Rhenium had been widely used in nuclear energy, aerospace, semiconductor, medical and chemical industries due to its excellent thermal shock resistance and corrosion resistance. Pure rhenium products were usually made by powder metallurgy method, then further deformed to obtain pure rhenium products with required properties and sizes. When the rhenium powder was pressed, the morphology and particle size distribution of rhenium powder would have an important impact on the sintering density of the billet, and then affect the subsequent deformation processing and product performance. Therefore, it was of great significance to analyze and study the effect of powder morphology on the density of pure rhenium billets through the proportion of rhenium powder and particle size distribution and sintering experiments. Three kinds of powders were treated in batch, and five kinds of powder samples were obtained. Pure rhenium powder was pressed into 80 mm × 80 mm slab and sintered at 2350 ℃. The samples were observed by JSM-6380LV scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) with ZeissEVO-18 electron microscope. D10 was the maximum particle size corresponding to 10% of the particles in rhenium powder, D50 was the maximum particle size corresponding to 50% of the particles, also known as average particle size, and D90 was the maximum particle size corresponding to 90% of the particles. D50 of conventional powder was the largest, the particle size of mixed powder with spherical rhenium powder decreased gradually, and the particle size of ultrafine rhenium powder was the smallest. For rhenium powders with the same morphology, the ratios of D50/D10 and D90/D10 of No.1 and No.2 powders were very similar, and the sintering densities of both powders were more than 92% (> 19 g•cm-3). The particle size ratio of No.4 powder was close to that of No.1 and No.2 powders, but the density value was smaller. It could be seen that the particle morphology played an important role in the sintering process for mixed rhenium powder. The irregularity of powder shape led to the increase of bonding strength between particles. There were some ultrafine particles in No.3 powder, and the fine particles were evenly distributed among the large particles. High density could be obtained by pressing sintering. No. 4 and No. 5 samples contained spherical rhenium powder, the spherical rhenium powder particles formed a skeleton structure when pressed, and large holes were formed among the skeletons, which was easy to produce arch bridge effect. The irregular powder was not easy to flow to fill these holes, so the density after sintering was only 87%, which was lower than 90% of that of No. 1 and No. 2 powders. By observing the fracture surface of rhenium plate, it could be seen that there were obvious cavities. Obvious pits formed by grain boundary and particle shedding could be seen, and there was a small part of grain tearing morphology, which indicated that the fracture of pure rhenium was mainly grain cleavage, supplemented by a small amount of trans granular fracture. The density of sintered billet prepared by conventional powder was 19.5 g•cm-3, and the density was 92.8%. The tensile strength of sintered pure rhenium at room temperature was only 628 MPa, far less than 1002 MPa, and the elongation of sintered pure rhenium was only 10%, which was lower than the value in literature. The results showed that the fracture morphology of the sintered billet was similar after drawing at 1200 and 1600 ℃. Round or regular holes could be found, which were closed shrinkage holes in the sintered billet. The results showed that the grain size of rhenium plate did not change after drawing at 1200 ℃, and there were a lot of tearing traces and a small amount of grain cleavage. Further increasing the temperature to 1600 ℃, the grain size did not change obviously, and the grain cleavage phenomenon increased, which also corresponded to the change of mechanical properties. Compared with the better fluidity of tungsten powder and molybdenum powder, rhenium powder showed different characteristics. From the sintering experiment of pure rhenium powder, following conclusions could be obtained: the conventional rhenium powder had a wide range of particle size and diverse morphologies, and the sintering density could reach more than 92%; the ultra-fine rhenium powder had a flaky morphology, the sintering density could reach more than 90%, but it was lower than that of the conventional rhenium powder, which might relat to the poor particle size distribution and particle mobility; spherical rhenium powder was easy to form framework structure during compaction, and the powder particles with irregular morphology were not easy to move to fill the gaps between the frameworks, which affected the increase of density; increasing sintering temperature did not change the grain size of pure rhenium, but the cleavage phenomenon increased. © Editorial Office of Chinese Journal of Rare Metals. All right reserved.
