Nb-based powder was fabricated via mechanical grinding. The influence of stearic acid on the grinding process was studied. The structural evolution and morphological evolution of the milled powder were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) analysis. It is indicated that an appropriate amount of stearic acid accelerates the particle refinement process and favors the production of superfine Nb-based particles with good dispersivity and high activity. However, an inappropriate amount of stearic acid has an adverse effect on the refinement process.
A fluidized bed jet milling process was used to make micro-fine high Nb-containing TiAl alloyed powders from the chippings obtained by crushing the Ti-45Al-8.5Nb-(W,B,Y) ingot.The influences of classifier frequency on powder characteristics were investigated.The results show that the powders with controlled average particle size can be prepared on a large scale.The powders with different sizes are all dominated by γ with aminor amount of α2-Ti3Al.The particle size significantly decreases with the classifier frequency increasing.At a classifier frequency higher than 38 Hz,the average particle size of the ground powders is lower than 25μm.The powders are composed of two differ-ent sizes of particles:shaped particles and some clastic particles,and both particle sizes meet the log-normal distribution.With the classifier frequency increasing,the both sizes decrease;meanwhile,the proportion of the clastic particles gradually increases,and the size distribution span value of the ground powders increases correspondingly.
Lu, Xin Zhu, Langping Liu, Chengcheng Zhang, Lin Wu, Mao Qu, Xuanhui
A high Nb containing TiAl alloy was prepared from the pre-alloyed powder of Ti-45Al-8.5Nb-0.2B-0.2W-0.02Y (at%) by spark plasma sintering (SPS). Its high-temperature mechanical properties and compressive deformation behavior were investigated in a temperature range of 700 to 1050-C and a strain rate range of 0.002 to 0.2 s-1. The results show that the high-temperature mechanical properties of the high Nb containing TiAl alloy are sensitive to deformation temperature and strain rate, and the sensitivity to strain rate tends to rise with the deformation temperature increasing. The hot workability of the alloy is good at temperatures higher than 900-C, while fracture occurs at lower temperatures. The flow curves of the samples compressed at or above 900-C exhibit obvious flow softening after the peak stress. Un-der the deformation condition of 900-1050-C and 0.002-0.2 s-1, the interrelations of peak flow stress, strain rate, and deformation tempera-ture follow the Arrhenius' equation modified by a hyperbolic sine function with a stress exponent of 5.99 and an apparent activation energy of 441.2 kJ·mol-1.
