Manufacturing of Composite Coatings by Atmospheric Plasma Spraying Using Different Feed-Stock Materials as YSZ and MoSi
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Manufacturing of Composite Coatings by Atmospheric Plasma Spraying Using Different Feed-Stock Materials as YSZ and MoSi2 D. Koch1 • G. Mauer1 • R. Vaßen1
Submitted: 28 June 2016 / in revised form: 31 January 2017 ASM International 2017
Abstract Yttria-stabilized zirconia (YSZ) is the state-ofthe-art material for the top coat of thermal barrier coatings. To increase the efficiency and lifetime of gas turbines, the integration of MoSi2 as a healing material was proposed. A new method of manufacture was explored in order to enable the spraying of a homogeneous mixed layer of YSZ and MoSi2. As the chemical and physical properties of these powders are very different, they require contrasting process conditions. Due to the evaporation of Si from MoSi2 at spraying conditions suitable for YSZ, more moderate conditions and a shorter time of flight are required for depositing MoSi2. At the same time, the spraying conditions still need to be sufficient for melting the YSZ particles in order to produce a coating. To obtain a homogeneous mixture, both conditions can be matched using an injection system that allows powder injection at two different locations of the plasma jet. Two-color pyrometry during flight (DPV-2000, Tecnar) was used to monitor the actual particle temperature. By optimizing the injection point for the MoSi2, a mixed coating was obtained without decomposition of the MoSi2, which has been analyzed by means of XRD and SEM. Keywords atmospheric plasma spray (APS) ceramics molybdenum disilicide particle temperature self-healing cracks thermal barrier coatings (TBCs) yttria-stabilized zirconia (YSZ) & D. Koch [email protected] R. Vaßen [email protected] 1
Institut fu¨r Energie- und Klimaforschung (IEK-1), Forschungszentrum Ju¨lich GmbH, Ju¨lich, Germany
Introduction The state-of-the-art material used for the manufacture of thermal barrier coatings (TBCs) by means of atmospheric plasma spraying (APS) is yttria-stabilized zirconia (YSZ) (Ref 1). An increase in the efficiency of gas turbines can be achieved by using higher inlet gas temperatures, and the extension of the lifetime for the TBC system used is optimal for reducing the maintenance rate of the component. YSZ experiences a critical phase transformation when operated at temperatures above 1200 C for a long time (Ref 2-4). In addition, the growth of a thermally grown oxide (TGO) layer leads to cracking at the interface between the bond coat (BC) material and the YSZ. These cracks can propagate into the YSZ coating, and cracks can also be initiated within the YSZ topcoat due to stresses close to the TGO (Ref 5-8). The integration of molybdenum disilicide (MoSi2) particles as a healing agent close to the interface is proposed in order to seal cracks before they propagate through the YSZ matrix and lead to a failure of the coating. This healing effect is supposed to be achieved by the oxidation of MoSi2 to form amorphous SiO2, which infiltrates the cracks during operation at a high temperature. SiO2 can then react with t
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