Papers by Keyword: Surface Engineering

Abstract: Diamond-like carbon (DLC) coatings are valued for their excellent wear resistance and ability to extend the life of mechanical components, supporting resource conservation. However, high residual stress and poor adhesion limit their practical use. Silicon-doped DLC (Si-DLC) can reduce stress and improve adhesion, though excess silicon lowers hardness, creating a trade-off. This study aimed to optimize both adhesion and hardness by adjusting the silicon-containing gas ratio and the number of stacked layers. Si-DLC was deposited on austenitic stainless steel (SUS304) using acetylene (C₂H₂) and tetramethylsilane (TMS) via plasma enhanced chemical vapor deposition (PECVD) at 170 °C with a 1.2 µm thickness. Higher TMS ratios increased silicon and hydrogen content in the Si-DLC layer. More layers reduced hardness and low-load wear resistance but enhanced durability under high loads.

Abstract: Conventional plasma nitriding can induce defects due to direct plasma formation on the surface of the treated material. To address this issue, the screen-assisted direct current plasma nitriding (S-DCPN) method was developed, which generates plasma on both the sample and a surrounding screen, thereby reducing such defects. In this study, S-DCPN was applied to ferritic stainless steel (SUS430) using austenitic stainless steel (SUS304) as the screen material. Treatments were performed at 633 K for 15 hours under gas pressures of 200 and 600 Pa, with varying gas compositions of 75 % N₂ – 25 % H₂, 50 % N₂ – 50 % H₂, and 25 % N₂ – 75 % H₂. To evaluate the effects of gas composition and pressure, a range of analyses was conducted, including X-ray diffraction (XRD), cross-sectional microstructural observations, glow discharge optical emission spectrometry (GD-OES), hardness testing, and corrosion testing. The results revealed the formation of the α_N phase, a supersaturated solid solution of nitrogen in ferrite, under all conditions. Nitrogen diffusion and surface hardness increased with higher hydrogen content, and corrosion resistance was notably enhanced under the 25 % N₂ – 75 % H₂ condition. These findings demonstrate the effectiveness of S-DCPN in improving the surface properties of ferritic stainless steel while maintaining or enhancing corrosion resistance.

Abstract: The results obtained by ISIM Timisoara to the development of the friction stir welding process (FSW) have supported the extension of the researches on some derived processes, including friction stir processing (FSP). The experimental programs (the researches) were developed within complex research projects, aspects regarding the principle of the process, modalities and techniques of application, experiments for specific applications, being approached. The paper presents good results obtained by friction stir processing of cast aluminum alloys and copper alloys. The optimal process conditions, optimal characteristics of the processing tools were defined. The complex characterization of the processed areas was done, the advantages of the process applying being presented, especially for the cast aluminum alloys: EN AW 4047, EN AW 5083 and EN AW 7021. The characteristics of the processed areas are compared with those of the base materials. The results obtained are a solid basis for substantiating of some specific industrial applications, especially in the automotive, aeronautical / aerospace fields.

Abstract: Austenitic stainless-steel has been widely used. Although it offers excellent corrosion resistance, processability, and nonmagnetic properties, it is inferior in terms of wear resistance and hardness. Therefore, the purpose of this study is to form iron boride on an austenitic stainless-steel surface using the spark plasma sintering (SPS) method and to evaluate its properties. The SPS method was utilized because the rapid heating involved in the process reduces the processing time. AISI 316L as a sample material was boronized for 3.6 ks at 1073 – 1273 K at applied pressures of 4 MPa and 8 MPa with a powder mixture of B₄C and KBF₄. The Vickers hardness profile results showed that the hardness of the untreated sample was ~ 200 HV whereas that of the boronized sample was ~ 2300 HV. The wear test profile showed that the wear resistance of the boronized sample was significantly improved. Moreover, according to elemental analyses, boron diffused from the sample surface to 200 μm and 60 μm when the applied pressure was 8 MPa and 4 MPa, respectively. This indicated that boron diffused to a greater depth when the applied pressure was increased.

Abstract: The article presents the results of research on the impact of laser surface treatment on selected steel properties. The laser treatment consisted of remelting and alloying high speed steel using hard ceramic phase powders. A high-power diode laser was used in the experiment to examine the effect of parameters such as beam power and powder type on the structure and properties of the surface layer. A structural mechanism was observed consisting in obtaining, after laser processing, a super fine crystalline structure and a dendritic structure at the remelting zone. Structural changes have been found to be associated with improved properties such as hardness, microhardness and wear resistance. Steel treated with conventional heat treatment was used as a comparative material.

Abstract: The paper presents some preliminary results regarding the combining of metallic, Cr3C2-20(Ni 20Cr) and ceramic (TiO₂) HVOF deposition of layers for corrosion protection applications. The deposited layers morphology was investigated by SEM and optical microscopy. The corrosion protection efficiency of the deposited layers was evaluated in 0.3M NaCl solution. The maximum corrosion protection efficiency was determined for the combination of layers using the carbide as the first layer although the inverse deposition order showed a small decrease. Depending on the main application (corrosion versus wear) one or the other are recommended.

Abstract: In order to improve the wear resistance of the surface of thick copperplate, A layer of Ni-Co-Cr alloy on thick copperplate surface is performed by laser –hybrid cladding process. In laser cladding processing, it is known that it is difficult to get good metallurgical bonding between the layer and copperplate. Micro-arc deposition technology is developed to get a thin alloy layer on the surface of thick copperplate, and then using laser cladding method to make thick coating. Micro organization analysis and wear resistance comparison experiments are taken to the specimen. From the microscopic structure analysis, it can be seen that the deposition and substrate form favorable metallurgy bonding, as a narrow metallurgical bonding zone, about 20μm in width. The micro- structure photos show that the coating is more compact, and crystal grains are refined grain composed of γ-Ni, Cr₇C₃ and CrB. The micro-hardness of the cladding zone is between 650HV~850HV, which is much higher than the copper substrate. Roughness measurement of the specimens shows that the cladding layer is smoother. The experiment’s result shows that laser-arc hybrid cladding can perform coating of Ni-Cr alloy, metallurgy bonding with the copperplate, on its surface.

Abstract: The low hardness and poor tribological performance of titanium alloys restrict their wide applications in automotive fields. Nitriding is widely used to improve tribological properties, wear resistance, and corrosion resistance of steel and titanium alloys. Plasma nitriding is becoming increasingly popular because of its high nitrogen potential, short treatment time, and low environmental impact. Recently, considerable interest has been devoted to alternative nitriding methods such as active screen plasma nitriding (ASPN). In this study, a Ti-6Al-4V titanium alloy was nitrided by ASPN using a titanium double screen in order to investigate the effect of applying the double screen on the microstructure of the nitriding layer. The Ti-6Al-4V sample was placed on the sample stage in a cathodic potential. A titanium double screen was mounted on the cathodic stage around the sample stage. The sample was treated for 1-25 hours at 600oC under 200 Pa in 75% N₂ + 25% H₂ atmosphere. After nitriding, glow discharge optical emission spectroscopy (GD-OES) revealed that the thickness of the nitriding layer composed of TiN tended to increase with increasing the nitriding time. The Vickers microhardness of the sample surface nitrided for 25 hours reached approximately 1300 HV. Ball-on-disk wear test revealed that a wear loss of nitrided sample considerably decreased than that of untreated sample.

Abstract: Several earth-abundant transition-metal oxides (e.g. Fe₂O₃, CoO, and Cu₂O) possessing suitable band gaps for solar water splitting exist, but energy level alignment is often sub-optimal, i.e. the conduction and valence bands do not straddle the water oxidation and reduction potentials. Here, using a nanocrystalline-TiO₂-based photoelectrochemical cell as a model system, we investigate the effect of tuning the semiconductor energy levels by adding Li⁺ ions to the electrolyte. The effect of LiClO₄ addition on band edges, interfacial recombination resistance, electron diffusion length, and charge-separation efficiency were quantified by impedance spectroscopy and analysis of incident photon-to-current efficiency spectra. We find that the TiO₂ band edges are shifted toward positive potentials by the addition of Li⁺, and that this increases the apparent electron diffusion length without affecting the charge-separation efficiency, most likely due to a change in the driving force for O₂ reduction. These results should prove useful in the modeling and optimization of solar water splitting cells employing metal oxide photoelectrodes.

Abstract: The surface of the magnetite nanoparticles has been engineered by the proteins available in the leaf extract of Datura inoxia. Fourier Transform Infrared (FTIR) study and by thermo gravimetric analysis (TGA) confirms the bonding between metal ions and the amide carbonyl group preset in the plant protein confirming the formation of core-shell structure. The plant protein coated magnetic Fe₃O₄ nanoparticles under investigation have an average size of about 14 nm (˂20nm). The isothermal magnetization curve of the ferrofluid appears in S-like sigmoid shape showing soft nonhysteretic magnetic behaviour at room temperature. The saturation magnetization (M_S), remanent magnetization (M_R), squareness (M_R/M_S) and coercivity value (H_C) increased with decreasing temperature from 300 K to 10 K. The increment of magnetization (45 to 53 emu/gm) might be due to the decrease in thermal energy while the enhancement of coercivity (0-208 O_e) is attributed to the exchange interaction at the interface between the ferromagnetic (Fe₃O₄) and diamagnetic surface layer of protein on the nanocrystalline magnetite. The magnetization value is much smaller in comparison with the bulk magnetite (92emu/g) due to surface spin disorder also approves core-shell structure of diamagnetic protein layer on the surface. The results show the ease of the synthesis to reinforce the colloidal stability where the super paramagnetic behaviour has been found to be restored. The core-shell moiety could play an important role in biological systems as a means of storing Fe⁺³ for an organism.