Preparation Of Nanocrystalline Tungsten-based Alloys And Heat Load Performance Study

The first wall materials of fusion reactors are subjected to a harsh service environment,which includes multi-field coupling of high thermal and thermal stress fields,as well as strong radiation fields.One of the key issues in developing future nuclear fusion devices is the selection of plasma-facing materials（PFMs）.In current fusion reactors,the high heat flux load of the divertor component is as high as 10-20 MW/m².Surface damage caused by heat loads during transient events like plasma disruptions and edge localized modes will significantly shorten the service life of components facing the plasma.Tungsten（W）is considered the most promising candidate for PFMs due to its excellent properties,such as high melting point,high strength,high sputtering threshold,low thermal expansion coefficient,and low retention of deuterium and tritium.In recent years,it has been found that nanocrystalline tungsten alloys have better strength,hardness,and radiation resistance than pure tungsten.Firstly,Ti was solubilized into the W matrix using high-energy ball milling,which achieved the goal of uniformly mixing the powder and refining the particle size.Subsequently,the discharge plasma sintering（SPS）method was used to precipitate Ti elements,anchor the grain boundaries,inhibit the growth of W grains during sintering,and disperse carbides throughout the W matrix.Using this method,we prepared a W-based alloy,W-3.2wt.%Ti-0.5wt.%ZrC（referred to as W-Ti-ZrC in this article）,with a dual-nanocrystalline structure（nanoscale second phase and nanoscale W grains）,and characterized its microstructure.The average size of the nanoscale second phase particles in the W grains was 5.6 nm.Combined analysis of TEM images and XRD full-profile fitting reveals that the high-energy ball milling process caused Ti and Zr elements to be solubilized into the W matrix.The low-temperature densification sintering by SPS method precipitated extremely fine nanoscale second-phase particles and synergistically refined the W grains.Nanoscale Ti particles on the W grain boundaries existed in the form of elemental Ti or Ti oxides,anchoring the grain boundaries and suppressing grain growth.Ti and Zr within the W grains can combine with the impurity O elements at the grain boundaries to form Ti O₂and Zr O₂,thereby reducing the segregation of impurity O at the grain boundaries and purifyin 0020g and strengthening the grain boundaries.Secondly,to evaluate the steady-state thermal load resistance of the nanocrystalline W-Ti-ZrC alloy,we used SPS to optimize the sintering process and prepared five different particle-sized（65 nm,85 nm,640 nm,960 nm,2130 nm）W alloys.We subjected each sample to 50 cycles of steady-state thermal load,which absorbed 10 MW/m²,15 MW/m²,and20 MW/m²power densities（APD）,respectively.We observed the surface morphology of the samples in two dimensions and the synaptic structure and roughness of the sample surface in three dimensions.It was found that the precipitation of Ti was the main cause of the surface morphology changes,and the nanocrystalline structure had a smaller increase in surface roughness after heating,which can better withstand steady-state thermal shock.The preparation strategy of solid solution followed by precipitation employed in this paper has provided a universal process for developing nanoscale second phase refractory alloys,which was applied to W alloys.Mechanical property and microstructure analyses have shown that the dual-phase nanocrystalline W-Ti-ZrC alloy exhibits extremely high hardness（～1714 HV）and strength（～6 GPa）,which can be attributed to the synergistic effect of uniformly dispersed second phase particles and nanoscale W grains.This provides useful guidance for the development of high-performance tungsten-base materials for plasma-facing first walls.