Co-authors​ :

 Burçak BOZTEMUR (TURKEY), Yue XU , Laima LUO , Mustafa Lütfi ÖVEÇOĞLU , Duygu AĞAOĞULLARI  

Tungsten (W) and its alloys are considered to the most promising plasma-facing materials (PFMs) in divertor components due to their high melting point, high strength at elevated temperatures, high elastic modulus, low thermal expansion, high sputtering threshold, and high resistance to neutron damage. However, the brittleness, severe plastic deformation, and crack growth were observed against helium irradiation. To overcome the severe problems, some elements are reinforced to the W. The rare-earth borides are known as an advanced ceramic material has a high melting point, high hardness, high thermal stability, low electronic work function, low thermal expansion coefficient, high neutron absorbability and low volatility. To enhance W properties, the high purity and nanoscale rare-earth boride (CeB6, NdB6, and ErB4) powders were produced with mechanochemical synthesis (MCS) in this study. The MCS process was conducted on 5 h at 920 rpm, and the purification was done with 4 M HCl leaching. These powders were reinforced as 2 wt.% to the pre-alloyed 99 wt.% W and 1 wt.% Ni (W1Ni) that is milled for 6 h at 800 rpm. The X-ray diffraction (XRD) method was used for the phase characterization of composite powders. According to the results, four main W peaks were obtained with a small amount of WC impurity from balls and vials. Then, the density and average particle size of composite powders were measured. In addition, the particulate morphology, size, and distribution were determined with the scanning electron microscope (SEM) by energy dispersive spectroscopy (EDS). The composite powders were compacted with hydraulic pressing (480 MPa, 1 min) and cold isostatic pressing (390 MPa, 1 min). Then, the pressureless sintering (PS, 1400 C for 1 h) was used for the activated sintering. Based on the XRD analysis, the same peaks were determined without impurity. The densities of PS’ed composites were measured with Archimedes’ principle. The microstructural analysis was examined by SEM/EDS. Three different phases as grey, black, and white were determined for the composites. For the Vickers microhardness of PS’ed 2 wt.% CeB6, NdB6, and ErB4 particulates reinforced W1Ni composites were measured as 6.79, 6.36, and 6.53 GPa, relatively. The wear volume loss of W1Ni-2 wt.% CeB6, NdB6, and ErB4 composites were measured as 0.99, 1.68, and 3.17×10-4 mm3, respectively. Furthermore, these results were supported by the wear rates and wear friction coefficient. The PS’ed composites were exposed to He+ ions at the Hefei University of Technology (HFUT). Some defects and vacancies because of helium ions caused the right shifting of XRD. Also, the microhardness of irradiated composites was increased after irradiation. The best results including higher hardness, lower wear volume and less deformation were obtained with CeB6 reinforcement. The mechanical and irradiation behavior of tungsten were investigated with this study.