Nanotechnologies and Advanced Materials

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Authors: Gheorghe Buluc, Iulia Florea, Romeu Chelariu, Oana Rusu, Ioan Carcea
Abstract: In this paper it is presented the microstructure and wear resistance of FeNiCrMnCu high entropy alloy. High entropy alloys are composed by at least five metallic elements in equimolar or non-equimolare proportions. High entropy alloys a brand new category of metallic materials, appeared to be a new effort in materials science and engineering, which attracted great interest. To obtain FeNiCrMnCu high entropy alloy we used an 8000 Hz induction furnace. The chemical composition was determined by EDAX. Microstructural analysis was performed using optical microscopy and SEM (scanning electron microscopy), which showed that the FeNiCrMnCu high entropy alloy has a dentritic structure and form a solid solution. Choosing copper as the main element (copper tends to segregate in interdentritic region due to its positive enthalpy of mixing with many common elements) [1], along with the iron, nickel, chromium and manganese, led to obtaining a dentritic structure specify for solid solution, which, however, did not lead to a significant hardness for FeNiCrMnCu high entropy alloy. In this work we selected pure metallic elements like: Fe, Ni, Cr, Mn and Cu. The quantity of alloy developed has 1.5 kg. Friction and wear resistance were the studied by using a reciprocating sliding test machine, in a pin on disk configuration, using aluminum as counter face. Hardness value regarding FeNiCrMnCu high entropy alloy was 184 HV and medium friction coefficient value for FeNiCrMnCu high entropy alloys was 0.86 for 28 minutesc and 1.13 for the first 20 seconds.
Authors: Maria Baciu, Elena Raluca Baciu, Ramona Cimpoeşu, Irina Gradinaru
Abstract: The investigations conducted aimed at determining the microstructural and chemical modifications produced in a Ni-Cr-Mo alloy following electrocorrosion in Afnor artificial saliva by using SEM electronic microscopy and EDS chemical analysis. By 2D and 3D microscopy and by qualitative determinations of the luminous variation we could notice the effects of electrocorrosion tests on the surface of the metallic material, and by EDAX qualitative and quantitative determinations (Point, Line and Mapping modes) of the surface chemical composition we could determine the chemical modifications produced following the corrosion tests.
Authors: Florentina Potecaşu, Octavian Potecaşu, Francisco Manuel Braz Fernandes, Petrică Alexandru, Alexandru Alexa
Abstract: This study presents the result of the researches regarding the obtaining of NiTi alloy through powder metallurgy (PM) as a possible alternative to present technologies (melting through induction in vacuum—MIV and re-melting with electric arch in vacuum—VAR). The researches made by the authors have aim at the obtaining of Ni-Ti materials with fine grain or ultrafine grain through powder metallurgy techniques, starting from ordinary metallic powders of Ti, Ni, Cu, with grain size less than 100 micrometers, and also using processing through severe plastic deformation (HPT — high pressure torsion). The fabrication through PM has an important advantage because a product requires low processing subsequent considering that it can get with sizes and shape very similar to the final ones, which is not negligible if one takes into account that the alloys Ni-Ti do not excel on cutting processability. Cylindrical samples were produced by cold uniaxial compression, at the specific pressure of 600 MPa, dosed in a proportion of 52.5 % Ni + 43.5 % Ti + 4.0 % Cu, mass composition. The compressed samples, after the sintering in vacuum and severe plastic deformation have been characterized by X-ray diffraction (XRD) , differential scanning calorimetry (DSC) and optical microscopy.
Authors: Tamara Radu
Abstract: The Ni-P coatings on steel strips were obtained by electroless method. Experiments were performed at three pHs, respectively: 6.6; 5.11 and 4.32 with immersion times 5 and 12 minutes at 80 - 85°C. Deposits were caractherized by energy-dispersive analysis (EDS), scanning electron microscopy (SEM) and optical microscopy. The chemical composition shows an increased of phosphorus content at the pH descrease, so at the pH-6.6 the phosphorus content in the coating is 4.74 wt% and at pH-4.32 is 12.42 wt% P. Regardless of the pH value is observed was some chemical dishomogeneity of layers the more pronounced with as the pH value is higher. Alongside Ni and P the layers can contain small amounts of oxygen and other elements coming from the nickel bath impurities and from working environment. Also it shows the surface morphology in correlation with the deposition process parameters and surface defects possible.
Authors: Lucica Balint, Gina Genoveva Istrate
Abstract: Research has shown the relationship among hardness, usage and corrosion resistance Ni-P-Al2O3 composite coatings on steel support heat treated. The electroless strips were heat treated at 200°C, 300°C, 400°C, 500°C and 600°C. Further studies on corrosion, hardness and usage revealed changes in properties, compared to the initial state, both on the strips coated with Ni-P and the ones coated with Ni-P-Al2O3 composite. The samples have been studied before and after the heat treatment via Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Energy Dispersive X-ray Analysis (EDX) and X-Ray Diffraction (XRD). The results show that untreated Ni-P layers exhibit strong corrosion resistance, while hardness and usage increase with heat treatment temperature, with a peak at 400 °C. Using suspended particles co-deposition, led to new types of layers, some with excellent hardness and usage properties. Corrosion resistance increase with heat treatment. Coating layers can be adjusted to the desired characteristics, by selecting proper parameters for the expected specific results.
Authors: Liviu Gurau, Carmela Gurau, Gheorghe Gurau
Abstract: The contribution of this paper is to provide the effect of chemical composition on both cost and mechanical properties for steel used to wind turbine tower. Each chemical element has been chosen to contribute to the desired final properties. After establishing the chemical composition has been set up metallurgical route. To determine the influence of chemical composition and thermomechanical treatments a series of experimental tests were conducted to evaluate the structure and mechanical properties. A detail analysis involving macroscopic feature and microstructure analysis of the microalloyed steel was also performed by optical microscopy (OM).The mechanical properties were evaluated by tensile test and Charpy V-Notch test. The experimental tests and analysis results show that there are significant improved in the material properties of thick steel plates when comparing it with the Standard, EN10025/3-2004.
Authors: Anisoara Ciocan, Beatrice Tudor
Abstract: The purpose of this research is to analyze the making technology of clean steel used in the oil, gas and petrochemical industry. The steel was obtained into conventional electric arc furnace. To enhance the steel quality a secondary refining treatment was applied. The purity characteristics of the steel A516 Grade 65, before and after the treatment in the vacuum arc degassing equipment are discussed and compared. The deoxidation, desulphurisation in the presence of basic slag and degassing by injecting an inert gas and also by vacuum exposure are effective in reducing non-metallic inclusions and for chemical composition control. Data from 31 melts obtained in two industrial conditions are presented according to steel making parameters. The variation of chemical composition, especially of content of S, P, and the cleanliness of the steel in terms of content of non-metallic inclusions are analyzed.
Authors: Costel Durduc-Roibu, Elena Drugescu
Abstract: The research examines the improvements of mechanical properties of yield strength and toughness for an optimized chemical composition B2 used in industrial trial in comparison with usual chemical composition A1 used for pressure steel grade with higher strength and toughness. For both chemical compositions we rolled three plates with thickness 8, 10 and 12 mm. Rolling mode was a control rolling followed by normalizing heat treatment. Samples from each plate from opposites corner in as rolled and normalized state was taken and tested: spectral analysis, mechanical properties: tension tests, Charpy-V notch impact test. Differences between A1 and B2 chemical compositions are given by the micro alloing elements used and the overall results showed increasing YS and toughness values in the range of euronorm requirements.
Authors: Elena Scutelnicu, Carmen Catalina Rusu, Bogdan Georgescu, Octavian Mircea, Melat Bormambet
Abstract: The paper addresses the development of advanced welding technologies with two and three solid wires for joining of HSLA API-5l X70 (High-strength low-alloy) steel plates with thickness of 19.1 mm. The experiments were performed using a multi-wire Submerged Arc Welding (SAW) system that was developed for welding of steels with solid, tubular and cold wires, in different combinations. The main goal of the research was to assess the mechanical performances of the welded joints achieved by multi-wire SAW technology and then to compare them with the single wire variant, as reference system. The welded samples were firstly subjected to NDT control by examinations with liquid penetrant, magnetic particle, ultrasonic and gamma radiation, with the aim of detecting the specimens with flaws and afterwards to reconsider and redesign the corresponding Welding Procedure Specifications (WPS). The defect-free welded samples were subjected to tensile, Charpy V-notch impact and bending testing in order to analyse and report the mechanical behaviour of API-5l X70 steel during multi-wire SAW process. The experimental results were processed and comparatively discussed. The challenge of the investigation was to find the appropriate welding technology which responds simultaneously to the criteria of quality and productivity. Further research on metallurgical behaviour of the base material will be developed, in order to conclude the complete image of the SAW process effects and to understand how the multi-wire technologies affect the mechanical and metallurgical characteristics of the API-5L X70 steel used in pipelines fabrication.

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