JOURNAL OF METALLURGICAL AND MATERIALS ENGINEERING (JOURNAL OF SCHOOL OF ENGINEERING)
Year:2018 | Volume:29 | Issue:1 |Papers Count:9

The viscosity of the sample decreases with an increase in fraction of the liquid phase. Beam bending test is the technique used for measuring viscosity. In this paper, an investigation of the deflection behavior of Cu-28Zn beams at various temperatures and times ranging from 910 to 950 ° C and 0 to 90 minutes was studied. The midpoint deflection was measured by in situ bending images. It is concluded that deflection of brass beam as a function of temperature is linear and is nonlinear in the case of time. This is due to zinc evaporation that effects the chemical composition and liquid volume fraction.

In this work, one-pot synthesis of modified silica nanoparticles with long-chain alcohol 1-Octadecanol bystober method at 70  C is presented. Hydrophobicity of particles increased dramatically by increasing the amount of 1-Octadecanol up to 7 wt. %. Surface modification was completed during the first 90 minutes. Additionalreaction time had no further effect. The most possible modification was obtained when the reaction took place at pH=8. Successful surface modification was confirmed by FT-IR spectroscopy, thermogravimetric analyses and contact angle measurements. X-ray diffraction patterns indicate an amorphous structure which did not significantly change by surface modification. Transmission electron microscopy images were used to investigate the morphology and dimension of the silica particles.

The present study investigates the effect of rotational speed and dwell time on the strength of Al-5083/St-12 friction stir spot joints. The welds were made using a newly developed FSSW process in which the tool pin did not penetrate into the lower steel sheet. Rotational speeds of 900 and 1100 rpm were applied in association with the dwell times in the range of 5-15 s. Results showed that the strength was first improved and then declined with increasing the dwell time. Furthermore, stronger joints were achieved at 900 rpm compared to the rotational speed of 1100 rpm.

In the present study, plain low carbon steel with 0. 033 wt. % carbon content was subjected to severe pressure during continuous cooling from austenite region. The pressure was increased gradually and then suddenly released. As a result, a microstructure composed of 80% lath martensite and 20% ferrite was produced. Results showed that the martensite formation is not only a function of the cooling rate but also the hydrostatic pressure which effects the austenite to ferrite transformation start temperature (Ar3).

In this study, morphology, mechanical and corrosion properties of Ni-P electroless coating was investigated using different pre-treatments on the Mg-Li (MA21) alloy. The results show that adding 125 g/l chromium trioxide and 110 ml/l nitric acid to the pickling solution can increase the uniformity of the intermediate layer and reduce the porosity of the Ni-P electroless coating. The MgF2 and LiF layer uniformity leads to the increase in the number of coating nucleation sites and a fine morphology. The corrosion rate of the MA21 sample, Ni-P electroless coating sample with 125 g/l CrO3 and 110 ml/l HNO3 was 63, 87 and 4 mpy, respectively. The test results of Ni-P electroless coating adhesion with pretreatment number 2 was double that of pretreatment number 1.

This study aims to investigate the effect of holding temperature and time of semi-solid SIMA process on the microstructure and mechanical properties of aluminum alloy 2024 and to compare it with T6 heat treatment. The results of scanning electron microscopy, EDX analysis and metallographic techniques showed that an increase in holding temperature and holding time would first lead to an increase in sphericity and then a decrease is observed. This process led to an increased formation of continuous eutectic microconstituent in the grain boundaries and also more cavities. The optimum cases represented an increase of 116% in elongation and 44% in toughness, and a decrease of 3. 7% in strength and 5. 5% in hardness in comparison with T6 heat treated sample. The results indicated the positive effects of SIMA process on the mechanical properties.

In order to improve the structural and mechanical properties of Al-1050, Al/Mg composite was processed on the surface of this alloy by using friction stir processing. Structural studies showed that one pass FSP on the as-received aluminum substrate changed the grain shape from stretched grains to equiaxed. Microstructural studies by scanning electron microscope equipped with EDS spot analysis and X-ray diffraction phase analysis revealed the formation of Al3Mg2 intermetallic compound in the 4-pass FS-processed sample. Microstructural studies revealed the significant effect of number of FSP passes and using of Mg particles on the grain size of the FSP area, i. e. grain size in this area changed from 50 10 μ m in the FS-processed sample with one pass and without Mg particles to 6 2 μ m in FS-Processed sample with four passes and Mg particles. Tensile strength test showed a 70% improvement of tensile strength of the composite compared to that of the base metal.

The fabrication and characterization of bone scaffold which was produced from hydroxyapatite and polyurethane foam were investigated. Thermal and mechanical properties of the scaffolds were studied via X-ray diffraction, scanning electron microscopy, and compression test and thermogravimetry technique. Also, hardness test, three-point bending and investigation of biological behavior were employed. The fabricated scaffolds showed high compressive strength with favorable percentage of porosity. Thus, it might be concluded that the polymer foam fabrication technique can be appropriate for producing bone scaffolds. By increasing the weight percentage of hydroxyapatite from 45 to 65, the density of the scaffold increased from 1. 37 to 1. 57 g/cm3 and compressive strength increased from 0. 82 to 1. 7 MPa while the porosity decreased from 57. 8 to 34. 39.

In this paper, the production of Cu-1wt%Cr-5wt%CNT nano-composites by wet milling process at three different levels of milling energy and two different pool volumes was investigated. The structural evolution and solid solution formation were evaluated by X-ray diffraction technique. The microstructure was characterized by scanning electron microscopy. The mechanical properties were also investigated by microhardness testing. The mean crystallite size was in the range of 44-94 nm depending on pool volume of milling medium and milling energy. It was found that wet milling at higher levels of milling energy and lower pool volumes of 10 ml can be a beneficial method of producing the nano-composite with the least damage introduction on homogeneously dispersed carbon nanotubes. Maximum hardness of 88 HV was obtained under optimum conditions.