Effect Of Test Method And Recrystallization On Ductile-brittle Transition Temperature Of Rolled Pure Tungsten

Tungsten(W)is considered as the first choice of plasma facing materials(PFM)in the fusion devices.Tungsten has excellent properties such as high melting point,high thermal conductivity,low sputtering rate,low fuel retention rate and low neutron activation,however it still has cracking problem in use.The researches on cracking behavior of tungsten material have indicated that the brittleness of tungsten material is the main cause of cracking when the temperature is lower than the ductile-brittle transition temperature(DBTT)during the heat cycles.In this paper,aimming at the crack problem of rolled tungsten material,starting from the test method and combining with the heat treatment process,the influence factors of DBTT are deeply studied,which provides some data support for the application of tungsten material in the future fusion reactor.As one of the key performance parameters of tungsten,in the literatures,a variety of test methods are used to obtain DBTT of tungsten,such as tensile test,impact test,bending test,fracture test,microhardness,etc.,but the DBTT measurement values obtained by different test methods can vary by several hundred degrees.In order to evaluate the performance of tungsten in fusion equipment,the four point bending test(4PBT)method was used to measure and analyze the DBTT of tungsten.DBTT of commercial rolled pure tungsten was obtained based on the analysis of strain rate and strength variation with temperature in four-point bending process.The results show that the DBTT values of industrial rolled pure tungsten measured by the standard 4PBT are less than 150?,which is lower than those measured by the tensile test and impact test of the same material.Then,the loading rate dependence of different DBTT test methods was confirmed by comparing the results of 4PBT and tensile test with different loading rates,and the reasons for the influence of test methods on DBTT measurement were analyzed and discussed.In addition to the performance evaluation of rolled pure tungsten as plasma-facing material(PFM)in fusion reactor,the increase of DBTT due to brittleness induced by irradiation and recrystallization is also a problem in the life evaluation of tungsten as PFM.The effect of recrystallization on DBTT is still controversial.Most studies suggest that DBTT increases after recrystallization,while some studies show that DBTT remains unchanged or decreases after recrystallization.In this paper,the DBTT change process of the samples in different directions relative to rolling with different recrystallization degree was studied by designed experiments.Through SEM observation,EBSD texture and dislocation analysis,the concrete mechanism of recrystallization effect on DBTT of rolled pure tungsten was further explored.The systematic study in this paper improves our understanding of the process that DBTT of tungsten material affected by different factors,provides an experimental basis for the performance evaluation and life evaluation of tungsten material.