Advanced Materials Research Vol. 1029

Abstract: The aim of this paper is, improving the characteristic of Ventilation mill for grinding coal which is one of the main part of steam power plants in the system that makes a significant influence on the level of energy efficiency with its work. Working parts of the mil during exploitation are dominantly exposed to intensive abrasive and erosive wear and also to impact loading at elevated temperatures, which can lead to damage and fracture of homogeneous materials, thus shortening their working life. For solving the problem of increasing the wear resistance of the parts for transport and coal grinding in power plants, to investigate the optimum application of technology in hard coatings by different procedures, and filer materials. Hard coatings were carried out with cold (plasma and arc treatment) and hot metallization (with concurrent and subsequent drowning). It has been used the additional materials of different chemical composition and properties based on Ni (NiCrBSi; NiCrBSiFe; NiCrBSi / WC) and Fe (FeCrCSiMo; FeCrCBSiTi; FeCrCBNiSi). The main goal of this paper is to make the selection of optimum hardfacing procedures, group of filler materials and hardfacing technology definition based on the results of structural and mechanical properties of samples, experimental model hardfacing. These were investigation of its structure, measurement and distribution of hardness in the samples, tribology characteristic samples with hard coatings. Based on the results of these tests there were selected the additional materials and procedures for applying hard coatings, which would be apply in the revitalization of parts in transport at and coal grinding.

Abstract: The paper presents a case study on the original solution of a flange shaft as part of the root area of a 5 kW wind turbine blade. There were analyzed the causes that led to the shaft breakage under wind loadings in extreme weather conditions, and consequently technical solutions have been searched in order to improve the shaft design making it more reliable as mechanical strength at extreme wind loadings. The flange shaft is a welded subassembly that keeps the blades attached to the rotor hub. The first part of the paper consists in an analysis referring the loading status, the materials used for blade manufacturing, the identification of critical areas where the breaking was initiated and also the causes for which the materials assumed and specified in the technical design and manufacturing technology failed under loading at wind gusts of about 30 m/sec. Based on this preliminary analysis, the second part of the paper presents the technical solutions which were considered in reference to the materials and the improved design concept aiming to provide the right mechanical strength necessary to withstand specific wind loadings in extreme weather conditions.

Abstract: Numerical simulations are powerful tool for analyzing and research in domain of mechanical constructions. In welded joints is very important to determine residual stresses and temperature distribution in sample, apropos, element of construction. In some cases doing the experiment is not possible, so numerical simulations can give the required results and overview of stress state, residual stresses, critical areas, displacement, temperature distribution and other data is needed for analyzing and improvement of constructions or parts of constructions. This analysis includes finite element model for the thermal and mechanical welding simulation. Welding simulation was considered as a sequential coupled thermo-mechanical analysis. The residual stress distribution and magnitude in axial direction was obtained. The paper also shows the results obtained in a simultaneously test of a butt welded thin steel sheet specimen by conventional methods and thermography. Numerical methods are also used in order to predict the crack of specimen. The obtained results confirm that it is very useful to use thermography and Finite Element Method (FEM) for early diagnostics of the complex structures in the exploitation conditions. In this paper is obtained good agreement of results between experiment and Numerical simulations.

Abstract: Paper presents the finite element modeling for the stress and temperature as a result of the metal deposition technology. In this case, this research method is the only one that offers information because of the working condition that are total unfavourable for stress and strain gauges. By selecting the most appropriate initial condition, the output data are very close to real result. In the paper, the temperature behavior is model because its influence in structural transformation and the stress because it can cause problems in the situation of an incorrect working technology.

Abstract: This paper investigates the laser welding of AISI 304 stainless steel thin sheets. For the experimental procedure a 3,3 kW Nd:Yag laser was used. Nine samples were realised during this study and the influence of the process parameters on to the geometry and microstructure of the weld bead is analysed. The best result in case of 0,5 mm stainless steel laser welding are obtained by using a density power in the range of 700-850 kW/cm² associated with a minimum spot diameter of 0,4 mm. The weld bead compositional content was determined by an X ray dispersive field analyses. A decreasing of Mn and Si content into the weld zone was produced mainly by the burning and vaporization effects during the laser welding. Good tensile behaviour of the joints was obtained at all samples with fracture was produced at 600 MPa.

Abstract: This study aims to determine the optimal parameters for cold metal transfer MIG welding of aluminum thin sheets. Starting from this perspective, the filler material of Al5Mg full wire type and a synergic regime of welding with a low linear energy were used. The characterization of welded joints was achieved by macro – microscopic analyses, mechanical tests (microhardness and tensile) aiming to lower the thermo - mechanically affected zone. The results highlight the major influence of the welding parameters over the weld bead geometry and tensile behaviour of the joint.

Abstract: In the last twenty years the cavitation erosion resistance of various welded materials was subject of extensive studies. Despite these, the research field is still opened. The multitude of materials used for the fabrication of hydraulic equipment and the variety of the operating conditions in hydropower units require adapted solutions. This paper presents the investigations made on welded overlays realized using an impact resistant hardfacing alloy, recommended by manufacturers for protection against cavitation erosion. The material was characterized by metallographic investigations (light microscopy, scanning electron microscopy and EDX–analyse), Vickers micro hardness tests, residual stresses measurements carried out by the hole-drilling strain-gage method and cavitation erosion tests using the vibratory method. The results of the cavitation erosion tests were correlated to the behaviour of the martensitic stainless steel 1.4313 (grade X3CrNiMo13-4 corresponding to EN 10088-3) frequently used for the manufacturing of the hydraulic turbine components.

Abstract: Sealing of nuclear fuel material inside the fuel element clad must create a leak-tight "safety barrier" to prevent the release of radioactive products to environment. High quality welds are mandatory to withstand harsh conditions (radiation, pressure, temperature, corrosion) making possible the safe operation of nuclear reactors. The joint design, material selection and welding technique must be combined by smartly balancing possible technological options to yield the best attainable quality for the intended purpose; these choices are discussed in the paper. For thin-walled clad to end-plug welding, heat flow pattern as determined by joint design and fitting accuracy proved to be crucial for the fusion boundary shape and moreover for the success rate in automate welding. Consequently, Finite Element Analysis of the transient thermal field during welding was performed, in order to determine the best compromise with reasonable machining precision for parts. The main features of the developed thermal model and some results illustrating its good predictions vs. actual welds are also presented. Helium-shielded pulsed welding was initially preferred to minimize HAZ, distortion and porosity but unfortunately important cast-to-cast variation in penetration was observed with Inconel-600 plugs, due to Marangoni effect. Extensive work was done to overcome this, mainly through variation of pulsing and of the shielding gas; depth-to-width ratio can be noticeably improved with no material addition. Out of welding classic cladding materials, studies were initiated at INR on joining oxide-dispersion strengthened (ODS) alloys and specialty austenitic formulations (e.g. 15/15Ti) since they are candidate materials of great interest for the next generation of nuclear reactors.

Abstract: The main objective of this paper is to evaluate the mechanical properties, chemical and corrosion resistance of four types of metallic coatings: FeCr, FeCoCr, and FeCoCrNi, FeCrNi sprayed through thermal spraying in electric arc on an anchor substrate type 95Ni5Al or 78.3Ni20Cr1. 4Si0.3Fe. The five layers tested were deposited on carbon steel support low alloyed and the obtained results have provided a picture regarding the possibilities of using of the deposits. Because these types of alloys are used to increase the wear resistance of tools, it is very important to know their behaviour is saline environment, because the contributions brought by this paper would increase the applicability domain of these materials (could be used to recondition by thermal spraying the tools used in naval and petroleum industry). The researches of the obtained deposits have been carried out through several methods to screen their performance. Therefore, there have been done investigations on the microstructural morphology of the deposit, by optical microscopy (OM) and scanning electron microscopy (SEM). The OM and SEM results have sought to determine the degree of uniformity of the deposits and the amount of pores and oxides in layer. The physical properties of coatings were also evaluated by adhesion and porosity quantification. The corrosion resistance was evaluated by exposing samples in saline fog chamber. The corrosion products formed on the surface layers were investigated by scanning electron microscopy (SEM) analysis of the SEM. The intermediate alloy 78.3Ni20Cr1.4Si0.3Fe used as anchoring layer allowed the reducing of the pores and micro cracks frequently found in the ordinary 95Ni5Al alloy. It has been observed that the deposits based on NiCrCo are good enough to be used as an efficient coating of carbon steel in aggressive marine environments.

Abstract:

Submerged arc welding (SAW) is one of the most versatile welding processes. All steel grades, from non- to high alloyed, including Ni-based alloys, can be welded with a combination of various techniques. The process became common worldwide for these properties, and shows a high degree of growth in countries with significant heavy industry. In the process, a large amount of slag is formed from the flux, which is treated as waste. The slag contains non-renewable raw materials, minerals. The mining, processing represents a significant environmental impact. Short life cycle of products from high-energy input is not compatible with the eco-thinking. That is why recycling of these materials is highly appropriate from environmental and economical aspects. The paper presents a method in which the slag can be used as a valuable flux component with significant cost- and waste reduction by ensuring no loss of mechanical properties.