MICROSTRUCTURE AND MICROHARDNESS EVALUATION FOR NiCrAlY MATERIALS MANUFACTURED BY SPARK PLASMA SINTERING AND PLASMA SPRAYING

NiCrAlY deposited by different thermal spraying methods is commonly used as the bond coat material in thermal barrier coatings (TBCs). In the present study, two experimental coatings were deposited by hybrid water stabilized plasma (WSP-H) and radio frequency inductively coupled plasma (RF-ICP) using the same feedstock powder. Spark plasma sintering (SPS) was used to manufacture a compact NiCrAlY from the same feedstock powder as a reference material. Microstructure, internal oxidation, phase characterization and quantification of the mechanical behaviour in terms of microhardness were studied. The investigations clearly showed microstructural and mechanical differences between the NiCrAlY samples manufactured by different plasma technologies. The results confirmed that SPS and RF-ICP provide dense structures with no oxides due to the fabrication under protective atmosphere and similar mechanical properties. Thus, RF-ICP may be used for deposition of very dense coatings with microstructure and hardness comparable to compacted materials prepared by SPS.

Application of Laser-Ultrasound for Characterization of Plasma-Sprayed Ceramics

Laser-based resonant ultrasound spectroscopy (RUS) method was applied to measure elastic constants of a porous calcium titanate coating manufactured by water-stabilized plasma-spraying (WSP). To enhance the reflectivity of the polished surface of this material for the lasers applied at RUS measurements, a thin coating of sodium metasilicate (waterglass) was used. It is discussed how the metasilicate affects the acoustic properties of the underlying porous material and experimentally shown that such a surface treatment enables the characterization of the structural processes in these materials at elevated temperatures.

Heat load and deuterium plasma effects on SPS and WSP tungsten

Tungsten is a prime choice for armor material in future nuclear fusion devices. For the realization of fusion, it is necessary to address issues related to the plasma–armor interactions. In this work, several types of tungsten material were studied, i.e. tungsten prepared by spark plasma sintering (SPS) and by water stabilized plasma spraying (WSP) technique. An intended surface porosity was created in the samples to model hydrogen/helium bubbles. The samples were subjected to a laser heat loading and a radiation loading of deuterium plasma to simulate edge plasma conditions of a nuclear fusion device (power density of 108 W/cm2 and 107 W/cm2, respectively, in the pulse intervals up to 200 ns). Thermally induced changes in the morphology and the damage to the studied surfaces are described. Possible consequences for the fusion device operation are pointed out.

Influence of Preheating Temperature on the Quality of the Interface between Plasma Sprayed Coatings and Substrate

This study was aimed to investigate the effect of the substrate preheating temperature on the overall quality of the coating/substrate interface. The coatings (stainless steel) were deposited using a water stabilized plasma torch (Institute of Plasma Physics, Prague, i.e. IPP, Czech Republic) on steel substrates. Three sets of samples were prepared under identical spraying and grit blasting condition; substrate preheating temperature was the only parameter which was varied, i.e. preheating to 150°C, 250°C and 350°C. Higher preheating temperature led to a significant increase in the coating adhesion.