Microstructure and thermal stability of sintered pure tungsten processed by multiple direction compression
(School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, China)
Abstract: Multiple direction compression (MDC) was conducted on sintered pure tungsten (99.9%, mass fraction) with different reductions at 1423 K. The microstructure, microhardness and thermal stability of the MDC-processed samples were studied by X-ray diffraction (XRD), electron backscattered diffraction (EBSD) and differential scanning calorimetry (DSC) compared with those of the initial sintered tungsten. The results show that the dislocation density increases significantly with the reduction of MDC, ranging from 3.08×1014 m-2 for the initial sintered tungsten to 8.08×1014 m-2 for the tungsten after MDC with the reduction of 50%. The average grain size decreases from 83.8 to 14.7 μm and the microhardness value increases from HV0.2 417 to HV0.2 521. The recrystallization temperature for the tungsten samples processed by MDC is approximately constant at around 1600 K. The MDC of sintered tungsten results in a decrease of grain size concurrent with an increase of uniformly distributed nucleation sites, which leads to the improvement of the thermal stability.
Key words: multiple direction compression (MDC); sintered tungsten; dislocation density; mechanical properties; thermal stability