امیر سیف الدینی

One of the most crucial factors influencing the strength and quality of steels is the presence of non-metallic inclusions. Studies demonstrated that non-metallic inclusions in industrial parts diminish their fatigue strength. On the other hand, their hardness is another influential parameter affecting the fatigue strength of steels. Therefore, this research investigated the impact of non-metallic inclusions on the fatigue strength of AISI 304 steel with three hardness of 170, 250, and 330 Vickers. This research revealed that as the hardness decreases, the fatigue strength of the part also decreases. Additionally, an examination of the failure surfaces of the parts using scanning electron microscopy (SEM) indicates that non-metallic inclusions are the root cause of fatigue failure in the samples. Finally, employing Murakami relations, parameters such as stress intensity factor and critical inclusion size were determined for steel with hardness levels of 170, 250, and 330 Vickers. The critical inclusion size for steel with hardness levels of 170, 250, and 330 Vickers was calculated as 32.7, 24.8, and 15 micrometers, respectively.

Studies show that by applying coatings with amorphous structure on surgical instruments, the biocompatibility and corrosion resistance of these instruments can be increased. One of these coatings is Zr-based metal glass thin layer coatings. Therefore, in this research, after investigating the effect of different elements on the biocompatibility and corrosion behavior of coatings, first an alloy with the chemical composition of Zr30Cu20Al10Ag10Cr10Si10Br10 was designed and a thin disk of this alloy was produced using Spark Plasma Sintering, SPS, device. Then, thin layers of the alloy produced were applied on the 316 steel substrate using a Magnetron Sputtering machine. Initial investigations showed that the production coatings have a glass structure. Next, the hydrophobicity of the coating and its corrosion behavior in two environments, NaCl solution and Simulated Body Fluid was studied. The conducted tests showed that the application of the designed coating, by reducing the surfaces energy, increased the contact angle and as a result increased the hydrophobicity of the surfaces, transformed the surface of 316 steel from hydrophilic to hydrophobic. Also, the application of this coating due to its amorphous structure increases the corrosion resistance in the two environments of sodium chloride solution and Simulated Body Fluid. Examining the corroded surfaces indicates the occurrence of pitting corrosion phenomenon for the created coatings.

In this work, the effect of Ni addition on the glass forming ability (GFA) of FeMoPCB composite alloy was investigated and the optimal amount of Ni to improve GFA was determined. So, the thermal stability of this alloy with the various percent of nickel was investigated by not only experimental methods including; differential scanning calorimetry, X-ray diffraction, optical microscope and transmission electron microscopy but also computational methods such as α، β، γ and etc. The results of XRD test, TEM showed that in the presence of 10 at.% nickel , the glass-forming ability of this alloy increased, while in the presence of lower or higher percent nickel, different crystalline phases were detected. The presence of crystalline phases was also investigated by microhardness test. Finally, it was found that the results of the computational methods regardless of the experimental results don’t have enough accurate .

In this research, the effect of heating rate on oxidation kinetics of magnesium powder particles under non-isothermal conditions was studied. For this purpose, differential thermal analysis (DTA) and thermogravimetry analysis (TGA) was done on magnesium powder particles at three heating rates of 5, 10 and 20 K min-1 up to 1000 °C under air atmosphere. Also, in order to better understand the oxidation process of magnesium powder, three temperatures were selected according to the DTA curve at a heating rate of 20 K min-1. Then, samples of magnesium powder were heated up to these three temperatures with heating rate of 20 K min-1 and were subjected to X-ray diffraction (XRD) and scanning electron microscopy (SEM) for phase and microstructural analysis. Then, kinetic studies were performed using some isoconversional methods such as Starink and Friedman as well as direct and indirect fitting methods. The activation energy (E) and pre-exponential factor (lnA) for oxidation of magnesium powder were in the range of 327-956 kJ mol-1 and 45-135 min-1, respectively. The reaction models for heating rates of 5, 10 and 20 K min-1 were obtained to be A3/2, R2 and D1, respectively.

In the present study, effect of Ni alloying element on the characteristics of deposited weld metal of E7018-G electrode was evaluated. Therefore, electrodes contained different amounts of Ni (0-1.7wt.%) were designed, manufactured and welded via SMAW process. Microstructural studies revealed dichotomy effect of Ni on the deposited weld metal microstructure, i.e. increasing the Ni content up to 1.2wt.% improved the formation of acicular ferrite in the weld metal microstructure and caused significant grain refinement at the reheated zone of weld metal. While, higher Ni content (>1.2wt.%) resulted in some raising in the widmannstatten ferrite content in the weld metal. Strength multiplied by impact energy parameter (UTS×CVN) was used for mechanical properties assessment. Mechanical properties evaluation revealed the highest UTS×CVN parameter achieved in the weld metal contained 1.2wt.% Ni. Hardness of the weld metal increased with increasing Ni content which is related to the formation of micro constituents in the microstructure of weld metal and increasing their content with increasing Ni content.