Large Surface Roughness Research Articles

Improving the mechanical and anti-wear properties of AlTiN coatings by the hybrid arc and sputtering deposition

Arc-evaporated AlTiN coatings with remarkable adhesion and thermal stability are widely used in manufacturing. However, the large residual stress and surface roughness limit their high-level applications for advanced machining. In this study, a hybrid technique combining cathodic arc evaporation and magnetron sputtering was utilized to enhance the mechanical properties and wear resistance of AlxTi1-xN with x = ∼0.65. The hybrid AlTiN coatings exhibited a nano-multilayer architecture with alternating arc-evaporated and magnetron sputtered constituents, which decreased their residual stress from -7.1 GPa to about -5.0 GPa. In addition, the hybrid AlTiN showed higher indentation toughness than the monolithic coatings. The hybrid AlTiN coating with a target sputtering power of 7.0 kW showed excellent wear resistance at room and high temperature. At 800 °C, the hybrid coatings mainly showed abrasive and oxidation wear, while the monolithic AlTiN coating showed abrasive/oxidation wear and brittle failure.

Identifikasi Tegangan pada Permukaan Karet SBR-25 saat mengalami Kontak Abrasi: Investigasi Numerik

Keausan akibat abrasi pada komponen yang terbuat dari material karet seperti pada ban kendaraan atau seal sangat menentukan umur pakai dari komponen tersebut. Dalam material karet, ketika permukaan yang masih halus mengalami abrasi, maka akan terbentuk permukaan yang bergerigi secara paralel yang arahnya tegak lurus dengan arah gerak abrasi. Bentuk permukaan yang bergerigi ini akan terus menerus terbentuk selama proses kontak abrasi masih berjalan. Keausan abrasi terjadi akibat tegangan pada material karet melampaui tegangan patah material. Tetapi analisis keausan abrasi pada karet masih sangat sulit dilakukan secara analitik dikarenakan sifat karet yang non linier dan hyperelastic. Dengan menggunakan metoda numerik, tulisan ini membahas tegangan yang terjadi pada permukaan karet SBR-25 yang sudah terabrasi. Sebagai studi awal, analisis dilakukan dalam dua dimensi dengan menggunakan perangkat lunak komersial ABAQUS 6.14-5 dengan memodelkan karet yang kontak dengan indenter yang kaku. Simulasi dilakukan dengan variasi kedalaman indentasi, kekasaran permukaan dan dimensi gigi (chip). Secara umum hasil menunjukkan bahwa makin besar kedalaman indentasi dan kekasaran permukaaan akan meningkatkan nilai tegangan maksimum. Disisi lain, lokasi terjadinya tegangan maksimum (tegangan kritis) juga sangat dipengaruhi oleh kedalaman indentasi, kekasaran permukaan dan dimensi dari chip.

Study of prestress ultrasonic peening on bending curvature and surface properties of stiffened plates

Stiffened plates are commonly adopted as key structure components in aerospace due to light weight structure with high strength and stiffness. Ultrasonic peening (UP) is the key process for manufacturing of wing panels with stiffened plates; however, large bending strain is difficult to be generated during free UP, which significantly affects its surface properties. Prestress UP is adopted through applying prebending moment to stiffened plates before peening process and its effects on bending curvature, surface hardness and roughness, residual stress distribution under different peening parameters are analyzed. The results show that larger chordwise bending strain can be obtained in prestress UP and it increases with decreasing prebending curvature radius and decreasing offset distance as well as increasing firing pinvelocity. Compared to free UP, smaller surface roughness, larger surface hardness, larger and deeper compressive residual stress can be acquired in prestress UP and their differences between two UP ways increase with decreasing prebending curvature radius. Meanwhile, increasing firing pin velocity and decreasing offset distance are beneficial to hardening extent of peening and generation of large and deep compressive residual stress. However, large firing pin velocity results in large surface roughness and appropriate value of firing pin velocity should be used. Small offset distance will decrease the peening efficiency; therefore, comprehensive consideration of large bending deformation and peening efficiency should be considered. Prestress UP is effective to increase bending strain and improve surface properties of stiffened plate and this study can provide guidance for parameters selection.

Carbon Black from Diesel Soot for High‐Performance Wearable Pressure Sensors

AbstractThe rational design of high‐performance flexible pressure sensors with both high sensitivity and large workable range attracts great attentions due to the potential applications in wearable electronics and human–machine interfaces. Here, carbon black (CB) from diesel soot, an air pollutant produced during incomplete combustion of hydrocarbon fuels, is used as the active material to construct high‐performance flexible all‐textile pressure sensors. Due to the unique hierarchical structures and large surface roughness of the CB‐coated fabric, the pressure sensor exhibits outstanding performances, such as high sensitivity (81.61 kPa−1 within the range of 0–10 kPa), extrawide workable pressure regime (0–100 kPa), and rapid response and relaxation time (6 and 30 ms, respectively). Based on these superior sensing properties, its practical applications are demonstrated in detecting the signals of musical sound and of human physiology, showing its potential for health monitoring as wearable electronics.

Effects of Cobalt Content on the Microstructure, Mechanical Properties and Cavitation Erosion Resistance of HVOF Sprayed Coatings

Cobalt-based alloy coatings and WC-Co-based ceramic–metal (cermet) coatings have been widely used because of their desirable mechanical properties and corrosion resistance. In this work, the influence of Co content on the microstructure, mechanical properties and cavitation erosion (CE) resistance were investigated. A cobalt-based alloy coating, a WC-12Co coating, and a WC-17Co cermet coating were deposited by high-velocity oxygen fuel (HVOF) spraying on 1Cr18Ni9Ti substrates. Results indicate that the cobalt-based alloy coating had the largest surface roughness because surface-bonded particles of lower plastic deformation were flattened. The existence of WC particles had led to an increase in hardness and improved the fracture toughness due to inhibit crack propagation. The pore appeared at the interface between WC particles, and the matrix phase had introduced an increase in porosity. With the increase in Co content, the cohesion between matrix friction and WC particles increased and then decreased the porosity (from 0.99% to 0.84%) and surface roughness (Ra from 4.49 to 2.47 μm). It can be concluded that the hardness had decreased (from 1181 to 1120 HV0.3) with a decrease in WC hard phase content. On the contrary, the fracture toughness increased (from 4.57 to 4.64 MPa∙m1/2) due to higher energy absorption in the matrix phase. The WC-12Co and WC-17Co coatings with higher hardness and fracture toughness exhibited better CE resistance than the cobalt-based alloy coating, increasing more than 20% and 16%, respectively. Especially, the WC-12Co coating possessed the best CE resistance and is expected to be applicable in the hydraulic machineries.

Use of an Abrasive Water Cavitating Jet and Peening Process to Improve the Fatigue Strength of Titanium Alloy 6Al-4V Manufactured by the Electron Beam Powder Bed Melting (EBPB) Additive Manufacturing Method

Metal components made by additive manufacturing have large inherent surface roughness, and, as such, their strength and fatigue life can be reduced significantly versus wrought products. In order to improve these properties, a novel mechanical surface treatment that introduces compressive residual stress while simultaneously reducing the surface roughness is proposed. The proposed treatment uses cavitation peening combined with an abrasive slurry. The impact of the kinetic energy-charged abrasive particles, induced by collapsing water cavitation vapor bubbles, produces compressive residual stress, while the abrasive reduces the surface roughness. Plane-bending fatigue tests were carried out to determine the effectiveness of this treatment on the fatigue life and strength of titanium alloy Ti6Al4V manufactured by electron beam melting. It was demonstrated that the fatigue strength of an as-built specimen was improved from 169 MPa to 280 MPa by the proposed treatment.

Heat transfer prediction and critical heat flux mechanism for pool boiling of NOVEC-649 on microporous copper surfaces

Pool boiling performance of NOVEC-649 was experimentally studied on microporous surfaces prepared by an electrochemical deposition method. Microporous structures contribute to large surface roughness values and provide large quantities of cavities ranging from several hundreds of nanometers to several microns for bubble nucleation. The results show that a maximum enhancement of 600% in heat transfer coefficient and a maximum enhancement of 55% in critical heat flux are achieved on the deposited surfaces, compared with a smooth copper surface. Experimental heat transfer coefficients were compared with literature correlations, considering the effects of roughness and surface-liquid combination. Then a fitted Rohsenow correlation was discussed and developed to predict the present results. Experimental critical heat fluxes were compared with classical models. It was found that the critical heat flux on the smooth surface could be predicted by the lift-off model and the Kandlikar model, but these models cannot predict the critical heat fluxes on the deposited surfaces well. Following, the Kandlikar model was modified by further considering a wicking force and a roughness-factor-dependent surface tension force. The present modified CHF model was validated by comparing with present experimental data and the literature, with a deviation around ±30%.

Polyaniline Nanofiber Wrapped Fabric for High Performance Flexible Pressure Sensors.

The rational design of high-performance flexible pressure sensors with both high sensitivity and wide linear range attracts great attention because of their potential applications in wearable electronics and human-machine interfaces. Here, polyaniline nanofiber wrapped nonwoven fabric was used as the active material to construct high performance, flexible, all fabric pressure sensors with a bottom interdigitated textile electrode. Due to the unique hierarchical structures, large surface roughness of the polyaniline coated fabric and high conductivity of the interdigitated textile electrodes, the obtained pressure sensor shows superior performance, including ultrahigh sensitivity of 46.48 kPa−1 in a wide linear range (<4.5 kPa), rapid response/relaxation time (7/16 ms) and low detection limit (0.46 Pa). Based on these merits, the practical applications in monitoring human physiological signals and detecting spatial distribution of subtle pressure are demonstrated, showing its potential for health monitoring as wearable electronics.

Afforestation reduces cyclone intensity and precipitation extremes over Europe

Extratropical cyclones are the dominant weather pattern in the midlatitudes and cause up to 80% of precipitation extremes in some regions of Europe with a large societal and economical impact. Using a regional climate model and a cyclone-tracking algorithm, we study how idealized deforestation and afforestation of Europe affect long-term changes in the number and intensity of cyclones, and their effects on precipitation. The number of cyclones over Europe is smaller for afforestation compared to deforestation, with differences starting from 10% in regions near the west European coast and increasing towards the east to reach 80%. This decrease is caused by the larger surface roughness in afforestation. The winter precipitation extremes are considerably reduced with afforestation, without a large decrease in mean precipitation because of the balancing effect of increased weak and moderate precipitation. The mean precipitation increases over central and southern Europe as a result of the summer precipitation increase caused by larger evapotranspiration and access to deeper soil moisture in the presence of trees. These different region-specific effects of afforestation are generally positive and could provide an important mitigation tool in a changing climate.

Bonding performance of sintered nanosilver joints on bare copper substrates with different grain structures

Nanosilver paste as a state-of-the-art die-attach material for power electronics has been widely used in bare copper bonding. In this paper, bonding performance of sintered nanosilver joints on bare copper substrates with different grain structures was investigated. The bare copper joint with optimum bonding performance was obtained with copper substrate possessing smallest grain size (1.88 μm), strongest (001) texture and largest surface roughness (750.31 nm). It was thought copper substrate with smaller grain size provided more grain boundaries to facilitate the diffusion rate of Ag atoms on the surface of copper substrate and into the substrate, further leading to the greater contact area and longer inter-diffusion band to achieve stronger interfacial bonding. Meanwhile, faster diffusion at the interface did not interfere with the densification of sintered Ag layer. Therefore, the stronger interfacial bonding and well-densified Ag layer strengthened the sintered joint. It was also found (001) orientation could possibly be the most contributing to bonding strength, since the decrease of relative texture coefficient of (200) coincided with the reduced strength. Besides, rougher surface of copper substrate with smaller grain size after polishing could be another factor to improve bonding strength due to the larger contact area and mechanical interlocking.

Textile Display with AMOLED Using a Stacked-Pixel Structure on a Polyethylene Terephthalate Fabric Substrate.

An active-mode organic light-emitting diode (AMOLED) display on a fabric substrate is expected to be a prominent textile display for e-textile applications. However, the large surface roughness of the fabric substrate limits the aperture ratio—the area ratio of the organic light-emitting diode (OLED) to the total pixel area. In this study, the aperture ratio of the AMOLED panel fabricated on the polyethylene terephthalate fabric substrate was enhanced by applying a stacked-pixel structure, in which the OLED was deposited above the organic thin-film transistor (OTFT) pixel circuit layer. The stacked pixels were achieved using the following three key technologies. First, the planarization process of the fabric substrate was performed by sequentially depositing a polyurethane and photo-acryl layer, improving the surface roughness from 10 μm to 0.3 μm. Second, a protection layer consisting of three polymer layers, a water-soluble poly-vinyl alcohol, dichromated-polyvinylalcohol (PVA), and photo acryl, formed by a spin-coating processes was inserted between the OTFT circuit and the OLED layer. Third, a high mobility of 0.98 cm2/V∙s was achieved at the panel scale by using hybrid carbon nano-tube (CNT)/Au (5 nm) electrodes for the S/D contacts and the photo-acryl (PA) for the gate dielectric, enabling the supply of a sufficiently large current (40 μA @ VGS = −10 V) to the OLED. The aperture ratio of the AMOLED panel using the stacked-pixel structure was improved to 48%, which was about two times larger than the 19% of the side-by-side pixel, placing the OLED just beside the OTFTs on the same plane.

Simple Regression Model for Estimating Reflectance Reduction due to Random Surface Roughness

Radiative properties of rough surfaces differ from those of smooth surfaces due to their tendency to scatter electromagnetic waves. Accurate evaluation of property change of rough surfaces requires theoretical background and numerical techniques for solving the scattering of electromagnetic waves, which is challenging and time-consuming. Therefore, this study proposes a simple regression model for estimating the reflectance reduction due to random surface roughness. Because reflectance reduction is significant when multiple reflections occur due to large surface roughness, a Monte Carlo ray-tracing (MCRT) method based on geometric optics approximation was used to evaluate reflectance reduction. Then, a regression analysis based on the numerical results of the MCRT method was implemented. A regression equation was derived as a function of the smooth-surface reflectance and a roughness slope parameter. For silicon and aluminum surfaces, the results of the proposed regression model agreed with those obtained using the MCRT method under 4.4 % error limit. Hopefully, the proposed model can be used to easily bridge between radiative properties of rough surfaces and statistics of surface roughness without relying on laborious numerical techniques for light scattering problems.

Analysis Of The Effect Of Slope Of The Scratch Side Angle Through The Post Tool On Surface Level Surface At The Working Tool Stermination ST 37

The purpose of this research is to see the effect of slope of incision angle chisel through Tool Post to roughness of surface of object. The method used is a lathe ST 37, with 0.5 mm cutting depth, with side angle cutting angle by tilting the Post Tool, ie: 10˚ tilted to the left, 10˚ tilted right, 0˚ (perpendicular), 5˚ tilted right, and 5˚ tilted left. Feeding (constant feeding) is: 0.281 mm / rotation, main cutting corner of chisel 80˚ and cutting speed = 740 rpm. Then the workpiece measured the surface roughness by using Surface Tester Mitutoyo SJ-201P. The result showed that, the smallest surface roughness rate achieved was (ΣRap) = 7, 42 μm with N9 surface roughness class with the Post Tool angle 5 ° to the left. While the largest surface roughness rate achieved is (ΣRap) = 13, 76 μm with the surface roughness class N11 with the tool angle post 10 ° to the right. The value of the roughness level achieved is between N9 - N11.

Ultraviolet-excitation Polishing using Photocatalyst and Cathilon

The availability of ultraviolet-excitation polishing for 4H-SiC wafer and the chemical state of the 4H-SiC surface polished using photocatalyst and cathilon were investigated in absence and presence of an ultraviolet (UV). X-ray absorption fine structure (XAFS) spectroscopy conducted the qualitative analysis of the polished 4H-SiC surface. This analysis was used to clarify the oxides that are formed/removed by decomposition of cathilon dye and water during the polishing of 4H-SiC using TiO2 slurry, cathilon slurry and TiO2-cathilon slurry (mixed slurry), all of which included diamond particles. In polishing the previously sandblasted and handlapped 4H-SiC, TiO2 slurry provides large polishing efficiency and large polished surface roughness, and cathilon slurry provides small polishing efficiency and small polished surface roughness under UV irradiation. The large polishing efficiency, small polished surface roughness and large roughness decrease rate were attained using mixed slurry that is suitable to polish 4H-SiC under UV irradiation. The differences of XAFS spectrum are observed in UV absence/presence among three kinds of slurries. The XAFS analysis mainly investigates and indicates that some oxides form on the surface polished using cathilon and mixed slurries in UV absence/presence. Polishing using mixed slurry provides less volumes of oxides inside SiC on the polished surface, particularly.

Rapid methane hydrate formation in aluminum honeycomb

In order to investigate the effect of metal honeycomb on the formation kinetics of methane hydrate, gas consumption experiments were conducted in a stainless steel vessel filled with sodium dodecyl sulfate (SDS) and aluminum honeycomb (AH) at 274.2 K in the pressure range 5.0–9.0 MPa. The honeycomb structure provides several interconnected channels with large rough surfaces for the promotion of hydrate nucleation. Meanwhile, the excellent thermal conductivity of the metallic surface facilitates dissipation of the hydrate heat. The honeycomb channels can be considered as micro-vessels for the formation of gas hydrates, and each channel provides a “free-unimpeded thermal conduction surface” for heat transfer in the hydration system. When AH is introduced in the SDS system, the methane consumption and its rate surpassed the values recorded in the absence of AH. The maximum gas consumption and the rate reached 157.0 ± 1.9 cm3·cm−3 and 29.65 cm3·cm−3·min−1, respectively. Comparison with the SDS system under similar conditions revealed that the maximum gas consumption rates increased by 9.62–14.30%. We hope this work provides new insights into the kinetic behavior of the formation of gas hydrates in metal honeycombs.

Surface modification with special morphology for the metallization of polyimide film

Metallized polyimide (PI) film has great applications in the field of flexible electronics. Surface property adjustment is considered as an effective way to realize the metallization of PI film by chemical methods. In this work, we demonstrate a facile approach to fabricate metallized PI film via surface modification and electroless plating. Polyethyleneimine (PEI) cross-linked with glutaraldehyde (GA) is used as a modifier to act on the surface of alkali-treated PI film, and a special regular morphology is obtained. This PEI-modified PI film possesses not only functional groups for chemical bonding but also large surface roughness for mechanical locking with metallic copper layer. The resulting copper layer has low resistivity (2.30 μΩ·cm) and satisfactory adhesion to PI film (the highest score of 5B according to ASTM D3359), and the metallized PI sample exhibits reliable flexibility. These results demonstrate a promising potential of this approach in the field of PI film metallization with impact in wearables, light-weight, and flexible electronics.

Thermoelectric properties including thermal conductivity of electrodeposited bismuth selenide thin films fabricated using different acid solutions

Using electrodeposition to prepare thermoelectric thin films enables the fabrication of energy-harvesting devices with low manufacturing cost. However, it is difficult to compute the thermal conductivity of these electrodeposited thin films owing to their large surface roughness. In this work, we prepared electrodeposited bismuth selenide (Bi2Se3) thin films using hydrochloric acid (HCl) and nitric acid (HNO3) solutions and measured the thermal conductivity using the 3ω method. The Bi2Se3 thin films prepared using the HCl solution consisted of round grains with relatively large pores that reached the substrate appearing between the grains. In contrast, the Bi2Se3 thin films prepared using the HNO3 solution were composed of flake-like grains with the appearance of relatively small and shallow pores. As a result, the thermal conductivity could only be measured for the Bi2Se3 thin films synthesized utilizing HNO3 solution; however, the measured thermal conductivity was about 0.14 W/(m⋅K). The low value of thermal conductivity was attributed to their amorphous structure. To improve the electrical properties of Bi2Se3 thin films, the electrodeposited samples were subjected to a thermal annealing treatment. An improvement in the electrical properties of the thin films was noticed with an annealing temperature of 300 °C; however, the thermal conductivity also increased to 0.76 W/(m⋅K). Therefore, the dimensionless quantity which represents the performance of the Bi2Se3 thin film, ZT, was determined to be 0.08–0.09. Therefore, the effectiveness of the proposed method for preparing electrodeposited thin films while estimating the thermal conductivity and ZT was successfully demonstrated.

Comparison of polyglycolic acid acupoint catgut embedding therapy monofilaments for a juvenile pseudo-myopia surface modified by two processing methods

Polyglycolic acid (PGA) acupoint catgut embedding therapy (ACET) monofilament has been heavily used for juvenile pseudopia in the recent years. However, poor hydrophilicity and cytocompatibility have limited its development and wide practical application. In this context, this work is aimed to develop ACET materials with good comprehensive properties by surface modifications. Two different methods, namely ultrasound and plasma technologies, were selected to modify the surface property of PGA monofilaments to improve their wetting and compatibility with tissues, while minimizing degradation of the fibers. Moreover, the effects of these two processing methods on the structure, mechanical and in vitro properties of PGA were fully characterized. Both the ultrasound and plasma modified samples were observed to have a larger surface roughness, and their weights and diameters were decreased. Samples P-PGA1 (76.2° ± 1.4°) and P-PGA2 (73.5° ± 1.9°) exhibited the smallest contact angle values among their groups, respectively. The tensile properties and bending stiffness values of modified PGA decreased slightly, while their swelling ratios were greatly improved. All the prepared samples presented no toxicity (more than 75% cells being viable), and their cell attachment ratios (cultured for 48 h) were also enhanced. In summary, plasma and ultrasound modified PGA showed better hydrophilicity and in vitro properties compared to that of unmodified samples, while retaining the other excellent characteristics. These findings illustrated that the two processing methods were feasible and warrant further study in the application of ACET materials.

Depth-dependent hysteresis in adhesive elastic contacts at large surface roughness

Contact force–indentation depth measurements in contact experiments involving compliant materials, such as polymers and gels, show a hysteresis loop whose size depends on the maximum indentation depth. This depth-dependent hysteresis (DDH) is not explained by classical contact mechanics theories and was believed to be due to effects such as material viscoelasticity, plasticity, surface polymer interdigitation, and moisture. It has been observed that the DDH energy loss initially increases and then decreases with roughness. A mechanics model based on the occurrence of adhesion and roughness related small-scale instabilities was presented by one of the authors for explaining DDH. However, that model only applies in the regime of infinitesimally small surface roughness, and consequently it does not capture the decrease in energy loss with surface roughness at the large roughness regime. We present a new mechanics model that applies in the regime of large surface roughness based on the Maugis–Dugdale theory of adhesive elastic contacts and Nayak’s theory of rough surfaces. The model captures the trend of decreasing energy loss with increasing roughness. It also captures the experimentally observed dependencies of energy loss on the maximum indentation depth, and material and surface properties.

Atomic layer germanium etching for 3D Fin-FET using chlorine neutral beam

In case of using pure chlorine chemistry, Ge etching reactivity is three times higher than Si etching reactivity because of the larger lattice spacing in Ge. As a result, during the chlorine plasma etching of a Ge Fin structure, there are serious problems such as a large side-etching and large surface roughness on the Ge sidewall. Conversely, the authors found that several-ten nanometer-width Ge Fin structures with defect-free, vertical, and smooth sidewalls were successively delineated by chlorine neutral beam etching. Based on these results, the problems caused by chlorine plasma etching are considered to be due to the enhancement of chemical reactivity caused by defect on the sidewall with the irradiation of ultraviolet/vacuum ultra violet (UV/VUV) photons. Namely, it is clarified that the neutral beam etching could achieve real atomic layer etching by controlling the defect without any UV/VUV photons on the sidewall surface for future nanoscale Ge Fin structures.