دکتر مریم یوسفی

The functional graded Al/Al-Cu-Cr composite was developed by horizontal centrifugal casting method and the effect of mold speed on the microstructure and hardness was investigated. The microstructure assessment and identification of the resulting phases was performed using X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) equipped with an Energy Dispersive X-Ray Spectroscopy (EDS). The results showed that ternary in-situ Al/Al-Cu-Cr composite microstructure was consisted of four phases α-Al, Al2Cu, θCr(Al7Cr) and ζ-Al-Cr-Cu. The centrifugal force caused the separation and movement of the intermetallic particles containing chromium (θCr(Al7Cr) and ζ-Al-Cr-Cu) toward the outer region of the composites with a decreasing trend to the middle region. The Al2Cu particles distributed toward the inner region of the specimens and were evenly distributed from the inner region to the middle region. As the mold rotation speed increased, the observed separation gradient increased so that the maximum area fraction of intermetallic particles in the outer region increased from 17% at 600 rpm to 36% at 1800 rpm. The results showed that the in-situ Al/Al-Cu-Cr composite has a higher hardness than the binary Al/Al-Cr composite at the same conditions. So that an increment of 80 percent in hardness was observed for the Al/Al-Cu-Cr composite compared to the Al/Al-Cr composite in their outermost region. As the rotational speed increased from 600 to 1800 rpm, the maximum amount of hardness which was associated with the outermost region of the centrifugally cast Al/Al-Cu-Cr composite increased from 51 to 76 Brinell.

Fe-Co alloys have unique magnetic applications. Fe50Co50 alloy has the highest saturation magnetization value among Fe-Co alloys. Moreover, the introduction of Si into Fe can result in a decrease of magnetic anisotropy. In this study, in order to utilize combined advantages of Si and Co, the effect of adding 10 and 20 at.% Si on the microstructural and magnetic properties of Fe65Co35 alloy was investigated. For this purpose, initial powder mixtures with specific compositions were milled by means of planetary ball mill for different milling times. Microstructural properties and morphology of the obtained powders were analyzed by X-ray diffraction analysis (XRD) and scanning electron microscope (SEM). Also, magnetic properties of the samples were determined by means of vibration sample magnetometer (VSM). The results showed that the crystallite size was finer and more uniform and lattice strain was decreased slightly for longer milling times. Observations indicated that the addition of Si to the alloys leads to finer particles. The results also showed that increasing the Si content increases the reduction rate of lattice parameter and coercivity.