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Matilainen A.,University of Eastern Finland | Gjessing E.T.,University of Oslo | Lahtinen T.,University of Jyväskylä | Hed L.,Technology Center Ketek | And 3 more authors.
Chemosphere | Year: 2011

Natural organic matter (NOM) is found in all surface, ground and soil waters. During recent decades, reports worldwide show a continuing increase in the color and NOM of the surface water, which has an adverse affect on drinking water purification. For several practical and hygienic reasons, the presence of NOM is undesirable in drinking water. Various technologies have been proposed for NOM removal with varying degrees of success. The properties and amount of NOM, however, can significantly affect the process efficiency. In order to improve and optimise these processes, the characterisation and quantification of NOM at different purification and treatment processes stages is important. It is also important to be able to understand and predict the reactivity of NOM or its fractions in different steps of the treatment. Methods used in the characterisation of NOM include resin adsorption, size exclusion chromatography (SEC), nuclear magnetic resonance (NMR) spectroscopy, and fluorescence spectroscopy. The amount of NOM in water has been predicted with parameters including UV-Vis, total organic carbon (TOC), and specific UV-absorbance (SUVA). Recently, methods by which NOM structures can be more precisely determined have been developed; pyrolysis gas chromatography-mass spectrometry (Py-GC-MS), multidimensional NMR techniques, and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). The present review focuses on the methods used for characterisation and quantification of NOM in relation to drinking water treatment. © 2011 Elsevier Ltd.


Alam M.M.,Lulea University of Technology | Kaplan A.F.H.,Lulea University of Technology | Tuominen J.,Tampere University of Technology | Vuoristo P.,Tampere University of Technology | And 7 more authors.
Materials and Design | Year: 2013

Fatigue cracking of laser clad cylindrical and square section bars depends upon a variety of factors. This paper presents Finite Element Analysis (FEA) of the different macro stress fields generated as well as stress raisers created by laser cladding defects for four different fatigue load conditions. As important as the defect types are their locations and orientations, categorized into zero-, one- and two-dimensional defects. Pores and inclusions become critical close to surfaces. The performance of as-clad surfaces can be governed by the sharpness of surface notches and planar defects like hot cracks or lack-of-fusion (LOF) are most critical if oriented vertically, transverse to the bar axis. The combination of the macro stress field with the defect type and its position and orientation determines whether it is the most critical stress raiser. Based on calculated cases, quantitative and qualitative charts were developed as guidelines to visualize the trends of different combinations. © 2012 Elsevier Ltd.


Alam M.M.,Lulea University of Technology | Powell J.,Lulea University of Technology | Kaplan A.F.H.,Lulea University of Technology | Tuominen J.,Tampere University of Technology | And 7 more authors.
Journal of Laser Applications | Year: 2013

A laser clad and machined cylindrical structural steel rod was fatigue tested under four-point bending load. The resulting fracture could be tracked back to a spherical surface pore in the Co-based coating. Due to an oxide inclusion, the pore was not identified by dye penetrant inspection. Two circular buckling strain patterns that were detected beside the pore at the surfaces after fracture confirm local plastic deformation prior to crack initiation. In order to calculate the stress field around the surface pore, linear elastic finite element analysis was carried out. For four-point bending load, a surface pore generally exceeds the maximum stress of a smooth rod as long as the pore is located within an azimuthal angle of ±55°, which was the case for the presented as well as for another pore initiated sample. © 2013 Laser Institute of America.


Tuominen J.,Tampere University of Technology | Nakki J.,Technology Center Ketek Ltd | Pajukoski H.,Tampere University of Technology | Hyvarinen L.,Tampere University of Technology | Vuoristo P.,Tampere University of Technology
Surface Engineering | Year: 2016

Several different tool steel grades were deposited on mild steel by the laser-cladding process with coaxial powder feeding. With bidirectional scanning pattern, most of the grades were deposited crack-free with hardness up to 1000 HV without additional preheating. In a 3-body abrasion wear study, the laser clad Ralloy® WR6 with significant portion of retained austenite exhibited superior abrasive wear resistance compared with the predominantly martensitic tool steel coatings (M2, M4, H13, HS-23, HS-30) and the reference material, Raex® Ar500 wear resistant steel. The abrasion wear resistance of austenitic–martensitic WR6 tool steel was further enhanced by the external addition of 20% volume percentage of relatively large (45–106 µm) vanadium carbides. In single point scratch tests, predominantly martensitic tool steels outperformed austenitic–martensitic tool steels and wear resistant steel. The differences in wear performances were explained by different wear mechanisms and types of contact between the abrasive and the surface. © 2016 Institute of Materials, Minerals and Mining


Tuominen J.,Tampere University of Technology | Nakki J.,Tampere University of Technology | Nakki J.,Technology Center Ketek Ltd | Pajukoski H.,Tampere University of Technology | And 2 more authors.
ICALEO 2012 - 31st International Congress on Applications of Lasers and Electro-Optics | Year: 2012

Industrial laser cladding is usually conducted with 3-6 kW continuous wave gas and solid state lasers. Applications include wide variety of small components or restricted areas in larger components typically for process, aerospace, mining and energy industries. The constant development in laser technologies has made it possible to build increasingly powerful solid state lasers with good beam absorption, high electrical efficiency and low maintenance. The availability of these fiber, disc and diode lasers with power outputs in excess of 10 kW enables to increase the productivity considerably in laser cladding. This is of great interest for large area cladding applications which have suffered from poor cost efficiency with current laser cladding technologies. Increasing the power in laser cladding sets, however, high demands for beam shaping and material feeding techniques which are crucial to final coating properties and industrial applicability of these processes. This paper describes the most recent developments in high power laser cladding including the use of powder, wire and strip consumables at laser power levels up to 15 kW.


Nakki J.,Tampere University of Technology | Nakki J.,Technology Center Ketek Ltd | Tuominen J.,Tampere University of Technology | Vuoristo P.,Tampere University of Technology
ICALEO 2012 - 31st International Congress on Applications of Lasers and Electro-Optics | Year: 2012

Some properties of laser claddings made with several commercially available alloy 625 powders were investigated. Nickel based alloy 625, generally known also as Inconel 625, is widely used also on laser claddings due to its good corrosion properties in various environments. The general specification of alloy 625 is quite permissible and it has been discovered that there can be relatively large variation on properties of alloy 625 powders depending on powder manufacturer and powder batches. And these variations on powder lead to variations on properties of subsequent cladding. The emphasis on this study is especially on the variation of the tendency to hot cracking on laser cladding.


Tuominen J.,Tampere University of Technology | Nakki J.,Tampere University of Technology | Nakki J.,Technology Center Ketek Ltd. | Pajukoski H.,Tampere University of Technology | And 3 more authors.
Journal of Laser Applications | Year: 2015

Hydraulic piston rods on oil and gas drilling platforms, hydro-power stations, chemical plants, and underground mines are exposed to severe tribo-corrosive conditions under static and dynamic mechanical loads. Piston rods made of carbon, quenched and tempered (QT) and stainless steels are frequently surface coated with methods such as thermal spraying, hard chrome plating, and overlay welding. Unfortunately, several premature failures have been reported particularly in marine applications due to insufficient coating properties. Laser cladding has recently drawn lot of attention in this field due to high coating quality and significant improvements in productivity. In this study, several potential Fe-, Ni-, and Co-based alloys were laser clad on carbon and QT steels. Their corrosion and mechanical performances were explored in long-term salt spray, immersion, hardness, abrasive wear, and four-point bending fatigue tests. Most of the laser coatings outperformed hard chrome in corrosion properties, but hardness values were somewhat lower. In single point abrasion tests (scratch tests), the hardest laser coatings, however, outperformed hard chrome due to brittle nature of hard chrome layers. Postmachining induced significant superficial hardness increases in laser coatings, which was the main reason for good wear performance. Fatigue performance was strongly dependent on material pairs, presence of cladding defects, and applied loads. © 2015 Laser Institute of America.


Nakki J.,Tampere University of Technology | Nakki J.,Technology Center Ketek Ltd | Tuominen J.,Tampere University of Technology | Pajukoski H.,Tampere University of Technology | Vuoristo P.,Tampere University of Technology
ICALEO 2013 - 32nd International Congress on Applications of Lasers and Electro-Optics | Year: 2013

The effect of impurity or minor alloying elements boron, aluminium and titanium of alloy 625 on laser cladding was studied with hot cracking tests and high speed video imaging. Results show that hot cracking tendency was increased when small amount of boron was added to powder while the addition of aluminium and titanium appeared to decrease hot cracking. Aluminium and titanium had also a strong effect on dilution, penetration depth and melt pool surface behaviour.


Pajukoski H.,Tampere University of Technology | Nakki J.,Tampere University of Technology | Nakki J.,Technology Center Ketek Ltd. | Thieme S.,Fraunhofer Institute for Material and Beam Technology | And 3 more authors.
Journal of Laser Applications | Year: 2016

In the last few years, coaxial laser heads have been developed with centric wire feeding equipment, which enables the laser processing of complex-shaped objects in various applications. These newly developed laser heads are being used particularly in laser brazing experiments in the automotive industry. This study presents experimental results of using a coaxial laser head for cold- and hot-wire cladding application. The coaxial wire cladding method has significant improvements compared with the off-axis wire cladding method such as independence of the travel direction, alignment of the wire to the laser beam, and a reduced number of controlling parameters. These features are important to achieve high quality coatings. Cladding tests were conducted on mild steel with a coaxial laser wire welding head using Ni-based Inconel 625 and Thermanit 2509 super duplex stainless steel solid wires in order to determine the properties of the cladding process and the coatings deposited. The corrosion resistance of the obtained coatings was examined by long-term acetic acid salt spray (AASS) and electrochemical critical pitting temperature tests. The test results showed that by using the coaxial wire cladding method, defect-free high quality and corrosion resistant Inconel 625 and super duplex stainless steel coatings with low dilution were achieved. The average pitting temperature for Thermanit 2509 duplex coating was 75 °C in 1M NaCl solution, which was comparable to wrought 2507 duplex stainless steel. Low diluted Inconel 625 coating survived the AASS test for 2000 h without signs of corrosion. © 2015 Laser Institute of America.


Rajan R.,Tampere University of Technology | Rajan R.,Technology Center Ketek Ltd | Riihivuori J.,Tampere University of Technology | Rainosalo E.,Technology Center Ketek Ltd | And 2 more authors.
Journal of Reinforced Plastics and Composites | Year: 2014

Viscose fabric-reinforced unsaturated polyester composites were successfully prepared through vacuum infusion process. Unidirectional viscose fabric was modified by two different organosilane coupling agents and by acetylation treatment. The main objective was to study the influence of fabric treatment on the mechanical and water absorption properties of the composites. Flexural, tensile and impact properties of composites were studied. The results from mechanical testing of composites pointed out that 3-aminopropyltriethoxy silane treatment increased the flexural and impact strengths of the composites with respect to untreated fabric composite. The impact strength of 3-aminopropyltriethoxy silane-treated fabric composites almost doubled compared to the value of untreated fabric composite. Among all the composites under study, those with fabrics treated by 2 vol% 3-aminopropyltriethoxy silane in ethanol/water (95:5) solution exhibited significant improvement in water uptake resistance. An unsaturated polyester gelcoat and topcoat were applied as the outer surface on the composites with untreated fabric. This was done in order to investigate the visual surface appearance and evaluate the gelcoat and topcoat effect on water absorption after accelerated water immersion test. The regenerated cellulose fibre as reinforcement shows high potential to be used as an alternative for natural bast fibres, especially, when toughness of material matters. Chemical treatment of regenerated cellulose fibres could result in improvement in properties of polymer composites, considering that the appropriate treatment method is selected for the corresponding fibre-matrix system. © 2014 The Author(s).

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