Elimination Of Surface Defects Research Articles

Elimination of surface defects in luminescent crystals through solid-liquid interface friction.

In this work, we report a simple yet robust strategy for eliminating surface defects in red-emitting fluorides through solid-liquid interface friction under elevated temperature and high pressure. This method is minimally dependent on the solvent type and especially excels at stripping away the abundant surface defects caused by mechanical crushing.

Targeted Elimination of Surface Defects in Carbon Fibers: Formation of a Hybrid Structure Combining Rigidity with Flexibility from Sonochemical-Induced Directional Growth of Nano-ZIF-8 and Subsequent Annealing.

Currently, the mechanical performance of carbon fibers (CFs) has yet to fully realize its theoretical potential. This is predominantly attributed to the significant constraints posed by surface defects, greatly impeding the widespread application of carbon fibers. In order to address this issue, we employed a sonochemical-induced approach in this study to achieve in situ growth of nanoscale zeolitic imidazolate framework-8 (ZIF-8) at the surface defects of carbon fibers. After high-temperature treatment, the structure of ZIF-8 decomposed into ZnO and inorganic carbon, reinforcing the carbon fiber structure from both flexible and rigid aspects. Our research indicates that when the temperature reaches 500 °C, a substantial portion of ZIF-8 undergoes thermal decomposition, giving rise to zinc oxide and inorganic carbon. The flexible inorganic carbon and rigid ZnO form a meshlike structure, which welds to the surface defects of carbon fibers, resulting in strong interactions and contributing to the delay of fiber fracture. Compared to unmodified carbon fibers, the mechanical performance increased by approximately 15.86%. Based on the aforementioned analysis, this method can be considered a direct and effective approach for reinforcing carbon fiber structures, presenting a novel approach for the precise elimination of surface defects on carbon fibers.

Technological Methods of Ensuring the Reliability of Lock Connections in Marine Gas Turbines

Abstract The article presents the test results of the surface quality parameters after broaching of heat-resistant steels of grades: 1.7335 (13CrMo4-5) and 1.4841 (X15CrNiSi25-20). The aim of the work is to determine the technological methods of obtaining the lowest treated surface roughness, surface layer hardening and the elimination of surface defects after broaching. To investigate the influence of cutting conditions (cutting speed, tool geometry and feed) on surface roughness and hardness, the physical modeling method of the broaching was used. As a result of the research, recommendations for improvement of the main parameters of the surface layer quality when broaching samples from selected grades of heat-resistant steels.

Increasing the crack resistance when pressing pipes made of 08Kh13N4M1F steel

The main factor determining the possible appearance of continuity defects in hotpressed pipes is the physical nature of the material subjected to deformation, namely, its plasticity. Alloying of a metal contributes to a decrease in its plasticity and an increase in the resistance to plastic deformation, which, on the one hand, increases the stress level during hot deformation, and, on the other hand, reduces the threshold stress value corresponding to the onset of metal fracture. The introduction of computer simulation tools, in particular software products based on the finite element method, made it possible to perform an analytical study of the features of the stress-strain state of the metal during hot pressing of steel pipes. Particular attention in the modeling is paid to the deformation conditions of the surface layers of the metal, since one of the characteristic surface defects of hot-pressed pipes is cracks and ruptures. The dependences of the stress-strain state on the technological parameters of the pressing process are revealed, namely, the nature of the change in the stress-strain state of the surface layers of the pressed shell along the deformation zone length, the effect of temperature, elongation coefficient and friction coefficient on the change in the stress-strain state are determined, the degree of the plasticity resource use by the Kolmogorov failure criterion is assessed. On the basis of the results obtained, a set of theoretical and experimental studies was carried out to investigate the mechanisms of the formation of surface defects in hot-pressed pipes, technological parameters and technological tool parameters that contribute to the elimination of surface defects were determined.

Sensitive and Reliable Fluorescent Thermometer Based on a Red-Emitting Li2MgHfO4:Mn4+ Phosphor.

Contactless fluorescent thermometers are rapidly gaining popularity due to their sensitivity and flexibility. However, the development of sensitive and reliable non-rare-earth-containing fluorescent thermometers remains a significant challenge. Here, a new rare-earth-free, red-emitting phosphor, Li2MgHfO4:Mn4+, was developed for temperature sensing. An experimental analysis combined with density functional theory and crystal field calculations reveals that the sensitive temperature-dependent luminescence arises from nonradiative transitions induced by lattice vibration. Li2MgHfO4:Mn4+ also exhibits reliable recovery performance after 100 heating-cooling cycles due to the elimination of surface defects, which is rare but vital for practical application. This study puts forward a new design strategy for fluorescent thermometers and sheds light on the fundamental structure-property relationships that guide sensitive temperature-dependent luminescence. These considerations are crucial for developing next-generation fluorescence-based thermometers.

High-efficient and reversible temperature sensor fabricated from highly luminescent CdTe/ZnS-SiO2 nanocomposites for rolling bearings

CdTe quantum dots (QDs) have broad application prospects in the field of thermal monitoring of bearing rotating components owing to the linear temperature dependence of their photoluminescence. However, their practical application can be limited by irreversible thermal stability. In this work, we synthesized CdTe/ZnS-SiO2 nanocomposites by a reversed-phase microemulsion method based on CdTe QDs prepared in an aqueous phase. The structure and optical performance of as-synthesized CdTe/ZnS-SiO2 were characterized. CdTe/ZnS-SiO2 shows high photoluminescence, outstanding reversible thermal stability, and low biotoxicity because of the elimination of surface defects on the QDs by the ZnS layer and inorganic protection by the SiO2 layer. The photoluminescence spectra of CdTe/ZnS-SiO2 show linear relationship and reversible thermal stability during heating and cooling cycle processes from room temperature to 80 °C, which facilitates their practical application as temperature sensors. The highly efficient and reversible temperature sensor fabricated from highly luminescent CdTe/ZnS-SiO2 nanocomposites has significant application value in the thermal monitoring field, especially for high-speed bearings under various conditions.

Comparative analysis of methods for improving the quality of hardened pipe and bar stock for agricultural machinery parts

The problem of obtaining a high-quality surface is acute in thermal, chemical-thermal and thermomechanical processing of products of rolling production. But, due to the fact that many metallurgical plants are insufficiently equipped with cleaning tools for these types of processing, the required surface quality of metal products is not ensured. Operations related to the removal of defects in the surface of rolled products employ from 30 to 60% of the workers in rolling shops. The need for cleaning leads to a rupture of the production flow, since the metal must be pre-cooled for inspection and cleaning of defects. As a result, the total cost of cleaning is 2 - 3 times higher than the cost of performing the main technological operations - heating and deformation of the metal. In this regard, the combined methods of hot rolling with simultaneous hardening and elimination of surface defects are of particular interest, which gives significant energy savings and excludes etching operations in solutions of sulfuric and hydrochloric acids. The paper considers new methods for stripping rolled stock before deformation in the high-temperature thermomechanical treatment (HTMT) mode of cylindrical hot-rolled solid and hollow billets with screw compression (SC) deformation, combining, along with a high-performance method of shaping and strengthening of rolled products, environmentally friendly (acid-free) methods of surface cleaning, as well as methods of removing surface layer defects combined with mechanical processing. At the same time, simultaneously with cleaning the surface and increasing the accuracy of rolled products, the structure of the surface layer is formed by the mechanism of phase transformations during thermomechanical processing. The type of fracture changes at low-temperature destruction from brittle to ductile. It should also be noted, that there is the need for further development of such well-proven cleaning methods as blade and waterjet processing, which allow, when cleaning rolled products from any steel grades from scale, to implement the most reliable cleaning system, ensure effective removal of surface and deeper defects, increase yield, reduce energy consumption and fit well into the continuous rolling mill line. According to recent studies, waterjet treatment increases the fatigue life of hollow cylindrical parts by up to 15%.

Effect of laser polishing on the microstructure and mechanical properties of stainless steel 316L fabricated by laser powder bed fusion

While metal additive manufacturing has seen significant growth in recent years, the surfaces produced often need post-processing to improve surface finish, mitigate residual stresses, and remove surface-connected porosity. Laser polishing, by means of remelting a thin layer of the surface, is one post-processing method being investigated for surface finish improvements and other surface enhancements. In this work, the surface morphology and microstructure of laser powder bed fused (L-PBF) stainless-steel 316 L (316 L) before and after laser polishing are characterized by optical microscopy (OM), scanning electron microscopy (SEM), electron back-scatter diffraction (EBSD), and transmission electron microscopy (TEM). In addition, the cross-sectional microhardness of the samples is measured and reported. Additionally, the as-built and laser-polished sample's tensile properties are characterized using uniaxial tension tests. The results indicate that the surface roughness of as-built 316 L (Sa = 4.84 μm) can be substantially reduced through laser polishing (Sa = 0.65 μm). After laser polishing, the average grain diameter is reduced and the proportion of low angle grain boundaries (2°~5°) is increased in the L-PBF 316 L. The maximum sub-surface hardness reaches 262 HV, and both the tensile strength and ductility of 316 L are increased after laser polishing. This enhancement is attributed to thermal cycling stresses, grain refinement, the elimination of surface defects, and dislocation strengthening after laser polishing.

EXPERIENCE ON IMPLEMENTATION OF HOT IN-PLACE RECYCLING OF ASPHALT CONCRETE IN UKRAINE

Rehabilitation of asphalt concrete layers of road pavements using HIR technologies enables effective elimination of surface defects (rutting, cracking, raveling, bleeding (flushing)) including defects caused by the non-conformity of asphalt concrete to the standard specifications. Due to the economical and ecological advantages, HIR technologies belong to the present-day effective alternative methods of rehabilitation of asphalt concrete pavements. In Ukraine, HIR technologies were first applied on intermediate repair works on an area of the international road I-01 “Kyiv-Chernihiv-Novyye Yarylovichi” in the 2013. Now, HIR technologies have been applied on repair works on numerical objects including areas on such state motor roads as I-01, I-06, N-09, R-10, R-67. The presented paper analyzes the results of monitoring of materials and technologies which was aimed on HIR performance investigation supported by State Road Agency of Ukraine (Ukravtodor) throughout 2014-2018. The results of monitoring of HIR technologies including laboratory evaluation of materials and also field testing of the rehabilitated pavements led to the conclusions fitted by the world-wide experience on implementation of HIR technologies. 1. Being applied to the structurally sound pavements, HIR provides effective elimination of surface defects of flexible pavement to a depth of (50-60) mm including defects caused by the non-conformity of asphalt concrete to the standard specifications. However, HIR is not suitable for existing asphalt pavements which have too much variation in asphalt concrete composition and thickness within the project limits. 2. The efficiency of asphalt pavement rehabilitation using HIR technologies largely depends on precise engineering consideration which determines the efficiency of preparatory (repair) works including some special works such as: – correction of cracks in case of cracking that extends below the depth of hot recycling; – re-compaction of an unbound base layer(s) in case of the insufficient compaction causing “alligatored” network-like cracking of asphalt pavement. 3. Proper technical and working conditions of the rehabilitated pavement during the nominal life cycle could be maintained by overlaying the surface treatment using bituminous emulsion materials or by single-pass overlaying a new hot-mixed asphalt concrete layer. Investigations accomplished during the implementation of HIR technologies allow enhance quality of recycled materials and also promote the entire adaptation of HIR technologies to the Ukrainian standards. Keywords: asphalt pavement rehabilitation, hot in-place recycling, recycled asphalt concrete, field testing, road pavement strength measurement, rutting measurement.

Super Bright Luminescent Metallic Nanoparticles.

It is found that, by curing the surface defects that quench photoexcited carriers, luminescence efficiency of metallic nanoparticles can be dramatically increased. For Ag nanoparticles, as much as 300 times increase in photoexcitation induced luminescence is observed upon surface adsorption of ethanethiol. The same treatment increases Au nanoparticle luminescence efficiency by a factor of 3. A model based on the elimination of surface defects by the sulfur-metal bond formed upon thiol adsorption can quantitatively account for the observations, which also indicate that nanoparticles without proper surface treatment typically have low luminescence quantum yields.

Mesoporous binder-free monoliths of few-walled carbon nanotubes by spark plasma sintering

Carbon nanotubes with few walls (FWCNTs) are prepared by catalytic chemical vapor deposition. Transmission electron microscopy investigations for each sample show the average number of walls (3, 4 and 8) as well as the internal and external diameter distributions. Binder-free FWCNT monoliths are prepared by spark plasma sintering (SPS) at temperatures in the range 1000–1600 °C. A combination of techniques including Raman spectroscopy, scanning- and transmission electron microscopy, electron microdiffraction is used to characterize the samples. Compared to the FWCNT powders, the high temperatures used for SPS favor the elimination of surface defects in CNT walls but also some limited amorphization, without dramatic damage to the CNTs. Increasing the SPS temperatures produces an increase in densification. N2 adsorption–desorption cycles revealed that the powders and monoliths show microporosity and, mostly, mesoporosity. Some monoliths show a specific surface area equal to about 500 m2/g. The 4WCNTs when consolidated into monoliths by SPS at 1000 or 1100 °C are able to retain a high amount of mesoporosity that contributes to a high porous volume of the order of 0.8 cm3/g.

Elimination of Surface Defects in High Tensile Steel for Wheel Rim Application

One of the important applications of high tensile steel grades is in wheel rims by the automotive industry. High tensile steel facilitates vehicle weight reduction under the ‘Go Green’ initiative. Along with weight reduction, in recent times, the surface quality requirement of steels for wheel rim applications has also gained a significant focus, and in many cases, it is becoming the cause of rejection at the customers’ processing line. It is known that owing to chemistry requirements such high strength steel grades generally show peritectic behavior during solidification and are prone to surface defects. Tata Steel India produces several wheel rim grades of varying strength levels. In one such high manganese and micro-alloyed peritectic steel grade, the rejection by the customer on account of surface defects was a major concern. The defects consisted of typical longitudinal cracks of varying dimensions along with the unique defects in transverse direction named tear marks on the surface of 100-mm-thick plates rolled from 215-mm-thick slab. In subsequent stages, these plates were processed into rim profiles through hot working by the wheel customer. The paper highlights how systematic study led to arrive at root causes and helped redesign steel chemistry to ensure zero rejection for surface quality without affecting mechanical property requirements.

Microscopic Investigations into the Effect of Surface Treatment of Cathode and Electron Transport Layer on the Performance of Inverted Organic Solar Cells.

Surface treatments of various layers in organic solar cells play a vital role in determining device characteristics. In this manuscript, we report on the influence of surface treatment of indium tin oxide (ITO) electrode and electron transport layer (ETL), ZnO, on the photovoltaic performance of inverted organic solar cells (IOSC) and their correlation with the surface chemistry and surface potential as studied using X-ray photoelectron spectroscopy (XPS) and Kelvin probe force microscopy (KPFM), using the device structure glass/ITO/ZnO/P3HT: PCBM/MoO3/(Au or Ag) (P3HT, poly(3-hexylthiophene-2,5-diyl), and PCBM, phenyl-C61-butyric acid methyl ester). Our results show that although ozonization of ITO leads to an improvement in the device power conversion efficiency, the ozonization of a subsequent ZnO layer results in a decreased performance mainly because of a decrease in the fill factor (FF). However, subsequent methanol (CH3OH) treatment of ZnO layer on an ozonized ITO electrode shows substantial improvement with device efficiencies exceeding ∼4% along with superior reproducibility of the devices. Furthermore, a detailed analysis of the surface wettability, chemistry, and surface potential using contact angle measurements, XPS, and KPFM attribute the improvements to the elimination of surface defects and the changes in the surface potential. Finally, impedance analysis suggests that methanol treatment of the ZnO layers leads to the development of a favorable nanophase structure with higher conductivity, which is otherwise indiscernible using microscopic methods.

Probing Surface Structure Quality of ZnO Nanorods by Second Harmonic Generation

The surface quality of ZnO nanorod after postannealing was inspected by second harmonic generation (SHG) with the assistance of photoluminescence (PL) spectra, and the X-ray photoelectron (XPS) spectroscopy. The SHG is sensitive to the quality of the surface structure, which involves the elimination of surface defects and restructuring. Oxygen (O)-deficient defects and surface defects were generated during the growth of ZnO nanorods. The PL and XPS analyses indicate that the surface defects on ZnO nanorods were reduced at annealing temperatures above 600 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C. The bulk crystal structure was repaired for higher activation temperatures (> 700 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C) concluded by X-ray diffraction. Results from SHG revealed the relationship between surface restructuring of ZnO nanorods and annealing temperature.

Synthesis of the uniform hollow spherical Sr2SiO4:Eu2+ phosphors via an h-BN protective method

The uniform hollow spherical Sr2SiO4:Eu2+ green emitting phosphors have been successfully synthesized using hollow silica spheres as templates by an h-BN protective method. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results directly confirmed the existence of the hollow spherical structure with a narrow size distribution and a shell thickness of 15–25nm. The h-BN protective film, observed by high resolution TEM, plays an important role in the formation of the hollow spherical morphology and the improvement of photoluminescence properties. Comparing with the Sr2SiO4:Eu2+ micron-phosphor prepared by the traditional solid state reaction method, the hollow spherical phosphor with nano-sized grains exhibits stronger green emission under ultraviolet–blue light excitation. This could be attributed to the elimination of surface defects by the h-BN coating. This research gives an economic and convenient way to synthesize uniform spherical phosphors with high quantum efficiency.

Photocatalytic Activity Enhanced via g-C3N4 Nanoplates to Nanorods

The transformation of graphitic carbon nitride (g-C3N4) from nanoplates to nanorods was realized by a simple reflux method. The photocatalytic activity and the intensity of the photocurrent response of g-C3N4 nanorods under visible light were about 1.5 and 2.0 times those of g-C3N4 nanoplates, respectively. The formation mechanism of g-C3N4 from nanoplates to nanorods was demonstrated that g-C3N4 nanoplates undergo a possible exfoliation and regrowth process and a rolling mechanism of lamellar structure, which is responsible for elimination of the surface defects in the reflux process. During the transformation of g-C3N4 from nanoplates to nanorods, the enhancement of photocatalytic activity and photocurrent intensity in g-C3N4 nanorods was mainly attributed to the increase of active lattice face and elimination of surface defects.

Development of on-the-Machine Surface Modification Technology in EDM

As a method of processing cemented carbide, sinking electrical discharge machining (EDM) is generally used. However, typical surface defects, such as cracks, microcraters and recast layer, lead to a decreased surface integrity, probably resulting in a short tool life. Under the present situation, the recast layer is removed by polishing. However, this process extends the machining time and increases the cost of production of metal molds. Therefore, it is desirable to eliminate these surface defects by some methods. Thus, an on-the-machine surface modification technology in EDM, for the complete elimination of surface defects, was developed in this study. The surface defects are eliminated using a sinking electrical discharge machine by introducing surface integrity machining for EDM (SIME) after applying finishing EDM. SIME is conducted by applying voltage to the constant gap between electrode and workpiece in deionized water. It can be considered that a recast layer including cracks is selectively eliminated by the dissolution of cobalt based on the electrolytic action during SIME. As a result, the surface defects generated by EDM could be completely eliminated by incorporating SIME into EDM.

The effect of excimer laser surface treatment on the pitting corrosion fatigue behaviour of aluminium alloy 7075

An excimer laser (KrF) operating at a wavelength of 248 nm was used to modify the surface microstructure of 7075-T651 aluminium alloy. The aim was to improve both the corrosion resistance and the pitting corrosion fatigue resistance of the alloy by means of laser surface melting (LSM). The microstructure and the phases of the modified surface structure were analysed, and the corrosion behaviour of the untreated and the laser-treated specimens were evaluated by immersion test. The fatigue resistance of the 7075 alloy has been presented in the form of S/N curves. A microscopical examination and the transmission electron microscopy (TEM) study revealed that LSM caused a reduction both in number and size of constituent particles and a refinement of the grain structure within the laser melted zone. As a result, the corrosion resistance of the aluminium alloy was improved. There was a significant reduction in the number of corrosion pits and shallow attack occurred. The fatigue test results showed that under dry fatigue conditions, the total fatigue life of the laser treated specimens, in which the crack initiation period is of considerable significance, was lower than that of the untreated specimens. However, after shot peening, the fatigue life of the laser treated specimens was recovered. This was primarily attributed to the elimination of surface defects, but also be in part, due to the introduction of compressive residual stresses in the surface layer of the specimen. The fatigue resistance of the shot peened laser-treated specimens, tested in 3.5 wt% NaCl solution with 48 hrs prior immersion, was greater than the untreated specimens with an increase of two orders of magnitude in fatigue life. This was primarily due to the elimination of surface defects and the reduction of corrosion pits.

Modification of polyacrylonitrile (PAN) carbon fiber precursor via post-spinning plasticization and stretching in dimethyl formamide (DMF)

This study investigates the possibility of using a post-spinning plasticization and stretching process to eliminate suspected property-limiting factors in polyacrylonitrile-based carbon fibers. This process was performed with the intention of removing surface defects (to improve tensile strength), attenuating fiber diameter (to promote more uniform heat treatment), and reducing molecular dipole interactions (to facilitate further molecular orientation). Among the various organic and inorganic solutions tested, treatment using aqueous dimethyl formamide (DMF) offered far and away the best properties and was therefore selected for further testing. Tested individually (as single filaments), fibers exposed to 80% DMF for 10 s gave the highest precursor values of elastic modulus (9.07 GPa) and tensile strength (675 MPa). While fibers treated in 80% DMF gave a 73% improvement in elastic modulus and a 53% improvement in tensile strength over as-received PAN, limitations in sample preparation and carbonization necessitated a reduction in DMF concentration (to 30%) to allow extraction of individual carbon fibers for tensile testing. Despite this compromise, results for fibers carbonized at 1000°C ultimately showed a 32% improvement in carbon fiber elastic modulus and a 14% improvement in carbon fiber tensile strength over regularly prepared carbon fibers. These results show that, to a certain extent, improvements in PAN precursor properties can translate to corresponding improvements in subsequently produced carbon fibers. Additional characterization using wide angle X-ray scattering (WAXS) and scanning electron microscopy (SEM) suggests that these improvements are due in part to improved lateral order as well as the successful elimination of surface defects and prevention of skin-core formation.

疲労 ワイヤ放電加工を受けた超薄肉ＷＣ‐Ｃｏ合金板の疲労強度特性

To produce the precise stamping dies for ultra fine LSI lead frame, fatigue strength properties of WC-Co alloy plates of 0.1mm in thickness with different WC particle size, machined by wire electric discharge (WED) and/or by subsequent abrasive flow (AF), were investigated. The WED machining significantly reduced the fatigue strength of the ultra thin alloy plates from about a half to a quarter that of ground specimens. Coarsening of WC particles and surface removal of around 1-2μm by AF machining, however, enhanced the fatigue strength. This was principally caused by that they lowered tensile residual stress in machined surface layer. It was suggested that suppression of initial micro-crack propagation due to coarse WC particles and elimination of surface defects due to the AF machining also improved the fatigue strength although their contributions were very smaller than that of the residual stress.