TiCN薄膜的超硬与自润滑特性研究

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"Superhard and self-lubrication of TiCN film" 本文主要探讨了TiCN薄膜的超硬特性和自润滑机理，作者包括孙长庆、B. K. Tay等，发表在科研领域，标签指出这是一篇首发论文。研究内容涉及到表面键收缩和非键电子孤对作用在氮化物表面的影响。 TiCN（钛碳氮化物）是一种复合陶瓷材料，因其优异的耐磨性、硬度和耐腐蚀性而在各种工业应用中受到青睐。本研究揭示了两种关键的表面现象：键收缩和非键电子孤对相互作用，并通过新的实验发现提供了进一步的证据。通过纳米压痕技术，研究人员发现TiCrN和GaAlN表面在相对较低的压痕载荷（<1.0mN）下弹性恢复率可高达100%，这意味着它们具有极高的韧性。同时，TiCrN表面的硬度比其块体材料提高了约100%。键收缩是导致TiCN表面硬度增强的关键因素，据估计，键收缩程度约为12%~14%。这种收缩使表面的化学键更加紧密，增强了材料的硬度。另一方面，非键电子孤对的弱相互作用则有助于提高材料的弹性恢复能力。这种作用降低了拉曼振动的频率，并且使得电子孤对断裂的临界载荷降低，这对理解材料的自润滑性质至关重要。 PACS编码（Physical and Chemical Classification Society）81.40.J，33.15.F，73.20.F，41.20.C•ecqsun分别对应物理化学中的不同领域，可能涉及材料科学、固态物理学和力学性能等相关研究。这项研究深入解析了TiCN薄膜的微观结构对其超硬和自润滑性能的影响，为优化和设计高性能涂层材料提供了理论依据。这些发现对于改善机械部件的耐磨性和降低摩擦系数具有重要意义，特别是在高温、高压或高负荷的工程应用中，例如切削工具、航空航天组件和精密机械等领域。

Pauling (metallic)

radius of atom reduces with the reduction of their coordination numbers

(CNs). Due to the termination of the lattice periodicity in the surface normal, a surface

provides such an environment for bond contraction. Sinnott

indicated that the bond

contraction depends on the reduction of CN and it is independent of the nature of the bond.

Such a bond contraction and the rise in surface-to-bulk volume ratio of small particles will

enhance the crystal field and the corresponding physical properties of a nanosolid. It is

anticipated that at surface, the local mechanical properties such as the hardness and Young's

modulus will be enhanced because these quantities depend on the binding energy at

equilibrium atomic separation.

The above predictions have initiated us to do an experimental survey with Raman

spectroscopy (HeNe laser, normal incidence), nanoindentation and pin-on-disk slide friction.

Raman gives information about lattice vibration in energy space and does no matter with the

depth of penetration of the light. By taking the relative change, one may exclude the errors in

nanoindentor caused by the tip size or other possible resources.

Fig. 1 compares the low-frequency Raman shift for typical Al and Zr oxides, Ti and

amorphous carbon nitrides and amorphous carbon and Tungsten carbides. As anticipated, the

lone-pair features for oxides are stronger than the features for nitrides while no such features

can be resolved for carbides below 1000 cm

-1

wavenumber. The peak position depends on the

reduced atomic mass, µ, of the compounds, and the force constant, k, of the interatomic

interaction (ω ∝ (k/µ)

1/2

). Numerical analysis using a 2-3 power potential

could give the

force constant and simulate these features that were attributed to the hydrogen bond

vibrations with ~0.05 eV binding energy.

The hydrogen bond is actually composed of a lone

pair and a covalent bond. The vibration of the covalent-bond has contributed to the spectra at

much higher frequencies. Therefore, these features come from the vibration of the weak

interaction of lone pairs. The trends shown in Figure 1 evidence sufficiently for the existence

of nonbonding lone pair interaction as a result of the sp-orbital hybridization of the

electronegative additives and of the "4-n" rule for lone pair production.

The elastic recovery is defined as the ratio of area covered by the unloading curve to the area

covered by the loading curve in the load-depth profile of nanoindentation. Nanoindentation

profiles in Fig. 2 confirm the predictions of high elasticity of the nitride surfaces contributed

by the lone pair interaction. For AlGaN,

the elastic recovery is as high as 100% with lower

load (0.7 mN). As it can be seen that for the amorphous carbon film, the absence of lone pairs

makes the carbide less elastic than a nitride under the same scale of indentation load. For CN

and TiN, the elastic recovery ranges from 65% to 85% with higher load (5 mN).

The change

of the elastic recovery with load indicates a critical load value for the lone pair interaction.

One might argue that diamond should give a high elastic recovery at all the possible loads,

but no means or harder alternative materials can be used to detect this intuition. Therefore,

the nonbonding interlayer interaction enhances the elasticity of nitride surfaces at very low

load. Defect or dislocations, as well as the tip effect may induce errors in measurement but it

does no matter with the nature of a surface; in particular, taking the relative changes of the

quantity will remove such errors. Such a high elasticity by nature furnishes the nitride surface

with self-lubricative property for nano-tribological applications.

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