Nuclear fusion power generation utilizes the energy generated during the fusion reaction of hydrogen at over 100 million degrees Celsius. plasma facing components (PFC) of the fusion reactor are exposed to extremely high temperature environments such as thermal load of about 0.1 MW/m2 to 10 MW/m2 an...
Nuclear fusion power generation utilizes the energy generated during the fusion reaction of hydrogen at over 100 million degrees Celsius. plasma facing components (PFC) of the fusion reactor are exposed to extremely high temperature environments such as thermal load of about 0.1 MW/m2 to 10 MW/m2 and radiation and mechanical ablation. Therefore, Fusion facing materials should maintain sufficient toughness, high-temperature strength, and safety at high temperatures. It should also be excellent in thermal conductivity, corrosion resistance, tritium retention, resistance to neutron irradiation damage, and good compatibility with the plasma.
In order to apply it to PFC, we developed a tungsten coating method on ferritic martensitic steel (FMS) substrate by vacuum plasma spray (VPS) coating process. The plasma discharge method of the VPS process can be classified into the direct current (DC) method and the radio frequency (RF) method. Tungsten coating experiments were performed using DS-VPS and RF-ICP system, and the characteristics of each coating layer were compared. The thickness of the tungsten coating layer formed using the DC-VPS equipment was 2.5 mm, the hardness was about 400 HV, the surface roughness was about Ra 3.92 ㎛, and the porosity was 0.85%. The thickness of coating layer formed by using the RF-ICP system was about 4.3 mm, the hardness was about 170 HV, the surface roughness was about Ra 5.84 ㎛, and the porosity was 23.2%.
We also developed a large-area coating process to apply the tungsten coating method to the actual shape of the PFC. In the 9-point position, the Vickers hardness was about 350 HV, the surface roughness was about 4.5 ㎛, the porosity was about 1%, and the coating layer thickness was about 600 ㎛. The uniformity was 95.3% The illuminance was 96.6%, the porosity was 77.9%, and the coating thickness was 95.2%.
The developed tungsten coating was evaluated by heat flux test using 55kW DC arc torch of vacuum plasma spray coating equipment. It was to confirm the integrity of the plasma facing material which must withstand high temperature loads in the extreme environment of the fusion reactor. Thermal integrity was confirmed by applying heat flux for 10, 20, 30 and 60 seconds under the condition of 10 MW/m2 required for the ITER(International Thermonuclear Experimental Reactor) class fusion reactor.
When the space shuttle re-entry at speed of 8 km/s, the surface temperature is about 1,500℃. Sample return capsules in the United States and Japan have a high temperature of 10,000℃ when reentry at 12 km/s and receive extreme heat loads. Heat resistant materials for high temperature extreme environments should have high strength, light weight, heat resistance, thermal conductivity and thermal dimensional stability. Carbon/carbon composites are used as typical heat-resistant materials in the aerospace industry due to their excellent heat resistance characteristics. However, it has a disadvantage that oxidation starts at a relatively low temperature of about 500 ℃.
Ultra-high temperature ceramics coating method using VPS coating process was developed to prevent oxidation of carbon/carbon composites at relatively low temperature. The HfC (hafnium carbide) which have the highest melting point in ultrahigh temperature ceramics and The TiC (Titanium carbide) with superior abrasion resistance was selected to develop the coating process. To improve the bonding strength between the coating layer and the carbon/carbon composite substrate, the HfC/TiC multilayer coating process was developed to continuously form the HfC layer of about 40 ㎛ thickness on the TiC layer of about 50 ㎛ thickness. The adhesion strength between the coating layer and the substrate was measured by a universal material testing machine. This indicates that the bonding strength between the HfC layer and the substrate is improved due to the TiC layer.
The developed HfC single layer coating and HfC/TiC multilayer coating were performed ablation test under the condition of 30 second, Mach 2, heat flux of 5.87 MW/m2 using a supersonic arc heated wind tunnel capable of simulating the earth reentry environment. The mass reduction rate was 11.310% for the carbon composite, 0.025% for the HfC single layer coating, and -0.524% for the HfC/TiC multilayer coating. It was confirmed that the ultra-high temperature ceramic coating was satisfactory for the purpose of preventing oxidation of the carbon/carbon composites.
In this study, we have developed a coating composite material by using VPS coating process that can be applied to ultra-high temperature extreme environment such as fusion reactor and earth re-entry environment. In addition, heat flux tests and ablation tests were performed to apply heat-resistant material of plasma facing components and reentry vehicle.
Nuclear fusion power generation utilizes the energy generated during the fusion reaction of hydrogen at over 100 million degrees Celsius. plasma facing components (PFC) of the fusion reactor are exposed to extremely high temperature environments such as thermal load of about 0.1 MW/m2 to 10 MW/m2 and radiation and mechanical ablation. Therefore, Fusion facing materials should maintain sufficient toughness, high-temperature strength, and safety at high temperatures. It should also be excellent in thermal conductivity, corrosion resistance, tritium retention, resistance to neutron irradiation damage, and good compatibility with the plasma.
In order to apply it to PFC, we developed a tungsten coating method on ferritic martensitic steel (FMS) substrate by vacuum plasma spray (VPS) coating process. The plasma discharge method of the VPS process can be classified into the direct current (DC) method and the radio frequency (RF) method. Tungsten coating experiments were performed using DS-VPS and RF-ICP system, and the characteristics of each coating layer were compared. The thickness of the tungsten coating layer formed using the DC-VPS equipment was 2.5 mm, the hardness was about 400 HV, the surface roughness was about Ra 3.92 ㎛, and the porosity was 0.85%. The thickness of coating layer formed by using the RF-ICP system was about 4.3 mm, the hardness was about 170 HV, the surface roughness was about Ra 5.84 ㎛, and the porosity was 23.2%.
We also developed a large-area coating process to apply the tungsten coating method to the actual shape of the PFC. In the 9-point position, the Vickers hardness was about 350 HV, the surface roughness was about 4.5 ㎛, the porosity was about 1%, and the coating layer thickness was about 600 ㎛. The uniformity was 95.3% The illuminance was 96.6%, the porosity was 77.9%, and the coating thickness was 95.2%.
The developed tungsten coating was evaluated by heat flux test using 55kW DC arc torch of vacuum plasma spray coating equipment. It was to confirm the integrity of the plasma facing material which must withstand high temperature loads in the extreme environment of the fusion reactor. Thermal integrity was confirmed by applying heat flux for 10, 20, 30 and 60 seconds under the condition of 10 MW/m2 required for the ITER(International Thermonuclear Experimental Reactor) class fusion reactor.
When the space shuttle re-entry at speed of 8 km/s, the surface temperature is about 1,500℃. Sample return capsules in the United States and Japan have a high temperature of 10,000℃ when reentry at 12 km/s and receive extreme heat loads. Heat resistant materials for high temperature extreme environments should have high strength, light weight, heat resistance, thermal conductivity and thermal dimensional stability. Carbon/carbon composites are used as typical heat-resistant materials in the aerospace industry due to their excellent heat resistance characteristics. However, it has a disadvantage that oxidation starts at a relatively low temperature of about 500 ℃.
Ultra-high temperature ceramics coating method using VPS coating process was developed to prevent oxidation of carbon/carbon composites at relatively low temperature. The HfC (hafnium carbide) which have the highest melting point in ultrahigh temperature ceramics and The TiC (Titanium carbide) with superior abrasion resistance was selected to develop the coating process. To improve the bonding strength between the coating layer and the carbon/carbon composite substrate, the HfC/TiC multilayer coating process was developed to continuously form the HfC layer of about 40 ㎛ thickness on the TiC layer of about 50 ㎛ thickness. The adhesion strength between the coating layer and the substrate was measured by a universal material testing machine. This indicates that the bonding strength between the HfC layer and the substrate is improved due to the TiC layer.
The developed HfC single layer coating and HfC/TiC multilayer coating were performed ablation test under the condition of 30 second, Mach 2, heat flux of 5.87 MW/m2 using a supersonic arc heated wind tunnel capable of simulating the earth reentry environment. The mass reduction rate was 11.310% for the carbon composite, 0.025% for the HfC single layer coating, and -0.524% for the HfC/TiC multilayer coating. It was confirmed that the ultra-high temperature ceramic coating was satisfactory for the purpose of preventing oxidation of the carbon/carbon composites.
In this study, we have developed a coating composite material by using VPS coating process that can be applied to ultra-high temperature extreme environment such as fusion reactor and earth re-entry environment. In addition, heat flux tests and ablation tests were performed to apply heat-resistant material of plasma facing components and reentry vehicle.
주제어
#Extreme environment Vacuum plasma spray Plasma facing components Tungsten coating Ultra-high temperature ceramics coating Multilayer coating
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