METALLURGICAL ENGINEERING
Year:2019 | Volume:21 | Issue:4 (72)|Papers Count:7

In this study، the effect of zinc on microstructure and solidification characteristics of super high strength Al-Zn-Mg-Cu has been investigated. The solidification studies were performed using cooling curve thermal analysis. This method represents quick and accurate results of solidification path of an alloy. The microstructure studies showed increment in the amounts of zinc increases the dendrite arm spacing (DAS)، fraction of second phases and eutectic structure and results in a coarse dendrite structure. However، the zinc content did not affect the present phases in this alloying system. Thermal analysis evaluations revealed decrease in nucleation temperature with zinc addition. The formation of Al13Fe4 phase was observed using by cooling curve. The solidification range in the presence of 8wt. % of zinc was 175 ° C although the adding of zinc up to 25 wt. % increased it to 190 ° C. Cooling curves represented the increase of the fraction of eutectic structure which was in accordance with image analysis results. The addition of zinc resulted in the decrease of the solidified fraction at dendrite coherency point from 0. 32 to 0. 1 which matched by increment in porosity fraction from 0. 09 to 0. 32.

Ilmenite can be upgraded through pre-reduction of pellets of ilmenite with the aim of reduction of iron oxides to metallic iron, and subsequent smelting of the pellets to obtain a high-titania slag. In this research, the effect of parameters such as rotation speed and rotation angle in a disk-pelletizer as well as the amounts of moisture and binder in the pellets on the pelletization process was studied. The optimum conditions to obtain pellets with required physical and mechanical properties were determined. 1-5% bentonite and a mixture of bentonite-Fundo cement were used as binder. Drop number and crushing strength standard tests were conducted on green and dry pellets. A slope of 40° , rotation speed of 30 rpm and pelletizing time of 60min yielded the highest pelletizing efficiency for the disk-pelletizer. The optimum amount of moisture was determined to be 9wt%. It was found out that an increase in the percentage of bentonite showed increasing-decreasing effect on strength and drop number, the optimum amount of bentonite addition being 3-4wt%. The use of mixtures of Fundo-bentonite in the pellets had an increasing effect on strength, but athigher temperatures the strength of pellets containing mixtures of Fundo-bentonite showed a decrease in comparison with that of the pellets containing only bentonite.

In recent decades، there has been considerable interest in magnetic nanoparticles study field، which is an applicable، high، productive، effective since it can be utilized as an agent for the wide bio، experimental، scientific and industrial applications. As the wide range of application ofsuperparamagnetism nano Fe3 O4، especially in bio fields، Magnetite and Functionalized magnetic nanoparticles composed of Fe3 O4 particles stabilised by Silane derivations prepared by the co-precipitation method. For characterization of core-shell crystallographic structure of synthesized magnetic nanoparticles، X-ray diffractometer used. Produced MNPs morphology andtheir size distribution observed by scanning electron microscopy. In order to confirm the modification of magnetite surface with alkyl Silane some physical techniques، including Fourier transform infrared spectroscopy، element analysis (CHNS)، and for magnetic measurement of magnetic nanoparticles (MNPs)، Vibrating Sample Magnetometer، and finally for measurement of MNPs surface’ s zeta potential and hydrodynamic diameter، zetasizer and Dynamic light Scattering used respectively. Results of referred techniques indicated that all the core-shell MNPs synthesized successfully and major step of functionalization of MNPs well have done.

In this research, Ni2AlSi intermetallic compound was synthesized by mechanical alloying and its formation mechanism was compared with NiAl intermetallic compound during mechanical alloying. For this purpose, Ni50Al50 and Ni50Al25Si25 powder mixtures were mechanically alloyed for 30 h. Phase, microstructural and morphological evolutions of the powder mixtures were studied by X-ray diffraction and scanning electron microscope. Also, thermal behavior of the powders was investigated by differential thermal analysis. It was found that NiAl and Ni2AlSi nanocrystalline intermetallic compounds were successfully synthesized after 30 h of mechanical alloying. The reaction pathway of Ni50Al50 powder mixture was direct reaction between Ni and Al elemental powders to produce NiAl intermetallic compound without any solid solution formation or intermediate phase during mechanical alloying. Also, during mechanical alloying of Ni50Al25Si25 powder mixture, first NiAl intermetallic compound formed. In continue, with dissolution of Si into NiAl lattice, (Ni, Si)Al intermetallic compound formed. Finally, with further mechanical alloying, (Ni, Si)Al phase transformed to ordered Ni2AlSi intermetallic compound (super lattice structure).

Microstructural evolution and mechanical properties of in-situ Al5083 composites with 1 and 5 volume percent of TiB2 reinforcement particles were investigated. It was revealed that hot extrusion process results in a uniform, more homogeneous and less clustered structure of TiB2 particles compared with the as-cast structures. Scanning electron microscopy showed that TiB2 particlesin the Al5083-1 vol% TiB2 composite have a nearlyequiaxed morphology and round shape with an average size of ~ 0. 5 μ m. While, the morphology of TiB2 particlesin Al5083-5 vol% TiB2 composite is hexagonal with an average size of ~ 2 μ m. Also, the grain size reduces by adding TiB2 reinforcement particles to the Al5083 alloy. It was shown that the hardness, yield strength, young’ s modulus, and ultimate tensile strength of the Al5083-TiB2 composites increase with increasing TiB2 content. This can be attributed to the effect of TiB2 particles as a high hardness reinforcement phase and also the smaller grain size of the matrix which was resulted by adding the TiB2 particles.

The present research aimed to study the effects of simultaneous and separate addition of niobium oxide and chromium oxide on microstructures, the tetragonal zirconia phase stability, and sintered density of alumina-zirconia composite. The powder metallurgy method was used to prepare the powder of desired composites. To this end, alumina and zirconia powders (with a constant weight of 10%) were used as the main materials and 1% niobium oxide and 0. 6% chromium oxide powders were applied as additives. Powdered composite samples were centrally pressurized into a mold and then were sintered at 1300-1500° C. The phases were identified using the X-ray diffraction and microstructures were studied by a scanning electron microscope. Sintered density, hardness, grain size, and the number of zirconia phases were also calculated. The results showed that hardness and sintered density substantially increase with the addition of niobium oxide and chromium oxide, as the density and hardness of the sample containing 1% niobium oxide and 0. 6% chromium oxide powders were obtained 3. 72 g/cm3 and 1263 HV, respectively. The density and hardness of samples increased with the addition of niobium oxide and chromium oxide. In addition, the simultaneous addition of niobium oxide and chromium oxide to alumina-zirconia composite reduced the sintering temperature by 100° C. The alumina grain size increased with the addition of a certain weight percent of niobium oxide and chromium oxide. However, the effects of niobium oxide were greater, as it caused the growth of alumina grains and instability of the tetragonal zirconia phase.

Copper has been widely applied in many areas for its high electrical and thermal conductivities, favorable combinations of strength and ductility, and excellent resistance to corrosion. However, it’ s difficult to join commercial pure copper by conventional fusion welding processes due to the influence of oxygen, hydrogen, impurity and high thermal conductivity. To overcome these difficulties, in this study, we used a friction stir Processing Procedure and annealed and quenched raw materials. Grain sizes in base metal and stir zone were calculated by using the Digimaizer and also the phase percent was calculated by Clemex. Results show that there was no zinc evaporation happened and due to the finer microstructure of 63BA, the higher microhardness was obtained. Due to the presence of zinc element as an alloying element, α phase in single phase and α and β phase in dual phases matrix, and also the hardness of α phase in stir zones, there are many preferred places to nucleate which formed during plastic deformation and obtained fine grain microstructure. The stir zone has the dynamic crystallized grains including two phases microstructure, α , and β where the amount of α phase is 58 % and β phase is 42 % which with considering the base metal structure, the amount of β is reduced and the amount of α phase is increased.