Research and application of the hottest superhard

2022-08-05
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Research and application of superhard film coating materials

Abstract: CVD, PVD tin, tic, TiCN, TiAlN and other hard film coating materials have been increasingly widely used in tools, molds, decoration and other industries, but still can not meet many difficult to process materials, such as high silicon aluminum alloy, various non-ferrous metals and their alloys, engineering plastics, non-metallic materials, ceramics, Processing requirements for composite materials (especially metal matrix and ceramic matrix composites). It is this objective demand that leads to the research progress of new superhard film materials such as diamond film, cubic boron nitride (c-BN), carbon nitrogen film (CNx) and nanocomposite film. In this paper, the research status and industrial application prospect of these superhard material films are briefly introduced and reviewed

key words: superhard material film; Research progress; Industrial application

1 superhard film

superhard film refers to hard film with Vickers hardness above 40gpa. Not long ago, only diamond film and cubic boron nitride (c-BN) film could reach this standard. The hardness of the former was GPA (related to crystal orientation), and the hardness of the latter was 50 ~ 80gpa. The hardness range of diamond-like carbon (DLC) films can vary from 10GPa to 60gpa depending on the preparation method and process. Therefore, some diamond-like carbon films with high hardness (such as diamond-like carbon films prepared by vacuum magnetic filtration arc ion plating (also known as ta:c)) can also be classified as superhard films. Although the carbon nitrogen films (CNx) appeared in recent years do not have the crystalline state predicted by Cohen et al β- C3N4 exceeds the hardness of diamond, but the existing research results show that its hardness can reach 10GPa ~ 50gpa, so it is also classified as superhard film. The above-mentioned superhard thin film materials have the same characteristics. They all have large band gap and excellent semiconductor properties, so they are also called wide band gap semiconductor films. SiC and GaN films are also excellent wide band gap semiconductor materials, but their hardness is lower than 40gpa, so they are not superhard films

recently, a kind of superhard thin film materials are completely different from the above wide band gap semiconductor films. They are multilayer materials composed of ordinary hard films with nano thickness. Although the hardness of each layer does not reach the superhard standard, the nanocomposite multilayers composed of them show superhard characteristics. In addition, the hardness of tin/SiNx thin films compounded by nano grains was as high as 105gpa, which reached the hardness of diamond

this paper will briefly introduce the above-mentioned superhard thin film materials one by one, and comment on their industrial application prospects

2 diamond film

2.1 properties of diamond film

since the early 1980s, diamond film has been widely valued by countries all over the world. From the mid-1980s to the late 1990s, a global research upsurge (diamond fever) has been formed. This is because, in addition to unparalleled high hardness and high elastic modulus, diamond also has extremely excellent electrical (Electronics), optical, thermal, acoustic, electrochemical properties (see Table 1) and excellent chemical stability. Large natural diamond single crystals (diamonds) are very rare in nature and very expensive. However, the industrial diamonds synthesized by high temperature and high pressure are mostly powder products with small particle size, which can only be used as abrasives and tools (including diamond sintered bodies and polycrystalline diamond (PCD) products). The diamond films prepared by chemical vapor deposition (CVD) provide the possibility of utilizing all the excellent physical and chemical properties of diamond. After more than 20 years of efforts, CVD diamond films have been compared with the implementation of the highest quality IIA natural plastics in various fields in almost all physical and chemical properties (see Table 1). The research of CVD diamond films has entered the stage of industrial application

Table 1 Properties of diamond film

cvd diamond film

natural diamond

lattice constant ()

3.567

3.567

density (g/cm3)

3.51

3.515

specific heat CP (j/mol, (at 300K))

6.195

6.195 p>

elastic modulus (GPA)

1220*

hardness (GPA)

*

longitudinal wave velocity (m/s)

18200

friction coefficient

0 15

0.. 15

coefficient of thermal expansion( × 10 -6 ℃ -1)

2.0

1.1****.

thermal conductivity (w/cm.k)

21

22*

band gap (EV)

5.45

resistivity (Ω.Cm)

1016

saturated electron velocity( × 107cms-1)

2.7

2.7*

carrier mobility (cm2/vs)

electron

2200**

void

480

1600*

breakdown field strength( × 105v/cm)

100

dielectric number display impact experiment electromechanical constant

5.6

5.5

optical absorption edge (□ m)

0.22

refractive index (10.6 □ m)

2 42

2.42

optical transmission range

from ultraviolet to far infrared (radar wave)

from ultraviolet to far infrared (radar wave)

microwave dielectric loss (Tan □)

<0.0001

note: * ranks first among all known substances, * * ranks second among all substances, * * * is equivalent to invar alloy

(to be continued)

the imbalance between supply and demand has changed from the past state of oversupply to the current situation of supply shortage

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