Fabrication And Properties Of Tantalum Carbide Dispersion Strengthened Tungsten Based Materials

W materials offer excellent high temperature strength,good compatibility with liquid metals,and high thermal conductivity,and thus has been attracting growing interest as high-temperature structural materials such as plasma facing materials(PFMs)in future fusion reactors.However,the inherent brittleness and the relatively high ductile-brittle transition temperature(DBTT)of pure tungsten need to be overcome to fulfill such applications.In order to solve these issues,we develop a powder metallurgical method to improve mechanical properties with both high strength and ductility and thermal stability.This strategy has combined the advantages of grain-boundary(GB)purifying,nanosized carbide dispersion-strengthening and plasticity deformation.A methodical and innovative powder metallurgical method is developed from boundary concepts to fabricate engineering-applied bulk W materilas with high performances.We fabricated W-0.5 TaC specimens prepared by spark plasma sintering(SPS).According to the evolution of mechanical properties and thermal conductivity,the total elongation and ultimate tensile strength(UTS)of SPSed W-0.5wt.%TaC is 40.0%and 371 MPa,respectively.0.5wt.%TaC content was chosen as the optimized composition.The DBTT value for rolled W-0.5wt.%TaC is between 200? and 250?,much lower than that of SPSed W-0.5wt.%TaC(?600?).The total elongation and UTS of rolled W-0.5wt.%TaC at 250? are 12.2%and 680 MPa,respectively.It is found that TaC reacts with impurities of oxygen in W to form Ta2O5,reducing oxygen concentration at grain boundaries and thus enhance grain boundary strength and the ductility of tungsten materials.Fine-grained W-0.5 wt.%TaC plates were produced by an optimized multi-step process,consisting of high-energy ball milling,hot press sintering and subsequent rolling process.Grain refinement induced improvement in mechanical properties is achieved with ultimate tensile strength(UTS)of 982 MPa and total elongation(TE)as large as-12.0%at 200?.UTS values are over 570 MPa at all tested temperature ranging from RT to 500? and the TE increases to?0.5%at 400?.These good mechanical properties are attributed to advanced process routes.Hydrogen atmosphere during the fabrication reduces oxygen impurity contents and then decreases the amount of submicron oxide particles.The multi-step process routes generate optimal microstructures with nanometric TaC particles uniformly distributed in the submicron subgrains interior.Nano-sized particles could hinder grain boundary migration,reduce grain growth rate and thus keep microstructure stability,improving low-temperature strength and ductility of W-TaC plates.The tantalum carbide dispersion strengthened W-1.0 wt.%TaC was fabricated reflecting a combination of high mechanical properties and high thermal shock.The observed recrystallization activation energy is-478 kJ/mol.The effect of transient thermal loads(100 shots at RT)on the as rolled and fully recrystallized W-1.0 wt.%TaC plates have been investigated by employing an electron beam test facility.The thermal shock resistance is closely related to the ductility and strength of tungsten materials.The cracking thresholds are in the range of 0.22?0.33 GW/m2 for recrystallized W-TaC and 0.33-0.44 GW/m2 for as-rolled W-TaC,respectively.The thermal shock induced cracks are related to the microstructures like second phase particles and GBs:coarse Ta2O5 and Ta-Cx-Oy particles in WTAC and weak GBs from the recrystallization and grain growth in RWTAC becoming preferential crack initiations.The optimized fabrication routes for such refractory materials offer a general pathway for manufacturing bulk dispersion-strengthened tungsten materials,providing a useful guidance for developing high-performance tungsten-based PFMs.