Roughness Defects Research Articles

Effect of cutting speed on the surface integrity of face milled 7050-T7451 aluminium workpieces

The guarantee of surface integrity has become a primary objective for researchers when analysing the reliability of machined aircraft aluminium alloy structural parts in high-speed machining. This work studies the effect of cutting speed on the surface integrity of face milled 7050-T7451 aluminium workpieces. First, 7050-T7451 aluminium workpieces were face milled under dry conditions using three cutting speeds (200, 800, 1400 m/min) at constant feed (0.20 mm/tooth) and depth of cut (1 mm). An indexable face milling cutter with a diameter of 50 mm with five uncoated inserts was used in the face milling tests. During the machining process, cutting forces were acquired employing a Kistler dynamometer in order to understand the influence of the mechanical load on the final surface quality. The surface roughness produced by the milling process was measured using a portable rugosimeter. The residual stresses generated by the cutting process were measured by the hole-drilling technique. In addition, small specimens were cut out from the workpieces and microstructural alterations of the surface layer were analysed employing optical microscopy techniques. The results demonstrate that the magnitude of residual stresses and the thickness of the affected layer is sensitive to the cutting speed, while surface roughness and microstructural defects do not show significant variations for the tested conditions.

Surface integrity analysis in Heat Sink-based Dry Drilling of Titanium Alloy

The aerospace structural components made of titanium alloys being manufactured require no. of holes for their assembly. In the dry drilling of titanium alloy, excessive heat is generated at the cutting zones, which results in high mechanical and thermal damage to the surface integrity. The surface integrity of the machined component is an important characteristic, which influences functional behavior of the components being manufactured. Therefore, in this work, a unique heat sink-based dry drilling approach has been prepared to compare its effectiveness over dry drilling (without heat sink) of titanium alloys. In this approach, a highly conductive copper plate was used as a heat sink below the titanium work surface being machined. Drilled surfaces were analyzed for surface roughness, sub-surface deformation and surface defects. It is observed that the average surface roughness was reduced from 4 μm Ra to 1.5 μm Ra in heat sink-based drilling approach. An average sub-surface deformation thickness was reduced by 21% in the heat sink approach as compared to dry drilling. The drilled surface defects were found to be comparatively lower in the heat sink-based drilled surfaces.

Effects of Machine Parameter and Natural Factors on the Productivity of Loading and Haulage Equipment

The purpose of this research is to investigate the factors which affect the performance of the loading and hauling equipment at Skorpion zinc mine, Namibia and also to find possible solutions to eliminate them, so that the weekly Zinc Oxide and ex-pit waste tonnages required could be produced. This is due to the high demand of Zinc on the market. The investigation on road conditions was focused on the effects of rolling resistance, grade resistance and road widths from the road between bench 540 in pit 103 to the Zinc oxide medium grade stockpile. Cycle time data were obtained by time and motion study of the load/haul/dump cycle from bench 540 loading site to the stockpile. The data used for equipment matching by queuing theory (excel modelling) was obtained when the loaders where loading Arkose at different loading sites. The effects of different weather conditions i.e. mist, rain and wind on production where determined by collecting actual shift production tonnages and comparing with target shift production targets during this conditions. The results produced from time and motion studies show that the haul trucks have an average availability of 80.4% and utilization at 49.7% which are very low when compared to the benchmark value of 89% and 69% for availability and utilization respectively. Decline in performance time is caused by factors such as daily safety meetings, lunch breaks, blasting, tools break down and the daily machine service. Rolling resistance is also one of the factors affecting production time at the mine. The rolling resistance of different segments was determined by roughness defect scores (RDS). From calculations, it is clearly seen that if the RR could be reduced to 2% on every road segment, then each cycle period per truck can be reduced by 1.24 minutes. This will increase the production of the haulers and decrease the operating cost. It was recommended that the wearing course of the road surface be treated with a bitumen based dust suppression product in order to keep the surface’s rolling resistance to an absolute minimum (i.e. RR = 2%) [1]. The current average hauling road width is 15.987 m while the correct road width at Skorpion Zinc Mine must be 21.35 m to prevent bunching of trucks. It is therefore recommended that the haul roads be widened to 21.35 m width per segment.

TiO2 nanowire-templated hierarchical nanowire network as water-repelling coating.

Extraordinary water-repelling properties of superhydrophobic surfaces make them novel candidates for a great variety of potential applications. A general approach to achieve superhydrophobicity requires low-energy coating on the surface and roughness on nano- and micrometre scale. However, typical construction of superhydrophobic surfaces with micro-nano structure through top-down fabrication is restricted by sophisticated fabrication techniques and limited choices of substrate materials. Micro-nanoscale topographies templated by conventional microparticles through surface coating may produce large variations in roughness and uncontrollable defects, resulting in poorly controlled surface morphology and wettability. In this work, micro-nanoscale hierarchical nanowire network was fabricated to construct self-cleaning coating using one-dimensional TiO2 nanowires as microscale templates. Hierarchical structure with homogeneous morphology was achieved by branching ZnO nanowires on the TiO2 nanowire backbones through hydrothermal reaction. The hierarchical nanowire network displayed homogeneous micro/nano-topography, in contrast to hierarchical structure templated by traditional microparticles. This hierarchical nanowire network film exhibited high repellency to both water and cell culture medium after functionalization with fluorinated organic molecules. The hierarchical structure templated by TiO2 nanowire coating significantly increased the surface superhydrophobicity compared to vertical ZnO nanowires with nanotopography alone. Our results demonstrated a promising strategy of using nanowires as microscale templates for the rational design of hierarchical coatings with desired superhydrophobicity that can also be applied to various substrate materials.

Theoretical study on effects of exposure pattern width on line edge roughness and stochastic defect generation in fabrication of 16-nm-half-pitch line-and-space patterns by electron beam lithography

The resolution of electron beam (EB) mask writers has reached a 16 nm half-pitch. The suppression of stochastic phenomena such as line edge roughness (LER) and stochastic defect generation is an important issue in the high-resolution fabrication of photomasks and nanoimprint molds. In this study, the effects of exposure pattern width on LER and stochastic defect generation were theoretically investigated on the basis of the sensitization and reaction mechanisms of chemically amplified EB resists. The exposure pattern width affected stochastic bridging more than stochastic pinching and LER. The optimum pattern widths for the suppression of stochastic bridging in the fabrication of 16-nm-half-pitch line-and-space patterns were 8, 8, 10, and 12 nm for the sensitivities of 300, 240, 180, and 120 µC cm−2, respectively.

Damage-Free Smooth-Sidewall InGaAs Nanopillar Array by Metal-Assisted Chemical Etching.

Producing densely packed high aspect ratio In0.53Ga0.47As nanostructures without surface damage is critical for beyond Si-CMOS nanoelectronic and optoelectronic devices. However, conventional dry etching methods are known to produce irreversible damage to III-V compound semiconductors because of the inherent high-energy ion-driven process. In this work, we demonstrate the realization of ordered, uniform, array-based In0.53Ga0.47As pillars with diameters as small as 200 nm using the damage-free metal-assisted chemical etching (MacEtch) technology combined with the post-MacEtch digital etching smoothing. The etching mechanism of InxGa1-xAs is explored through the characterization of pillar morphology and porosity as a function of etching condition and indium composition. The etching behavior of In0.53Ga0.47As, in contrast to higher bandgap semiconductors (e.g., Si or GaAs), can be interpreted by a Schottky barrier height model that dictates the etching mechanism constantly in the mass transport limited regime because of the low barrier height. A broader impact of this work relates to the complete elimination of surface roughness or porosity related defects, which can be prevalent byproducts of MacEtch, by post-MacEtch digital etching. Side-by-side comparison of the midgap interface state density and flat-band capacitance hysteresis of both the unprocessed planar and MacEtched pillar In0.53Ga0.47As metal-oxide-semiconductor capacitors further confirms that the surface of the resultant pillars is as smooth and defect-free as before etching. MacEtch combined with digital etching offers a simple, room-temperature, and low-cost method for the formation of high-quality In0.53Ga0.47As nanostructures that will potentially enable large-volume production of In0.53Ga0.47As-based devices including three-dimensional transistors and high-efficiency infrared photodetectors.

Shot noise limit of chemically amplified resists with photodecomposable quenchers used for extreme ultraviolet lithography

In lithography using high-energy photons such as an extreme ultraviolet (EUV) radiation, the shot noise of photons is a critical issue. The shot noise is a cause of line edge/width roughness (LER/LWR) and stochastic defect generation and limits the resist performance. In this study, the effects of photodecomposable quenchers were investigated from the viewpoint of the shot noise limit. The latent images of line-and-space patterns with 11 nm half-pitch were calculated using a Monte Carlo method. In the simulation, the effect of secondary electron blur was eliminated to clarify the shot noise limits regarding stochastic phenomena such as LER. The shot noise limit for chemically amplified resists with acid generators and photodecomposable quenchers was approximately the same as that for chemically amplified resists with acid generators and conventional quenchers when the total sensitizer concentration was the same. The effect of photodecomposable quenchers on the shot noise limit was essentially the same as that of acid generators.

Effect of Reactive Ion Etch on 4H-SiC Mos Capacitor Performances

4H- Silicon carbide is a promising for power electronic devices operated at high voltages, high temperatures, and high frequencies due to its attractive material properties, such as high avalanche electric breakdown field (2.5 MV/cm), high electron mobility (1000 cm2/V. s), high thermal conductivity (4.9 Wcm-1K-1) and large bandgap (3.26 eV). While conventional double-implanted MOSFET (D-MOSFET) has been commercially successful, trench MOSFET is a fascinating device design for next-generation 4H-SiC power MOSFETs due to its low specific on resistance (RON) [1] and higher current density which can potentially reduce cost. Trench formation in mechanically hard and chemically stable 4H-SiC material requires reactive ion etching (RIE). This RIE step has been reported to introduce surface roughness and deep level defects [2-4] in SiC which may cause degradation of the channel mobility as well as the voltage blocking capability of the trench MOSFETs. These particular issues are critical challenges and need further attention. In this regard, we have studied the electrical properties of planer MOS capacitors fabricated on Si-face (<0001>) and A- face (<11–20>) 4H-SiC epitaxial layers, with and without RIE, prior to gate oxidation. Capacitance coupled plasma (CCP) RIE process was carried out to etch about 2μm of SiC, using NF3as the process gas. Before performing the gate oxidation, a sacrificial thermal oxidation was carried out on the etched samples to consume subsurface damage. The gate oxidation was followed annealing in nitric oxide (NO) for both etched and un-etched samples. Atomic force microscope (AFM) images revealed that almost atomically flat surfaces (RMS roughness= 0.3 nm) were obtained following RIEs as shows in Figure 1. Simultaneous high-low capacitance-voltage (C-V) measurements at room temperature was carried out to investigate RIE induced effects on effective charge density at the SiO2/4H-SiC interface and the interface trap density (Dit ) near the conduction band-edge of 4H-SiC. In addition, current-voltage (I-V) measurements were done at room temperature to investigate RIE induced dielectric breakdown effects. From the room temperature C-V data as shown in the Figure 2, it can be seen that C-V curves for MOS capacitors with or without RIE lie on top each with negligible flat-band voltage (VFB ) shift which suggests that the effective interfacial charge does not change significantly due to RIE (Table 1). Furthermore, extracted Dit profiles (Figure 3) with or without RIE MOS capacitors also shows no difference. In addition, comparable I-V data as shown in the Figure 4 also confirmed minimal effects induced by RIE. These results are inconsistent with previous results [4] where RIE was shown to generate significant amount of interface traps. This is most likely due to a much smoother surface obtained here after RIE as well the post-RIE sacrificial oxidation step which was implemented here. These results suggest that processes such as etching in an H2 environment at elevated temperatures not be necessary after RIE for trench MOSFET fabrication. In the ongoing work, we are analyzing possible deep level defects in the SiC bulk, introduced by RIE using deep level transient spectroscopy measurements. In this talk, detailed discussion of the methods in the context of trench MOSFETs and analysis of the obtained results will present. [1] B. J. Baliga, Fundamentals of power semiconductor devices 2010 (Springer Science & Business Media) [2] V. Khemka et al.: J. Electron. Mater. 27 (1998) 1128-1135 [3] K. Kawahara et al.: J. Appl. Phys. 108 (2010) 023706 [4] Gang Liu et al.: Appl. Surf. Sci. 324 (2015) 30–34 Figure 1

Effects of machining abuse on the surface properties of AISI 316L stainless steel

A Design of Experiments (DoE) approach was used to characterise the effects of dry machining at abusive conditions on the austenitic stainless steel AISI 316L. Surface roughness, hardness, martensite fraction, residual stresses and surface defects (welded chips, cracks) were evaluated against the cutting parameters (speed, depth-of-cut and feed) to build a model weighting their contribution. Results are presented in colour contour plots which allow for an in-depth understanding of the parameters' combined effects on the surface properties of the material upon dry milling. Using the statistical model it was possible to identify optimum combinations of cutting parameters on the grounds of minimising undesirable effects on the material. Eventually, a sample “risk of failure” map was derived by evaluating the impact of the process parameters' statistical variations.

Mechanical Characterization of Additive Manufacturing Processes

Objectives: To compare two of the most popular rapid prototyping processes of Stereolithography (SLA) and Selective Laser Sintering (SLS) from a product-based perspective, to help customers analyze them and make a choice between the two. Methods: This paper includes the qualitative testing of identical specimens created by SLA and SLS. The specimens are evaluated on the parameters of dimensional accuracy, tensile strength, water absorption, surface roughness, density, Vickers hardness and microscopic defect structure. The outcome of this study aims at helping people to understand SLS and SLA better in terms of the products they create so that it becomes easier for users to make a choice between the two. It also aims at highlighting the above mentioned statistical information about SLA and SLS so that they may be improvised and enhanced in the future. Findings: Based on the tests conducted, it was confirmed that the SLA specimens were better than the SLS specimens in the tensile strength, water absorption, surface roughness and density tests. The SLS specimens outperformed the SLA specimens in the dimensional accuracy and Vickers hardness tests. Thus it was concluded that the SLA specimens exhibited better mechanical and physical characteristics than the SLS specimens.

Material microstructure effects in micro-endmilling of Cu99.9E

This article presents an investigation of the machining response of metallurgically and mechanically modified materials at the micro-scale. Tests were conducted that involved micro-milling slots in coarse-grained Cu99.9E with an average grain size of 30 µm and ultrafine-grained Cu99.9E with an average grain size of 200 nm, produced by equal channel angular pressing. A new method based on atomic force microscope measurements is proposed for assessing the effects of material homogeneity changes on the minimum chip thickness required for a robust micro-cutting process with a minimum surface roughness. The investigation has shown that by refining the material microstructure the minimum chip thickness can be reduced and a high surface finish can be obtained. Also, it was concluded that material homogeneity improvements lead to a reduction in surface roughness and surface defects in micro-cutting.

Effect of Low Pressure on Surface Roughness and Morphological Defects of 4H-SiC Epitaxial Layers.

In this work, 4H-SiC epilayers are performed on 4° off-axis substrates under low pressure condition by horizontal hot wall chemical vapor deposition (HWCVD) with a standard chemistry of silane-propane-hydrogen, which focuses on the effects of growth pressure on morphology, basal plane dislocations (BPDs) and crystalline quality. It is found that morphological defects reduce with the decreasing of growth pressure, since the surface diffusion length of absorbed adatoms increases under low growth pressure, which suppresses the nucleation of adatoms on terraces and the formation of morphological defects. However, as the surface diffusion length increases under low growth pressure, the difference of growth velocity at steps is enhanced, which leads to the extension of the steps’ width and the formation of step-bunching. Besides variation of surface diffusion length, the phenomenon described above can be correlated with different dominate modes for the minimization of surface energy at varied growth pressure. Because of the contrary influence of increased C/Si ratio and enhanced step-flow growth on the propagation of BPDs, the dislocation densities of BPDs and threading edge dislocations (TEDs) in epilayers grown at varied pressures remain basically unchanged. The crystalline quality is almost independent of growth pressure based on high resolution X-ray diffraction (HRXRD) measurements.

Near-theoretical fracture strengths in native and oxidized silicon nanowires

In this letter, fracture strengths σf of native and oxidized silicon nanowires (SiNWs) were determined via atomic force microscopy bending experiments and nonlinear finite element analysis. In the native SiNWs, σf in the Si was comparable to the theoretical strength of Si〈111〉, ≈22 GPa. In the oxidized SiNWs, σf in the SiO2 was comparable to the theoretical strength of SiO2, ≈6 to 12 GPa. The results indicate a change in the failure mechanism between native SiNWs, in which fracture originated via inter-atomic bond breaking or atomic-scale defects in the Si, and oxidized SiNWs, in which fracture initiated from surface roughness or nano-scale defects in the SiO2.

Reaction ion etching process for improving laser damage resistance of fused silica optical surface

Laser induced damage of fused silica optics occurs primarily on optical surface or subsurface resulting from various defects produced during polishing/grinding process. Many new kinds of surface treatment processes are explored to remove or control the defects on fused silica surface. In this study, we report a new application of reaction ion etching (RIE)-based surface treatment process for manufacture of high quality fused silica optics. The influence of RIE processes on laser damage resistance as a function of etching depth and the evolution of typical defects which are associated with laser damage performance were investigated. The results show that the impurity element defects and subsurface damage on the samples surface were efficiently removed and prevented. Pure silica surface with relatively single-stable stoichiometry and low carbon atomic concentration was created during the etching. The laser damage resistance of the etched samples increased dramatically. The increase of roughness and ODC point defect with deeper etching are believed to be the main factors to limit further increase of the damage resistance of fused silica. The study is expected to contribute to the development of fused silica optics with high resistance to laser induced degradation in the future.

Competition Between Surface Defects and Residual Stresses On Fatigue Behaviour of Shot Peened Forged Components

The present study focusses on analysing and modelling the influence on fatigue behaviour of the surface of a hot-forged C70 connecting rod which undergoes a shot-blasting treatment. The shot-blasting heavily affects the surface and thus the fatigue properties. In addition, the forging process introduces large defects which also have an effect on the fatigue strength. So as to be able to determine which aspects of the surface integrity are the most influential in fatigue, various surface states were thoroughly characterised and then tested in high cycle fatigue in bending. The various aspects studied are the surface roughness and large defects, residual stresses, microstructure and hardness. The aim of this work is to develop a fatigue design approach that can take into account both the effect of the surface defects and that of the residual stresses on fatigue.

Metal Based Additive Layer Manufacturing: Variations, Correlations and Process Control

Additive layer manufacturing is emerging as the next generation in part manufacture. It is being adopted by aerospace, tool making, dental and medical industries to produce and develop new conceptual designs and products due to its speed and flexibility.It has been noted that parts produced using additive layer manufacturing are not to a consistent quality. Variations have been recorded showing inadequate control over dimensional tolerances, surface roughness, porosity, and other defects in built parts. It is, however, possible to control these variables using real-time processes that currently lack adequate process measurement methods. This paper identifies process variation and lists parameters currently being recorded during a commercial additive manufacture (AM) machine build process. Furthermore, it examines correlations between manufactured parts and real time build variations.

The role of AlGaN buffers and channel thickness in the electronic transport properties of Al x In1–x N/AlN/GaN heterostructures

We try to theoretically analyze the reported experimental data of the AlxIn1–xN/AlN/GaN heterostructures grown by MOCVD and quantitatively investigate the effects of AlGaN buffers and the GaNchannel thickness on the electrical transport properties of these systems. Also, we obtain the most important effective parameters of the temperature-dependent mobility in the range 35–300 K. Our results show that inserting a 1.1 μm thick Al0.04Ga0.96N buffer enhances electron mobility by decreasing the effect of phonons, the interface roughness, and dislocation and crystal defect scattering mechanisms. Also, as the channel thickness increases from 20 nm to 40 nm, the electron mobility increases from 2200 to 2540 cm2/(V s) and from 870 to 1000 cm2/(V s) at 35 and 300 K respectively, which is attributed to the reduction in the dislocation density and the strain-induced field. Finally, the reported experimental data show that inserting a 450 nm graded AlGaN layer before an Al0.04Ga0.96N buffer causes a decrease in the electron mobility, which is attributed to the enhancement of the lateral size of roughness, the dislocation density, and the strain-induced field in this sample.

Influence of Notch Effects Created by Laser Cutting Process on Fatigue Behavior of Metastable Austenitic Stainless Steel

Laser cutting is an attractive and innovative manufacturing process which has many advantages compared to conventional cutting methods. However, with increasing workpiece thickness an increase of the roughness along the kerf surface can be observed, which, in turn, can negatively affect the mechanical properties, in particular the fatigue strength. In this context, the purpose of the present study is to investigate the impact of the geometrical surface characteristics and microstructural changes after laser cutting in order to support the cutting process optimization concerning cyclic durability. Fatigue strength evaluation is performed with specimens cut out by high-power solid-state disk laser from sheets with thickness of 2, 4 and 6mm made of metastable austenitic stainless steel type 304. Cyclic tests are carried out using a resonant pulsation testing system at test frequencies around 100Hz at two different load modes, purely reversal load condition (R = -1) and tensile-tensile load condition (R = 0.1). In order to evaluate separately the effect of surface relief over the cutting kerf and burr in form of re-solidified drops, the fatigue specimens are tested at different surface conditions. The investigation comprises fractographic analyses in order to evaluate the influence of the surface roughness and surface-related macro defects on crack initiation. Additionally, phase analyses are performed to assess the deformation-induced phase transformation during cyclic testing and its influence on fatigue behavior, as well as microstructural investigation to analyze the material microstructural changes during the cutting process and its impact on material mechanical properties. The influence on fatigue strength of parts cut by laser is quantified and the characteristic dominating the fatigue life is identified.

Experimental Investigation for Distributed Defects in Ball Bearing Using Vibration Signature Analysis

Bearing play a pivotal role in rotating machinery. Failure analysis of the bearing is mostly studied by creation of artificial defect on various elements of the bearing and analysis is made with vibration signature tool for monitoring its condition. As localized bearing fault grows, becoming a distributed one, generate random signal with non-stationary components. In present paper effect of surface roughness on the vibration response of outer race of the ball bearing is analysed. Vibration spectrum produced by the single roughness defect under pure radial load at various locations on outer race of bearing is studied. Effect of roughness size, speed and load on the vibration response has been investigated. Results are presented in time and frequency domain. The experimental results are compared with ball pass frequency of outer race. Frequency response obtained from the experimental results is found identical with the theoretical ball pass frequency of outer race.

Roughness and micro pit defects on surface of SUS 430stainless steel strip in cold rolling process

Experiment on roughness and micro pit defects of SUS 430 ferrite stainless steel was investigated in laboratory. The relation between roughness and glossiness with reduction in height, roll surface roughness, emulsion parameters was analyzed. The surface morphology of micro pit defects was observed by SEM, and the effects of micro pit defects on rolling reduction, roll surface roughness, emulsion parameters, lubrication oil in deformation zone and work roll diameter were discussed. With the increasing of reduction ratio strip surface roughness Ra(s), Rp(s) and Rv(s) were decreasing along rolling and width direction, the drop value in rolling direction was faster than that in width direction. The roughness and glossiness were obtained under emulsion concentration 3% and 6%, temperature 55