Preparation Of Tungsten Based Materials With High Strength And Excellent Ductility And Their Hydrogen Plasma Irradiation Behavior

Fusion energy is considered to be the ultimate energy of mankind in the future due to its clean and efficient characteristics.The development of fusion energy is greatly limited by materials,especially the first wall materials directly facing high-temperature plasma,whose service environment is extremely harsh.Tungsten material is regarded as the most promising first wall material due to its high melting point,high strength,low sputtering rate and other advantages.However,tungsten material suffers severe brittleness at low temperature,which greatly limits its application.To solve this problem,the microstructure of different scales,such as phase interface,dislocations and grain boundaries,has been regulated,and the bulk tungsten materials with high strength and excellent ductility were designed and prepared,and their hydrogen plasma irradiation behavior was studied.Firstly,for preparing high-density sintered tungsten materials with fine grain structure,we adopt the hot-press sintering technology and use the optimized two-step sintering process to fabricate sintered pure W,W-TiC and W-Y2O3 alloys at relatively low sintering temperature(1800℃).The relative density of pure W is 94.9%,and the average grain size is 13.86 μm,which is much smaller than that of commercially sintered pure W(38.6 μm).The sintering properties of tungsten were effectively improved by the addition of small amounts of TiC and Y2O3 particles,and the relative densities of the W-TiC and W-Y2O3 alloys reached about 99%,and the grain sizes were refined to 2.61 μm and 3.57 μm,respectively.Benefiting from the high density and the refined grains,the nil ductility temperature(NDT)of pure W was reduced to 300℃(300℃ lower than that of commercial W).The sintered W-TiC with an ultimate tensile strength(UTS)of 1082 MPa achieves a significant increase in the strength of the sintered W material,while the sintered W-Y2O3 combines high strength with excellent ductility(NDT<300℃,UTS=634 MPa).Secondly,on the basis of sintered pure W,the medium-temperature high-energy rate forging technology is used to give full play to the role of dynamic recovery and promote the evolution of dislocations to form sub-grain boundaries to further refine the grains.A unique multi-scale microstructure was constructed in forged pure W(HERFW),including lamellar matrix grains,with profuse interior fine sub-grains,and high density of movable dislocations.HERF-W exhibited ductile strain at room temperature with UTS up to 1354 MPa;at 100℃,the total elongation(TE)reached 4.2%and UTS was maintained at 1300 MPa,which not only achieved a low NDT compared with the reported bulk tungsten materials,but also obtained a synergistic enhancement of the low-temperature strength and ductility of the bulk pure W.Then,to further improve the low temperature strength of tungsten materials,TiC and Y2O3 particles were introduced into the tungsten matrix,and W-0.5wt.%TiC(HERF-WTC)and W-1.0wt.%Y2O3(HERF-WYO)alloys were prepared.At the same time,the effect of phase interfaces with different properties on the strength improvement of tungsten alloys was studied.Microstructural characterization revealed that the average particles size in HERF-WTC is only 29 nm,which is much smaller than that of HERF-WYO(193 nm).The fine and well-dispersed TiC particles bring more significant strengthening effect,and the strength of HERF-WTC is higher than that of HERF-WYO alloy.High-resolution characterization and simulation calculations on the TiC/W interface reveal that the stable semi-coherent interface and strong interfacial atomic bonding between TiC particles and W matrix are the most essential reasons for TiC particles to remain fine.Finally,the hydrogen plasma irradiation behavior of HERF-W,HERF-WTC,and HERF-WYO was investigated,and the deuterium(D)injection experiment at 400 K was conducted(fluence range:5 × 1023 D/m2～1 × 1026 D/m2).The results showed that a large number of large-sized blisters formed on the surface of HERF-W at the lowest fluence,but retained the least amount of total D.W alloys showed minor surface blistering,but higher D retention than HERF-W.This difference is attributed to the high density of intrinsic defects inside the W alloys,which disperse D well and inhibit the formation of surface blisters,while the low density of intrinsic defects inside HERF-W makes the injected D easily accumulate and form blisters.The microstructure modulation proposed in this paper provides a feasible path for the preparation of high-performance refractory metals,and the developed W-based materials have good application prospects in fusion reactors.