Pulse plasma sintering (PPS) is a promising method for consolidation of powder materials, allowing to obtain dense products with improved properties. In this paper, the influence of PPS parameters, in particular the electric field, on the sintering process of quasicrystalline Al–Cr–Fe powder is investigated.
The starting material was Al70Cr15Fe15 powder obtained by gas atomization. Sintering was carried out in an IPS unit at different temperatures and pressures, as well as with varying current strength. The obtained samples were analyzed using X-ray diffraction, scanning electron microscopy, and density measurements.
It has been established that the use of an electric field has a significant effect on the kinetics of sintering. A decrease in the temperature of the onset of sintering and an increase in the density of the samples are observed, all other conditions being equal. It is assumed that the electric field contributes to the acceleration of diffusion processes and the activation of the surface of the particles, which leads to more effective compaction.
In this paper, Al–Cr–Fe powders obtained by gas atomization were consolidated by spark plasma sintering (SPS). Hypotheses describing the compaction mechanisms are proposed, and the effect of the electric field is studied. It is found that the initial stage of compaction is determined by the rearrangement of particles, while the subsequent stages are controlled by the motion of dislocations. Comparison of the X-ray phase analysis data of the SPS-treated sample and the vacuum-annealed sample demonstrates that the SPS process produces a larger number of decagonal Al–Cr–Fe phases. This effect is believed to be due to a decrease in the activation energy required to form critical nuclei in the presence of an electric field.
A mechanism for compaction of Al–Cr–Fe quasicrystals during SPS is proposed, taking into account the effect of the electric field. At the initial stage, the powder is heated due to Joule heat. Then, the electric field promotes the formation of plasma discharges between particles, which leads to surface cleaning and activation of diffusion processes. At the final stage, the material is compacted due to plastic deformation and grain boundary diffusion.
IPS is an effective method for consolidating quasicrystalline Al–Cr–Fe powders. The use of an electric field allows for a reduction in the sintering temperature and an increase in the density of the resulting products. A compaction mechanism is proposed that takes into account the effect of the electric field on the sintering process.
Author: RT Li, ZL Dong, KA Khor
Institute: School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore, School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore