Roughness Evolution Research Articles

Surface roughness evolution mechanism of the optical aluminum 6061 alloy during low energy Ar+ ion beam sputtering.

Ultra-smooth surfaces with low contamination and little damage are a great challenge for aluminum optical fabrication. Ion beam sputtering (IBS) has obvious advantages of low contamination and non-contact that make it a perfect method for processing aluminum optics. However, the evolution laws of aluminum surface morphology are quite different from conventional amorphous materials, which affects the roughness change and needs systematic research. Thus, in this paper, the roughness evolution of an aluminum optical surface (i.e., aluminum mirror) subjected to IBS has been studied with experimental and theoretical methods. The surface morphology evolution mechanisms of turning marks and second phase during IBS are revealed. The newly emerging relief morphology and its evolution mechanism are studied in depth. The experimental results find that IBS causes the coarsening of optical surfaces and the appearance of microstructures, leading to the surface quality deterioration. Turning marks have been through the process of deepening and vanish, while second phase generates microstructures on the original surface. The corresponding mechanism is discussed exhaustively. Preferential sputtering, curvature-dependent sputtering and material properties play important roles on surface quality deterioration. A modified roughness evolution mechanism and an improved binary sputtering theory are proposed to describe the polycrystalline sputtering phenomena. The current research can provide a guidance for the application of IBS in aluminum optics manufacture fields.

Role of interfacial adhesion on minimum wear particle size and roughness evolution.

Adhesion between two bodies is a key parameter in wear processes. At the macroscale, strong adhesive bonds are known to lead to high wear rates, as observed in clean metal-on-metal contact. Reducing the strength of the interfacial adhesion is then desirable, and techniques such as lubrication and surface passivation are employed to this end. Still, little is known about the influence of adhesion on the microscopic processes of wear. In particular, the effects of interfacial adhesion on the wear particle size and on the surface roughness evolution are not clear and are therefore addressed here by means of molecular dynamics simulations. We show that, at short timescales, the surface morphology and not the interfacial adhesion strength dictates the minimum size of wear particles. However, at longer timescales, adhesion alters the particle motion and thus the wear rate and the surface morphology.

Contribution in developing a rapid strategy in assessing hardened steel machining

The present work is a contribution to developing a strategy for rapid analysis of the behaviour of surface roughness and tool wear during machining hardened steel with carbide cemented cutting tools on conventional cutting machines. In agreement with dies and mould manufacturers in East Algeria, the strategy is based on the machining potential of the manufacturers, cutting tools manufacturer’s guidelines and recommendations from literature. The agreement suggested to focus on up and down shoulder finish milling of hardened AISI D3 tool steel using GC1030 insert on a conventional vertical milling machine. The strategy has been developed within five successive steps starting from the analyses of the performance of a machine tool to the definition of an experimental plan to respect. As expected, results show that down shoulder milling is the most suitable process rather than up shoulder milling which must be avoided whatever the hardening condition. In addition, the best performance of down shoulder milling is obtained when machining unhardened steel. In the as-received condition (31.6 HRc) when using down milling the cutting speed can be increased up to the maximum value of 113 m/min, however, the tool life obtained for this value is three times lower than that at Vc = 59 m/min. In 49 HRc hardening condition, milling at Vc = 59 m/min resulted in the good surface finish but with a tool life 6.5 times lower than the tool life when milling in the as-received condition. Vibration measurements provide a time referential data on the evolution of surface roughness together with corresponding tool wear. A time referential data on the evolution of displacement together with the corresponding tool life has been proposed as useful information to meet the needs of dies and moulds manufacturers when milling hardened steels.

Evolution of primary Si phase, surface roughness and mechanical properties of hypereutectic Al–Si alloys with different Si contents and cooling rates

ABSTRACT The solidification behaviour of hypereutectic Al–Si alloy melts at 70°C above the liquidus with different Si contents between 27 and 50 wt% and cooling rates from 50 to 300°C/min were studied using a confocal laser scanning microscope (CLSM). It was found that the primary Si size and surface roughness decreased while the wear resistance improved with higher cooling rates and lower Si contents. An interesting result showed that the hardness and wear resistance changed in an opposite direction with increase of Si content. The causes of the improvement of wear resistance are mainly attributed to a decreasing primary Si size and the corresponding surface roughness.

Effects of different contact film thicknesses on the surface roughness evolution of LY2 aluminum alloy milled surface subjected to laser shock wave planishing

Laser shock wave planishing technology (LSWP) was adopted to treat a milled surface of LY2 aluminum alloy in the present research. The effects of different contact films thicknesses on the surface roughness and surface profile of the milled surface were investigated. Experimental results indicated that the milling removal rate was related to the contact film thickness, and the thinner contact film, the higher removal efficiency. When a contact film of suitable thickness was used, the surface roughness of the workpiece was minimized, and surface subsidence and edge effects were not noticed after single LSWP, multiple LSWP, and overlapping LSWP. The roughness of the coarsest surface decreased from 2.56 μm to 1.16 μm after single LSWP. However, the roughness of this coarse surface decreased notably to 0.47 μm after multiple LSWP, and its surface profile precision were also guaranteed.

Argon beam prompted alterations in morphological, structural, optical and electrical properties of Na+[formula omitted]Ag+ ion-exchanged glass

Synthesis of Ag nanoparticles embedded soda lime glass with a 200 keV Argon ion beam at an off-normal angle of 30° has been presented in this report. Formation of nanoparticles was substantiated by transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), glancing incidence X-ray diffraction (GIXRD) and UV–Visible absorption spectroscopy. Atomic force microscopy (AFM) was used to study topography and evolution of surface roughness of synthesized samples with dose. Structural modifications induced in glass on embedding Ag nanoparticles were investigated using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, Rutherford back scattering spectrometry (RBS) and X-ray photoelectron spectroscopy (XPS). UV–Visible spectroscopy results were further analyzed for computing different optical constants like refractive index, optical energy gap and Urbach energy. UV–Visible transmission spectra revealed the presence of a narrow band in the UV region which hints towards the utility of such samples as UV based narrow bandpass filters. Emission bands observed in photoluminescence spectra originated due to 3DJ (J=1,2,3)→1S0 and 1D2→1S0 transitions amid the energy levels of Ag+ ions and Ag+ pairs. The current-voltage characteristics of the samples were further examined to study their electrical behavior and revealed that the electrical conductivity increased 5 times for the sample fabricated at highest dose in comparison to the pristine glass.

Non-monotonic evolution of surface roughness in a stainless steel during cold deformation

In this study, polished and unpolished sheet samples of austenitic stainless steel 316L were tensile strained to investigate the evolution of surface roughness based on Sa- and Ra characteristics. In polished steel sheets, surface roughness increases with the increase of true strain up to a maximum of e = 0.14. Thereafter, roughness decreases until e = 0.26 for approximately 25%, and then becomes independent on strain. The highest roughness levels are found to be localised primarily around surface grain boundaries. The roughness-strain correlation can be explained by grain rotation and cross-slip. Unpolished sheets demonstrate near-linear relationship between tensile strain and surface roughening due to the presence of an oxide layer. The layer has a thickness of approximately 1 μm with a morphology resembling the microstructure in the substrate. When strained, it appears to show two roughness components. First one is a shortwave component originating at the oxide grain boundaries, which is believed to be produced by the rotation of underlying grains. The second one is a longwave component, which is generated by the fracture of oxide layer due to lower ductility. The slope of roughness – true strain relationship is found to be also grain orientation-dependent.

Experimental evaluation of surface roughness variation of ductile materials due to solid particle erosion

The present research is related to an experimental analysis of the changes in surface roughness of ductile materials exposed to solid particle erosion. Physical data were obtained by an impingement jet facility for erosion times of 2.5, 5 and 10 h and wall inclination angles of 10, 20, 30 and 40°. Aluminium 5754, copper and brass (70%Cu-30%Zn) wall samples were subjected to erosion by quartz sand and spherical glass bead particles with a number mean diameter of 235.4 and 211.5 µm, respectively. Air velocity at the exit of the jet was approximately 26 m/s whilst particle velocity was about 9.5 m/s at the same location. Air velocity measurements (single phase flow) were performed at the exit of the impingement jet by using a one-component laser Doppler anemometer (LDA). To allow measurements of particle motion, a combined method of shadow imaging and particle image velocimetry (PIV) was applied. Particle images were recorded by a double shutter CCD-Camera with macro optics together with background illumination and the particle velocity field was calculated by PIV using a successive refinement of the interrogation area. Global erosion was quantified by weighing the mass of samples before and after each experimental run. Two-dimensional roughness profiles were acquired by optically scanning the surface of each sample after erosion and compared to the initial state of the surface. Changes in the material surface were assessed in the region with most pronounced erosion in terms of three roughness parameters: namely, arithmetic average height (Ra), mean spacing at the mean line (RSm) and standard deviation of the roughness angle (Δγ). Additionally, insights on the importance of wall roughness on particle behaviour in confined gas–solid flows as well as on modelling particle–wall interaction with rough walls are presented. Regarding the jet flow, results demonstrated the influence of inclination angle on air and particle velocity profiles. The optical measurements showed the influence of solid particle erosion, inclination angle and particle shape on the temporal evolution of surface roughness of the analysed materials. Finally, the experimental data allowed for the development of a simple correlation to estimate the dependency of Δγ on solid particle erosion and inclination angle as a function of time.

Growth front smoothing effects in extremely high pressure vapor deposition

Recent experimental chemical vapor depositions of silicon at extreme pressures of ~ 50 MPa (~ 500 atm) have been observed to generate remarkably smooth surfaces not predicted by low-pressure deposition models. In this paper, we propose an anti-shadowing mechanism where the collision of particles within the valleys of the surface growth front leads to smoothening. We conduct Monte Carlo simulations to simulate the evolution of film roughness at pressures between 1 and 50 MPa. We observe that surface roughness approaches an asymptotic invariant value that follows power law behavior as a function of pressure. The film thickness at which invariance begins is shown to have a similar power law behavior with respect to pressure. Our simulated results compare favorably with recent experimental observations and provide insight into the fundamental mechanisms underlying film evolution at pressures between one and hundreds of atmospheres.

Influence of Side Chain Hydrolysis on the Evolution of Nanoscale Roughness and Porosity in Amine-Reactive Polymer Multilayers

We report the influence of side chain hydrolysis on the evolution of nanoscale structure in thin films fabricated by the reactive layer-by-layer (LbL) assembly of branched poly(ethylenimine) (PEI) ...

Effect of tillage, slope, and rainfall on soil surface microtopography quantified by geostatistical and fractal indices during sheet erosion

Abstract Tillage and slope will influence soil surface roughness that changes during rainfall events. This study tests this effect under controlled conditions quantified by geostatistical and fractal indices. When four commonly adopted tillage practices, namely, artificial backhoe (AB), artificial digging (AD), contour tillage (CT), and linear slope (CK), were prepared on soil surfaces at 2 × 1 × 0.5 m soil pans at 5°, 10°, or 20° slope gradients, artificial rainfall with an intensity of 60 or 90 mm h−1 was applied to it. Measurements of the difference in elevation points of the surface profiles were taken before rainfall and after rainfall events for sheet erosion. Tillage practices had a relationship with fractal indices that the surface treated with CT exhibited the biggest fractal dimension D value, followed by the surfaces AD, AB, and CK. Surfaces under a stronger rainfall tended to have a greater D value. Tillage treatments affected anisotropy differently and the surface CT had the strongest effect on anisotropy, followed by the surfaces AD, AB, and CK. A steeper surface would have less effect on anisotropy. Since the surface CT had the strongest effect on spatial variability or the weakest spatial autocorrelation, it had the smallest effect on runoff and sediment yield. Therefore, tillage CT could make a better tillage practice of conserving water and soil. Simultaneously, changes in semivariogram and fractal parameters for surface roughness were examined and evaluated. Fractal parameter – crossover length l – is more sensitive than fractal dimension D to rainfall action to describe vertical differences in soil surface roughness evolution.

2D approximant lattice model: A framework for the simulation of amorphous film deposition

A 2D approximant lattice model has been developed for Monte Carlo simulation of amorphous film growth via physical vapor deposition at low temperature. The model allows for structural randomness of the deposited film by introducing a distribution of bond angle and bond length for the bond between incoming and substrate atoms, and it reduces the computational cost by discretizing the simulation domain into lattice points. The model has been tested by investigating the effects of bond angle and bond length ranges and surface relaxation distance on microstructure and roughness evolution of the deposited film. Simulation results show that the increase in bond-angle and bond-length ranges increases the amorphousness of the deposited film, as expected, while surface relaxation distance mainly affects the film density and growth exponent β: the film density increases while β decreases with increasing surface relaxation distance. The advantage of this model is in its ability to model the deposition of both crystalline and amorphous structures in one framework. In addition, its flexibility allows for the incorporation of other growth-process details such as surface diffusion, which may be crucial, depending on the material and the process, as well as extension to 3D for investigating and controlling interfacial roughness in realistic multilayered systems.

A laboratory demonstration of rail grinding and analysis of running roughness and wear

Rail grinding has been widely used for rail maintenance to keep the performance of the rail track at satisfactory levels. However, there is a lack of knowledge on the relationship between different grinding parameters and the effect on the rails and the post-grinding evolution of roughness and wear. Rail undergoes significant levels of stress during grinding to remove any defects that appear during its life-cycle which can cause significant microstructural change. By developing a method of demonstrating rail grinding it will allow further investigation of the process and potentially the exploration of different grinding patterns. Moreover, an analysis of the roughness of wheel and rail is an input parameter in most modern simulation tools that could be associated with the coefficient of friction. This paper reports a laboratory demonstration of rail grinding followed by a series of tests to determine the wear of the rail and if there is a relationship between friction coefficient and roughness. The rail specimens that were ground have undergone a phase transformation and showed White Etching Layer (WEL) on the contact surface. This was found to initially act protectively for the rail disc reducing the wear rates, but then contributed to crack formation. No clear long-term correlation was identified between the coefficient of friction and roughness during the testing, however a relationship could be drawn when test periods were studied individually.

Evolution of surface roughness of a cast Al-Si-Cu piston alloy during thermal exposure

In the present work, samples of Al-Si-Cu piston alloy after T6 heat treatment were exposed for 2 h at temperatures ranging from 400 to 550 °C. The evolution of surface roughness and microstructure of the alloy during thermal exposure was studied by combination methods of roughness profiles, optical and scanning electron microscopy as well as XRD analysis. It is found that the roughness and mass of the alloy increase with the raise of the thermal exposure temperature, and the increasing rates of them are slow as the exposure temperature is below 500 °C, but accelerates abruptly when the temperature is higher than 500 °C. The variation of surface roughness of the alloy is closely related to phase transformation and oxidation during the thermal exposure.

Dry mechanical-electrochemical polishing of selective laser melted 316L stainless steel

This paper aims to improve the surface quality of 316L stainless steel parts manufactured by selective laser melting (SLM) using dry mechanical-electrochemical polishing (DMECP). DMECP is an advanced surface finishing method combining the advantages of both mechanical and electrochemical polishing techniques in a more environmentally friendly manner. In this paper, the SLM process-related defects causing poor surface quality are analysed first. The material removal mechanism of DMECP is investigated to continuously remove the oxide layers formed during polishing. Surface morphology and roughness evolution under different polishing conditions are characterised. The top surface roughness can be reduced by over 91% from 8.72 μm to 0.75 μm compared to side surface by over 93% from 12.10 to 0.80 μm. The material removal on the top surface is more efficient than that on the side surface under the same polishing condition. The secondary defects formed during polishing can be removed using mechanical polishing mode. The chemical element composition of the polished surface exhibits almost identical content to the initial 316L powders. Compared with the initial dark and rough surfaces, the results validate the capability of DMECP as an effective tool to improve the SLM surface quality and achieve a mirror finish.

Electrolyte Additives for Controlling Roughness of Copper Electrodeposits Formed in Deep Eutectic Solvents

Due to their wide electrochemical stability window, non-toxicity, and highly solubility for metal salts, deep eutectic solvents (DESs) are attracting attention as new class of electrolytes for electrodeposition and energy storage applications. However, due to their viscous nature, DESs impose transport limitations implying rough or dendritic morphology of electrodeposits formed in them. In the present work, we investigated roughness evolution during copper electrodeposition in a DES containing choline chloride and ethylene glycol in a 1:2 molar ratio (ethaline). Cuprous chloride was added to the DES as the metal precursor. Further, polyethyleneimine (PEI) – a common electrolyte additive used in electrodeposition from aqueous media – was added to ethaline and its effects on roughness evolution were investigated. Steady-state polarization measurements confirmed that PEI suppresses copper electrodeposition kinetics. This manifests into micro-scale leveling of deposits and thus suppression of roughness amplification during electrodeposition, which was confirmed electrochemically as well as using optical profilometry. Effects of PEI concentration on electrochemical behavior and roughness suppression were investigated. Specifically, hysteretic response during cyclic voltammetry was observed under certain conditions. Implications of the PEI-induced hysteresis on suppression of roughness in high-efficiency rechargeable batteries will be discussed.

Comment on “Effects of different tillage practices on the hydraulic resistance of concentrated flow on the loess plateau in China” by J. Sun et al

For concentrated flows, which are characterized by small water depth and steep sloping beds, hydraulic conditions different from those typical of streams and rivers occur.In this study a new theoretically deduced flow resistance equation was tested using the experimental data by Sun et al. for three different tilled surfaces (Manual Dibbling, MD, Manual Hoeing, MH, and Contour Drilling, CD). At first, the profile parameter-relationship, which is the relationship between the velocity profile parameter Γ, the channel slope and the flow Froude number, was calibrated using rill flow data by Di Stefano et al. Then, the applicability of this relationship was tested by the measurements of Sun et al. The calculated Darcy–Weisbach friction factor values were generally lower than those measured by Sun et al. and this result was justified taking into account that the rill measurements used for calibrating the profile parameter-relationship simply correspond to grain resistance conditions. For taking into account both grain resistance and tillage induced surface roughness, the profile parameter-relationship was calibrated by the measurements by Sun et al. This calibration was carried out for each tillage practice (MD, MH and CD) and using all the measurements carried out during each 20 min – experimental run. This study was also developed using exclusively the data concerning the beginning of the experiment (0–4 min), in order to state the effect of the initial roughness, and those regarding the end of the experiment (16–20 min) to estimate the influence of the temporal evolution of roughness on the friction factor. The study proved that the Darcy–Weisbach friction factor due to grain resistance and tillage induced roughness can be accurately estimated using the proposed theoretical approach. A temporal variation of the Darcy–Weisbach friction factor was also recognized. Finally, the data were supportive of the slope independence hypothesis of flow velocity stated by Govers.

In situ multimodal imaging for nanoscale visualization of tribofilm formation

A third of the energy from fuel combustion in passenger car gasoline engines is lost due to friction. Carefully designed engine lubricants can recover some of these losses by reducing friction and wear by forming a nanometer-scale chemico-physico tribofilm between surfaces. Accordingly, attention has focused on developing oil formulations that form low-friction tribofilms. However, analyses of resultant tribofilms are typically conducted after tribo-tests with conventional characterization tools and do not offer insights into tribofilm formation and evolution, precluding information critical to tuning tribofilm properties. In this work, we developed a unique multimodal methodology based on Atomic Force Microscopy (AFM) with local probe heating for in situ tribological studies that activates friction modifiers and simultaneously captures the evolution of friction and surface roughness, with nanometer resolution. As a platform to demonstrate the ability of this methodology to visualize dynamics of tribofilm formation in situ, we apply it to molybdenum-based friction modifiers to distinguish key factors in their functionality and correlate nanoscale AFM and Friction Force Microscopy data to bench tribo-tests used in the industry. To decode the formation mechanisms observed in situ and underlying chemistry of tribofilms, we performed ab initio Molecular Dynamics (AIMD) simulations at comparable conditions. AIMD simulations confirmed both nanoscale and bench tribo-test results and showed deviations in molecular organization in tribofilms that are formed from different molybdenum-based friction modifiers that corroborates with surface functionality. With this innovative methodology, we demonstrate proof-of-principle in situ formation of molybdenum-based tribofilms directly on steel surfaces that could be applied generally to studying tribofilm formation.

Hysteresis effects and roughness suppression efficacy of polyethylenimine additive in Cu electrodeposition in ethaline

Deep eutectic solvents (DES) are environmentally-friendly electrolytes that are gaining interest for electrodeposition and energy storage applications. In these applications, metal electrodeposits with smooth, non-dendritic morphology are desired and thus effective strategies for suppressing roughness evolution are critically needed. A commonly employed and rather effective strategy for suppressing roughness evolution in metal electrodeposition is the use of electrolyte additives; however, the availability of such additives in DES electrolytes is limited and so is the understanding of the mechanisms through which additives suppress roughness amplification in DES media. In the present contribution, we demonstrate that polyethylenimine (PEI) is an effective electrolyte additive that suppresses roughness evolution during Cu electrodeposition in ethaline DES. PEI, due to its adsorption–deactivation properties, exhibits a unique hysteresis response during voltammetric studies of Cu electrodeposition – this response is analyzed using a mathematical model incorporating the relevant PEI transport, surface adsorption and deactivation processes. The model provides guidelines for selection of optimal conditions (e.g., PEI concentration) for effective suppression of roughness amplification in Cu electrodeposition.

Local smoothing of optical aluminum surfaces by reactive ion beam etching

Ion beam finishing techniques are commonly used for improvement of surface error topography of optical devices. Optical aluminum surfaces after manufacturing by single-point diamond turning meet the requirements for applications in the infrared spectral range. However, optics used for applications in the short-wavelength visible and ultraviolet spectral range demand improved surface qualities. To overcome the limitations mainly caused by structural and compositional inhomogeneities of aluminum alloys, a reactive ion beam machining process using oxygen and nitrogen operating gas is applied. This technology enables direct surface machining while preserving the initial roughness up to a 1-μm etching depth using low-energy ion beams. Moreover, the use of oxygen allows us to smooth the surface in the microroughness regime. Based on Monte-Carlo simulations and roughness evolution measured by atomic force microscopy, a more detailed discussion of the ion beam process is presented. Hence, a model scheme for direct smoothing of high-frequency surface features is suggested.