The influence of nanosized precipitates on Portevin-Le Chatelier bands and surface roughness in AlMgScZr alloy

The influence of different precipitate-dislocation interactions,namely dislocation shearing and bypass-ing mechanisms,on PLC bands and the resultant surface roughness in AlMgScZr alloy was investigated.Three-dimensional surface roughness was quantitatively measured by confocal microscopy.We find that the introduction of shearable precipitates increases the stress amplitude,decreases the PLC bands number and surface roughness.However,the stress amplitude decreases,the PLC bands number and sur-face roughness increase with shearable precipitates turning to nonshearable precipitates.By analyzing the precipitation strengthening mechanisms quantitatively,the influence of precipitates on PLC bands and the resultant surface roughness was explored.Furthermore,our study demonstrates that the shear-able precipitates can decrease the surface roughness by decreasing the number of PLC bands,which is instructive for designing structural materials with desirable mechanical property and surface quality.     

Equilibrium surface roughness of a strained epitaxial film due to surface diffusion induced by interface misfit dislocations

In recent years, developments in the microelectronics industry have led to extensive studies of the growth and characterization of thin solid films and their implementation in electronic and opto-electronic devices. A goal is to produce thin films with minimal bulk and surface defects. For those systems produced by epitaxial growth of a film on a substrate that has a slightly different lattice parameter, the stress associated with the elastic mismatch strain needed to satisfy the constraint of epitaxy provides a driving force for nucleation and growth of undesirable defects in the film material or on its surface. Among the most common defects are interface misfit dislocations, arranged more or less periodically on the film-substrate interface, which partially relax the elastic mismatch strain in the film. It has been observed that, for some material systems, surface roughness or waviness arises which correlates spatially with the positions of interface misfit dislocations. It is suggested here that the waviness along the surface may be a result of surface diffusion which is driven by a gradient in the chemical potential of the material along the surface. The chemical potential gradient arises from the nonuniform strain field of the interface misfit dislocations, as well as from the unrelaxed elastic mismatch strain. The focus here is on the development of a relatively simple model of this system which leads to an estimate of the magnitude and profile of surface waviness under conditions of thermodynamic equilibrium, i.e., after the material responds to the chemical potential gradient by seeking out a new configuration for which stresses are redistributed and the chemical potential is again uniform. The condition of uniform chemical potential for the final shape leads to an integro-differential equation for the equilibrium surface shape which is solved numerically. For representative values of system parameters, estimates of equilibrium surface roughness are obtained which can vary from less than one percent of film thickness to a significant fraction of film thickness. Although transient aspects of the process are not studied here, the characteristic time for achieving an equilibrium configuration is estimated.     

The surface modification of stainless steel and the correlation between the surface properties and protein adsorption

Protein adsorption on a biomaterial surface is of great importance as it usually induces unfavorable biological cascades, with the result that much surface modification research has had to be performed in an effort to prevent this. In this study, we developed surface modification methods for stainless steel, which is a representative metal for biomedical device. The stainless steels were first smoothened to different extents by electropolishing, in order to obtain a rough or smooth surface. On these two kinds of substrates, we introduced epoxide groups to the metal surface by silanization with 3-glycidoxypropyltrimethoxysilane (GPTS). Then, various polymers such as poly(ethylene glycol) (PEG), poly(tetrahydrofuran glycol) (PTG), poly(propylene glycol) (PPG) and poly(dimethylsiloxane) (PDMS) were grafted on the silanized stainless steels. Each surface modification step was confirmed by various analytical methods. Contact angle measurement revealed that the surface hydrophilicity was controllable by polymer grafting. Root-mean-square (RMS) data of atomic force microscopy showed that surface roughness was dramatically changed by electropolishing. Based on these results, the correlation between surface properties and protein adsorption was investigated. In the protein adsorption study, we observed that all of the polymer-grafted stainless steels exhibited lower protein adsorption, when compared with bare stainless steel. Moreover, a hydrophilic and smooth surface was found to be the best of choice for decreasing the protein adsorption.     

Fabrication of super-hydrophobic film with dual-size roughness by silica sphere assembly

Two simple approaches were developed for the fabrication of super-hydrophobic film with dual-size roughness by taking advantage of assembling silica micro- and nanospheres. Electrostatic adsorbing technique and template-directed self-assembly were used here. The dual-size surface, which mimics the surface topology of lotus leaves, comprises both the micro-scale and nano-scale roughness. After the roughened surface was chemically modified with a layer of fluoroalkylsilane, super-hydrophobicity with a water contact angle higher than 160° and sliding angle as low as 0.5° can be achieved. The simplicity and cheapness of this procedure may make widespread applications of this super-hydrophobic film possible.     

The influence of surface roughness on the starved lubrication of ball bearings

Abstract

A theoretical analysis is made for starved lubrication of a rigid point contact under the influence of surface roughness. The results show that both the directional property and the standard deviation of the combined surface roughness can affect the load carrying capacity of the lubricant film as well as the friction on the solid surfaces. The combined effects of speed ratio of the contiguous surfaces and the roughness on starved lubrication are also obtained. The results show that the effects of surface roughness may improve the starvation a little, but that they are not remarkable. A regression equation is found for determining the critically starved lubricant inlet level. Such an inlet level can indicate the minimum limit of lubricant supplied quantity, and, beyond this limit, the load carrying capacity of the lubricant film will decrease sharply. In addition, experiments have been carried out to observe the starved lubrication of a ball rolling on a flat glass disc. It is shown that higher surface speeds may make the starved condition much worse.     

Investigation of granular surface roughness effect on electrostatic charge generation

Electrostatic charge generation is a multivariable and complex issue whose working mechanism has never been fully understood. The objective of this paper is to investigate the effect of granule surface roughness on electrostatic charge generation. Two kinds of granule material, Polyvinyl chloride (PVC) and polypropylene (PP) were used with the granule size of 4 mm diameter, 2 mm height and the shape was cylinder or semi-cylinder. The working surfaces were grounded and roughness ranged from 0.140 to 8.600 μm. It was found that uneven surfaces tended to give rise to voids between two solids, where air stored in the voids was able to accelerate discharging. With the same roughness, PVC tended to generate more electrostatic charge than PP by one order of magnitude. For both materials, electrostatic charge generation first increased with surface roughness and then decreased. The maximum electrostatic charge generated was found to occur when the effects of interaction, contact area and voids discharging were at equilibrium. With the combined effect of humidity, surface roughness and contact area, highest electrostatics generation occurred near the mid-roughness tested in this work. Humidity had more effect on electrostatic charge generation as the granule working surface had lower roughness.     

Modelling the combined effect of surface roughness and topography on bacterial attachment

Bacterial attachment is a complex process affected by flow conditions,imparted stresses,and the sur-face properties and structure of both the supporting material and the cell.Experiments on the initial attachment of cells of the bacterium Streptococcus gordonii (S.gordonii),an important early coloniser of dental plaque,to samples of stainless steel (SS) have been reported in this work.The primary aim motivating this study was to establish what affect,if any,the surface roughness and topology of sam-ples of SS would have on the initial attachment of cells of the bacterium S.gordonii.This material and bacterium were chosen by virtue of their relevance to dental implants and dental implant infections.Prior to bacterial attachment,surfaces become conditioned by the interfacing environment (salivary pellicle from the oral cavity for instance).For this reason,cell attachment to samples of SS pre-coated with saliva was also studied.By implementing the Extended Derjaguin Landau Verwey and Overbeek(XDLVO) theory coupled with convection-diffusion-reaction equations and the surface roughness infor-mation,a computational model was developed to help better understand the physics of cell adhesion.Surface roughness was modelled by reconstructing the surface topography using statistical parame-ters derived from atomic force microscopy (AFM) measurements.Using this computational model,the effects of roughness and surface patterns on bacterial attachment were examined quantitatively in both static and flowing fluid environments.The results have shown that rougher surfaces (within the sub-microscale) generally increase bacterial attachment in static fluid conditions which quantitatively agrees with experimental measurements.Under flow conditions,computational fluid dynamics (CFD) simula-tions predicted reduced convection-diffusion inside the channel which would act to decrease bacterial attachment.When combined with surface roughness effects,the computational model also predicted that the surface topographies discussed within this work produced a slight decrease in overall bacterial attachment.This would suggest that the attachment-preventing effects of surface patterns dominate over the adhesion-favourable sub-microscale surface roughness;hence,producing a net reduction in adhered cells.This qualitatively agreed with experimental observations reported here and quantitatively matched experimental observations for low flow rates within measurement error.     

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.     

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.     

Effect of surface roughness on tribological properties of TiB2/Al composites

55 vol.% TiB₂/2024Al composites were fabricated by pressure infiltration method. The effect of surface roughness of GCr15 steel disc (Ra 0.606, 0.372, 0.023, 0.005 μm) on the tribological properties of composites was investigated. Results showed that with the change of surface roughness, there is an optimal value (Ra 0.023 μm) under which the friction coefficient and wear rate is the lowest. The optimal surface roughness is in the same order of mixture of TiO₂ and B₂O₃, observed on the surface of TiB₂ particles after pre-heating process. During sliding, the filling of this oxidation layer into the asperity gap of GCr15 and greatly reduces adhesion between aluminium and GCr15, furthermore, decreases the friction coefficient and wear rate.     

Tool materials influence on surface roughness and oversize in machining glass fiber reinforced polypropylene (GFR-PP) composites

Glass fiber reinforced Polypropylene (GFR-PP) is used in manufacturing industries like bicycles, auto bodies, aircraft, and civil applications due to superior properties. Machining of fiber-reinforced plastics is problematic especially when drilling due to their inherent in-homogeneity, anisotropy and limited plastic deformation. Drilling is often required to facilitate the assembly of the parts to get the final products. Surface quality in drilled composites is an essential design characteristic in many situations, such as accurate fits, aesthetic requirements, etc. The present work deals with detailed investigation on the influence of tool materials and machining parameters during drilling of GFR-PP composite material. The study mainly focused on machined surface quality such as surface roughness of the drilled hole and dimensional inaccuracies such as oversize of the hole. The better dimensional and surface quality of drilled hole is observed from solid carbide drill with a spindle speed of 2500?rpm and a feed rate of 0.05?mm/rev. Regression model is developed using experimental data for estimating the surface roughness and oversize. The developed model has high R-sq value which shows the strong relationship between the model and the response variables. The effect of drilling process parameters and associated interactions are discussed in detail.     

基于散斑强度相关函数的表面粗糙度测量方法

激光经过被测表面反射和散射后,通过自由空间传播至观察面上形成散斑图像,其统计分布依赖于被测表面的微观形貌。分析此散斑图像的二阶统计特性,导出了强度变化的相关函数和表面粗糙度参数之间的关系。以表面粗糙平均值Ra分别为0.1靘, 0.2靘, 0.4靘和0.8靘的平磨标准金属样块形成的散斑图像为例,根据强度变化相关函数的离散化定义,计算得到该相关函数值。结果表明,表面越粗糙,散斑越分散,强度变化的相关函数波动越大。因此,该参数可以反映不同的粗糙面,用其作为表征表面粗糙度的特征参数,扩大了测量范围。该方法实验系统简单,对于实际测量环境要求不高,对震动不是非常敏感,适于在线测量。     

Fatigue crack growth thresholds-the influence of Young''s modulus and fracture surface roughness

In the present investigation it is shown that the effective fatigue threshold is uniquely correlated to the Young's modulus for a wide range of metallic and composite materials (ΔK_th,eff=1.64·10⁻²·E). It is also demonstrated that the crack closure level K_cl increases with increased roughness of the fracture surface . K_cl and are quantitatively related via the equation for steels with widely different mechanical properties and grain sizes (120 MPa<R_p<1100 MPa, 1 μm<λ<100 μm). This relation can be extended to materials other than steels (e.g. aluminium and WC-Co alloys) by normalising against Young's modulus. The roughness value represents the standard deviation of height of the fracture surface and is shown to be simply related to the length and angle distributions of the linear length elements constituting the fracture profile.     

Effect of surface roughness on measurement of light distribution in intralipid suspension

Light distribution in the biological tissue phantom intralipid suspension with different interface roughness was measured for quantitative understanding of surface roughness effect. The results show that the surface roughness strongly affects light distribution inside the approximately semi-infinite biological tissue phantom. The phantom surface possesses a certain degree roughness and the effect of the surface roughness on measurement results of light distribution in tissue is substantial, so the measurement of light distribution in biological tissue needs to take surface roughness into account.     

Effects of thermal debinding on surface roughness in micro powder injection molding

Micro metal injection molding (μMIM) is a promising process for the replication of metallic microstructures. In the micrometer regime, surface roughness is important in view of the dimensional tolerance and the applications of microstructured parts. In this paper, the effects of debinding on the surface roughness of 316 L stainless steel microstructured parts were investigated. Experimental results showed that using higher heating rates during debinding increased the weight loss of debound parts. The debound parts of higher weight loss gave better surface finish after sintering. Comparing the increase of sintering time and temperature, the surface finish improvement was more significant for increasing temperature.     

Influence of growth rate on the structural and morphological properties of TiN, ZrN and TiN/ZrN multilayers

The effect of the deposition rate on the structural and morphological properties of TiN and ZrN single layers and TiN/ZrN multilayers deposited by radiofrequency reactive magnetron sputtering has been studied. The total pressure was kept constant and the growth rate variation was obtained by small difference of nitrogen concentration in the fed gas. The decreasing deposition rate results in a structural change in the thin films from (111) orientation to (100) one. As consequence the surface morphology becomes smoother. Films roughness is strongly related with texture and it decreases with an increase in the (100) X-ray diffraction line intensity. In order to achieve a clear interpretation of our experimental results, the ratio between the N⁺ ions of the plasma and the atoms number reaching the substrate was considered. At high deposition rate with respect to the N⁺ concentration, the chemical potential of transition metal on (100) growth surface is higher than (111) one favouring the (111) orientation of the films. On the contrary, when the growth rate is low with respect to the nitrogen concentration, the chemical potential of transition metal on (111) growth surface is higher than the (100) one leading to a preferential growth in the (100) direction.     

A fatigue crack initiation model incorporating discrete dislocation plasticity and surface roughness

Although a thorough understanding of fatigue crack initiation is lacking, experiments have shown that the evolution of distinct dislocation distributions and surface roughness are key ingredients. In the present study we introduce a computational framework that ties together dislocation dynamics, the fields due to crystallographic surface steps and cohesive surfaces to model near-atomic separation leading to fracture. Cyclic tension–compression simulations are carried out where a single plastically deforming grain at a free surface is surrounded by elastic material. While initially, the cycle-by-cycle maximum cohesive opening increases slowly, the growth rate at some instant increases rapidly, leading to fatigue crack initiation at the free surface and subsequent growth into the crystal. This study also sheds light on random local microstructural events which lead to premature fatigue crack initiation.     

Interfacial effects on the magnetic profiles and interlayer exchange coupling of Co/CoSi multilayers

Density functional calculations are conducted to investigate the interlayer exchange coupling (IEC) between ferromagnetic Co slabs mediated by a CoSi spacer in Co/CoSi(001) multilayers with CsCl crystalline structure. For both sharp and mixed Co-Si interfaces we calculated the magnetic moment distribution and the energy stability for ferromagnetic (F) IEC and antiferromagnetic (AF) IEC between the Co slabs as function of the spacer thickness. We show that mixing near to the interface noticeably modifies the IEC to the extent that this can change from an oscillatory IEC as function of the spacer thickness to an exponentially decaying AF behavior.     

表面粗糙度对PS-PVD热障涂层陶瓷层沉积的影响

研究基于等离子喷涂-物理气相沉积(PS-PVD)工艺的沉积表面的粗糙度对YSZ陶瓷层结构的影响,初步阐明了表面粗糙度对陶瓷层气相沉积过程的影响和涂层结构的形成规律。采用PS-PVD工艺在预制有NiCoCrAlYTa黏结层的K417G高温合金上制备YSZ陶瓷层;采用SEM、粗糙度检测仪、3D表面形貌仪等方法分析PS-PVD YSZ陶瓷涂层的形貌和结构特征。基体表面粗糙度对PS-PVD涂层结构有很大影响。结果表明:当基体表面粗糙度分别为 R a≤2μm, 2μm< R a<6μm, R a≥6μm时,涂层粗糙度分别在3.5~5,6~10,10~15μm区间;特征表面形貌"菜花头"的直径随着基体表面粗糙度的增加而逐渐增大, d P=38.5μm, d 280S =25.5μm, d 60S =38.7μm, d 24S =102μm, d S=137μm。表面粗糙度主要通过PS-PVD气相沉积过程中的阴影效应来影响涂层生长和形成差异性结构,随着基体表面粗糙度的增加,YSZ陶瓷层受阴影效应影响增大,表面形貌"菜花头"尺寸和柱状结构间间隙增大,形成更加疏松的结构。