Mechanical and tribological properties of TiN and SiCN nanocomposite coatings deposited using methyltrichlorosilane

The paper examines nanocomposite coatings based on TiN and SiCN obtained by plasma-enhanced chemical vapor deposition (PECVD) using methyltrichlorosilane (MTCS) as one of the precursors. The nanocomposite coatings demonstrate four types of structures depending on deposition modes: nc-TiN, nc-TiN/a-SiCN, nc-TiNC/nc-TiSi₂/a-SiCN, and nc-TiNC/nc-TiCl₂/a-SiCN. The nanohardness and elastic modulus of the coatings reach 31 and 350 GPa, respectively. The coatings on substrates of hard alloys, high-speed steel, and silicon increase the nanohardness of the base from 10 to 100%. The correlation between the H/E ratio and wear resistance is not observed. The coatings deposited at low radiofrequency powers demonstrate good adhesion to silicon substrates. It is shown that the use of MTCS as the main precursor allows one to obtain hard and wear-resistant nanocomposite coatings. __________ Translated from Poroshkovaya Metallurgiya, Vol. 47, No. 1–2 (459), pp. 125–133, 2008.     

Poly- and single-crystalline h-GaN grown on SiCN/Si(100) and SiCN/Si(111) substrates by MOCVD

This paper reports the growth of polycrystalline GaN on Si(100) and single-crystalline h-GaN on Si(111) substrates with a single-crystalline SiCN burffer layer by metalorganic chemical vapor deposition (MOCVD). From high-resolution x-ray diffraction (HRXRD) and scanning election microscopy (SEM) analyses, GaN on SiCN/Si(100) is polycrystalline and GaN on SiCN/Si(111) is single-crystalline. From photoluminescence analysis, the energy gaps of h-GaN/SiCN/Si(100) and c-GaN/SiCN/Si(100) are ∼3.4 and ∼3.2 eV at 300 K but shift to 3.5 and 3.3 eV at 15 K, respectively. A model to explain the growth mechanism is also proposed.     

Synthesis, electrical and magnetic characterization of core-shell silicon carbo-nitride coated carbon nanotubes

We demonstrate synthesis, electrical and magnetic characterization of silicon carbo-nitride (SiCN) coated multiwalled carbon nanotubes in a core-shell structure. The core formed by a carbon nanotube had a diameter in the range of 10-100 nm. The shell was synthesized by pyrolysis of an SiCN precursor on the surface of carbon nanotubes. Electrical resistivity of an individual composite nanotube was measured to be ~ 2.55 × 10³ Ω cm. The magnetic measurements performed by a superconducting quantum interference device on the composite nanotubes in the temperature range of 5-300 K show a reduced coercive field with increasing temperatures. The monolayer thick coating of an ultra high temperature multifunctional ceramic SiCN makes these composite nanotubes very promising for sensing applications in harsh environments.     

真空气氛下非晶硅碳氮(SiCN)陶瓷的高温晶化行为

以六甲基二硅氮烷为单一前驱体,采用电热裂解化学气相沉积技术制备了SiCN陶瓷. 借助X射线衍射仪、透射电子显微镜研究了真空环境中非晶SiCN陶瓷在1300～1900℃范围内的晶化行为,并根据研究结果,运用分解-结晶机理解释了其晶化过程. 非晶SiCN陶瓷在低于1300℃开始发生分解,形成富Si-C区域,并最终发生β-SiC结晶. 其结晶度随热处理温度的升高而愈加明显.在1700℃处理时发生β-SiC→α-SiC相变. 分解形成的N-难以与Si-结合形成富Si-N区域,最终以N₂形式溢出,在整个热处理温度范围没有出现氮气下热处理时存在的Si₃N₄结晶.     

C+注入a-SiNx∶H的原子化学键合的研究

常温下对低压化学气相沉积制备的纳米硅镶嵌结构的a-SiNx∶H薄膜进行C+注入，能量为30keV，剂量为2e17cm-2. 对C+注入的SiNx薄膜在800℃的温度下，进行2h的常规炉退火处理. 通过XPS,AES的测量得到，经800℃高温退火处理后的薄膜形成了部分SiCxNy结构. 用喇曼、XPS等分析手段对薄膜结构及成分进行了测量与分析，得到不同退火温度对离子注入形成SiCN薄膜结构与成分的影响，认为高温退火后薄膜中硅含量与SiCxNy薄膜的形成有重要的关系.     

Nitrogen Contents on Tribological Properties of Magnetron Sputtered SICN Coatings

SiCN COATINGS have stimulated wide interestbecause they exhibit many good properties for potentialindustrial applications,such as high opticaltransparency in Infrared(IR)region,wide bandgap,chemical inertness and high refractive index,goodinsulating property,good mechanical and tribologicalproperties(high hardness,elastic modulus,low friction,etc.)[1-4].Amorphous and/or hydrogenated SiCNcoatings can be prepared by various depositionmethods,such as laser ablation[5],plasma-assistedchemica…     

Microstructure and EMW absorption properties of CVI Si3N4–SiCN ceramics with BN interface annealed in N2 atmosphere

A kind of chemical vapor infiltration (CVI) Si₃N₄–BN–SiCN composite ceramic with excellent electromagnetic wave (EMW) absorbing properties is obtained by CVI BN interface and SiCN matrix on porous Si₃N₄ ceramics, and then annealed at high temperatures (1200°C‐1500°C) in N₂ atmosphere. The crystallization behavior, EMW absorbing mechanism and mechanical properties of the composite ceramics have been investigated. Results showed CVI SiCN ceramics with BN interface were crystallized in the form of nanograins, and the crystallization temperature was lower. Moreover, both EMW absorbing properties and mechanical properties of CVI Si₃N₄–BN–SiCN composite ceramics firstly increased and then decreased with the increase in annealing temperature due to the influence of BN interface on the microstructure and phase composition of the composite ceramics. The minimum reflection coefficient (RC) and maximum effective absorption bandwidth (EAB) of the composite ceramics annealed at 1300°C were ?47.05 dB at the thickness of 4.05 mm and 3.70 GHz at the thickness of 3.65 mm, respectively. The flexural strength and fracture toughness of the composite ceramics annealed at 1300°C were 94 MPa and 1.78 MPa/m^1/2, respectively.     

Enhanced electromagnetic microwave absorption properties of SiCN(Fe) ceramics produced by additive manufacturing via in-situ reaction of ferrocene

SiCN(Fe) ceramics with excellent electromagnetic wave (EMW) absorption performance were successfully prepared from a preceramic polymer doped with ferrocene. Additive manufacturing (Digital Light Processing), providing enhanced structural design ability, was employed to fabricate samples with complex architectures. During pyrolysis, ferrocene catalyzed the in-situ formation of a large amount of turbostratic carbon, graphite and SiC nanosized phases, which formed carrier channels in the electromagnetic field and increased the conductivity loss. Meanwhile, it also increased the dipole polarization, interface polarization and the dielectric properties of the material, which finally enhanced the EMW absorption capacity of SiCN(Fe) ceramics. When containing 0.5 wt% ferrocene, the material showed good performance with EAB 4.57 GHz at 1.30 mm, and RL_min −61.34 dB at 2.22 mm. The RL_min of 3D-SiCN-0.5 ceramics was −6 dB, and the RL of the X-band was lower than −4 dB at 2 mm.     

Cyclic thermal shock behaviors of carbon fibers reinforced SiCN ceramics with bio-inspired Bouligand-like architectures

Ceramic matrix composites (CMCs) are commonly used for high temperature components in aircrafts. However, thermal shock, as a typical loading case, will cause high thermal stresses in CMCs resulting in brittle fracture failure, and material cracking caused by thermal shock can further reduce the effectiveness of thermal protection function. In the present paper, we propose a bionic hierarchical fiber preform design method to improve the thermal shock resistance of ceramics. The effect of architectures of fiber preforms of continuous carbon fiber-reinforced CMCs on the thermal shock resistance was investigated to understand its importance and the related mechanical mechanisms. Thermal shock (cycling) tests were performed with continuous carbon fibers reinforced SiCN ceramic matrix composites (C_f/SiCN) prepared by PIP. 3D micro-CT scan and three-point bending tests were also conducted to evaluated the resultant damage. The results showed that smaller internal damage and higher thermal shock resistance can be obtained in comparison to pure SiCN ceramics, and the underlying mechanism can be explained by the fact that smaller pitch angle can resist the through-thickness crack propagation via promoting diffused in-plane damage. The present study offers a possibility in developing biomimetic C_f/SiCN ceramics with excellent thermal shock behavior.     

Dielectric and microwave absorption properties of polymer derived SiCN ceramics annealed in N2 atmosphere

Porous SiCN ceramics were successfully fabricated by pyrolysis of a kind of polysilazane. The effects of annealing temperature on the microstructure evolution, direct-current electrical conductivity, dielectric properties, and microwave absorption properties of SiCN in the frequency range 8.2–12.4 GHz (X-band) were investigated. With the increase of annealing temperature, SiC, Si₃N₄ and free carbon nanodomains are gradually formed in the SiCN. Both the SiC and free carbon nanodomains lead to the increases of the complex relative permittivity and loss tangent of SiCN. With the increase of the annealing temperature, the average real permittivity, imaginary permittivity and loss tangent increase from 4.4, 0.2 and 0.05 to 13.8, 6.3 and 0.46, respectively. The minimum reflection coefficient and the frequency bandwidth below −10 dB for SiCN annealed at 1500 °C are −53 dB and 3.02 GHz, indicating good microwave absorption properties.