Study On The Evolution Of Microstructure And Mechanical Property Of Rolled Pure Tungsten Served At High Temperatures

Pure tungsten is the most promising candidate material for the plasma facing materials(PFMs)because of it exerllent properties such as the highest melting point of 3695 K,good thermal conductivity and strength retention at high temperatures,low thermal expansion coefficient,and high sputtering threshold energy.Tungsten will be subjected to high heat flux loads up to 10-20 MW/m2 and giant temperature gradients.In terms of physical metallurgy,plastic deformation leads to the increase of the internal stored energy.Longterm survering under high temperatures,recovery,recrystallization and grain growth will occur in the deformed tungsten.These microstructural changes will cause degradation of the material properties,such as a loss in mechanical strength,or even embrittlement.In addition,the ductilt to brittle temperature will increase and the fracture toughness will reduce.These will not only affect the service life of the material,but also affect the 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 the present study,isothermal annealing process were mainly utilized to simulate the high temperature environments in the reactor.The mechanical properties and microstructure evolution of pure tungsten at high temperature were investigated.The the evolution of the mechanical properties of pure tungsten shows that the hardness degradation curve is divided into two stages during the isothermal annealing process.Hardness firstly decreased monotonously at a faster rate,during which recrystallization happened.Then the hardness decreases monotonously at a slower rate,which is the grain growth process.The rate of recrystallization increases with the increased deformation ratio and temperature.The rate of recrystallization of the tungsten plate with lower rolling ratio was sensitive to the temperatures.With the increase of deformation ratio,the influence of temperature on recrystallization rate became insensitive.Under deformed state,the tungsten grains are slightly elongated along the rolling direction when the deformation ratio is small,while under higher deformation ratios,the fibrosis and dynamic recrystallization are found.The effect of temperature on the grain size of W50 within fully recrystallization state is insignificant.However,the grain sizes of W67 and W90 within fully recrystallization after annealing at different temperatures decrease with the increased annealing temperatures.The grain size after complete recrystallization decreases with the increased deformation ratios and the microstructure uniformity of the annealed sheet with high deformation ratio is better than that of lower ones.When the annealing temperature is low,the completely recrystallized microstructure also contains a part of small-angle grain boundaries.When the annealing temperature increases,the distribution of grain boundary misorientation follows with the Mackenzie distribution.There exist significant differentcs in the textures of three rolled plates.The rolling texture of W50 is mainly {112} <110> and the other components are all random.The rolling texture of W67 is mainly the {111} <112> component in ?-fiber texture,the {112} <110> component in ?-texture and the rotational cubic component and the {001} <100> component in the ?-fiber texture.Compared with W50 and W67,the W90 rolling texture was mainly {112} <111> and Goss texture.The texture of W50 annealed at 1250 °C and 1300 °C inherited the rolling texture.The main texture of W67 annealed at lower and intermediate temperature is the ?-fiber texture components.The recrystallization texture of W67 after annealling at 1250 ? is between cubic texture and cubic texture.The recrystallized texture after annealing at 1300 ? is mainly cubic texture and few rotating cubic texture.When the annealing temperature is increased to 1350 ?,the recrystallization texture is totally different from the low temperature annealing,which is mainly the {111} <110> component in the ?-fiber texture.The recrystallization texture of W90 after annealing at three temperatures is quite different.The the main texture is cubic texture when annealed at 1250 ?.The recrystallized texture after annealing at 1300 ? is random.When the annealing temperature is increased to 1350 ?,the recrystallization texture is mainly the {001} <110> component in the rotating cubic texture.