Influence of silicon content on the microstructure and hardness of CrN coatings deposited by reactive magnetron sputtering

CrN and CrSiN films were deposited on the stainless steel and silicon substrates by DC magnetron sputtering and their microstructural features were investigated by X-ray diffraction (XRD), scanning electron microscope (FE-SEM/EDS), and atomic force microscopy (AFM). The influence of Si content along with process parameters such as power on the microstructural characteristics of Cr–Si–N and CrN films were investigated and compared between each other. The power and increasing Si contents strongly influence the microstructural and hardness of the deposited films. XRD analysis of the coatings indicates a grain refinement with increase in Si content during deposition of coatings, which is tandem with AFM and SEM results. Also, the surface roughness and particle size are decreasing with addition of Si in the films. The hardness of CrN and CrSiN was measured by microhardness tester and found that introduction of Si content in the CrN system increases its hardness from 1839 Hv to 2570 Hv.     

Hot hardness of Si3N4-based materials

The Vickers hardness of dense Si₃N₄ ceramics of the Si-Ce-Al-O-N system was investigated from room temperature to 1200°C. A sloppy decrease of hot hardness occurred above 850–900°C. A compensation law was observed between the pre-exponential factors of the hot-hardness dependence on the reciprocal of absolute temperature, and the values of the activation energy of hardness. This relationship shows that the low-temperature deformation mechanism, such as microplasticity, is competing in parallel with a grain-boundary diffusion-controlled creep process in the high-temperature range.     

衬底偏压对CrN／Si3N4纳米多层膜结构和力学性能的影响

采用磁控溅射法在不同基底偏压条件下制备了CrN／Si3N4纳米多层膜,用x射线衍射仪、原子力显微镜及纳米压痕仪表征,结果表明,衬底偏压对CrN／Si3N4纳米多层膜微观结构、界面结构、硬度和磨损性能有重要影响;漂浮电位时,导致多层膜界面粗糙,CrN呈（200）、（111）共同生长,硬度和弹性模量低;当偏压变化时,界面宽度和粗糙度变化不大,硬度和模量变化的主要原因是不同衬底偏压下的晶格畸变导致两层材料弹性模量变化和晶粒尺寸变化。与漂浮电位相比,涂层的屈服应力和断裂韧性有所增强。     

Structure, hardness and thermal stability of nanolayered TiN/CrN multilayer coatings

Nanolayered TiN/CrN multilayer coatings were deposited on silicon substrates using a reactive DC magnetron sputtering process at various modulation wavelengths (Λ), substrate biases (V_B) and substrate temperatures (T_S). X-ray diffraction (XRD), nanoindentation and atomic force microscopy (AFM) were used to characterize the coatings. The XRD confirmed the formation of superlattice structure at low modulation wavelengths. The maximum hardness of the TiN/CrN multilayers was 3800 kg/mm² at Λ=80  Å, V_B=−150 V and T_S=400°C. Thermal stability of TiN, CrN and TiN/CrN multilayer coatings was studied by heating the coatings in air in the temperature range (T_A) of 400-800°C. The XRD data revealed that TiN/CrN multilayers retained superlattice structure even up to 700°C and oxides were detected only after T_A?750°C, whereas for single layer TiN and CrN coatings oxides were detected even at 550°C and 600°C, respectively. Nanoindentation measurements showed that TiN/CrN multilayers retained a hardness of 2800 kg/mm² upon annealing at 700°C, and this decrease in the hardness was attributed to interdiffusion at the interfaces.     

Development of microstructure during the fabrication of Si3N4 by nitridation and pressureless sintering of Si:Si3N4 compacts

The technique for the fabrication of Si₃N₄ which was investigated involves the nitridation of Si:Si₃N₄ powder compacts containing additions of sintering aids (e.g. Y₂O₃ and Al₂O₃) followed by pressureless sintering. The development of microstructure during fabrication by this method has been followed by X-ray diffraction and analytical electron microscopy. As well as being important for the sintering process, it was found that the sintering aids promote nitridation through reaction with the surface silica on the powder particles. During nitridation extremely fine grained Si₃N₄ forms at silicon powder particle surfaces and at tunnel walls extending into the interior of these powder particles. Secondary crystalline phases which form during nitridation are eliminated from the microstructure during sintering. The- to-Si₃N₄ phase transformation is completed early in the sintering process, but despite this the fully sintered product contains fine-Si₃N₄ grains. The grains are surrounded by a thin intergranular amorphous film.     

Fabrication,mechanical properties and microstructure analysis of Si3N4/SiC nanocomposite

Ceramic nanocomposites, Si₃N₄ matrix reinforced with nano-sized SiC particles, were fabricated by hot pressing the mixture of Si₃N₄ and SiC fine powders with different sintering additives. Distinguishable increase in fracture strength at low and high temperatures was obtained by adding nano-sized SiC particles in Si₃N₄ with Al₂O₃ and/or Y₂O₃. Si₃N₄/SiC nanocomposite added with Al₂O₃ and Y₂O₃ demonstrated the maximum strength of 1.9 GPa with average strength of 1.7 GPa. Fracture strength of room temperature was retained up to 1400 as 1 GPa in the sample with addition of 30 nm SiC and 4 wt% Y₂O₃. Striking observation in this nanocomposite is that SiC particles at grain boundary are directly bonded to Si₃N₄ grain without glassy phases. Thus, significant improvement in high temperature strength in this nanocomposite can be attributed to inhibition of grain boundary sliding and cavity formation primarily by intergranular SiC particles, besides crystallization of grain boundary phase.     

Si3N4/FePd/Si3N4薄膜的晶体结构和磁性能研究

采用磁控溅射的方法制备了Si₃N₄/FePd/Si₃N₄三层膜, 研究了非磁性材料Si₃N₄作为插入层对磁记录FePd薄膜结构与磁性能的影响。结果表明, 热处理后Si₃N₄分布在FePd纳米颗粒之间, 抑制了FePd晶粒的生长, 与纯FePd薄膜相比, Si₃N₄/FePd/Si₃N₄薄膜的颗粒明显得到细化; 通过添加Si₃N₄层, FePd薄膜的晶体学参数c/a从0.960减小到0.946, 表明Si₃N₄可以有效促进FePd薄膜的有序化进程, 同时提升了矫顽力和剩磁比, 分别提高到249 kA/m、0.86; 随着600℃退火时间的进一步延长, 添加Si₃N₄的薄膜磁性没有迅速下降, 在较宽的热处理时间范围内磁性能保持在比较高的水平, 提高了抗热影响的能力。Si₃N₄作为插入层对FePd薄膜的磁性能具有较大的提升作用, 这对磁记录薄膜的发展具有重要意义。     

Thermal conductivity of unidirectionally oriented Si3N4w/Si3N4 composites

-silicon nitride whiskers were aligned unidirectionally in silicon nitride sintered with 2 wt% Al₂O₃ and 6 wt% Y₂O₃. It was be densified by the Gas Pressure Sintering (GPS) method. Thermal conductivity of the sintered body with different amount of - silicon nitride whiskers was measured by the direct contact method from 298 K to 373 K. This unidirectionally oriented -silicon nitride whiskers grew into the large elongated grains, and improved also the thermal conductivity. The amount of -silicon nitride whiskers changed the microstrcuture, which changed the thermal conductivity.     

Evaluation of Si3N4 joints: bond strength and microstructure

Joining of pressurelessly sintered silicon nitride ceramics was carried out using adhesive slurries in the system Y-Si-Al-O-N in a nitriding atmosphere. The effects of bonding parameters, such as joining temperature (1450–1650°C), applied pressure (0– MPa) and holding time (10–60 min), on the bond strength of joint were evaluated. A typical microstructure of the joint bonded with the optimum adhesive was investigated. The three point bend testing of joined samples with 3 × 4 × 36 mm³ in dimension was employed to study the bond strength of joints. The results show that an optimum joining process was achieved by holding at 1600°C for 30 min under an external pressure of 5 MPa and the maximum bond strength was 550 MPa, compared to 700 MPa of unbonded Si₃N₄ ceramic, using the adhesive having the Si₃N₄/(Y₂O₃ + SiO₂ + Al₂O₃) ratio of 0.39. The good bond strength is attributed to the similarity in microstructure and chemical composition between joint zone and ceramic substrate. The fracture modes were classified into two types according to the values of bond strength. This revised version was published online in September 2006 with corrections to the Cover Date.     

Fabrication and microstructure characterization of continuously porous Si2N2O–Si3N4 ceramics

The microstructure of continuously porous Si₂N₂O–Si₃N₄ ceramics fabricated for use in environmental filters by a multi-pass extrusion process was investigated using SEM, XRD and TEM techniques. The matrix regions of the nitrided Si₂N₂O–Si₃N₄ porous bodies were composed of many Si₃N₄ particles and short Si₂N₂O fibers. However, in the continuously porous regions, many network type Si₂N₂O fibers, 200–420 nm in diameter, with a high aspect ratio were observed. After post-sintering of the nitrided bodies at 1800 °C, the diameter of the fibers increased to about 2–3 μm, while their length was shortened. The values of bending strength, relative density and hardness of the post-sintered Si₂N₂O–Si₃N₄ bodies were about 117.6 MPa, 73.6% and 616 Hv, respectively.     

偏压对CrN/Si3N4纳米多层膜结构、硬度和断裂韧性的影响

利用磁控溅射法在不同基底偏压条件下制备了CrN/Si3N4纳米多层膜,分别用X射线衍射仪、原子力显微镜及纳米压痕仪表征多层膜的微观结构及力学性能,结果表明,衬底偏压对CrN/Si3N4纳米多层膜微观结构、界面结构、硬度和磨损性能有重要影响。漂浮电位时多层膜界面粗糙,CrN呈(200)、(111)共同生长,硬度和弹性模量低,有偏压且变化时界面宽度和粗糙度变化不大,硬度和模量变化的主要原因是不同衬底偏压下的晶格畸变导致两层材料弹性模量变化和晶粒尺寸变化。基底偏压的优化有助于改善涂层的屈服应力和断裂韧性。     

A quantitative evaluation of microstructure in Si3N4/SiC platelet and participate composites

A microstructural evaluation of Si₃N₄ containing 15–40 vol% SiC platelets or particles is presented. All the composites were fully densified by hot isostatic pressing without external addition of sintering aids. Size, morphology, surface roughness and crystal structures of the SiC phases before and after sintering were compared in order to discuss the structural stability of the reinforcements up to 2050 °C in Si₃N₄ matrix. Morphology and phase characteristics of the grain boundary are also discussed. In addition, homogeneity and isotropy of the composite bodies were quantitatively examined by image analysis techniques and it was recognized that, for a similar degree of dispersion, the characteristic of three-dimensional randomness could be preserved only at V _f<30% in the composites containing high aspect ratio platelets.     

Mechanical properties and microstructure in sintered and HIPed SiC particle/Si3N4 composites

Pressureless sintered (PLS) and gas-pressure sintered (GPS) Si₃N₄, PLS and GPS SiC particle/Si₃N₄ composites, and PLS + HIP and GPS + HIP SiC particle/Si₃N₄ composites were produced. Investigation of their mechanical properties showed that PLS + HIP and GPS + HIP composites, containing SiC particles in the beta-silicon nitride grains, yield higher bending strength, although its fracture toughness remains at the same level. This is attributed to the fact that the added SiC particles inhibit excessive growth of beta-Si₃N₄ grains without changing the fracture behaviour. However, this investigation also found precipitation during the reaction between SiC and nitrogen in gas pressure sintering, resulting in a low Young's modulus and low density in the GPS composite.     

ICVI法制备Si3N4P/ Si3N4 复合材料致密化行为数值模拟

根据Si₃N₄ 颗粒增强体的结构特点及等温化学气相法( ICVI) 的工艺特点, 对Si₃N₄ 颗粒增强Si₃N₄ 复合材料的致密化过程进行了数值模拟。用球形孔隙模型表征Si₃N₄ 颗粒增强体的结构特征, 用传质连续方程表征先驱体在预制体中的浓度分布。为了检验模型的准确性和适用性, 进行了相应的实验验证。模拟结果与实验结果具有相似的致密化规律, 预测的渗透时间和孔隙率与实验结果均十分接近, 表明本文中建立的数学模型可以较好地表征Si₃N₄P / Si₃N₄ 复合材料的ICVI 过程。     

Reaction between Si3N4 and Fe-Ni alloy

In relation to the joining of silicon nitride ceramics to metal, the reaction between Si₃N₄ and Fe-Ni alloy was investigated under a nitrogen or an argon atmosphere at temperatures from 1123 to 1573 K. Reaction rates were determined by thermogravimetry and reaction products were examined by X-ray diffraction. Fe-Ni-Si solid solution, Ni₃Si, Ni₅Si₂, NiSi₂, Fe₃Si, Fe₅Si₃ and FeSi were produced. The initial rate obeyed a linear rate law. The rate at the late stage of reaction was described by a parabolic rate law or Fick's second law. The reaction mechanism and the rate-determining step were proposed.     

Investigation of Si and Ge growth on Si3N4/Si

The growth of Si and Ge on silicon nitride surfaces has been investigated using scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and Auger electron spectrometer (AES). In the early stages, Si or Ge nanoclusters appeared irrespective of the different substrates. When annealed, the Si clusters were more stable against coalescence than those of Ge. As these clusters continued to grow, crystalline facets started to form. Both Si and Ge islands grew predominantly with (111)-oriented top facets on the crystalline Si₃N₄(0001)/Si(111). By contrast, they both grew in random orientation on the amorphous Si₃N₄ surface. Low-index facets such as (111) and (001) coexisted with high-index facets such as (113).