ar-N2混合气氛中反应溅射的方法可以高效率地沉积具有高硬度的含氧化物纳米多层膜。在VN/SiO₂和VN/AlON纳米多层膜中,由于NaCl结构VN层晶体结构的模板效应,通常溅射态为非晶的SiO₂或AlON层在其厚度小于约1 nm时能够晶化,并与VN层共格外延生长,从而使多层膜的硬度得到明显提高,最高硬度分别达到34GPa和30Gpa;随着自身厚度的进一步增加,SiO₂或AlON层逐渐转变为以非晶态生长,阻断了纳米多层膜的共格外延生长,多层膜的硬度随之降低。而模板层VN的厚度改变对纳米多层膜的生长结构和力学性能影响相对较小。2.对ZrO₂/TiN纳米多层膜的研究表明,与立方结构的氮化物一样,四方结构的ZrO₂也呈现出影响另一沉积层（TiN）晶体生长的模板效应,在此效应下,通常仅以立方结构存在的TiN在层厚小于1.8nm时被强制改变其晶体结构,形成与ZrO₂相同的亚稳态四方晶体结构,并与ZrO₂共格外延生长。随TiN层厚的增加,ZrO₂晶体层对TiN赝晶生长的模板效应逐渐减弱,TiN又以其稳定的NaCl结构生长,多层膜的共格外延生长结构遭到破坏,形成了四方结构ZrO₂和立方结构TiN交替生长的非共格纳米多层结构。ZrO₂/TiN纳米多层膜没有显示出硬度明显升高的超硬效应,其原因与多层膜中的共格应变使得两调制层材料模量差异的减小有关。3.在TiAlN/Si₃N₄纳米多层膜中,由于TiAlN层晶体结构的模板作用,溅射态为非晶的Si₃N₄在厚度小于0.6nm时被晶化,并与TiAlN层形成共格外延生长,多层膜产生硬度高达52GPa的超硬效应。随着层厚的增加,Si₃N₄转变为以非晶态生长,多层膜的硬度也随之降低。高温稳定性研究表明,该体系纳米多层膜具有良好的高温结构稳定性,即使在900℃的温度,多层膜仍能保持其晶体结构和调制结构的稳定,其硬度也依然明显高于TiAlN单层膜。但多层膜的抗氧化性并没有相对于TiAlN单层膜得到明显提高。4.论文的研究发现,两调制层形成共格结构是纳米多层膜获得超硬效应的必要条件。模量差强化是纳米多层膜获得超硬效应的主要机制,但应考虑各调制层模量在共格生长形成的交变应力场作用下的改变。基于这一研究结果,论文对现有高硬度纳米多层膜的设计准则提出了修正和补充:1)两调制层应形成共格外延生长。两调制层形成共格界面是纳米多层膜产生超硬效应的必要条件,但多层膜在材料组合上并不仅限于晶格参数相近的两种材料,借助于纳米多层膜晶体生长的模板效应,两种结构类型不同的晶体材料、甚至其中一种为非晶的材料也可形成产生超硬效应所必须的共格界面结构;2)调制层在形成共格结构后材料的模量差应尽可能大。共格生长的两调制层存在模量差是纳米多层膜获得超硬效应的主要原因,但是,对于各调制层的模量,应是纳米多层膜形成共格结构后在交变应力场作用下的改变值,而非各调制层以单层膜形式存在时的模量。以上对设计准则的修正和补充,大大拓展了高硬度纳米多层膜的材料组合空间。更多还原

【Abstract】 The ceramic hrad films, such as TiN, have been widely applied in some fields of surface modification and protection inclunding coatings of cutting tools. The development of dry and high-speed cutting demands protective cutting-tool coatings with not only high hardness but also good thermal stability at high temperatures. Nanomultilayer films show much potential in the coatings fields of cutting tools, for they can obtain high hardness due to the superhadrness effect and especially can present flexiable performace modification by changing their constituents. Additionally, the nanomultilayer films can obtain high hardness by designing their structure, which shows more research value. However, it’s impossible to design the superhard nanomultilayer only according to the theory now, which leads that the experiments are still the main intestigation method to obtain the nano-multilayer films with high hardness.In this work, VN/SiO₂, VN/AlON, ZrO₂/TiN and TiAlN/Si₃N₄ nanomultilayer films were synthesized by magnetron sputtering method, and their microstructure and mechanical properties were characterized by XRD, TEM, EDX, SEM and nanoindentation. The main studies in this work are described as follows: It was investigated that the reactive sputtering method to synthesize the oxide-composed nanomultilayer films, the template effect in nanomultilayer films with different structural template layer that the crystal template can affect the growth of the other layer, the high-temperature thermal stability of nanomultilayer films, and the strengthening models of nanomultilayer films. Finally, the present designing rule for nanomultilayer films with high hardness were modified and supplemented based on the research results.The main conclusions in this work are summarized as follows:1. The studies on the VN/SiO₂ and VN/AlON multilayers indicate that the reactive sputtering method with higher deposition rate can be successfully used to synthesize the oxide-composed multilayers with high hardness. The results show that, under the template effect of Nacl-type VN, normally amphorous SiO₂ and AlON with very low thickness （<1nm） can be crystallized and further grow epitaxially with VN layer, accompanied by a remarkable increase in hardness of multilayers. On further increase of SiO₂ and AlON layer thickness, the SiO₂ and AlON gradually transform into amorphous structure, resulting in a rapid decline in hardness. On the other hand, the change of VN layer thickness shows a relatively small effect on the growth structure and mechanical properties of the nanomultilayers.2. The studies on ZrO₂/TiN multilayers show that the tetragonal structural ZrO₂ also presents the template effect like the NaCl-type structural TiN. Under this template effect, TiN with layer thickness lower than 1.8nm can grow into metastable tetragonal structure and grow epitaxially with ZrO₂. With further increase of thickness, TiN gradually transforms into NaCl-type structure and blocks the epitaxial gowth of multilayers, resulting in a rapid decline in crystal integrity. In addition, ZrO₂/TiN multilayers don’t present the superhardness effect, for the coherent strain in multilayers can change the modulus of the modulation material.3. The studies on TiAlN/Si₃N₄ multilayers show that under the t1emplate effect of TiAlN, normally amorphous Si₃N₄ with low layer thickness （<⁰.6nm） can be crystallized and grow epitaxially with TiAlN layer, accompanied by a remarkable increase in hardness. On further increase of layer thickness, Si₃N₄ gradually changes into amorphous structure, resulting in a quick decline in hardness. The research about the thermal stabilities of nanomultilayer films indicates, TiAlN/Si₃N₄ nanomultilayer films present good high-temperature structural stability, and their crystal structure and modulation structure can still be stable even at 900℃, which results in their higher hardness than TiAlN single film. However, TiAlN/Si₃N₄ nanomultilayer films don’t show apparently higher oxidation resistance than TiAlN single film.4. The studies indicate that it’s necessary to form a coherent structure for nanomultilayers in order to obtain high hardness, The modulus-difference strengthening dominates the superhardness effect compared with the alternating stress field strengthening, but it should be taken into account that the effect of alternating stress field on the modulus of modulation layers in nanomulatilayer films. Based on these studies, the present designing rule for nanomultilayer films with high hardness were modified and supplemented in this work, which were mainly described as follows:1) The two modulation layers should form the coherent structure;It’s necessary to form a coherent structure between the two modulation layers for nanomultilayer films to obtain high hardness, but it doesn’t mean that the lattice parameters of two modulation layers have to be nearly equal. Under the template effect, the nanomultilayer films can also grow into coherent structure even if their lattice parameters have a large difference.2) The modulus difference of two modulation layers under the coherent strain should be as large as possible;A large difference between the modulus of two modulation layer with coherent structure is the main reason for nano-multilayer films to obtain high hardness. However, herein the modulus isn’t the modulus of the bulk constituents of multialyers, but the modulus of two modulation layer under the coherent strain in nanomultilayers.The above modification and supplement to the present designing rule can expand the scope of material combination for nanomultilayer films with high hardness.更多还原