【作者】 刘艳；

【导师】 李戈扬；

【作者基本信息】 上海交通大学 ， 材料学， 2007， 硕士

【摘要】 以TiN为代表的氮化物硬质薄膜作为刀具涂层取得了巨大的成功,有力地推动了制造业规模化加工的发展,高速切削与干式切削等加工技术的发展,又对刀具涂层提出了更高的硬度和高温抗氧化性方面的要求,高硬度的氮化物薄膜因抗氧化能力不佳而难以满足此要求。Sproul基于纳米多层膜的超硬效应,提出采用两种氧化物制备兼具高硬度和高抗氧化性纳米多层膜的技术路线,但按此路线所制备的多层膜未能得到硬度的提高。本论文基于纳米多层膜晶体生长的模板效应,设计并制备了在ZrO₂中插入TiN层形成的ZrO₂/TiN纳米多层膜。研究了TiN在四方ZrO₂模板效应下晶体化并形成赝晶体的条件,以及纳米多层膜生长结构的改变及其对多层膜力学性能的影响,结合现有强化理论,讨论了四方结构体系纳米多层膜的超硬机制。论文还发展了一种金属基体上制备薄膜截面TEM样品的实验技术。本论文关于纳米多层膜的研究在材料体系的拓展,理论研究的深入以及实验方法的创新三个方面取得了一些进展。本论文主要研究结果如下:1.对ZrO₂/TiN纳米多层膜的生长结构的研究发现,与NaCl结构氮化物一样,四方结构的ZrO₂也存在模板效应,在此效应下,仅以NaCl结构存在的TiN层在厚度小于1.8nm时被强制形成与ZrO₂相同的四方结构赝晶体,并与ZrO₂形成共格外延生长的柱状晶。这种结构上连续而成分周期变化的柱状晶呈现远高于ZrO₂单层膜的强烈（111）择优取向,显示了氧化物/氮化物纳米多层膜生长的相互促进效应。TiN层随厚度的进一步增加,又改变为以NaCl结构晶体生长,多层膜的共格外延生长结构遭到破坏,多层膜呈现四方结构ZrO₂和立方结构TiN交替生长的特征。2.力学性能研究发现,共格外延生长的ZrO₂/TiN多层膜的硬度和弹性模量随TiN层厚度的增加而迅速上升,并在TiN层厚为1.1nm时达到最高值19.4GPa和235GPa。随TiN层厚的继续增加和多层膜共格外延生长结构的消失,ZrO₂/TiN纳米多层膜的硬度和弹性模量迅速下降,当TiN层厚达到2.2nm时,多层膜的硬度和弹性模量已经降低到与ZrO₂单层膜相当的水平,分别为11.4GPa和181GPa。3.采用现有纳米多层膜超硬机制理论对以四方结构为模板的ZrO₂/TiN纳米多层膜研究发现,多层膜共格外延生长时因晶格失配所产生的交变应力场是多层膜获得超硬效应的必要条件和主要因素。并对其他多层膜体系的理论计算与分析发现,多层膜共格外延生长并产生的交变应力场同样是它们的共同特征。由此得出结论,交变应力场很有可能是产生超硬效应的本质及关键所在。4.针对目前多数薄膜TEM截面样品制备技术的报道以硅片为基底的现状,论文发展了一种金属基体上薄膜TEM截面样品的制备方法,详细归纳并优化了各道制样工序。更多还原

【Abstract】 Nitrides hard thin films, representatived by TiN, have achieved a big success,which strongly boost the development of modern manufacturing and the processing technology of high-speed cutting and dry machining.Meanwhile,there comes more request for high hardness and good high- temperature resistance as well in cutting coatings.However,nitrides itself can’t meet such needs due to its low-temperature resistance.Based on the super-hardness effect in nanomultilayers, Sproul proposed a route to prepare nanomultilayers utlizing two oxides in order to obtain both high hardness and good oxidation resistance .Unfortunately,it failed.On the basis of the superlattice growth and template effect in nanomultilayers,the paper designed and prepared ZrO₂/TiN nanomultilayers by adding TiN into ZrO₂ thin film.And the condition of the form of pseudocrystal under the template effect of ZrO₂ and the rule of hardening mechanism in tetragonal structure nanomultilayers combined with existing harderning theories were studied.In addition,the paper also developed an experimental technology for TEM sample preparation from thin films deposited on metallic substrates.The results come as follows in three areas including extending in nanomultilayers system, deeper research in existing hardening mechanism theory and innovation in experimental methods.Compared with NaCl-structure nitrides, ZrO₂ with tetragonal structure shows the template effect as well. Influenced by the template effect of tetragonal structured ZrO₂ layers, TiN layers grew in a tetragonal pseudocrystal the same structure as ZrO₂, rather than the face centred cubic they used to be under the sputtering conditions and coherent interfaces formed between the neighbor layers when TiN layer thickness was less than 1.8nm.And this kind of column crystals with continual structure and periodical variation in composition present a much more intensive （111） preferred orientation than ZrO₂ monolithic,which shows a mutual-promotion effect in the crystal growth of oxide/nitride thin films.And with the further increase in the thickness of TiN layer,TiN changed to NaCl-structure and the coherent epitaxial structure was broken.The nanomultilayers were characterized as alternative growth by tetragonal ZrO₂ and cubic TiN layers after then.With the study of mechanical properties,the hardness and elastic modulus of ZrO₂/TiN nanomultilayers with coherent epitaxial structure increase remarkablely with the increase of TiN layer thickness,and reach a maximum to 19.4GPa and 235GPa,respectively when TiN layer is 1.1nm thick.With the further increase of TiN layer thickness and disappearing of coherent epitaxial structure,the hardness and elastic modulus of ZrO₂/TiN decrease abruptly.When the thickness of TiN layer is 2.2nm, the hardness and elastic modulus decrease to the same level of ZrO₂ monolithic as 11.4Gpa and 181Gpa,respectively.Based on the existing theory about hardening mechanism, the thesis studied the superhardness mechanism in ZrO₂/TiN thin film where tetragonal structure plays as a template.When there is a coherent epitaxial growth, the alternate stress field due to the lattice dismatch leads to a high hardness.Actually, according to other multilayers with high hardness, alternate stress field is the shared feature of the multilayer systems that have high hardness enhancements. And it is not only the essential qualification, but also the main factor for the superhardness effects.Aimed at the situation that the technique about cross-sectional TEM sample preparation mostly focuses on films deposited on silicon wafer, the thesis developed a new method for thin films deposited on metallic substrates. And each step of the procession is described in detail.更多还原