Study On Synthesizing Fe_xAl_y/Al₂O₃ Nanocomposite By Mechanical Active-Spark Plasma Sintering

In recent years , iron aluminides are excellent candidates for high temperature application due to combination of their good corrosion resistance at elevated temperatures under oxidizing and sulfudizing atmospheres, low density, low cost and excellent properties of welding. However, commercialization of these intermetallics has been limited because of the low ductility exhibited at room temperature.In this paper, we used crystal refinement to improve the mechanical properties of the intermetallics. And the Al₂O₃ powder was selected to combine with Fe, Al powders. First, mechanical milling was used to get mechanical active and super-fine powders , then , the mixed powders were sintered by Spark Plasma Sintering. SEM, EDXA and XRD were used to analysis microscope structure, reaction process, crystal shape and size of sample , in the meanwhile, the samples' density, rigidity and mechanical property were tested. The paper mainly discussed the effects of sintering process of Fe-40at%Al/Al₂O₃, the course of sintering reaction, the transit of microstructure, the size of crystal and the function of Al₂O₃ in mechanical milling and sintering courses; and the effects of sintering process of Fe-28Al/Al₂O₃, the strengthen mechanism, rupture mechanism and the effects of Cr.The results shows: During the mechanical milling, if we selected a good ball-milling condition for this work: the ball to powder ratio is 13:1,the rotate speed is 170rpm. After 25 hours milling, mechanical activation, nanosizing of composite powders and intruding of strengthen phase can be realized at the same time; In addition, Al₂O₃ greatly effected the ball-milling and sintering processes. For Fe40at%Al/ Al₂O₃ composite powders, the best process parameters of sintering are: the ball-milling time is 25h, the sintering temperature is 1050℃, the sintering time is 15min,the keep time of high temperature is 5min, the heating rate is 70°C/min and a uniaxial pressure of 40MPa was applied. The results show that the average size of FeAl crystal is 127nm, the average size of Al₂O₃ crystal is 113nm, and we obtained super-fine crystal composites. For Fe28at%Al/ Al₂O₃ composite powders, the best process parameters of sintering are: the ball-milling time is 25h, the sintering temperature is 1400℃C, the sintering time is 15min, the keep time of high temperature is 5min, the heating rate is 93℃/min and a uniaxial pressure of 40MPa was applied. The results show that the density of the sample is up to 98%.