The influence of substrate temperature and spraying distance on the properties of plasma sprayed tungsten and steel coatings deposited in a shrouding chamber

• Published in: Surface & coatings technology 2017-05, Vol.318, p.217-223
• Main Authors: Matějíček, Jiří, Vilémová, Monika, Nevrlá, Barbara, Kocmanová, Lenka, Veverka, Jakub, Halasová, Martina, Hadraba, Hynek
• Format: Article
• Language: English
• Subjects: Atmospheric plasma spraying; Bonding; Coatings; Fusion reactor materials; Heat transfer; Heating; Interlayers; Oxidation; Oxygen content; Plasma facing components; Plasma spraying; Porosity; Properties (attributes); Shrouding; Steel; Substrate temperature; Substrates; Thermal conductivity; Tungsten; Tungsten steels
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2016.10.055

Plasma spraying is among the alternative technologies for manufacturing tungsten-based coatings or graded interlayers for plasma facing components of fusion devices. The main limitation lies in the relatively low thermal conductivity, stemming from the anisotropic porosity and imperfect bonding between the splats. For several materials, it has been shown that increased substrate temperature leads to improved intersplat bonding and increased coating density. However, spraying of metals at elevated temperatures in ambient atmosphere is accompanied by enhanced oxidation. This work is focused on the effects of substrate temperature on the properties of plasma sprayed tungsten and steel coatings. A range of substrate temperatures was achieved by varying the preheating temperature, pauses between torch passes, spraying distance and intensity of cooling. To suppress oxidation, the substrates were placed in a special shrouding chamber flushed with argon-hydrogen mixture. The coatings were characterized for their structure, porosity, hardness, thermal conductivity and oxygen content. A marked improvement of these properties with substrate temperature was observed and correlated to the spraying parameters. •Tungsten and steel were deposited by atmospheric plasma spraying at a variety of substrate temperatures.•Argon-hydrogen shrouding was applied to suppress oxidation.•Improved coating properties were achieved by increased substrate temperature, short spraying distance and shrouding.