Surface Formation Mechanism Research Articles

Electrochemical dissolution behavior of heat treated laser solid formed Inconel718

Microstructure characteristic and its effects on electrochemical dissolution behavior of horizontal plane (HP) and vertical plane (VP) in the laser solid formed (LSF) Inconel718 alloy after double aging (DA) heat treatment (DA-LSF Inconel718) were investigated. Compared to the as-deposited one, DA-LSF Inconel718 shows more phases and presents electrochemical anisotropy between HP and VP including the polarization curves, current efficiency curves and surface roughness. It is caused by different electrochemical dissolution processes on HP and VP and proved that surface energy has no obvious effect. Three models were proposed to illustrate electrochemical dissolution behavior, surface formation mechanism and electrochemical anisotropy, respectively.

A Novel Multi-Functional Electrolyte Additive for Ni-Rich Cathode Materials

Ni-rich layer oxides Li[Ni x CoyMn1−x−y ]O2 (x ≥ 0.8, NCMs) are promising advanced cathode materials for high-energy Li-ion batteries because of their high specific capacity (≥ 200 mAh g−1) with an average discharge voltage of 3.8 V vs Li+/Li, as compared to the commercialized cathode materials (e.g. LiCoO2, LiFePO4).1 However, the instability of cathode–electrolyte interface causes the structural degradation of cathode active material and the electrolyte consumption, as well as gas evolution due to oxidative decomposition of electrolyte, resulting in a rapid capacity fading.2 Thus, improvement in the stability of cathode–electrolyte interphase is a key requirement to inhibit their structural degradation and enhance their electrochemical properties. The formation of a protective surface film via electrolyte additives is considered a cost-effective and reliable way to improve the cathode–electrolyte interfacial stability, as the stable surface film, uniformly distributed over the entire cathode surface, would prevent direct contact of oxide with the electrolyte, still allowing Li+ transport between the cathode and electrolyte.3 In this work, we report the high-performance NCM cathode through interfacial stabilization using a novel electrolyte additive. The details of surface film stability and formation mechanism, and their relation to gas evolution as well as cycling performance would be discussed.

Setting of Natural Fracture Splitting Surface on Connecting Rod and Its Formation Mechanism

To break through the limitation of fracture splitting process on material selection and solve problems during fracture splitting such as parts tearing, failing to split, dropping dregs, fracture surface deformation and so on, a new technique of setting natural splitting surface in casting blank is proposed, aiming to achieve brittle fracture along pre-set surface during fracture splitting process. In this research, casting blanks are produced with metal molds. A layer of AZ31 foil is set in advance before casting, the layer interacts with liquid LD10 aluminum alloy, forming a brittle interface layer across the whole casting, then a fracture splitting hole is machined in the middle of the casting blank and cracking grooves are machined on the inner hole near the interface to achieve fracture splitting. Experiment revealed that the initial crack on the specimen starts from the root of the cracking groove, and the crack basically expands along the pre-set fracture splitting surface. The fracture surface is characterized by flaky brittle fracture. There is residual magnesium and pellumina, which have characteristics of melt with low-melting point, and micro-porosity in the fracture. Further analysis suggests that the formation mechanism of a natural fracture splitting surface can be described as follows: the magnesium foil with strong oxidation in high-temperature alloy liquid interacts with the pellumina at the front of liquid flow, which forms a interface. Meanwhile a layer of melt with a low-melting point forming as a result of interface reaction is pushed to the edge of the grain boundary, and surface liquid film shrinks to be micro-porosity. With such a combined effect it finally forms the brittle surface, which provides the condition for conducting subsequent fracture splitting process.

Surface formation mechanism in ultraprecision diamond turning of coarse-grained polycrystalline ZnSe

Zinc selenide is an excellent infrared optical material. In this study, ultraprecision diamond turning experiments were carried out on coarse-grained polycrystalline ZnSe (p-ZnSe) under various conditions and the corresponding surface formation mechanisms were investigated by examining the surface topography, chip morphology, material microstructural change, and cutting forces. Two kinds of surface defects were observed (i.e. plowing-induced micron-scale cleavage craters and tearing-induced submicron-scale tearing pits). It was determined that plowing induced micron-scale cleavage craters could be suppressed by reducing undeformed chip thickness. Furthermore, it was ascertained that tearing-induced submicron-scale tearing pits could be restrained by using a cutting tool with a zero rake angle. The minimal surface roughness was dominated by grain boundary steps formed when the cutting tool crossed twin boundaries at a large angle. A model was proposed for correlating surface defects and boundary steps with crystal orientations and cutting directions. By using a large-nose diamond tool for cutting, a smooth surface of 1.5 nm Sa was obtained. In addition, a zinc blende to cinnabar phase transformation was observed in the cutting chips, and metallization of cutting chips occurred at an extremely small undeformed chip thickness (~20 nm). Moreover, it was discovered that phase transformation inside the workpiece depends on the radius of the tool nose. The findings of this study provide an important reference for ultraprecision machining of brittle polycrystalline materials.

Surface Formation Mechanisms in Selective Laser Melting of Cobalt-Chromium-Molybdenum Powder

Selective laser melting (SLM) is a manufacturing technology of metal parts of any shapes with target mechanical properties by means of laser melting. This paper discusses the effect of SLM parameters: laser output power, laser movement velocity, scanning pitch and preheating temperature of a powdered material on surface formation mechanism, namely, its physical configuration when melting cobalt-chromium-molybdenum powdered material Со28Cr3Mo. The study points at structural differences of melted surfaces even under identical process parameters. Several types of surface formation are identified, e.g. homogenous melt, coagulated particles, and shapeless particles. Vapor pressure, Marangoni effect, and heat effect of a melted powder are stated to be key reasons for rough surface. This research is of high importance for understanding the effect of SLM parameters on formation of a target quality surface, positive stability and repeatable accuracy of the process.

Wafer Flatness Modeling in Chemical Mechanical Polishing

Flatness is an important criteria for evaluating wafer quality. Chemical mechanical polishing (CMP) is an effective method to process wafers and to improve the wafer flatness. Therefore, a flatness model is necessary for optimizing CMP process variables through investigating the wafer surface formation mechanism as well as the influences of CMP parameters on the wafer flatness. However, most studies pay attention to the roughness change of a wafer surface. Besides, there is little literature about the flatness of CMP modeling wafers. In this study, a wafer flatness model based on the material removal during CMP was established. The surface pressure distribution of the wafer surface was obtained by finite element simulation. The relative velocity distribution of the abrasive particles and the wafer surface during polishing were acquired by the numerical simulation, introduced to develop the flatness model. Finally, the influences of different process parameters on flatness were investigated. The flatness model established agreement between the calculated and the experimental results.

Rigorous design of outermost surface of TiO2 via one-step single-mode magnetic microwave field toward highly efficient visible-light photocatalyst

Among numerous efforts toward preparation of visible-light TiO2, recently design and control for chemical structure of TiO2 outermost surface have been paid strong attention to enhance photocatalytic performance. We have previously succeeded in direct synthesis of structurally well-controlled TiO2 with highly concentrated Ti3+ from metal titanium particle via single-mode magnetic microwave (SMMW)-assisted reactions. Here, we demonstrate synthesis of Ti3+ and interstitial nitrogen (Nint) co-doped TiO2 in Ar/O2/N2 system during one-step SMMW-assisted reactions, where chemical structure of outermost surface is rigorously controlled. In addition, such one-step-generated TiO2 shows significant thermal stability which has not been achieved in previously reported deficient TiO2 even through several step reactions. Additionally, the synthesized co-doped TiO2 with specific surface structures shows superior visible-light photocatalytic performance for photo-degradation of rhodamine B. The mechanism of outermost surface formation is systematically investigated by characterizations of XRD, XPS, UV–Vis absorption and PL. It demonstrates that the specific TiO2 surface including highly concentrated Ti3+ and Nint can be attributed to the rapid heat-dynamics during the reaction, which enhance the efficiency for separation of photo-excited carriers. The one-step SMMW-assisted reactions on metallic particle as bottom-up process will open new strategy for material design of functional metal oxides.

Dynamic observation of crack generation during wheel scribing from lateral and back sides using a high-speed camera

Wheel scribing is a technique widely used in dividing glass substrates. However, the optimization of scribing conditions and tool geometry depends on empirical rules because the dominant factors of crack generation and fracture surface formation are not fully understood. The present study visualizes the crack generation/propagation behavior in the contact area between the scribing wheel and glass substrate employing high-speed imaging. Median cracks appeared under the wheel when the wheel came into contact with the glass, with the cracks being located on a single plane. The fracture surface morphology depended on whether the median cracks were connected with each other. We discuss the formation mechanism of the fracture surface on the basis of the observations of crack generation/propagation behavior.

Biocompatibility of micro/nanostructures nitinol surface via nanosecond laser circularly scanning

Abstract We present three novel scanning patterns on nitinol by nanosecond laser for controllable fabricating biocompatible micro/nanostructures. The surface morphology and formation mechanism of micro/nanostructures were respectively observed and analyzed. The production of surface oxide film provides a biocompatible cell living environment. Also, micro/nanostructures greatly promote cell adherence and growth. It is worth noting that ns laser circularly scanning can effortlessly produce various micro/nanostructures and endue biologically inert nitinol implants with enhanced osseointegration and bioactivity.

Formation behavior of laser-induced periodic surface structures on stainless tool steel in various media

The formation of laser-induced periodic surface structure (LIPSS) has been observed on various materials. As LIPSS can be used for modifying various surface properties such as wettability, tribology and optical performance, the control of the period and topography of LIPSS is an important issue. In this study, picosecond pulsed laser irradiation was performed on a stainless tool steel in various types of media including the air, water, sugar syrup (water and sucrose (C12H22O11)), decane (C10H22), and ethanol (C2H5OH). Different surface morphologies were observed on the steel surface after laser irradiation, depending on the types of media. A strong relationship was identified between the period of LIPSS and the refractive index of liquid. In addition to the change of LIPSS period, complicated mesh patterns were formed on the surface irradiated in decane and ethanol, indicating the significant effect of thermal conductivity of the liquids on surface formation mechanisms. This study demonstrated the possibility of controlling the period and topography of LIPSS by using different media.

Study on the surface forming mechanism of the solid–liquid two-phase grinding fluid polishing pipe based on large eddy simulation

To study the surface forming mechanism of the solid–liquid two-phase abrasive flow processing, the large eddy simulation method was used. Taking a 90° stainless steel elbow as the research object, the action mechanism of the dynamic pressure, wall shear force, flow state of the abrasive flow at different cross-sections, formation of the vortex, and trajectory of the abrasive flow on the inner surface of the elbow with abrasive flow composed of solid-phase silicon carbide and liquid-phase hydraulic oil are discussed. This study explores the distribution characteristics of the flow pattern of solid–liquid two-phase abrasive flow. Moreover, the wear and erosion of the abrasive grain and the wall of the workpiece are discussed. The mechanism of surface formation of solid–liquid two-phase abrasive flow is revealed.

Enhancement of surface discharge in catalyst pores in dielectric barrier discharges

The generation of high-density plasmas on the surface of porous catalysts is very important for plasma catalysis, as it determines the active surface of the catalyst that is available for the reaction. In this work, we investigate the mechanism of surface and volume plasma streamer formation and propagation near micro-sized pores in dielectric barrier discharges operating in air at atmospheric pressure. A two-dimensional particle-in-cell/Monte Carlo collision model is used to model the individual kinetic behavior of plasma species. Our calculations indicate that the surface discharge is enhanced on the surface of the catalyst pores compared with the microdischarge inside the catalyst pores. The reason is that the surface ionization wave induces surface charging along the catalyst pore sidewalls, leading to a strong electric field along the pore sidewalls, which in turn further enhances the surface discharge. Therefore, highly concentrated reactive species occur on the surfaces of the catalyst pores, indicating high-density plasmas on the surface of porous catalysts. Indeed, the maximum electron impact excitation and ionization rates occur on the pore surface, indicating the more pronounced production of excited state and electron-ion pairs on the pore surface than inside the pore, which may profoundly affect the plasma catalytic process.

Surface characterization and formation mechanism of the ceramic TiO2-xNx spherical powder induced by annealing in air

Mechanism for the formation of titanium oxynitride (TiO2-xNx) on the surfaces of spherical Ti powder particles upon heat treatment in air at 500, 600, 700 and 800 °C was investigated. The results showed that the first at 500 °C a hexagonal closed packed (HCP) TiOx film was formed while aTiO2 film was observed after annealing at 600 °C and eventually a TiO2-x-Nx layer coated the spherical Ti particles at 700 and 800 °C due to N diffusion within the TiO2 crystal lattice. The resulting surface structure was studied by means of x-ray diffraction (XRD) while the surface morphology of the powders was characterized using the scanning electron microscope (SEM) attached with energy dispersive x-ray spectroscopy (EDS) detector. The AFM images confirmed that when the N content increases (800 °C-heat treated sample) the powder loses its triangular grains (700 °C-annealed sample) to irregular shaped grains.

Experimental Investigation on Direct Micro Milling of Cemented Carbide.

Cemented carbide is currently used for various precise molds and wear resistant parts. However, the machining of cemented carbide still is a difficult challenge due to its superior mechanical properties. In this paper, an experimental study was conducted on direct micro milling of cemented carbide with a polycrystalline diamond (PCD) micro end mill. The cutting force characteristics, surface formation, and tool wear mechanisms were systematically investigated. Experimental results show that cemented carbide can be removed with ductile cutting utilizing the PCD tool with a large tool tip radius. Micro burrs, brittle pits, and cracks are the observed surface damage mechanisms. The tool wear process presents microchipping on the cutting edge and exfoliating on the rake face in the early stage, and then severe abrasive and adhesive wear on the bottom face in the following stage.

Surface Plasmon Resonance, Formation Mechanism, and Surface Enhanced Raman Spectroscopy of Ag+-Stained Gold Nanoparticles.

A series of recent works have demonstrated the spontaneous Ag+ adsorption onto gold surfaces. However, a mechanistic understanding of the Ag+ interactions with gold has been controversial. Reported herein is a systematic study of the Ag+ binding to AuNPs using several in-situ and ex-situ measurement techniques. The time-resolved UV-vis measurements of the AuNP surface plasmonic resonance revealed that the silver adsorption proceeds through two parallel pseudo-first order processes with a time constant of 16(±2) and 1,000(±35) s, respectively. About 95% of the Ag+ adsorption proceeds through the fast adsorption process. The in-situ zeta potential data indicated that this fast Ag+ adsorption is driven primarily by the long-range electrostatic forces that lead to AuNP charge neutralization, while the time-dependent pH data shows that the slow Ag+ binding process involves proton-releasing reactions that must be driven by near-range interactions. These experimental data, together with the ex-situ XPS measurement indicates that adsorbed silver remains cationic, but not as a charged-neutral silver atom proposed by the anti-galvanic reaction mechanism. The surface-enhanced Raman activities of the Ag+-stained AuNPs are slightly higher than that for AuNPs, but significantly lower than that for the silver nanoparticles (AgNPs). The SERS feature of the ligands on the Ag+-stained AuNPs can differ from that on both AuNPs and AgNPs. Besides the new insights to formation mechanism, properties, and applications of the Ag+-stained AuNPs, the experimental methodology presented in this work can also be important for studying nanoparticle interfacial interactions.

Near-Net Shaping Control of Triangular Stacking in Laser Cladding Process

Abstract Fabrication of complex parts with irregular geometric cross-section can be realized through precise control of triangular stacking in laser cladding process. This paper deals with the optimization of overlapping ratio and scanning strategy in order to obtain near-net shaping parts. First, multi-track overlapping surface formation mechanisms and surface flatness evaluation method are described. Then, the effects of overlapping ratio and scanning strategy on surface flatness are investigated and optimized. Afterwards, the formation of triangular stack under the optimized parameters are evaluated in terms of accuracy and metallographic aspects. The results show that the minimum flatness occurred when the overlapping ratio is about 20 %. Changing the scanning sequence from left-to-right to center-to-sides can help reduce the negative effects caused by the accumulated heat during the material deposition process, thereby improving the performance efficiency of the cladding.

Modelling of surface formation mechanism during burnishing of aluminium

Burnishing is a finishing process which levels the roughness of machined surfaces and increases the hardness by micro-forming. In this paper, a novel two-dimensional finite element model for the diamond ball burnishing process on aluminium is presented, which allows a prediction of the surface structure. The force, step over distance, and tool geometry during the burnishing process are taken into account by the model and the results are verified by experimental investigations. The verification shows that the model is able to predict all geometrical surface aspects like roughness, sinking-in and bulge formation for reasonable process parameters.

Surface collapse control under thick unconsolidated layers by backfilling strip mining in coal mines

Surface subsidence induced by mineral extraction from underground mines can significantly affect the ecological environment and human life. Surface collapse is extremely hazardous and typically occurs without warning. In China, numerous surface collapses have occurred during mining operations in coal mines located under thick unconsolidated layers. Via analysis of the stability of the bearing structure (arch structure in unconsolidated layers and key strata in rock strata) based on their effects on strata movement, our study reveals the formation mechanism of surface collapses and the roles played by two critical parameters: mining length and mining height. It is speculated that the bearing structure cannot be self-stable and will collapse during longwall mining with increasing mining length and mining height. As a result, the ground surface will collapse on the longwall face gob accompanied by the failure of the bearing structure. With these risks in mind, this study proposes a backfilling strip mining method via determination of the appropriate longwall face length and mining height to guard against bearing structure failure and thus avoid surface collapse. A field trial of the technique was conducted at a suitable Chinese coal mine located under thick unconsolidated layers. The maximum surface subsidence observed was only 0.369 m, which is 92% less than the subsidence in longwall face (LW) 3A04. No surface collapse occurred during the mining process. Thus, our results indicate that the proposed technique can successfully prevent surface collapse during longwall mining under thick unconsolidated layers.

Researches on formation mechanism of ultra-smooth surface during ion beam sputtering of fused silica

Ion beam figuring (IBF) is well identified as a highly deterministic method for the final figuring of nanometer-precision optical surfaces, where the figuring process involves an atomic/molecular material removal mechanism by using ion beam sputtering (IBS). However, IBS-induced nanoscale phenomena make the ultra-smooth surface formation process full of uncertainties that these phenomena would seriously influence the fabrication of high-performance optical components. In this work, the microscopic morphology evolution theories, including the IBS-induced microscopic behaviors and microscopic material densification dependent sputtering, are investigated to discuss the ultra-smooth surface manufacturability of fused silica. Our research results indicate that IBS-induced nanostructuring behaviors can be used for the preparation of ultra-smooth surfaces, which requires smoothing effects dominate over sputtering roughening during the surface morphology evolution. Meanwhile, we find that IBS is very sensitive to the change of the microscopic material properties, and specifically the ultra-smooth manufacturing process would be seriously affected when the surface/subsurface damages are generated in the former machining procedure. To control the microscopic material change and achieve ultra-smooth surface, a combined manufacturing technology including chemical-mechanical polishing (CMP) and IBF is proposed. Through the experimental investigation, fused silica with surface roughness down to 0.1nm root mean square (RMS) level is obtained by using this combined technology, which demonstrates the feasibility of our proposed method.

Mechanisms of surface formation at treatment with compression plasma flows

The mechanisms of the formation of the surface relief at treatment with intense plasma flows are considered in this paper. The main attention is paid to the formation of a wave-like relief of the surface. On the basis of the presented theoretical model for the formation of wave-like surface relief, it is shown that the inhomogeneous velocity field formed in the melt during its radial motion over the target surface leads to an increase in the elastic energy of the melt. It can be accompanied by the melt decomposition into separate fragments. If the elastic energy is sufficient to form a new surface the fragmentation of the melt takes place. The decomposition of the melt will not be observed if the time during which the elastic energy necessary for decay is stored is less than the characteristic hydrodynamic time. It is shown that the thinner ring of the melt is broken down into smaller fragments with the same difference in the velocities of the outer part of the melt and the inner one. As the velocity difference increases, the fragments become more elongated, which agrees well with the experimental data. Thus, the phenomenon observed in the experiment of the formation of the wave-like relief of the surface was explained.