Thick tungsten layer coating on ferritic-martensitic steel without interlayer using a DC vacuum plasma spray and a RF low pressure plasma spray method

Tungsten has been attracted as one of promising candidates for plasma-facing materials in a next fusion reactor because of its many advantages. However, since the tungsten is difficult to machine and requires high cost techniques for joining to various substrates, alternative methods such as plasma spray coating have been developed. In this work, therefore, we coated thick tungsten layer on a ferritic-martensitic steel by a 60 kW radio-frequency low pressure plasma spray system and a 55 kW direct-current vacuum plasma spray system. Thick tungsten coating over 2 mm using both systems without any interlayer was obtained by inserting a substrate preheating process. We also discussed the characteristics of coated tungsten layers such as hardness, micro-structure, porosity, surface morphology, and crystal structure which were investigated using Vickers hardness tester, field emission scanning electron microscopy, microscope, 3-dimensional surface measuring system, and X-ray diffraction, respectively.