Preparation And Properties Of Rare Earth Oxides Composite Doped Ultra-fine Tungsten Matrix Composites By Wet Chemical Method

Tungsten(W)has an advanced physical and mechanical properties,such as,high energy threshold for physical sputtering,low tritium retention,high melting point of all metals,high temperature strength and good thermal conductivity,is considered to be one of the most promising candidate materials for the first wall in a future fusion power plant.However,tungsten itself still has a series of brittleness problems,such as low temperature brittleness,irradiation brittleness et al.Researchers usually introduce a single second phase into tungsten to improve the performance.Although this refines the grain size to a certain extent and improves the mechanical properties of W material,it also has some disadvantages,such as low bonding between the second phase particles and the matrix,large second phase size and so on.To further improve the performance of tungsten,this paper chose to use wet chemical method to prepare Y³⁺and La³⁺doped tungsten matrix composite precursor powder.By adjusting the doping ratio of Y³⁺and La³⁺,the submicron tungsten matrix composite powder was obtained after reduction.Then,the powders with the best properties are sintered by spark plasma to investigate the effects of sintering temperature and pressure on the microstructure and properties of the sintered body.Finally,the W-Y₂O₃-La₂O₃composite materials prepared by different processes are tested by irradiation and laser thermal shock.The main conclusions are as follows:(1)W-Y₂O₃-La₂O₃ composite powders of different components prepared by wet chemical method combined with hydrogen reduction are uniform and fine,and their particle sizes were all submicron.The second phase Y₂O₃ and La₂O₃ are evenly distributed on the W particles.The addition of La element can be solid solution with Y,so that the crystal cell of Y₂O₃ expands,and it can better match the lattice parameters of tungsten,optimize the existence state of the second phase Y₂O₃ at the grain boundary,and then improve the refining effect of the second phase Y₂O₃ on the grain.With the increase of lanthanum content,the grain size of sintered body decreases first and then increases.The microhardness and relative density increased first and then decreased.The bulk with W-0.25 wt.%(90 at.%Y₂O₃+10 at.%La₂O₃)has the best properties,the average grain size is 3.15?m,the relative density is over 99%,and the microhardness is 492 HV_0.2.The second phase size is about 50 nm,and the W(110)crystal plane forms an approximate semi-coherent interface with the Y-La-O(222)crystal plane.(2)The influence mechanism of pressure and temperature on densification is different.Temperature affects the densification by affecting the rate of atomic diffusion,and pressure promotes the formation and growth of sintering neck by affecting the contact between powders.The dispersion strengthening of the second phase is closely related to the sintering process.The moderate pressure can not only ensure the good contact between the powders,but also prevent the second phase from reducing its grain refinement due to the agglomeration and growth in the low temperature section of sintering.Appropriate temperature can not only ensure sufficient diffusion rate of atoms,improve the density of materials,but also prevent the excessive growth of grains.Through the analysis of the sintering curve and the grain size,relative density and microhardness of the sintered blocks,it is difficult to produce fine grains,high density and high hardness blocks by simply increasing the sintering pressure and sintering temperature.The optimal sintering process is as follows:the temperature rise to 800? at a heating rate of100?/min,and the heat stay at 800? for 5 min.Meanwhile,the pressure rises from the initial 14 MPa to 75 at a uniform rate within 5 min.Then,the temperature rise to 1600? at a heating rate of 100?/min and the heat is kept for 1 min.After the heat preservation,the furnace cooled to room temperature.(3)Due to the existence of a large number of pores and micron-size second phase particles in samples with pressure of 50 MPa,the existence of pores and second phase particles will increase the probability of helium ions contacting and trapping the material,thus aggravating the material damage.The surface damage of the sample at 75 MPa is the least after irradiation,which is attributed to the high density of the material and the apparent refinement of the tungsten grains due to the presence of nanoscale second phase particles.The Fuzz is not obvious on the surface of the tungsten matrix of the sample irradiated at the pressure of 100,but there is obvious sputtering phenomenon in the micron second phase.The average power density increased in the range of 0.36-0.72 GW/m²,and the surface damage of different samples showed a trend of increasing gradually.Under the same power density,compared with samples with different sintering pressures,the microstructure of samples prepared under 75 MPa pressure is the best,showing better thermal shock damage resistance.