Thermal shock behavior of Tungsten & Tungsten alloy materials under transient high heat load conditions S. Kanpara*, S. Khirwadkar, S. Belsare, K. Bhope, R. Swamy, P. Mokariya, N. Patel, T. Patel, N. Chauhan, N. Jamnapara
Institute for Plasma Research, Gandhinagar-382428, INDIA *
[email protected] Motivation All high heat load events are combined with high local energy depositions Estimated Heat Loads On Divertors of ITER-like Tokamak which may lead to surface melting, evaporation or cracking and finally to an Steady state Heat Loads: erosion of the plasma facing materials. Typical heat load for time period more than 10s : 10MW/m2 Worst heat load for time period less than 10s : 20MW/m2 In order to study the effects of such loads on different grade of Tungsten Transient Heat Loads: materials, transient heat load experiments have been carried out on Tungsten During Edge Localized Mode (ELM) Event with Time Period in range 0.1ms to 1.0ms: & Tungsten alloy materials, synthesized using Powder Metallurgical process For typical case of 3MJ energy released during an ELM: 0.5 – 1.0 MJ/m2 (Freq ~ 10-20 Hz); with advanced sintering method called Direct Sintering Process (DSP). For worst case of 15MJ energy released during an ELM : 2 MJ/m2 (Freq ~ 0.01Hz);
Material Details
Results Surface Temperature Details
Development of Pure Tungsten (W) & Tungsten + 1wt.% La2O3 (WL) using Direct Sintering Press (DSP), Dr. FRITSCH Company, Germany
1600
Surface Temp
W (ref) W-L (DSP) W (DSP)
1500
1400 1400
Sintering Parameters:
Material Properties (major)
Sintering temperature: 2390°C Pressing force: 39.22 MPa Soaking time: 15 mins Sintering Parameters: Sintering cycle time: 1 hour 30 mins Sintering temperature: 2390°C Heating Rate: 100°C/min Pressing force: 39.22 (MPa) Vacuum/Inert gas: Vacuum Soaking time: 15 mins
1000 800 600 400 200
Type of Material
Sintering cycle time: 1 hour 30 mins Heating Rate: 100°C Vacuum/Inert gas: Vacuum
1x10
0
2x10
0
3x10
0
4x10
0
5x10
0
Time (ms)
DSP W
19.3
18.60 (96.37%)
Density (g/cc) Thermal Conductivity (W/mK) at RT
Temperature vs Time plot (simulation data)
DSP WL
17.89 (94.50%)
1100 1000 900
700
0
Plansee Tungsten (reference)
1200
800
0
Material Properties
1300
o
Surface Temp ( C)
o
Surface Temp ( C)
1200
0.00
1.00x10
0
2.00x10
0
3.00x10
0
4.00x10
0
5.00x10
0
Time (ms)
Temperature vs Time plot (Experimental data from IR Thermography)
• Transient thermal analysis for heat transfer is performed on the tungsten samples considering heat transfer coefficient of 40000 W/m2K • The total time duration considered for the analysis is 5 sec with pulses of 20 ms ON and 1 sec OFF with the actual incident heat flux.
Ultrasonic Testing
Micro Hardness (HVN at 400gmf)
173
163
150
490
520
480
UT of Plansee W_before and after heat load testing
UT of Pure W (DSP) before and after heat load testing
UT of WL before and after heat load testing
Image of Tungsten material (as sintered)
Micro Structural Analysis
Transient High Heat Load Testing
Schematic diagram of HHFTF at IPR
SEM image of Pure W (DSP) before heat load testing
SEM image of WL before heat load testing
SEM image of Pure W (DSP) before heat load testing
SEM image of WL after heat load testing
Experimental setup of Tungsten samples in HHFTF with cooling connections
SEM image for crack network observed in WL sample after heat load testing
SEM image for crack width measurement in WL sample
Surface Profilometry Analysis
Samples were prepared from Developed W & WL material of size 12.5mm radius (at 120 deg angle) with 5mm thickness along with reference (Plansee) Tungsten. Samples were subjected to transient high heat load conditions relevant to the ITER-like Divertor to study the materials damage using High Heat Flux Test Facility (HHFTF) at IPR. The targets were exposed by series repeated pulsed surface heat loads for 500 cycles in energy density range of 1.0–3.14 MJ/m2 and a pulse duration of 20 ms ON and 1 s OFF time. Transient Heat load conditions Sr. No.
EB Power at 45keV Energy
Pulse Duration
(W)
FWHM of Gaussian Beam Profile (mm)
(ms)
(MJ/m2)
1
8.84E+04
14.2
12
1.68
2
8.07E+04
13.3
15
2.17
3
1.15E+05
17.2
20
2.48
4
8.84E+04
14.2
20
2.79
5
8.07E+04
13.3
20
2.89
6
7.57E+04
12.8
20
2.96
7
7.57E+04
12.8
20
2.96
8
6.23E+04
11.2
20
3.14
9
6.23E+04
11.2
20
3.14
o Cooling Parameters: Water @16bar,RT,80LPM
Energy Density Averaged Over (2 x FWHF)
Surface Roughness profile of WL sample at heat load exposed area. Sa = 252 nm
Surface Roughness profile of WL sample at crack area. Sa = 503 nm
Surface Roughness profile of WL sample at un-exposed area. Sa = 128 nm
Summary
Pure W & WL Material is developed for use as Plasma Facing application with desired properties using DSP . Transient high heat load testing of Pure W, WL and reference (Plansee W) has been carried out at energy density from 1.68 MJ/m2 to 3.14 MJ/m2 for 500 cycles with 20ms ON & 1 s OFF time. Pure tungsten materials (reference and newly developed) material could withstand all of the thermal cycles without any damage but WL shows micro crack. Damage of material is occurred mainly at the grain boundaries. Ultasonic Testing shows the defect in the WL sample which is further investigated in detail by SEM. After transient heat load experiments, network of micro and macro cracks observed in WL samples. Maximum width of crack measured was 14.89 µm. Surface profilometry conducted at the variuos locations i.e., at exposed surface, at crack point and at un-exposed area. Significant variation in surface roughness is observed in WL sample. Future work will be focused on damage studies of W & WL material with different heat load conditions related to ITER like Divetor plasma facing components.
o Vacuum condition: 8.8 x 10-5 mbar
References o Number of cycles: 500 cycles o OFF time: 1 second (s)
th 10
1. 2. 3. 4. 5. 6.
N. Klimov, et.al. Journal of Nuclear Materials 390–391 (2009) 721–726 N. Klimov, et.al. Journal of Nuclear Materials 415 (2011) S59–S64 I.E. Garkusha, et.al. Journal of Nuclear Materials 415 (2011) S65–S69 B. Riccardi, et.al. Fusion Engineering and Design 88 (2013) 1673– 1676 Y. Kikuchi, et.al. Journal of Nuclear Materials 438 (2013) S715–S718 M. Roedig, et.al. Journal of Nuclear Materials 417 (2011) 761–764
Asia Plasma and Fusion Association (APFA), Gandhinagar – INDIA, 14-18 December 2015
