纯W高压扭转显微组织演化过程TEM分析

TEM Analysis of Microstructure Evolution Process of Pure Tungsten Under High Pressure Torsion

在相对较低温度下完成了纯W不同扭转圈数高压扭转实验,通过EBSD、TEM及HRTEM观察了纯W高压扭转过程中的显微组织形貌及微观结构。结果表明,随着等效应变增大,纯W材料显著细化,位错密度增加,非平衡晶界增多。高压扭转过程中小角度晶界向大角度晶界转化现象明显,且位错结构逐渐转移至晶界,细小晶粒内部无明显缺陷。当等效应变增大至5.5时,由于部分晶粒尺寸与位错平均自由程相近,晶粒变形方式由晶内滑移向晶界滑移转变。

Refractory metal tungsten has wide applications in many fields such as aerospace, national defense, military and nuclear industry due to its excellent comprehensive mechanical properties. As the demand for high-performance materials in the new era is increasing, existing materials cannot meet the performance requirements under extreme conditions. The high pressure torsion(HPT) process can produce severe shear deformation and densify the material effectively, leading to ultrafine-grain structure with non-equilibrium grain boundaries and having a significant effect on improving the overall performance of pure tungsten materials. HPT process is used to prepare an ultrafine-grain material with excellent comprehensive performance, which can broaden the application field of refractory metal tungsten and promote the engineering application of high-performance materials. The HPT experiment was carried out on commercial pure tungsten at a relatively low temperature, and the microstructure evolution during HPT processing at various turning numbers has been investigated by means of EBSD, TEM and HRTEM.It was found that with the strain increasing, the grains were refined significantly, dislocation density and the ratio of non-equilibrium grain boundary increased obviously. Moreover, it was transparent that the low angle grain boundary transform into high angle grain boundary during HPT processing. At the same time,the dislocation structure moved to grain boundary gradually so that there was no obvious defect in fined grains. When the equivalent strain increased to 5.5, the deformation mode of grains transformed from intracrystalline sliding to grain boundary sliding, because the size of some grains was close to the mean free path of dislocation.