Modified Metal Surface Research Articles

Ignition and combustion characteristics of coal-water-oil slurry placed on modified metal surface at mixed heat transfer

We experimentally determined ignition and combustion of a sessile droplet of coal-water-oil slurry on modified steel samples at mixed heat transfer (radiation, conduction, and convection). The surfaces were modified by two different methods: using abradants and nanosecond laser irradiation. It was shown that a texture of steel samples formed by abradants allows changing the spreading diameter of a 50-mg coal-water-oil slurry droplet (0.44 mm in diameter) from 0.628 mm to 0.743 mm, and, thereby, changing the ignition delay time more than 2 times (from 0.108 s to 0.212 s). A multimodal hierarchical texture formed on steel samples after laser texturing allows increasing the effective contact area of a coal-water-oil slurry droplet with a conductive heat source by more than 18% at identical values of the droplet spreading diameter. This intensifies the droplet heating, increases the formation rate of a combustible vapor-gas mixture, and decreases the ignition delay time by 10–20% (to 0.093 s). A texture formed by laser irradiation increases the number of nucleation centers and intensifies puffing. Modification of steel by nanosecond laser irradiation makes it possible to diminish the intensity of ash deposition on the heating surface after the combustion of coal-water-oil slurry.

Surface characterization of a modified cold work tool steel treated by powder‐pack boronizing

AbstractThe present work examines the effects of pack‐boronizing treatment on the surface characteristics of modified industrial cold‐work tool steel intended for polymer crushing. Particular attention is paid to optimizing the process parameters to improve the tool surface properties and thus achieve a satisfactory tool life. To this end, a series of samples were subjected to boronizing treatment within the temperature range from 800 °C to 1000 °C for soaking periods of 2 h, 4 h, 6 h and 8 h. The structural and mechanical properties of the modified metal surface were analyzed using optical and scanning electron microscopy, x‐ray diffraction, microhardness testing and pin‐on‐disk tribotesting. The adhesion quality of the boride layer‐substrate was carried out using the adhesion test Daimler Benz Rockwell‐C. The corrosion properties were determined by the electrochemical polarization method. Experimental results showed that the optimum temperature‐temporal conditions of 900 °C/4 h that are the intermediate processing parameters led to a better compromise between the intended properties, in terms of resistance to wear and corrosion, as well as adhesion quality.

Influence of structure formation and properties of bimetal produced by ultrasound-assisted explosive welding

The aim of this paper was to study how ultrasonic vibrations during explosive welding influence the formation of the structure and properties of bimetal plate. The effect of changes in joint formation kinetics and in the structure and properties of the bimetal plate formed by explosive welding assisted by ultrasonic vibrations was determined. Ultrasound-assisted explosive welding resulted in improved strength and microhardness and decreased wave parameters and molten metal amount in the wave vortex areas compared to explosive welding without ultrasound. The influence of the propagation scheme, frequency and amplitude of the ultrasonic vibrations on the structure and property formation of the bimetal plate during explosive welding was demonstrated. The results of the influence of ultrasound on the weldable zone of dissimilar metals are discussed. Ultrasonic treatment of metal produces a decrease in yield stress, which results in modified metal surface layer properties and conditions for joint formation of collided plates during explosive welding.

Metal Surface Defect Detection Using Modified YOLO

Aiming at the problems of inefficient detection caused by traditional manual inspection and unclear features in metal surface defect detection, an improved metal surface defect detection technology based on the You Only Look Once (YOLO) model is presented. The shallow features of the 11th layer in the Darknet-53 are combined with the deep features of the neural network to generate a new scale feature layer using the basis of the network structure of YOLOv3. Its goal is to extract more features of small defects. Furthermore, then, K-Means++ is used to reduce the sensitivity to the initial cluster center when analyzing the size information of the anchor box. The optimal anchor box is selected to make the positioning more accurate. The performance of the modified metal surface defect detection technology is compared with other detection methods on the Tianchi dataset. The results show that the average detection accuracy of the modified YOLO model is 75.1%, which ia higher than that of YOLOv3. Furthermore, it also has a great detection speed advantage, compared with faster region-based convolutional neural network (Faster R-CNN) and other detection algorithms. The improved YOLO model can make the highly accurate location information of the small defect target and has strong real-time performance.

Effects of modified metal surface on the formation of methane hydrate

In this study, the influence of modified metal surface on the induction time, gas consumption, hydrate growth rate and water conversion to hydrate was investigated. Results demonstrated that the metal surface reduced the induction time by 60% and decreased the stochasticity of hydrate nucleation by 72% at 5.0 MPa in 100 ppm sodium dodecyl sulfate solution. The promotion effect was more significant at 4.1 MPa that the induction time was shorten from 600 min to 142 min. Both the induction time and stochasticity of nucleation decreased with the decreasing hole sizes of metal surface. It also demonstrated that the metal surface increased the gas-liquid interfacial curvature, which decreased the energy barriers for gaseous methane molecules transferring into liquid phase. As a result, the metal surface facilitated the dissolution of methane and increased the kinetics of hydrate growth and water conversion to hydrate. Moreover, the water conversion increased with the height of metal surface in 3 mol% tetrahydrofuran solution due to the capillary force caused by the hydrophilicity of metal surface, while it hindered the migration of water molecules as the metal surface was coated with hydrophobic paraffin, which resulted in few hydrate growth on the upper metal surface and the decrease of water conversion to hydrate.

Laser-based plastic-metal-joining with self-organizing microstructures considering different load directions

Innovative multi-material lightweight construction enables reducing dead weight while maintaining and preferably boosting the components' performance. The implementation of multi-material parts (e.g., plastic-metal-components) requires reliable joining processes since a direct connection between these materials is not feasible due to their different physical and chemical properties. In order to avoid additional weight through adhesive bonding, riveting or fasteners, thermal direct joining with a modified metal surface is a promising approach. Within a first process step, the metal surface is modified by laser-microstructuring. To enlarge the boundary surface and create undercut structures, random self-organizing micro- and nanostructures are generated with ultrashort pulsed laser radiation on stainless steel samples. In the subsequent direct thermal joining process, both joining partners are clamped together. The metal is heated up with diode laser radiation, and through heat conduction, the polymer melts and flows into the generated cavities. After cooling-down, a firm joint between both materials is created, which is based on mechanical interlocking and increased specific adhesion between the joining partners. The mechanical strength of the joint depends strongly on the load direction. In the presented contribution, the strength of the joint between stainless steel and glass-fiber-reinforced and non-reinforced thermoplastics (PP) is investigated for three different load directions (tensile shear, tensile and peel).

Effects of Surface Morphology on the Wear and Corrosion Resistance of Post-Treated Nitrided and Nitrocarburized 42CrMo4 Steel

The surface of alloyed carbon steel was subjected to thermochemical modification by nitrocarburizing and nitriding with or without postoxidation in order to improve its mechanical properties, corrosion, and wear resistance. Treated samples were characterized by testing their basic properties (compound layer thickness, nitriding, nitrocarburizing depth, and surface hardness) according to standards. Detailed estimation of the modified metal surface was performed by additional testing: X-ray diffraction, microstructure, surface roughness and topography, and wear and corrosion resistance. The surface layer obtained after nitrocarburizing treatment consists mainly of e-Fe2-3(N,C) and γ’-Fe4(N,C); similarly, the nitrided surface is formed by e-Fe2-3N and γ’-Fe4N iron nitrides. The surface layer after postoxidation contains additionally Fe3O4. The results obtained show that nitrocarburization, nitridation, and postoxidation result in better mechanical, wear, and corrosion resistance of 42CrMo4 steel, and postoxidized sample properties are influenced by surface morphology.

Post‐oxidizing effects on surface characteristics of salt bath nitrocarburized AISI 02 tool steel type

AbstractThe effect of post‐oxidizing treatment on the characteristics of modified surface layers produced by salt bath nitrocarburizing on the industrial American Iron and Steel Institute (AISI) 02 tool steel types is investigated. Nitrocarburizing treatment is performed for 6 h and 8 h at 570 °C and post‐oxidizing treatment for 30, 60 and 90 min at 520 °C, using argon–steam mixture. Formed layers are characterized by their basic properties such as thickness layer, depth, surface hardness and wear resistance. Detailed estimation of the modified metal surface quality, in terms of chemical composition, formed phases, microstructures and diffusion mechanisms are performed by metallographic techniques, EDX, X‐ray diffraction, scanning electron microscopy (SEM) and glow discharge optical electron spectroscopy (GDOES). The corrosion resistance was investigated in 0.4 M H2SO4 solutions, using steady‐state electrochemical polarization methods. The obtained results revealed the existence of a superficial oxide layer which consists of magnetite (Fe3O4) and hematite (Fe2O3) and the presence of an ε‐phase associated with a small amount of γ′‐phase. Important improvements in wear, microhardness and corrosion resistance occur after these treatments and it is specifically concluded that the sole application of a nitrocarburizing treatment does not significantly ameliorate the corrosion resistance of the as‐received steel. In fact, post‐oxidation treatment contributes to increase corrosion resistance by forming a dense magnetite layer and at the same time, it partially covers the compound layer pores. Copyright © 2009 John Wiley & Sons, Ltd.

Modification of carbon steel surface by the Tenifer® process of nitrocarburizing and post-oxidation

The surface of the non-alloyed carbon steel was subjected to thermochemical modification by salt bath nitrocarburizing with or without post-oxidation based on the Tenifer procedure in order to improve mechanical properties, corrosion and wear resistance. Nitrocarburized layers were characterized by testing their basic properties (compound layer thickness, nitrocarburizing depth, surface hardness) according to current standards. Detailed estimation of the quality of the modified metal surface was performed by additional testing of chemical compositions by EDX and X-ray diffraction, microstructure, surface roughness and topography, and corrosion resistance. The corrosion resistance was investigated in a water solution of 5% NaCl using electrochemical polarization methods and electrochemical impedance spectroscopy. The corrosion properties of the treated and nontreated samples are compared among themselves and with the properties of austenitic stainless steel.The surface layer obtained after nitrocarburization treatment consists mainly of ε-Fe2–3N and γ′-Fe4N. The surface layer of the samples after post-oxidation consists also of ε-Fe2–3N and γ′-Fe4N, but contains additionally Fe3O4.The results obtained show that nitrocarburizing and post-oxidation treatments, based on the Tenifer procedure, result in better mechanical and corrosion properties of non-alloyed carbon steel. The corrosion properties of the thermochemically modified non-alloyed carbon steel were improved and approach the corrosion properties of austenitic stainless steel, known for its very good corrosion resistance.

Structure and electrochemical behaviour of 4,7-diazaheptyl-trimethoxy-silane and vinyl-trialkoxy-silane adsorbed at silver surface

Novel self-assembled monolayers were obtained on silver using 4,7-diazaheptyl-trimethoxy-silane (SiN) and vinyl-trialkoxy-silane (SiVA, where the alkyl group is 3,6,9,12,15,18,21,24,27,30,33,36,39,42,45,48,51,54,57,60-eicozaoxa- hexaheptaconan). It was shown that thus modified metal surface was protected against electrooxidation. A densely packed monolayer remained stable and did not desorb from the Ag electrode on the potential cycling. The structure of SiN and SiVA as well as their complexes with Li + cations were calculated and visualised by the AM1d and PM5 semi-empirical methods.

Creating Chiral Surfaces for Enantioselective Heterogeneous Catalysis: R,R-Tartaric Acid on Cu(110)

One of the most successful ways of inducing enantioselectivity in a heterogeneous catalytic system is by the adsorption of chiral “modifier” molecules on the reactive metal surface. However, little is known about the nature of the active sites present on the modified metal surface and how such modifiers bestow chirality to an achiral metal surface. In this paper we report the behavior of R,R-tartaric acid adsorption on a Cu(110) surface using high-resolution surface analytical techniques. R,R-Tartaric acid is known to be an extremely successful modifier molecule for the enantioselective hydrogenation of methyl acetoacetate, the simplest β-keto ester, to the R-enantiomer of the product molecule methyl 3-hydroxybutyrate. A combination of low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and Fourier transform reflection−absorption infrared spectroscopy (FT-RAIRS) techniques has allowed us to demonstrate that a complicated adsorption phase diagram exists for this system. A rich vari...

Study of UV Laser Ablation of Nitrided Steels Using Inductively Coupled Plasma Atomic Emission Spectrometry

A depth profile study of nitrided steels containing Ti or V sputtered in the surface layer was performed by means of laser ablation inductively coupled plasma atomic emission spectrometry. An Nd:YAG laser was used in the Q-switched mode and operated at 355 and 266 nm. The laser ablation patterns were obtained on the material surface by moving the ablation cell relative to the laser beam by means of an XY-translator. Depth resolution was obtained by using successive limited numbers of ablation cycles. The corresponding transient signals of Ti or V and Fe were measured simultaneously with a dual monochromator. The effect of the number of cycles, the laser power and laser wavelength on the time-dependent behaviour of the Ti or V and Fe line intensities was studied along with the erosion rate. It was found that the erosion rate was lower than 0.6 μm per cycle and depended on the depth of penetration. Emission of sputtered Ti and V was mainly observed in an external layer of less than 2 μm. The laser wavelength did not modify the shape of the crater but significantly changed the line intensity of Fe. The Fe line intensity was also enhanced during the ablation of the nitrided steel compared with the ablation of untreated steel. This study contributes to the knowledge of behaviour of the modified metal surface during interaction with the laser radiation, which is important for development of the method for determination of composition of nitrided surface layers.