Atmospheric plasma sprayed W coating/Detonation sprayed W-steel composite coating/steel substrate-based coating system for the tokamak first wall

To study the manufacturing method of the tungsten armored first wall of tokamak devices, the W-316 L steel (W-SS) composite coatings were fabricated on 316 L steel substrates by detonation spraying (DS) as the interlayer of pure tungsten coatings manufactured by atmospheric plasma spraying (APS). The main characteristics and performance under transient heat shocks of the APS W/DS W-SS /substrate-based three-layer coating system were studied and compared with the APS W/substrate-based coating system. The results showed the porosity of the DS W-SS was about 1.9% with most of the pores smaller than 70 nm. In contrast, the porosity of the APS W reached about 8.6% and most of the pores were up to hundreds of nanometers. The bonding strength tests proved that both the adhesions of APS W to DS W-SS and DS W-SS to the substrate were much higher (almost 1.5 times) than the adhesion of APS W to the substrates. The three-layer specimens performed much better than the APS W/substrate specimens during the transient heat shock tests as expected. Besides, a special microstructure variation occurred on the three-layer specimens before its damage under the tests which was considered helpful to prolong its life-span under high heat flux. In a conclusion, the DS W-SS interlayer improved the service performance of the APS W/substrate-based coating significantly and demonstrates its potential for application in current tokamak experimental devices.