Machinability of AA 2024 aluminum alloy by fiber laser engraving process

The main objective of the present study is to investigate the machinability of AA 2024-T351 aluminum alloy by laser beam-assisted engraving process. The surface in a defined area was machined with the engraving process parameters of scan speed, frequency, and pulse width. While surface roughness measurements were performed to characterize the texture of the processed surface with laser engraving parameters, machining depth measurements were carried out to determine the material removal capacity. In addition, a mathematical relation was built for engraving depth and surface roughness using the response surface methodology. An increase in scan speed and pulse width led to a decrease in engraving depth and surface roughness. Unlike the scan speed and pulse width, any increase in frequency led to increased surface roughness and decreased engraving depth. After processing with lower pulse width and scan speed, a chaotic topography was formed on the surface. The effects of process parameters on engraving depth and surface roughness were analyzed statistically using factorial analysis. Except for the frequency, all parameters for surface roughness were statistically significant, whereas all parameters for engraving depth were statistically significant.     

TC4钛合金超声深滚表面强化技术的研究

采用一种新型表面机械强化技术-超声深滚技术(UDR)对钛合金试样进行了表面强化处理。研究了超声深滚处理对试件的残余应力、加工硬化和表面形貌及表面粗糙度的影响。结果表明:超声深滚处理引入了高幅值、大深度的残余压应力、加工硬化量适度并且显著降低了表面粗糙度。根据以上结果分析了该技术的优势和应用前景。     

Modeling and measurements of atomic surface roughness

We present a geometrical model of atomic topography with which to obtain a quantitative assessment of surface roughness. A series of two- and three-dimensional atomic surface roughness equations with sufficiently realistic parameters is developed to permit quantitative comparison with scanning-tunneling microscope and atomic-force microscope (AFM) experimental results. The model is sufficiently simple that one can easily use it to interpret experimental data. Tables are provided with estimated values for two- and three-dimensional rms atomic surface roughness in pure metal crystals and ionic crystals based on the atomic surface roughness equations. We use these roughness equations to determine the roughness of cleaved muscovite mica [essentially, KAl(2)(OH)(2)Si(3)AlO(10)]; the calculated values for both two- and three-dimensional roughness are consistent with those obtained in our AFM measurements. In addition, we demonstrate both theoretically and experimentally that atomic surface roughness is never zero.     

Large-angle in-plane light scattering from rough surfaces

An in-plane light scattering setup that is capable of measuring large azimuthal scattering angles is presented. This type of measurement makes it easier to probe large k(parallel) at a fixed k(perpendicular) value (k(parallel) and k(perpendicular) are momentum transfer vectors parallel and perpendicular to the surface, respectively). Therefore the system allows us to explore small lateral scale and large vertical roughness (approximately lambda, the wavelength of the probe beam) of a rough surface. In-plane intensity measurements from a rough backside Si wafer and a Cu thin-film surface are reported. The structure factor that is related to surface roughness parameters is obtained from the measured in-plane intensity profiles. Both scalar (Beckmann-Kirchhoff) and vector (Rayleigh-Rice) theories have been applied to interpret the experimental data. The roughness parameters obtained from the scattering measurements are compared with those measured by atomic-force microscopy.     

Ti-6Al-4V合金表面超声振动滚压强化研究

采用超声振动滚压加工技术对Ti-6Al-4V合金表面进行处理,探究该项技术对Ti-6Al-4V合金表面质量的影响。通过对该工艺加工前后的Ti-6Al-4V合金进行表面粗糙度参数、XRD图谱、截面微观形貌、表层残余应力及显微硬度的对比分析,结果表明:经该工艺处理后的合金表面各项粗糙度参数皆有明显降低;加工后的合金表面XRD图谱的衍射峰减弱且宽化,衍射角向高角度方向偏移;加工后的合金表层β相组织相较加工前明显细化,且随着深度增加β相组织逐渐增大;在距离表面约50μm位置的残余应力值最大可达到-967 MPa;加工后的合金表面显微硬度可达到421HV,且在0~140μm的深度范围内,显微硬度随着深度的增加逐渐减小至与基体硬度一致。经超声振动滚压加工后的Ti-6Al-4V合金表面质量显著提高,有利于提高其零部件的使用性能。     

Nanoscale surface modification of a prosthetic material: case of Ti6Al4V into Ringer's solution

Nanoscale surface modification of Ti6Al4V prosthetic material was investigated at 37 degrees C into a physiological liquid named Ringer's solution. The root-mean-square surface roughness evolution of the material as a function of immersion time was evaluated by atomic force microscopy (AFM) and 3D reconstruction of scanning electron microscope images (SEM). The results obtained from both techniques clearly showed a decrease of the root-mean-square surface roughness during the first 6 hours of immersion in the physiological liquid that is followed by a stability of the roughness value at longer durations. Moreover, the study of the roughness parameters extracted from AFM measurements is used to explain the smoothing process occurring at the interface between the prosthetic material and the physiological liquid.     

球形表面粗糙度测量中两种干涉图像处理方法

讨论了用带有数字图像处理和计算系统的麦克尔逊干涉涉显微镜测量像人工关节这样的球形表面粗糙度的方法，用数字图像处理方法处理等倾干涉和等厚干扰这两种干扰图像，并萃取出反映被测球面微观不平度信息的干涉带的边界线。本文推导了用最小二乘拟合原理计算标准最小二乘圆和圆弧的算法以及用获取的被测表面的微面不平度偏差计算表面粗糙度参数的方法。     

Effect of surface roughness on nanoindentation test of thin films

By using the two-dimensional quasicontinuum method, the nanoindentation process on a single crystal copper thin film with surface roughness is simulated to study the effect of surface morphology on the measurements of mechanical parameters. The nanohardness and elastic modulus are calculated according to Oliver-Pharr’s method. The obtained results show a good agreement with relevant theoretical and experimental results. It is found that surface roughness has a significant influence on both the nanohardness and elastic modulus of thin films determined from nanoindentation tests. The effect of such factors as the indenter size, indentation depth and surface morphology are also examined. To rule out the influence of surface morphology, the indentation depth should be much greater than the characteristic size of surface roughness and a reasonable indenter size should be chosen. This study is helpful for identifying the mechanical parameters of rough thin films by nanoindentation test and designing nanoindentation experiments.     

Surface Integrity and Fatigue Behavior for High-Speed Milling Ti–10V–2Fe–3Al Titanium Alloy

Influence of cutting parameters on surface integrity when milling Ti–10V–2Fe–3Al is investigated based on high-speed cutting experiments. Surface integrity measurements, fatigue fractography analysis, and fatigue life tests are conducted to reveal the effect of surface integrity on crack initiation and fatigue life. The results show that under given experiment conditions, surface roughness decreases linearly when increasing cutting speed or decreasing feed per tooth. The latter has a greater impact on surface roughness than the former. Compressive stress can be detected on all machined surfaces. With the increase of feed per tooth or cutting speed, respectively, residual stress presents a linear increase. Cutting parameters have no significant impact on micro-hardness. When the surface roughness ranges from 0.5 to 1.0 μm, the effect of surface residual stress on fatigue life is more than that of surface roughness. When the surface residual compressive stress increases, the fatigue life improves significantly. Compared with 60 m/min, when cutting speed is 100 or 140 m/min, the surface roughness decreases, the surface residual compressive stress increases, and the fatigue life improves by 124 and 59%, respectively. Under a tensile load, fatigue crack on machined surface of Ti–10V–2Fe–3Al titanium alloy originates at the cross-edge of the specimen surface. With the increase of surface roughness, the area ratio of fatigue crack propagation zone, and fatigue fracture zone decreases.     

Standard Reference Specimens in Quality Control of Engineering Surfaces

In the quality control of engineering surfaces, we aim to understand and maintain a good relationship between the manufacturing process and surface function. This is achieved by controlling the surface texture. The control process involves: 1) learning the functional parameters and their control values through controlled experiments or through a long history of production and use; 2) maintaining high accuracy and reproducibility with measurements not only of roughness calibration specimens but also of real engineering parts. In this paper, the characteristics, utilizations, and limitations of different classes of precision roughness calibration specimens are described. A measuring procedure of engineering surfaces, based on the calibration procedure of roughness specimens at NIST, is proposed. This procedure involves utilization of check specimens with waveform, wavelength, and other roughness parameters similar to functioning engineering surfaces. These check specimens would be certified under standardized reference measuring conditions, or by a reference instrument, and could be used for overall checking of the measuring procedure and for maintaining accuracy and agreement in engineering surface measurement. The concept of “surface texture design” is also suggested, which involves designing the engineering surface texture, the manufacturing process, and the quality control procedure to meet the optimal functional needs.     

Random phase mask as a model of rough surface. Part I. Theory

There have been numerous attempts to correlate light scattering measurements with the characteristics of surface roughness. Another but considerably more difficult approach is to solve the inverse scattering problem. A number of different empirical models of surface roughness have been used to characterize surfaces including the sine grating, triangle grating (echelette), and rectangle grating. In this paper, we use, for the first time, the random phase mask model, which is a two-dimension orthogonal grating with a stochastic distribution of square “defects” with size a. We describe our calculations of the polarizing characteristics of the random phase mask and discuss the influence of each of the parameters of defects on polarizing angles. The analysis was carried out for multiple-angles-of-incidence ellipsometric measurements.     

Wavelet uniformity of plasma-processed surface roughness

A technique to characterize the nonuniformity of surface roughness (NSR) is presented. A discrete wavelet transformation (DWT) was used to quantitatively differentiate surface patterns. The technique was evaluated with the data collected from the etching of silicon oxynitride films in a C₂F₆ inductively coupled plasma. 3-D surface images were obtained by using atomic force microscopy. Vertical and lateral NSRs were investigated as a function of process parameters, including radio frequency source power, bias power, and pressure. The NSR data were correlated to experimental measurements of the surface roughness. It is noticeable that for any parameter variations there exist nearly identical NSRs. For each parameter variation, there was at least one specific NSR consistent with the surface roughness measurement. Selected NSRs can be utilized to monitor a variation in NSR and surface roughness simultaneously. Also, NSR may be more stringently optimized by controlling NSRs in a directional fashion.     

Optical roughness measurements with fringe projection

The characterization of roughness of engineering surfaces over an area is an important task for different applications as well as for manufacturing processes. The surface roughness is in particular an important factor in determining the performance of a workpiece. We demonstrate that the fringe projection technique allows very fast three-dimensional surface inspections. The inspection time for an entire measurement is reduced to less than 5 s with standard hardware. Based on a zoom stereo microscope setup, we demonstrate a modular measuring instrument. The magnification-dependent vertical resolution can be as high as 0.1 microm. The special properties for roughness measurements are demonstrated, especially the comparability with a tactile sensor and with other optical sensors, which is discussed in connection with amplitude parameters.     

Surface properties of hard protective coatings studied by optical techniques

The paper describes optical study of SiC, C and NiC layers deposited on Si substrates by double beam ion sputtering (DBIS) method. The following optical methods: ellipsometry, bidirectional reflection distribution function (BRDF) and total integrated scattering (TIS) studies have been applied. The obtained results allowed us to determine the refractive indices, extinction coefficients and the roughness parameters of DBIS films. Also surface profiles of optical constants determined from scanning ellipsometric measurements have been presented. The power spectral density functions (PSD) of surface roughness for studied samples have been determined. The influence of the deposition technology on film topography has been discussed.     

Measurement and Modeling of the Emittance of Silicon Wafers with Anisotropic Roughness

The unpolished surface of crystalline silicon wafers often exhibits non-Gaussian and anisotropic roughness characteristics, as evidenced by the side peaks in the slope distribution. This work investigates the effect of anisotropy on the emittance. The directional-hemispherical reflectance of slightly and strongly anisotropic silicon wafers was measured at room temperature using a center-mount integrating sphere. A monochromator with a lamp was used for near-normal incidence in the wavelength region from 400–1000 nm, and a continuous-wave diode laser at the wavelength of 635 nm was used for measurements at zenith angles up to 60°. The directional emittance was deduced from the measured reflectance based on Kirchhoff’s law. The geometric-optics-based Monte Carlo model that incorporates the measured surface topography is in good agreement with the experiment. Both the experimental and modeling results suggest that anisotropic roughness increases multiple scattering, thereby enhancing the emittance. On the other hand, if the wafer with strongly anisotropic roughness were modeled as a Gaussian surface with the same roughness parameters, the predicted emittance near the normal direction would be lower by approximately 0.05, or up to 10% at a wavelength of 400 nm. Comparisons also suggest that the Gaussian surface assumption is questionable in calculating the emittance at large emission angles with s polarization, even for the slightly anisotropic wafer. This work demonstrates that anisotropy plays a significant role in the emittance enhancement of rough surfaces. Hence, it is imperative to obtain precise surface microstructure information in order to accurately predict the emittance, a critical parameter for non-contact temperature measurements and radiative transfer analysis.     

精细雾化抛光氮化硅陶瓷的抛光液配制参数优化

采用超声精细雾化施液抛光对氮化硅陶瓷基体进行抛光,研究了不同的pH值、磨料浓度以及氧化剂含量对氮化硅陶瓷基体抛光的材料去除率的影响,优化了pH值、磨料浓度及氧化剂含量,并与传统的化学机械抛光进行了对比。结果表明:当二氧化硅磨粒质量分数为5wt%,氧化剂含量为1wt%,pH值为8时,材料去除率MRR为108.24nm/min且表面粗糙度Ra为3.39nm。在相同的抛光参数下,传统化学机械抛光的材料去除率MRR为125nm/min,表面粗糙度Ra为2.13nm;精细雾化抛光的材料去除率及表面粗糙度与传统抛光接近,但精细雾化抛光所用抛光液用量仅为传统抛光所用抛光液用量的1/9。     

铝合金表面超疏水涂层的火焰喷雾热解法制备及其耐蚀性能

采用火焰喷雾热解与表面修饰相结合的方法在铝合金表面制备了具有一定耐蚀性能的超疏水表面。以六甲基二硅氧烷溶液为前驱液,通过火焰喷雾热解方法,首先在铝合金表面沉积SiO2纳米颗粒构建粗糙结构,再以氟硅烷溶液进行表面修饰,获得了具有154.9°静态接触角,滚动角<2°的超疏水表面。通过电化学测试,对比了构筑超疏水表面前后的铝合金样品的耐蚀性能。结果表明沉积层与低表面能物质协同作用,通过对腐蚀性离子的有效隔离,提高了铝合金基体的耐蚀性能。     

碳/碳复合材料切削表面粗糙度的评定方法及评定参数研究

通过对航空航天领域应用的碳,碳（C／C）复合材料和硬铝材料切削表面进行三维表面粗糙度测量实验,研究了C／C复合材料切削表面粗糙度的二维评定与三维评定方法、幅度表征参数及分形表征。结果表明：对于C／C一类的复合材料需选用三维评定参数才能准确表达其切削表面粗糙度的真实特征;表面均方根偏差比表面算术平均偏差更适合作为C／C复合材料切削表面粗糙度的幅度评定参数,表面粗糙度的三维标准应优先选用表面均方根偏差作为评定参数;表面分形维数可作为C／C复合材料切削表面粗糙度的表征参数之一。     

Influence of impact velocity on fragmentation and the energy efficiency of comminution

Comminution processes such as crushing and grinding are essential stages in mining and mineral processing operations to reduce the size of ore and rock, and to liberate the valuable mineral for beneficiation. Comminution is energy-intensive and responsible for most of the energy used during mineral recovery. Energy efficiency is very low since almost all the energy is dissipated as heat instead of generating new surface area. This paper reports on studies conducted on strain rates achieved by various velocities of impacts that enhance energy efficiency and mineral liberation. The research focuses on understanding comminution fracture mechanics and on quantifying the distribution of energy with respect to generating new surface area. In interpreting breakage energy phenomena, accurate measurements of surface roughness and surface area are essential. A novel approach to measure surface roughness and surface area based on a fractal analysis procedure has been developed. Changes in surface roughness of broken specimens under variable loading rates were studied using a laser probe to generate 3D topographical maps of the fracture surfaces. The results indicate that surface roughness and hence, specific surface area, increase with increasing loading rate by several orders of magnitude as particle size decreases to 1 μm. Below this limit, surface roughness begins to diminish from particle–particle attrition. An apparatus to measure the quantitative parameters of impact at different velocities on aggregated rock samples is proposed. Experiments are being carried out at projectile velocities up to 500 m s⁻¹ utilizing a compressed-air device. The results suggest possible efficiency improvements in breakage under the velocity of impact.     

Influence of surface roughness on the polarimetric characteristics of a wire-grid grating polarizer

The influence of surface roughness on the polarimetric performance of a wire-grid polarizer (WGP) is numerically investigated using rigorous coupled-wave analysis over 100 random surface realizations. Surface roughness is modeled with a Gaussian surface, represented by two independent parameters: surface height deviation and correlation length of a profile. The results show that WGP performance can suffer from significant degradation as well as increased deviation with surface roughness, although the extent varies with specific parameters. The influence of roughness was also examined with respect to grating period as a WGP parameter and incident light properties, such as wavelength and angle.