Microstructures,Thermal and Mechanical Properties of Pure Tungsten—A Comparison Between Selective Laser Melting and Hot Rolling

A comparative study on the influence of different manufacturing methods(selective laser melting and hot rolling)on the microstructure,mechanical and thermal behaviours of tungsten(W)was presented for the first time.The results indicated that the selective laser melting(SLM)W exhibited a finer grain sizes,a lower strength ductility,hardness and thermal conductivity compared to hot-rolled W.The main reason for this result was that the laser underwent rapid heating and cooling when it was used to melt W powder with high energy density,resulting in large internal stress in the sample after manufacturing.Subsequently,the internal stress was released,leading to the generation of microcracks at the grain boundaries,thereby affecting the performance of SLM W samples.In addition,the higher fraction of high-angle grain boundaries(HAGBs)of SLM W was found to be the key factor for intrinsic brittleness.Because the HAGBs are the preferred crack paths,which could promote crack propagation and decrease fracture energy.

Microstructural evolution and thermal fatigue damage mechanism of second-phase dispersion strengthened tungsten composites under repetitive thermal loads

In a fusion reactor,plasma-facing tungsten(W)materials inevitably suffer severe thermal shock,and the performance of W materials under repetitive high heat loads is one of the key concerns for long-term stable operation of the reactor.In this work,the microstructural evolution and thermal fatigue resistance of two representative W-0.5 wt.%ZrC(WZC)and W-1.0 wt.% Y_(2)O_(3)(WYO)composites were investigated under cyclic heat loads.Due to the intrinsic properties of ZrC and Y_(2)O_(3)particles such as coefficients of thermal expansion,particle size and distributions in W grains,the WZC composite exhibited a better thermal shock resistance than WYO.After thermal loads with the absorbed power density(APD)≥22 MW/m^(2),WYO showed obvious grain growth,Y_(2)O_(3)particles shedding and degradation of mechanical properties.While,in the case of WZC,these damage behaviors only occurred when APD≥25 MW/m^(2).Furthermore,an interesting crack mechanism in W composites was revealed due to interface debonding and progressive shedding of second-phase particles from the W matrix.The microstructures and tensile properties of the thermally loaded WZC and WYO specimens were also investigated and the correlations between the microstructure evolution and performance degradation are demonstrated.The results are useful for evaluating the thermal fatigue resistance of oxide/carbide dispersion strengthened W composites and their application in future fusion reactors.

The thermal stability of dispersion-strengthened tungsten as plasma-facing materials:a short review

One key challenge for the development of fusion energy is plasma-facing materials.Tungsten-based materials are promising candidates for plasma-facing components(PFCs)in the magnetic confinement nuclear fusion reactors because of their high melt temperature,high-thermal conductivity,high-thermal load resistance,low tritium retention,and low sputtering yield.In fusion reactors,PFCs are exposed to high-thermal flux,because there are some transient events such as plasma disruptions,edge-localized modes,and vertical displacement events(VDEs).Especially,in VDEs,a heat flux of 10-100 MW m−2 with duration of milliseconds-to-several seconds can induce recrystallization and then change the microstructure of tungsten-based plasma-facing materials,leading to instability of microstructures.Then,a significant degradation of material properties is caused such as a reduction of mechanical strength and fracture toughness,a rise in the ductile-to-brittle-transition tempera-ture well,and decrease of irradiation/high-thermal load resistance.Therefore,many efforts were devoted to improve the thermal stability of tungsten-based materials as high as possible,such as oxide dispersion strengthening,carbide dispersion strengthening,and K bubbles dispersion strengthening.Here,the thermal stabilities of various dispersion-strengthened tungsten materials are reviewed by evaluating their recrystallization temperature and the corresponding hardness evolutions.In addition,the possible development trends are proposed.

Microstructure and mechanical properties of tungsten composite reinforced by fibre network

In this paper the tungsten-fibre-net-reinforced tungsten composites were produced by spark plasma sintering （SPS） using fine W powders and commercial tungsten fibres. The relative density of the samples is above 95%. It was found that the recrystallization area in the fibres became bigger with increasing sintering temperature and pressure. The tungsten grains of fibres kept stable when sintered at 1350℃/16 kN while grown up when sintered at 1800℃/16 kN. The composite sintered at 1350℃/16 kN have a Vickers-hardness of -610 HV, about 2 times that of the 1800℃/16 kN sintered one. Tensile tests imply that the temperature at which the composites （1350℃/16 kN） begin to exhibit plastic deformation is about 200℃-250℃, which is 400℃ lower than that of SPSed pure W. The tensile fracture surfaces show that the increasing fracture ductility comes from pull-out, interface debonding and fracture of fibres.