变形量对纯钨热导率及再结晶温度的影响

Effects of Deformation on the Thermal Conductivity and Recrystallization Temperature of Pure Tungsten Rods

采用粉末冶金及高温锻造工艺制备了3种规格的纯钨棒材,研究了不同变形量钨棒的微观组织、热导率及再结晶温度的差异。结果表明,随着变形量的增加,纯钨棒的相对密度和维氏硬度都呈现出先快速上升后趋于平缓的趋势,晶粒长径比逐渐增大且晶粒组织逐渐细化,最终呈现出纤维状。由于密度提升及孔隙率降低,纯钨棒的热导率及热扩散系数都随对数应变的增大有一定的提升,而当纯钨棒趋于完全致密化后,其热导率差异较小。对数应变为1.57的纯钨棒的再结晶温度最高,约为1520℃。经1450℃保温1 h退火后,对数应变0.88的纯钨棒整体晶粒组织已经明显变大,而对数应变为2.95的纯钨棒已经形成等轴晶。对数应变为2.95的纯钨棒再结晶后的晶粒组织比对数应变为0.88和1.57的要更加均匀细小。

Pure tungsten rods with three different logarithmic strains were fabricated by powder metallurgy and subsequent high temperature forging processes.The effects of deformation degrees on the microstructure,thermal conductivity and recrystallization temperature was studied.The results showed that:with the rising logarithmic strain,both relative density and Vickers hardness increased fast at first and then became stable.The aspect ratio of grains increased gradually whereas the grain size decreased,and the microstructure finally became fibrous with deformation increasing.The thermal conductivity and thermal diffusivity increased with deformation degree at first due to the improvement of densification and decrease of porosity.However,as the pure tungsten was approaching full densification,the change of thermal conductivity was minor.The rod with logarithmic strain of 1.57 had the highest recrystallization temperature of 1520℃.After annealing at 1450℃for 1 h,the whole grain structure of pure tungsten rod with logarithmic strain of 0.88 has obviously increased,even pure tungsten rods with logarithmic strain of 2.95 have formed equiaxed crystals.By comparsion,the grain structure after recrystallization for rod with logarithmic strain of 2.95 was smaller and more uniform compared to that of rod with logarithmic strain of 0.88 and 1.57.