纯钨高压扭转组织与性能的微观尺度分析

Microstructure Evolution and Micro-mechanical Properties of Pure Tungsten During High Pressure Torsion

采用高压扭转技术在550℃、1.5 GPa压力下成功制得具有细晶组织的难熔金属钨,借助EBSD技术研究了高压扭转变形组织晶粒尺寸、晶界角度以及晶粒取向的演化规律,结合纳米压痕实验结果,分析了应变对工业烧结纯钨微观力学性能的影响机理。结果表明,高压扭转后材料内部微孔隙有效闭合,组织细化显著,大角度晶界含量快速升高。在应变较低时出现较为明显的沿<101>方向的择优取向;随着应变的增加,择优取向消失,组织趋于均匀。应变较高(扭转5圈)时在三叉晶界处出现了细小的动态再结晶晶粒。高压扭转变形引起的孔隙闭合、晶粒细化、晶格畸变、位错密度增加和大角度晶界形成,导致屈服强度和纳米硬度随变形量的增大而不断提高;而在致密度、残余内应力和高密度位错的共同作用下,变形试样的弹性模量显著高于工业烧结纯钨,但随着应变量的增大略有降低。

Near-equiaxed fine grains with the average grain size of 1.21 μm of pure tungsten were fabricated via high pressure torsion(HPT) at 550 °C under 1.5 GPa. The influence of HPT processing with various turning numbers on microstructure and micro-mechanical properties of sintered commercially pure tungsten was investigated by EBSD and nano-indentation experiments. It is found that the pores in the material are closed effectively, the grains are refined significantly and the ratio of high angle boundary increases rapidly after HPT processing. Moreover, when the strain is relatively low(at the turning number of 1), there is a preferred grain orientation along <101>, which weakens to disappear with the strain increasing;when the strain is high(at the turning number of5), some small dynamic recrystallites are generated at grain boundary. In addition, the nanohardness and yield strength increase obviously as the strain increases, which is due to pores closure, grain refinement, lattice distortion, dislocation density increase and high angle grain boundary formation;the combination of relative density, residual stress and high density dislocation, makes the elastic modulus of HPT-processed samples higher than that of sintered commercially pure tungsten, but it decreases slightly with the strain increasing during the processing.