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Karleby, Finland

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.

Matilainen A.,University of Eastern Finland | Gjessing E.T.,University of Oslo | Lahtinen T.,University of Jyvaskyla | Hed L.,Technology Center Ketek Ltd | 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.

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

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