Reduction In Surface Damage Research Articles

End milling of DIN 1.2714 die steel with cryogenic CO2 cooling

Currently, cryogenic coolants are used instead of normal cutting fluid in transferring excessive heat from the cutting region and retaining cutting tool edge sharpness during the machining process, and to eliminate the hazardous effects of cutting fluids. In this investigation, end milling experiments with various cooling approaches were performed on DIN 1.2714 die steel using titanium aluminum nitrate-coated carbide tool inserts under dry, conventional coolant, and cryogenic CO2 environments. The end milling performance under CO2 environment has been compared with those under dry and wet conditions regarding cutting temperature (Tc), feed force (Fx), normal force (Fy), axial force (Fz), surface roughness (Ra), tool wear, surface and chip morphology, and residual stress. The consequences of these machining environments were evaluated. Using cryogenic CO2 cooling technique reduced the Tc values by approximately 50.49 % and 64.42 % compared with those of wet and dry conditions, respectively. Similarly, CO2 cooling diminished the cutting forces, namely, Fx, Fy and Fz. As a result, Ra values reduced by approximately 59.81 % and 67.15 % compared with those of wet and dry conditions, respectively. Cryogenic CO2 caused a significant reduction in surface damage and abrasion wear in the machined surfaces and cutting inserts, respectively. No substantial changes in residual stress were observed at the cut surfaces.

High Uniformity Normally-OFF p-GaN Gate HEMT Using Self-Terminated Digital Etching Technique

A normally-OFF p-GaN gate AlGaN/GaN high-electron-mobility transistor with high ON-state resistance ( ${R}_{ \mathrm{\scriptscriptstyle ON}}$ ) uniformity was realized using a self-terminated digital etching technique. ${R}_{ \mathrm{\scriptscriptstyle ON}}$ uniformity control was improved by simultaneously using an AlN etching stop layer in an epitaxial design and a novel digital etching procedure. Digital etching includes the multiple-cycle oxidation and the wet etching of p-GaN layers and provides easy control of p-GaN removal depth and surface damage reduction at the gate-to-drain and gate-to-source spacing areas. Low-frequency noise and pulse measurements indicated that device surface traps and current collapse phenomena were suppressed.

Testing and analyses of copolymer fibers based on 5-amino-2-(p-aminophenyl)-benzimidazole

Fibers containing 5-amino-2-(p-aminophenyl)benzimidazole are being considered for use as reinforcement in soft body armor applications. Past research in this laboratory has resulted in a suite of tests that have been used to detect degradation in other fibers and are now being applied to the fibers in question. Due to the architecture of the yarns in this study, two methods to extract single filaments for tensile testing were described and analyzed. A dry method resulted in fibers with surface damage, reflected in a high standard deviation in strength. A wet extraction method showed a reduction in surface damage and a lower standard deviation in strength. Fourier Transform Infrared analysis detected signs of hydrolysis in the fibers that were exposed to water. Although no noticeable loss in tensile strength was noted upon exposure, the possibility of hydrolysis in these fibers may indicate a need for further study.

Normally-off AlGaN/GaN high-electron-mobility transistor using digital etching technique

A normally-off AlGaN/GaN high-electron-mobility transistor (HEMT) with a recessed-gate structure fabricated by novel digital etching is reported. Digital etching consists of multiple cycles of oxidation and wet etching of the oxide, and has the merits of easy control of the recess depth and reduction of surface damage in comparison with conventional dry etching. However, in conventional digital etching, the oxidation process involves the possibility of undercutting. In the digital etching, a reactive ion etcher was used and recess etching without any undercut was confirmed. Normally-off operation and the improvement of transconductance were confirmed in an AlGaN/GaN HEMT fabricated by this technique.

Self-Healing of Abrasion Damage in Epoxy Resin–Ionic Liquid Nanocomposites

The present work describes the self-healing, under ambient conditions, of abrasion surface damage in epoxy resin (ER) modified by a dispersed ionic liquid (IL) phase. The abrasion resistance of ER containing a 9 wt.% of the IL 1-octyl, 3-methylimidazolium tetrafluoroborate (ER + 9IL) was determined by multiple scratching under constant load and by single scratching under progressively increasing load, and compared with that of neat ER. ER + 9IL shows higher instantaneous penetration depth and residual depth values than neat ER. In the case of ER, the viscoelastic recovery process ends after 30 min. For ER + 9IL, the recovery process continues with time to reach a total healing of multiple scratch abrasion grooves after 22–25 h at room temperature. For single scratches under the maximum load of 20 N, ER + 9IL shows an 88 % reduction in surface damage with respect to ER, after 24 h at room temperature. The addition of IL reduces hardness and tensile strength, while increases elongation at break by a 42 %. Hardness test scars on ER + 9IL show an area reduction of approximately 55 % after 5 h. Results are discussed upon the basis of optical and electron (SEM) microscopy and 3D profilometry.

Design changes improve contact patterns and articular surface damage in total knee arthroplasty.

The Optetrak PS (Exactech, Inc., Gainesville, FL) has been a well-functioning posterior stabilized knee replacement since its introduction in 1995. In 2009, the Optetrak Logic incorporated modifications to the anterior face of the tibial post and the corresponding anterior articulating surface of the femoral component to reduce edge loading on the polyethylene post. In this study, we provide the rationale for the design change and compare the damage on retrieved tibial components of both designs to demonstrate the effectiveness of the design modifications in decreasing post damage. We integrated retrieval findings of tibial post damage with finite element analysis to redesign the anterior tibial post-femoral box articulation. We then used subsequent retrieval analysis on a 3:1 matched sample of 60 PS and 20 Logic inserts to examine the impact of the design change on polyethylene damage. Polyethylene stresses were markedly reduced when rounded contact geometries were incorporated. The comparison of the new and old designs using retrieval analysis demonstrated that the redesign led to reduction in surface damage and deformation on the tibial post. This study shows the use of a design cycle by which a problem is identified through retrieval analysis, analytical tools are used to suggest design solutions, and then retrieval analysis is applied again on the new design to confirm improved performance. Anterior post damage has been markedly reduced through the introduction of design changes to the post-box geometry.

Improved reverse current-voltage characteristics of a 4H-SiC PiN diode by bias-enhanced reduction of surface damage

This paper introduces a phenomenon in which the leakage current of a 4H-SiC PiN diode was dramatically reduced without destruction during a bias stress. The reverse current-voltage characteristics of the 4H-SiC PiN diode were improved by using the bias-stress technique employing this phenomenon. Compared to a PiN diode bias-stressed for 10 s, a PiN diode bias-stressed for 600 s showed about a 2 order of magnitude lower leakage current and a 2.2 times higher breakdown voltage (1322 V for a PiN diode having an epi-layer thickness of 8 µm, which approaches 89% of the ideal value for a 1-dimensional (1-D) parallel plate structure).

Two-Step Plasma-Texturing Process for Multicrystalline Silicon Solar Cells With Linear Microwave Plasma Sources

Surface texturing of crystalline silicon solar cells allows reduction of the reflection of sunlight and enhances photon generation. Plasma-based texturing offers significant advantages over the conventional wet approach, i.e., reduced Si consumption, thin wafer compatibility, increased throughput, and reduced chemical waste. However, it still suffers from insufficient electric yield, i.e., bad performance of plasma-processed solar cells. This paper describes advances made in plasma texturing by means of a linear microwave plasma source. The advantage of a two-step plasma-texturing process is demonstrated, leading to a smoother surface roughness, and resulting in an increased open-circuit voltage, together with a reduced processing time. In addition, the described technology allows a significant reduction of surface damage and could be implemented on a production line for crystalline silicon solar cell manufacturing.

Temperature-Dependent Characteristics of a Low Temperature Deposition Approach on a Pseudomorphic High Electron Mobility Transistor

The temperature-dependent characteristics of an AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (PHEMT) with an electroless plated (EP) deposition approach are studied and demonstrated. Based on the low temperature and low energy deposition, the EP deposition approach can form a better metal-semiconductor interface with the reduction in surface damage. Experimentally, the EP-based device shows a significantly improved dc performance. Good experimental results, including a high Schottky barrier height of 0.831 (0.759) eV, low ideality factor of 1.10 (1.32), high turn-on voltage of 0.75 (0.51) V, low reverse leakage current of 3.9 (161.4) μA/mm, improved threshold voltage of -0.43 (-0.61) V, and high maximum transconductance of 225.8 (160.9) mS/mm, are obtained at 300 (500) K. Moreover, the EP approach also has the advantages of easy operation and low cost.

Workpiece surface integrity considerations when finish turning gamma titanium aluminide

Gamma titanium aluminides (γ-TiAl) are currently being evaluated by aeroengine manufacturers as possible replacements for conventional titanium alloys and nickel based superalloys in gas turbine engines. Unfortunately, even when machining using operating parameters selected to minimise workpiece damage, turned surfaces contain cracks and microstructural alterations. The paper initially reviews prior work on the surface integrity of γ-TiAl produced by various machining processes. Following on from this, surface integrity data from a full factorial experiment are presented when turning Ti–45Al–2Mn–2Nb+0.8 vol.% TiB 2 employing extremely fine finishing cuts. Workpiece surfaces/subsurfaces were evaluated in relation to microstructural alterations, strain hardening/microhardness changes, and 2D surface roughness (Ra). All the machined surfaces contained cracks, cracked TiB 2 particles, deformed microstructure and microhardness increases regardless of the operating parameters. However, when comparing the surfaces with those obtained in previous work using more abusive parameters, a significant reduction in surface damage was obtained.

ChemInform Abstract: Analysis and Reduction of Surface Damage in Silicon Following Hydrogen Passivation.

AbstractTreatment of polycrystalline Si with a hydrogen ion beam (Kaufman‐type source) is found to improve the electronic properties, but also to create a certain degree of surface damage which is quantified by near UV reflectivity and RBS measurements.

Analysis and Reduction of Surface Damage in Silicon Following Hydrogen Passivation

The Kaufman ion source used to passivate defects in polycrystalline silicon solar cells also produces surface damage. This damage has been quantified with Rutherford backscattering, and this quantification has allowed for a measure of surface damage using UV reflectivity. The latter is a rapid, easy technique which simplifies the task of assessing the degree of surface damage. The implications of this work for reducing surface recombination and making higher efficiency solar cells using hydrogen passivation are discussed.

Investigation into the lubricating effectiveness of molybdenum disulphide dispersion in a fully formulated oil

A four ball machine was used to study the effect of molybdenum disulphide on anti-seizure properties of a fully formulated engine oil. The exact nature of the additives in the oil was not available but it is assumed that the oil contains the normal additive package contained in a fully formulated engine oil ie anti-wear, anti-oxidants, corrosion inhibitors etc. Standard wear tests were carried out with 0–20% MoS 2 dispersed in the oil for a range of loads. Wear was measured in terms of the size of the scars on the bottom balls. Electron microscopy and micro-probe analysis were then employed to study the topography and chemical composition of the worn surfaces. This was followed by a study of microstructural and hardness variations immediately below worn surfaces. It was concluded that due to chemical breakdown of MoS 2 at 5% concentration there was very little improvement in the surface protection under boundary conditions, but with 10% MoS 2 the surface temperatures are not high enough to cause the breakdown of MoS 2 and a substantial reduction in surface damage is achieved.

ROLE OF WAXBLOOMS IN PREVENTING ATTACHMENT TO BRASSICAS BY THE MUSTARD BEETLE, PHAEDON COCHLEARIAE

Mustard beetles (Phaedon cochleariae (Fabricius)) adhered slightly better to hairy leaves than to glaucous leaves of Brassica oleracea but by far the best adhesion was to glossy leaves. Scanning electron micrographs illustrate how adhesion between the climbing setae on the tarsi of P. cochleariae and the leaf surfaces was hindered by the vertical rods and dendritic plates on glaucous leaves. The importance of the wax bloom in determining colonisation of brassicas by insects is discussed.WACHSAUSSCHEIDUNGEN AUF BRASSICA‐BLÄTTERN BEHINDERN SENFKÄFER (PHAEDON COCHLEARIAE) AM KLETTERNSenfkäfer (Phaedon cochleariae) konnten sich etwas besser an haarigen Blättern von Brassica oleracea halten als an wachsigen Blättern, weitaus am besten war aber die Adhäsion an glatten Blättern (P<0.05). Scanning‐elektronenmikroskopische Aufnahmen zeigen, wie die Adhäsion zwischen den Steigborsten der Tarsen von P. cochleariae und den Blattoberflächen behindert wurde durch die vertikalen Leisten und durch die dendritischen Platten auf den wachsigen Blättern. Die Bedeutung der Wachsausscheidungen für die Kolonisation von Brassica durch Insekten wird diskutiert.