【作者】 乌晓燕；

【导师】 李戈扬；

【作者基本信息】 上海交通大学 ， 材料加工工程， 2009， 硕士

【摘要】 硬质薄膜材料在包括刀具涂层在内的表面改性领域有重要的应用。以TiN为代表的氮化物薄膜在刀具涂层上已取得了巨大的成功,而硬度更高的碳化物薄膜作为刀具涂层材料尚未得到充分的研究。两种材料以纳米量级交替沉积形成的纳米多层膜常具有硬度异常升高的超硬效应。纳米多层膜材料组合的多样性及由此带来的性能可裁剪性使其成为一条获得兼具高硬度和优异综合性能的有效途径,而这类两相纳米结构薄膜通过微结构强化而不是传统的通过强键能获得高硬度的强化机制更具理论研究价值。已有的研究表明,具有超硬效应的纳米多层膜多由两种氮化物组成或以氮化物为基组成,较少涉及包括碳化物在内的其他陶瓷材料。近期的研究发现,共格外延生长是纳米多层膜获得超硬效应的重要微结构特征和必要条件,模板效应对纳米多层膜获得共格外延生长结构具有重要意义。然而,对模板效应已积累的实验结果主要涉及氮化物,这种使多层膜获得共格外延生长结构的模板效应的普遍性还需要进一步在材料种类和结构类型方面积累更多的例证。本论文采用金属V靶在氩气和乙炔混合气氛中,通过反应溅射制备了碳化钒薄膜,研究了乙炔分压对薄膜的成分、相组成和力学性能的影响;在此基础上进一步制备了VC/Si3N4和V2C/Si3N4纳米多层膜,研究了不同晶体结构碳化物对非晶Si3N4晶体化的模板效应以及相应纳米多层膜的微结构与力学性能的影响。论文取得的主要研究结果如下:1.采用在Ar-C2H2混合气体中的射频反应磁控溅射技术可以方便地合成碳化钒薄膜。碳化钒薄膜的化学成分、相组成、微结构以及相应的力学性能对C2H2分压非常敏感,在C2H2分压为混合气体总压~3%附近时可以获得硬度与弹性模量较高的立方结构的VC薄膜。此时薄膜的硬度与弹性模量也分别为各种结构碳化钒薄膜中的最高值,分别为35.5GPa和358GPa;在C2H2分压为混合气体总压~1.5%时附近时,可制得具有六方结构的V2C薄膜,其硬度和模量分别为31.3GP和260GPa;较高的C2H2分压下,薄膜的碳含量增加,在六方结构的γ-VC薄膜中产生非晶碳相,薄膜的硬度和弹性模量亦随之降低。2.由于在Ar-C2H2混合气体中溅射陶瓷Si3N4靶所得的薄膜不会渗碳,仍为Si3N4薄膜,因而改变C2H2的分压,通过反应溅射金属V靶和Si3N4陶瓷靶,可以方便地制备不同晶体结构类型的VC/Si3N4和V2C/Si3N4纳米多层膜。3.纳米多层膜中晶体生长的模板效应具有普遍性,立方结构的VC和六方结构的V2C都具有使非晶Si3N4层在厚度小于约1nm时晶体化并分别与VC和V2C形成共格外延生长的模板效应。与已有的报道相对照,实验展示的以上结果为模板效应的普遍性提供了材料(碳化物)和结构(立方和六方)方面的新例证。4.研究表明,共格外延生长的VC/Si3N4纳米多层膜产生了硬度升高的超硬效应,最高硬度为41GPa,明显高于VC单层薄膜约35.5GPa的硬度。而同样形成共格外延生长结构的V2C/Si3N4纳米多层膜的硬度仅为约22GPa,大大低于V2C单层膜31.3GPa的硬度值。共格生长结构所产生的交变应力场改变了各调制层的模量是导致以上两种纳米多层膜力学性能不同的原因。更多还原

【Abstract】 The ceramic hard films are widely used in surface modification, like coatings on cutting tools. The nitrides films, such as TiN, have achieved great success. However, not sufficient researches are carried on the carbides films, which have much higher hardness.Nanomultilayers, deposited by two kinds of materials alternatively in nano-meter scale, have superhardness effect. Nanomultilayer films have much potential in the coatings fields of cutting tools, for they can obtain high hardness due to the superhadrness effect and can present flexiable performace modification by changing their constituents. Additionally, the nanomultilayer films can obtain high hardness by designing their microstructure, which has more research value.The present researches show that most of the superhard nanomultilayers are composed of nitrides, not so many about the carbides. The recent research shows that the coherent epitaxial growth is the vital microstructure and necessary condition for the nanomultilayer to obtain superhardness. Yet, the most experiment results are about the nitrides, the universality of template effects due to the coherent growth in nanomultilayers requires more examples in different styles and structures of materials.In this thesis, vanadium carbide coatings with different carbon content were synthesized by reactive magnetron sputtering in Ar-C2H2 mixture. The effect of C2H2 partial pressure on the compositions, phases, microstructures and mechanical properties of coatings are investigated. Moreover, VC/Si3N4 and V2C/Si3N4 nanomultilayrs are synthesized to research on the effects of different crystal structured carbides on the amorphous Si3N4 and corresponding microstructure and mechanical properties.The results are showed as follows.1 Vanadium carbide films can be easily synthesized by R.F. reactive magnetron sputtering in Ar-C2H2 mixture. Vanadium carbide coatings with different carbon contents were synthesized by reactive magnetron sputtering in Ar-C2H2 mixture. The compositions, phases, microstructures and mechanical properties of coatings are sensitive to the effect of C2H2 partial pressure. The cubic VC coating with preferable mechanical properties, peak hardness of 35.5GPa and elastic modulus of 358GPa, can be obtained when the C2H2 partial pressure of about 3%. The hexagonal V2C coating can be obtained when the C2H2 partial pressure of about 1.5%. The hardness and elastic modulus are 31.3GPa and 260 GPa,.The presence of excessive carbon with increased C2H2 partial pressure in theγ–VC coatings leads to the decrease of hardness and elastic modulus.2 No carburization occurs in the Si3N4 films synthesized by sputtering vanadium target and Si3N4 target in the Ar-C2H2. Therefore, by changing the partial pressure of C2H2, VC/Si3N4 and V2C/Si3N4 nanomultilayers can be synthesized separately.3 The template effect exists universally in the growth of nanomultilayer. The normally amorphous Si3N4 crystallize and grow epitaxially with either the cubic VC or hexagonal V2C when thickness is below 1 nm. Compared with the present researches, the above results contribute the additional examples for the universality of the template effect from the material (carbides) and crystal structure (cubic and hexagon) aspects.4 The results show that, VC/Si3N4 nanomultilayer with the coherent epitaxial growth structure shows the superhard effects with the peak hardness of 41GPa, which is higher than that of the VC film of 35.5 GPa. On the contrary, the hardness of V2C/Si3N4 nanomultilayer with the coherent epitaxial growth structure as well is only 22 GPa, which is lower than that V2C film of 31.3w GPa. The changes of modulus resulted from alternating stress field from coherent growth is the reason of the difference of mechanical properties in the two kind of the films.更多还原