Effects Of Deformation Ratio And Annealing Temperature On The Recrystallization Behavior Of Pure Tungsten

Tungsten-based materials are considered to be one of the candidate for plasma-facing materials(PFMs,such as the first wall and diverter material)in fusion reactors,which have to withstand high temperatures during service.Elevated temperature may alter microstructure of the material by recovery,recrystallization and grain growth.Also,it may cause degradation in material properties as a loss in mechanical strength and embrittlement.This will not only affect the service life of the material,but also affect the service safety of the plasma device.Therefore,it is of great scientific value and engineering significance to study the damage behavior of pure tungsten under high temperatures.In this research,isothermal annealing process are main used to simulate the high temperature environments in the reactor.The mechanical properties and microstructure evolution of pure tungsten at high temperature were studied and the service life was predicted.The study of the mechanical properties of pure tungsten after annealing shows that the recrystallization temperature decreases with the increased rolling ratio.The recrystallization temperatures of pure tungsten subjected to 50%,67% and 90% thickness reduction(W50,W67 and W90)are about 1307 ?,1130 ? and 1072 ?,respectively.As the amount of deformation increases,the driving force of recovery becomes larger,recovery coefficient also becomes bigger,and the recovery period will be shorter.During the isothermal annealing process,micro-hardness decreases monotonically and recrystallization volume fraction increases monotonously.With the higher temperature and the increasing deformation,recrystallization process occurs faster.The recrystallization kinetics of W50,W67 and W90 were calculated to be 478 KJ / mol,496 KJ / mol and 447 KJ / mol by using the classical JMAK equation.W50,W67 and W90 were predicted to have a service life of 172.7 years,72.3 years and 8.5 years at 900 ?,respectively,indicating that W50 has the longest service life.In addition,the microstructural evolution of pure tungsten under isothermal annealing process shows that the recrystallization grain size increases with the increased annealing temperature and the recrystallized grain size decreases with the enlarged rolling ratio.The grain arrangement of as-received rolled plates has a great effect on the recrystallization grain distribution and the recrystallized texture can partially inherit the orientation of the rolling texture.The size of the original grains affects the size of the recrystallized grains.The average grain size of rolled plates reduces with the increased of thickness reduction and the microstructure will be more uniform.Thus,the totally amount of the dislocations,the nuclei and the recrystallized grains increase,which will introduce smaller recrystallized equiaxed grains.XRD indicates that there is a strong(110)basis texture in the process of RD/ND surface deformation of 90% rolled plate.During isothermal annealing at 1350 ?,the texture strength of(110)matrix weakened first and then increased a little.The results of EBSD show that a large number of low-angle grain boundary will transition to high-angle grain boundary during the recrystallization annealing process.The boundary orientation of the fully recrystallized grains satisfies random distribution.