Suppressing the surface roughness and columnar growth of silicon nitride films

The growth and structure evolution of silicon nitride films prepared by radio frequency magnetron sputtering at low pressure were investigated for thickness changes. Grazing-incidence X-ray reflectivity, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy were used to study the structure, surface roughness and composition, respectively, of the films. It was found that with an increase in thickness from 5 to 830 nm, the silicon nitride films have a similar surface structure and their surface roughness only slightly increases. The surface roughness of all the silicon nitride films is only a little more than 0.2 nm, much less than previously reported results. AFM measurement of the fractured film surface indicated that thin silicon nitride films with a thickness below approximately 300 nm have a dense, smooth and uniform structure, and columnar structures gradually appear only in thick films. These results are mainly attributed to the special design of the sputtering system and the energetic particle bombardment of the growing surface, by which the surface roughness and columnar growth were suppressed.     

Microgrinding of Nanostructured Material Coatings

This study is aimed at experimentally investigating the effect of microgrinding process on the surface finish, subsurface damage and residual stresses of thermally sprayed nanostructured WC/12Co (n-WC/12Co) and Al₂O₃/13TiO₂ (n-Al₂O₃/13TiO₂) coatings. The material removal mechanisms are discussed. Surface textures are measured with stylus profilometry, scanning electronic microscopy (SEM) and atomic force microscopy (AFM), and analyzed using conventional methods and scale-sensitive fractal analysis. Residual stresses are measured with glancing incident X-ray diffraction (GIXD) technique that is capable of providing the depth profiles of residual stresses. Investigated is also grinding damage to the coatings.     

Signal fidelity and tracking force in stylus profilometry

This paper presents an experimental study of the influence of tracking force the signal fidelity in stylus profilometry. To do this, a simple, retrofit variable force actuator has been designed, built and assessed. This consists of a permanent magnet attached to the stylus arm about which is a noncontacting solenoid actuating coil. This simple device readily provides a continuously variable stylus force over the range 0.01 to 15 mN.Using this, surface finish values on specimens of steel, aluminium, brass and copper have been measured over a range of stylus loads and traverse speeds. Analysis of these traces has been carried out both by evaluation of the surface finish parameters, Rq, Ra, RMS slope and RMS peak curvature and a qualitative analysis using scanning electron microscopy. As might be expected, results indicate that stylus techniques give consistently reproducible values over a wide range of loads and speeds. However, limits are identified outside which erroneous values of surface finish parameters may be obtained or damage incurred if excessive loads or improper tracking speeds are used.     

Ultrananocrystalline Diamond-Coated Microporous Silicon Nitride Membranes for Medical Implant Applications

Ultrananocrystalline diamond (UNCD) exhibits excellent biological and mechanical properties, which make it an appropriate choice for promoting epidermal cell migration on the surfaces of percutaneous implants. We deposited a ~150 nm thick UNCD film on a microporous silicon nitride membrane using microwave plasma chemical vapor deposition. Scanning electron microscopy and Raman spectroscopy were used to examine the pore structure and chemical bonding of this material, respectively. Growth of human epidermal keratinocytes on UNCD-coated microporous silicon nitride membranes and uncoated microporous silicon nitride membranes was compared using the 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide (MTT) assay. The results show that the UNCD coating did not significantly alter the viability of human epidermal keratinocytes, indicating potential use of this material for improving skin sealing around percutaneous implants.     

Synthesis of ultralong Si3N4 nanowires by a simple thermal evaporation method

Large-scale vapor-solid synthesis of ultralong silicon nitride (Si3N4) nanowires was achieved by using simple thermal evaporation of mixture powders of active carbon and monoxide silicon. The products were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy. The results suggest that the silicon nitride nanowires have a smooth surface, with lengths of up to several hundreds of microns and diameters of 100-300 nm. A detailed study of both the chemical and structural composition was performed. Such ultralong silicon nitride nanowires demonstrate potential applications as materials for constructing nanoscale devices and as reinforcement in advanced composites.     

微结构砂轮对不同陶瓷的磨削性能

基于阵列微孔的微结构砂轮和普通砂轮对氧化铝、氮化铝、氧化锆及氮化硅陶瓷材料的不同磨削性能,对比研究不同砂轮和不同陶瓷材料的磨削力、比磨削能、表面粗糙度及表面崩边特征。结果表明：相比普通砂轮,微结构砂轮提高了氧化铝、氮化铝及氧化锆陶瓷的磨削力和比磨削能,降低了表面粗糙度,而对氮化硅陶瓷的磨削力及表面粗糙度影响不明显;相比其他陶瓷,氮化硅陶瓷具有较高的磨削力和比磨削能。从磨削加工表面特征上看,氧化铝、氮化铝陶瓷以脆性去除方式为主,氧化锆以塑性去除为主,而氮化硅则兼具塑性和脆性去除特征;微结构砂轮加工表面崩边尺寸大于普通砂轮的崩边尺寸,氧化铝和氮化铝陶瓷的表面崩边尺寸明显大于氧化锆和氮化硅陶瓷的。     

Characterization of TiBN films grown by ion beam assisted deposition

This paper presents one of the first attempts to measure and model the ellipsometric data for ternary nitride coatings in general and TiBN coatings in particular. TiBN coatings with a functionally graded underlayer of Ti/TiN have been deposited at low temperatures (<200 °C) on a silicon substrate using ion beam assisted deposition (IBAD). The coating selected for detailed analysis had a total thickness of 1.5±0.2 μm. The deposited structure was characterized post-deposition using X-ray diffraction (XRD), atomic force microscopy (AFM), Rutherford backscattering (RBS), X-ray photoelectron spectroscopy (XPS), infrared spectroscopic ellipsometry (IR-SE), and visible-light spectroscopic ellipsometry (VIS-SE). The primary phases (TiB₂, TiN, and BN) in the film were identified using XRD. The surface morphology and nanocrystalline nature of the coating (grain size of 5–7 nm) were deduced using AFM. The chemical composition and phase composition of the sample was determined from RBS and XPS measurements and was subsequently deduced from the analysis of the VIS-SE data. The refractive indices for the constituent phases were deduced from the investigation of TiB_2, TiN and BN single layers with SE. Good correlation was observed between RBS, XPS and VIS-SE for the data on the TiBN sample. XPS and IR-SE suggested that BN formed in the amorphous form. The chemical composition study using these various techniques shows that in-situ SE is a potential technique to control the growth of ternary nitride coatings. Finally, the mechanical properties of the coating were evaluated using a nanoindenter. The hardness and elastic modulus were measured to be 42 GPa and 325 GPa, respectively.     

表面状态对690TT合金腐蚀及应力腐蚀行为的影响

采用扫描电镜、原子力显微镜和表而粗糙度测量仪对具有不同表面状态的690TT合金表面形貌进行了表征与比较。采用零电荷电位测量、动电位扫描和电化学快慢扫描等方法对不同的690TT合金的腐蚀行为进行了比较。结果表明,与机械抛光样品相比较,打磨样品表面起伏较严重,拥有更大的表面粗糙度值;在相同的腐蚀环境中,打磨样品比机械抛光样品表现出更大的腐蚀速度和更高的应力腐蚀开裂敏感性。分析认为,单纯的表面较大粗糙度和残余应变均能够促进690TT合金的腐蚀。实验中打磨690TT样品表现出的较高腐蚀速度和应力腐蚀开裂敏感性是由其较大的表面粗糙度和表面残余应变综合影响结果。     

Plasma and ion-beam-assisted deposition of multilayers for tribological and corrosion protection

Multilayers of Ti/TiN and Al/AlN were deposited on steel and silicon by magnetron sputtering and ion-beam-assisted deposition. Compositions and film thicknesses were determined by Rutherford backscattering. Hardness was measured with a dynamic ultramicrohardness tester. The corrosion protection potential in an aqueous environment was evaluated by electrochemical techniques. The results are discussed in terms of the structure and composition of the multilayer arrangement. It turns out that the multilayer coatings generally show a better corrosion protection performance than both the pure metal and the pure nitride films, with an optimum ratio of nitride film thickness to metal film thickness for a maximum corrosion protection effect. The hardness values are in between that of nitride single film and those of metal single films. Deposition of multilayers with the possibility of selecting the thickness ratio of metal to nitride film for particular mechanical and chemical requirements allows a controlled adaption of the film features to a given application problem.     

Surface roughness measurement on machined surfaces using angular speckle correlation

Surface roughness is of great importance in fields, such as tribology, semiconductor technology and medicine. Stylus techniques, in which a stylus is drawn along the surface and the vertical movement of the stylus is recorded, have been used traditionally in measuring surface roughness. Non-contact methods, such as optical ones, have the advantage that they can be used for the in-process measurement of surface roughness. In this paper, results of the measurement of surface roughness using angular speckle-correlation on machined surfaces are presented. Surfaces of approximately 1.6 < R_a < 6.3 μm have been measured, the surfaces being classified in the same manner as when using a stylus instrument. ASC is a technique that also allows in-process measurement of the roughness of surfaces on machined surfaces. A new technique to achieve increased repeatability by using an angle detection unit is also presented in this paper.     

Measurement of optical surfaces generated by diamond turning

For the manufacture of ultraprecision parts an entirely controlled machining technology is required as well as the capability of a complete evaluation regarding microgeometry and integrity of the generated surfaces. Optical and stylus profilometry are the commonly used technologies for determining surface roughness. Furthermore, atomic force microscopy AFM is frequently applied for 3D characterization of the microtopography.In this paper the application of atomic force microscopy in the field of diamond turning is presented by means of measuring and manufacturing examples. Typical applications are the manufacture of metal mirrors from aluminum, copper and electroless nickel substrates by diamond turning and fly-cutting operations using monocrystalline diamond tools. The atomic force microscope is used for the evaluation of the microtopography of these mirrors, which is decisive for their optical properties and quality. Additionally, the atomic force microscope can be used for measurements of microstructured components and the diamond tools itself. In this case, AFM is not only used for roughness measurement, but also for inspection and verification of the actual, respectively, the produced geometry of the components and the tools. The examples given in this paper illustrate the great potentials of atomic force microscopy in the field of ultraprecision machining.     

AFM and light scattering measurements of optical thin films for applications in the UV spectral region

Combination of atomic force microscopy and scattering measurements allows controlling the microstructure of substrates and optical thin films in the nanometer scale and of surface homogeneity over large areas. Results are presented of measurements on superpolished and conventionally polished substrates as well as on thin film fluoride coatings, demonstrating the capabilities of these measurement techniques.     

氮化硅──氧化镁──二氧化铈的无压烧结

对氧化硅－氧化镁－二氧化铈无压烧结的研究表明：MgO－CeO_2是一种非常有效的氮化硅助烧剂，MgO－CeO_2的含量及烧结工艺对氮化硅的致密化及机械性能有强烈的影响，本文讨论了这些影响规律，当氧化镁与氧化铈共存时，二氧化铈更容易与氮化硅颗粒表面的二氧化硅反应形成难熔的窗铈的玻璃相，无压烧结的氮化硅－氧化镁－二氧化铈陶瓷，其相对密度可超过98％，强度超过920MPa，这在目前的各种无压烧结的氮化硅材料中，是非常高的，Si－Mg－Ce－O－N系统在理论研究和实用上都有极大的价值。     

Effect of boron addition on the microstructures and mechanical properties of thermomechanically processed and tempered low carbon bainitic steels

Thermomechanical process and tempering heat treatment were employed to produce the experimental steel plates. The effect of boron addition on the microstructure and mechanical properties of low carbon bainitic steels was studied in this paper. Microstructure observation and crystallographic features were conducted by using optical microscopy, SEM, TEM and electron back scattering diffraction (EBSD) analysis. The results showed that under the same rolling processes and heat treatment conditions, a substantia...     

The effect of ELID grinding on the flexural strength of silicon nitride

Advanced structural ceramics, such as silicon nitride-based materials, are of significant interest due to their excellent physical and mechanical properties. However the cost of grinding these ceramics, an integral part of their fabrication, is very high and can result in surface and subsurface damage to the material. These defects can significantly reduce the strength and reliability of the finished component and are sensitive to grinding parameters. In this investigation, the effect of finish electrolytic in-process dressing (ELID) grinding on the flexural strength of silicon nitride specimens were studied. Kyocera's silicon nitride SN 235, in the form of Modulus of Rupture (MOR) specimens, were ground using the application of ELID grinding with a # 6000 grit sized cast iron bonded diamond (CIB-D) grinding wheel. A significant improvement in the strength of the Si₃N₄ specimens was noted when finish ELID grinding was performed. This was the result of ductile regime grinding using the application of finish ELID grinding. Another method to improve the flexural strength of silicon nitride specimens will also be addressed in this paper.     

Optimized Tension for AZ31B Thin Sheets Rolled with On-Line Heating Rolling

On-line heating rolling mill which could efficiently preheat sheet and apply tensile force on both ends of the sheet along rolling direction(RD) was used to investigate the effect of tension on mechanical behavior and shape quality of magnesium sheets. For revealing the infl uence mechanism, many analysis techniques including optical microscope, electron backscattered diffraction, macrotexture and transmission electron microscope were performed. The shape defect, edge wave, could be eliminated under higher tension along RD, which was attributed to more uniform distribution of microstructure and microstrain. Nevertheless, it is undesirable that the forward tensile force exceeds 3 kN in present work because the strength decreased for high recrystallization level when the tensile force is beyond this value. Furthermore, the main deformation mode was still slip during rolling process despite of accompanying twining, e.g., double twins, but more prismatic slip activated when tensile force exceeds 3 kN. The distribution of shear bands was affected by the applied tensile force that they appear as "V" shape along RD at a low forward or backward tensile force, while they appear as reticulate shape under applied tensile force of 5 kN.     

Mechanical properties of plasma-deposited silicon-based inhomogeneous optical coatings

Amorphous hydrogenated silicon nitride, oxide and oxynitride films are deposited by plasma-enhanced chemical vapour deposition (PECVD) using a dual-mode microwave/radio-frequency (MW/RF) plasma system. Optical filters are prepared by varying the film composition either abruptly (discrete, homogeneous multilayer structure) or continuously (graded-index, inhomogeneous structure). The coatings are characterised both optically, by spectrophotometry and spectroscopic ellipsometry, and mechanically, with depth-sensing indentation and low-load microscratch testing. A comparison is made between the properties of the homogeneous multilayer and the inhomogeneous multilayer structure with the corresponding optical performance. This multiple technique approach for characterisation was proved to be efficient for analysis of the optical and mechanical behaviour of coatings, and it provides a possibility for optimising the deposition process. It is demonstrated that the graded system exhibits a higher mechanical strength and a better toughness than the discrete structure.     

Ellipsometric analysis and optical absorption characterization of nano-crystalline diamond film

A nano-crystalline diamond （NCD） film with a smooth surface was successfully deposited on silicon by a hot filament chemical vapor deposition （HFCVD） method. Scanning electron microscopy （SEM）, atomic force microscopy （AFM）, RAMAN scattering spectra, as well as spectroscopic ellipsometry were employed to characterize the as-grown film. By fitting the spectroscopic ellipsometric data in the energy range of 0.75-1.50 eV with a three-layer model, Sildiamond＋non-diamondldiamond＋ non-diamond＋voidlair, the optical constants are obtained. The refractive index of the NCD film varies little from 2.361 to 2.366 and the extinction coefficient is of the order of 10^-2. According to the optical transmittance and absorption coefficient in the wavelength range from 200 to 1 100 nm, the optical gap of the film is estimated to be 4.3 eV by a direct optical transition mechanics.     

Plasma Spray Deposition Enhancement of Titanium Nitride Layer Using Nitrogen-Contained Plasma Irradiation of Titanium Substrate as a Pre-spraying Method

Reactive plasma spray of TiN ceramic coating attracts much attention over the years because of its ability to deposit thick layers on various metal surfaces. However, some mechanical properties of the coating such as its hardness should be improved. In this study, initially a thin layer of titanium nitride was prepared on a titanium substrate during irradiation of titanium substrate by a thermal DC nitrogen-contained plasma jet. Then, during reactive plasma spraying, Ti particles were injected into plasma jet, converted to titanium nitride and huddled on to the substrate. This new hybrid method (primary plasma irradiation and post-reactive plasma spraying) for deposition of TiN coatings would combine the advantages of both plasma-enhanced chemical vapor deposition and reactive plasma spraying methods in part. It resulted in a thick and hard layer of titanium nitride film. Sample produced by this method was analyzed with x-ray diffraction confirming titanium nitride production. Vickers hardness was measured using optical microscopy which was around 1319 H_v300g. To study the cross section of the layer, optical microscopy and scanning electron microscopy (SEM) were used.     

Low Temperature Plasma Nitriding of H13 Steel for Improved Surface Hardness

AISI H13 steel samples were plasma nitrided to improve their surface hardness using a locally developed combined reactor.Pre-ionized RFICP plasma was employed in combination with DC glow discharge and thermal emission source to achieve the nitride precipitates in iron-matrix under low sample temperature.Thick nitride layers over 150 microns could be realized with low RF power of 100 W under the processing time between 1-20 h and low sample temperature of 300℃.The gas mixtures of H2 and N2 were utilized while the processing pressure and the DC bias to the sample were maintained at 0.5 torr and 300 V,respectively.Scanning electron microscope(SEM),energy dispersive X-ray spectroscopy(EDS),glancing incident angle X-ray diffractometer(GIXD)and Vickers hardness test were employed to characterize the properties of sample surfaces.Significant increases of surface hardness to over 1,000 HV were observed after treatment.