Experimental Study On Thermal Fatigue And Plasma Irradiation Of Tungsten Materials

Magnetic confinement fusion what the most likely way to achieve controlled thermonuclear fusion is the most important way to solve human energy problems in the future.An important task in the field of fusion research is to find and study the Plasma-facing materials?PFMs?with excellent properties,including the first wall material and the filter material,and the processing of high performance Plasma-facing materials components.Tungsten?W?is considered to be the most likely plasma facing material in future fusion reactor due to its excellent performance.As a PFMs in a fusion device,tungsten materials are tested by high thermal shock and high dose of neutron and deuterium and helium plasma.The thermal fatigue damage of the tungsten surface and the radiation damage caused by high dose irradiation under high heat flux affect the stability of the plasma and the safety of the device,and even lead to the failure of the plasma material.Therefore,it is of great scientific significance to study the damage behavior of tungsten materials in thermal load and plasma irradiation.This paper improves the quantitative analysis method of thermal fatigue crack damage,and provides a basis for the life evaluation of tungsten oriented plasma materials.To studied the thermal fatigue and D radiation properties of tungsten PFM,the thermal fatigue and deuterium irradiation experiments of tungsten materials were carried out by electron beam equipment and linear plasma generator.In addition,two new ideas of PFM improvement are proposed,which are stacked structure and surface"gas channel",and the experimental results are tested to improve the thermal fatigue and radiation performance.In this paper,the quantitative analysis method of thermal fatigue damage is improved on the basis of the existing general thermal fatigue classification evaluation method?semi-quantitative evaluation?.The quantitative evaluation parameters,such as the surface density,line density and the average width of the crack surface are proposed.The computer software is used to process the scanning electron microscope?SEM?and mark the crack area.The surface and line density and the average width of the cracks can be calculated.Thus the objectivity and the quantitation of the evaluation of the thermal fatigue damage are greatly improved.The TD/RD tungsten samples were recycled for 500,1000,1500 and 2000 times at 36 MW/m² power density by electron beam equipment,and the surface cracks were quantitatively analyzed.The results show that cracks on the surface of the material will form a vicious circle with the increase of cycle times,and the network cracks will expand into super large cracks.Because of high grain boundary density,RD tungsten samples with vertical rolling direction show better thermal fatigue resistance.The expansion of cracks in length direction and the extension of width direction depend on each other.For different rolling directions,the preferred direction of crack propagation is different.For RD tungsten sample,crack first extends on length,while TD tungsten sample preferentially expands on width.A laminated structure made of copper foil with different thickness is put forward and assembled into a combined sample with copper block system.The samples were scanned for 3000 times at the same electron beam power density 28MW/m².The experimental results show that the surface of laminated structure is subjected to uniaxial stress,and the cracks produced after thermal fatigue are more thinner and more perpendicular to the direction of foil.By quantitative analysis of the damage degree of surface cracks,it is found that the relative surface density,the density and width of the main crack lines are far lower than that of the copper bulk.The smaller the thickness of copper foil is,the more compact the surface structure is,and the stronger the thermal fatigue cracking performance is.To some extent,the surface of laminated structure can inhibit the initiation and propagation of cracks,and the thermal fatigue resistance is better.By using a linear plasma generator,the TD/RD tungsten are irradiated by three radiation doses of D under 50 eV plasma energy and¹×10 ²² ion/m ²s beam density.The experimental results show that the deuterated bubbles formed on the surface of tungsten are mainly round bubbles under the irradiation of D.With the increase of dosage,the size and density of deuterium bubble increased gradually,and the deuterium bubble showed a multi-layer structure.The probability of producing flat bubbles increased obviously,and the dependence of the bubble on grain orientation gradually weakened.The RD tungsten in parallel rolling direction showed better anti-radiation foaming performance,and the foaming density at low,medium or high radiation dose was far less than that of TD tungsten.Under low irradiation,the deuterium bubble on the surface of RD tungsten is smaller,but the growth rate of the bubbles is larger.So that,the size of the bubbles on the surface of RD tungsten near and beyond the TD tungsten sample.In addition,the surface of RD tungsten,TD tungsten and recrystallized tungsten materials were formed by FIB groove,and the D plasma irradiation experiment was carried out.The results show that the bubble density of the three different tungsten samples is obviously lower than that of other regions after irradiation.And the slot scheme can form the"gas channel"on the surface,what inhibit the retention of the gas on the surface to a certain extent,reduce the surface blister and improve the radiation resistance of the plasma.