Effect of composition and milling parameters on the critical ball milling of Ti-Si-B powders

摘要

The absence of brittle phases and elevated temperature during ball milling of a powder mixture containing a large amount of ductile component can contribute to reach an excessive agglomeration denoting a critical ball milling (CBM) behavior. This work reports in the effect of composition and milling parameters on the CBM behavior of Ti-Si-B powders. High-purity elemental Ti-Si-B powder mixtures were processed in a planetary ball mill in order to prepare the Ti_6Si_2B compound and two-phase Ti+Ti_6Si_2B alloys. TiH_2 chips instead of titanium powder were used as a starting material. To avoid elevated temperature in the vials during ball milling of Ti-Si-B powders the process was interrupted after each 10min followed by air-cooling. Following, the milled powders were hot-pressed at 900 ℃ for 1 h. Samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS). Short milling times followed by air-cooling contributed to obtain a large amount of powders higher than 75% in the vials. Only Ti and TiH_2 peaks were observed in XRD patterns of Ti-Si-B and TiH_2-Si-B, respectively, suggesting that extended solid solutions were achieved. The large amount of Ti_6Si_2B and Ti+Ti_6Si_2B structures were formed during hot pressing from the mechanically alloyed Ti-Si-B and TiH_2-Si-B powders.