فهرست مطالب mahmood sharifitabar

In the present study, metallurgical tests including quantometry, X-ray diffraction analysis, and microstructural investigations with optical and scanning electron microscopes were emplyed to investigate the effect of composition and microstructure on the mechanical properties of the cast ingots and extruded profiles manufactured in Balouch Aluminum Company. Results showed that the concentrations of Fe, Si and Cu were higher than the standard composition of 6063 Al alloy. Optical micrographs sowed that pores were mainly observed at the center of ingots. According to XRD analysis, in addition to FCC phase, an iron aluminide intermettalic phase was identified in the structure of ingots. The formation of intermetallic phase was confirmed by energy dispersive analysis attached to the scanning electron microscope. Tensile test results illustrated that the presence of pores and the distribution of intermetallic phases declined the strength and formability of the alloy. The ultimate tensile strengths at the surface and center of the ingot were 103 and 71MPa, respectively. Fractography of samples indicated that the presence of pores and the intermetallic phase led to a combination of ductile and brittle fracture durin tensile test.

Sponge-like porous cerium oxide particles were prepared through the self-propagating high-temperature synthesis process. Then, the synthesized powder was used to modify the carbon paste electrode (CPE/porous CeO2) for voltammetric determination of uric acid (UA) in biological fluids. Under optimal conditions, the linear concentration-response relationship was in the range of 0.25-10 and 10-300 µM, and a detection limit of 60 nM (S/N=3) was obtained. In addition, the proposed sensor showed excellent selectivity towards UA over common co-existing species such as ascorbic acid, ibuprofen, dopamine, and acetaminophen. Good repeatability of sensor responses (Relative standard deviation (RSD) < 3.2%), superior reproducibility (RSD < 2.8%), and excellent storage stability (error < 5% after 1 month storage at room temperature) along with appropriate recovery values (in the range of 99.2 -102.7%) demonstrate the applicability of CPE/porous CeO2 for the determination of UA levels in biological fluids.

The present study deals with the fabrication and investigation of structure, microstructure, mechanical properties and corrosion resistance of 2209 duplex stainless steel parts made by wire arc additive manufacturing method. The formation of ferrite and austenite phases was confirmed by XRD analysis. There was a non-uniform distribution of ferrite and austenite phases in the microstructure of the as-welded microstructure. The tensile and Vickers microhardness tests were employed to evaluate mechanical properties. The results showed that the mean values of yield and tensile strengths were respectively 2.7 and 5.5% higher and the elongation was 4.5% lower in the welding direction than the building direction. Post-processing heat treatment at 1000 °C for 30 min led to the grain refinement of the alloy, the formation of equiaxed microstructure, increase in the austenite volume fraction, and increasing the mean hardness from 318 to 376 HV. The fractography of the tensile test specimens revealed the ductile fracture mode in all samples. Corrosion test results showed that the heat treatment improved the corrosion resistance of the alloy.

In the present study, a dissimilar joint was established between 321 stainless steel and X65 high-strength low-alloy steel by shielded metal arc welding process using 308 and 309 stainless steel electrodes as filler materials. Then, the structure, microstructure, hardness, and tensile properties of the joints were investigated. Results showed that austenite and delta ferrite phases developed in the structure of the joints. Microstructure characterization confirmed that the volume fraction of delta ferrite in the microstructure of 309 weld metal was higher than the 308 electrode weld metal. A ferritic+martensitic layer was formed at the interface of both weld metals and X65 steel. The hardness of 308 and 309 weld metals was 30% and 38% higher than the low alloy steel base metal, respectively. Tensile test results showed that the strength of the joint set up using 309 electrode was 1.5% higher and its elongation was 26% lower than the joint made by 308 electrode. In all specimens fractured occurred at the interface between the weld metal and the low alloy steel. A mixed ductile-brittle fracture mode was observed on the fracture surface of tensile test specimens.

In the present study, Inconel 625 alloy walls were fabricated by wire arc additive manufacturing method. Microstructure, hardness, tensile properties at room temperature and 700 ˚C, and high-cycle fatigue strength in both welding and building directions of samples were evaluated. The microstructure of the wall contained dendritic Ni-based solid solution along with MC carbide, Laves, and delta inter-dendritic phases. Moreover, the Vickers hardness value decreased from 380 HV near the substrate to 300 HV in the top layer. Also, yield and tensile strengths along the welding direction were 6.6 and 8.6% higher and the elongation was 23% lower than the building direction, respectively. Furthermore, fatigue test results with the stress ratio of 0.1 showed that the number of cycles to failure was slightly higher in the welding direction. Fractography of the samples illustrated that all fatigue cracks initiated from the surface. This confirmed the soundness of the walls manufactured by this method.

In the present study, resistance upset butt welding was used as a solid-state process for joining Ti-6Al-4V alloy. Results showed that melting and subsequent solidification of the alloy at the joint interface promoted the development of a cast microstructure along with some pores. However, by applying the constant upset pressure of 1.62 MPa, the pore volume fraction decreased considerably with decreasing the welding current from 110 A/mm2 to 55 A/mm2. Hardness test results showed that the weld interface and the base material had the highest (352 HV) and the lowest (318 HV) values, respectively. The microstructure of the interface consisted of ά martensite and Widmanstätten laths. The tensile strength of the joints varied between 550 and 883 MPa depending on the welding parameters used. In the optimum condition, the maximum strength of the joint was about 94% of the base metal strength. Fractography of samples confirmed that the formation of pores deteriorated the strength of the joints.

In this research, titanium carbo-nitride coatings were synthesized on the surface of Ti-6Al-4V alloy by nitro-carburizing route and the detachment mechanism of the coatings were investigated. For this purpose, rectangular blocks were embedded in a carbon containing graphite cup. Then, the cup was placed in a tubular furnace containing nitrogen gas. After coating in different temperatures between 1200 and 1400 ˚C for 20 to 60 min soaking times, structure and microstructure of the coatings were investigated by X-ray diffraction, Raman analysis and scanning electron microscope equipped with energy dispersive spectroscopy (EDS). Moreover, the effect of coatings on the corrosion resistance of the alloy in an aqueous solution containing 5.2 mol HCl, 3.2 mol HNO3 and 3.2 mol HF was investigated. Results showed that the maximum thickness of the titanium carbo-nitride coating for the sample treated at 1400 ˚C for 60 min was about 50 μm. However, the possibility of coating detachment increased with increasing the coating temperature. It was due to the formation of Al-rich layer at the interface of the coating and the substrate and the formation of Ti3Al brittle phases, as well as the difference between the thermal expansion coefficient of the coating and the substrate. Corrosion test results showed that the formation of the coatings decreased the corrosion rate of the Ti-6Al-4V alloy from 130g.m-2.min-1 for the bare alloy to 10g.m-2.min-1.