یاسر وحیدشاد

Studying the parameters that influence additive manufacturing and determining the optimal conditions for part production is a complex challenge. Research is actively focused on understanding how process conditions affect the evolution of microstructure and the resulting mechanical properties of fabricated components. A study was conducted to investigate the effect of selective laser melting additive manufacturing process parameters on the mechanical properties of Maraging 300 steel samples. The mechanical properties were determined using 2D digital image correlation on flat tensile samples (in accordance with the ASTM E8 standard). Laser scanning speed (70, 100 mm/s), hatch distance (100, 150, 200 μm), and layer thickness (20, 40 μm) were evaluated for their effects on mechanical properties. The desired mechanical properties were extracted using the digital image correlation test, a non-contact optical method for measuring mechanical properties. According to the results of the study, the laser scanning speed significantly influences the mechanical properties of samples more than other additive manufacturing parameters according to the relationship between the selected parameters and the laser energy density and their effect on the molten pool. Based on the results, the optimal sample is made with a scanning speed of 70 mm/s, a hatch distance of 200 μm, and a layer thickness of 20 μm. This sample has a yield strength of 1785 MPa, an ultimate strength of 1816 MPa, an elongation of 17.4%, and a Poisson ratio of 0.34.

This research focused on investigating additive manufacturing factors using Selective Laser Melting (SLM) with maraging grade 300 steel powder via Taguchi method. The main objectives were to explore the influence of process parameters and achieve optimal levels. Experiments were exactly designed with the assistance of Mini-Tab software. The study specifically targeted scanning speed, hatch distance, layer thickness, and scanning strategy for fabricating tensile samples. Comprehensive characterization using optical and scanning electron microscopes examined mechanical and microstructural properties. The analysis revealed that the optimal levels for achieving desirable results were as follows: scanning speed of 100 mm/s, layer thickness of 20 microns, hatch distance of 0.15 mm, and implementing the Stripe scanning strategy in the XY direction. The output results showed significant findings, with a final tensile strength of 951 MPa, porosity measured at 0.4%, and an impressive relative density of 99.6%. In conclusion, this research provides valuable insights into optimizing the selective laser melting process with maraging grade 300 steel, offering crucial knowledge about effective process parameters for obtaining optimal mechanical and microstructural properties in the additive manufacturing of tensile samples.

The present study focuses on optimizing the mechanical properties and microstructure of laser welding in Haynes 25 (L-605) cobalt-based superalloy. Initially, the influence of laser welding variables such as laser power, pulse frequency, welding speed, and pulse width on the mechanical and metallurgical properties of the weld joints is investigated. By examining the welding variables, the values of G (thermal gradient) and R (cooling rate) are calculated, and their ratio (G/R) and cooling rate (G×R), which predominantly affect the solidification microstructure, are determined. The structural correlation with the mechanical properties resulting from welding is examined.  In this research, it is considered to obtain the welding variables to create a high percentage of the structure in the form of equiaxed dendrite. Microstructural analysis reveals the growth of equiaxed grains and dendritic structures in the weld zone. The high cooling rate in the weld pool leads to dendritic solidification starting from columnar dendrites at the weld walls and ending in equiaxed dendrites at the center of the weld. The microhardness value in the weld zone is HV 328, which is very close to the microhardness of the base material. The tensile strength of the weld samples reaches about 93% to 94% of the base metal tensile strength. Tensile testing of the weld samples indicates a ductile-brittle fracture. Examination of the scanning electron microscope confirms the presence of dimples, intergranular cracks, and microvoids in the fracture zone.

Mesoporous gamma-alumina granules, which are known as a common catalyst support in industrial applications were synthesized via the sol gel-oil drop method having a diameter of 1-2 mm. The effect of calcination temperature (450 and 750 °C) on the properties of gamma alumina granules were studied and the functionality of 20 wt% iridium catalyst on the alumina granules for hydrazine decomposition was evaluated. The presence of gamma-alumina as the only constituent phase up to 750 °C was revealed by XRD analysis. According to N2 adsorption-desorption analysis, the specific surface area of gamma alumina granules calcined at 450 and 750 °C was 303.05 and 227 m2/g, respectively. HR-TEM analysis was used to investigate the granules’ morphology, and the capability of the granules as a support for iridium catalyst was evaluated during the hydrazine decomposition test. Using alumina granules calcined at 750 °C as the catalyst support, the hydrogen selectivity reached 22% and the decomposition rate was 235 h-1, and the granules’ crushing level was as low as 7% during the test, indicating that the granules have an acceptable surface area, pores diameter, and interconnectivity.

In recent decades, the use of metal matrix composites and functionally graded materials for achieving a combination of mechanical and physical properties has increased. In this research, an in-situ centrifugal casting method was used to make the samples. The primary composite used in this method was Al-15wt.% Mg2Si. In situ prepared functionally graded samples were successfully manufactured at 1000, 1300, and 1700 rpm rotational speeds. Optical microscopy was used to examine the microstructure of the samples, and a Vickers hardness tester was used to examine the mechanical properties. The cross-section of the fabricated samples was divided into two parts, the reinforced and the matrix parts. Porosity increased as a destructive parameter in the reinforced area. The hardness increased as the volume fraction of particles in the reinforced area was increased. Also, hardness increased in the chilled zone due to the fine-grains and trapped particles in that area. Solutionizing heat treatment was performed for the fabricated samples. By observing the microstructure, there was no change in the placement trend of the primary particles, but the morphology of the primary and eutectic Mg2Si particles were changed. Hardness increased after heat treatment while its gradient did not change.

Properties of brazed joints could be affected by some factors like temperature, time, clearance, surface roughness and alloy elements. Actually they influence on the formation of intermetallic compounds in brazed joints. Since intermetallic compounds are brittle, they considerably degrade the mechanical properties of joints. In this study the mechanical strength and microstructural characterization of AISI 316 brazed joints with BNi2 filler metal in different temperature has been investigated. Brazing temperatures changed from 1050 °C, 1100 °C, 1150 °C and 1200 °C for a holding time of 60 min then, the influence of this variable on the brazing strength were examined. Tensile test samples were evaluated at room temperature and metallography samples and fractured tensile sample scanned by a microscope. The results showed that the higher brazing temperature leads to diffusion of boron element into base metal and less volume formation of intermetallic compound phase in the brazing joint and consequently more tensile strength.

In this investigation, the effect of plasma arc welding (PAW) process parameters on the welding quality of Ti-6Al-4V alloys is studied. These parameters including current, welding linear velocity and plasma gas composition that affected on the weld bead width. Macrograph results indicated that there is a certain range of electric current and linear velocity, which within the range, the full penetration welding obtains, and the weld bead is free from defect. As a result, the mechanical properties are favorable and comparable to those of the base material. It can be protected weld bead from oxidation with argon gas (5N). Furthermore, the automation of the process resulted in repeatability of the plasma arc welding is very good and the weld quality is well controlled. The results indicated that increasing the amount of helium gas, increases the welding area and the higher penetration depth of the weld. Examination of the microstructure of the weld region shows that there are three serrated alpha phase, alpha-beta phase (Widmanstätten) and the martensitic phase in the weld microstructure.

In this study, CuInS2 nanoparticles have been synthesized via one-pot facile thermolysis route and the decomposition temperature of CuCl and InCl3 complexes were investigated. The stabled colloidal CuInS2 compound has been prepared by solving CuCl and In2(SO4)3 as cationic elements, thiourea (SC(NH2)2) as sulfur source and PVP as surfactant in the nontoxic and cost effective solvent of Diethylene glycol ((CH2CH2OH)2O) and ethylene diamine(C2H8N2) . The samples were characterized by X-ray diffraction for structural evauation, Fourier transform infrared (FTIR) for revealing the formed complexes and capping agents and absorbance spectrophotometer (UV-VIS) for detecting optical properties. The results revealed that the In2(SO4)3 was decomposed when the temperature was more than 210 °C and CuInS2 compounds with polytypism crystalline structure (chalcopyrite and wurtzite) was formed. Furthermore, increasing the temperature from 120 °C to 240 °C, facilitates formation of the chalcopyrite crystalline structure rather than the wurtzite structure.

In this research, we have synthesized Ag-TiO2 nanocomposite with an optimized concentration of 1% by sol-gel method. Rhodamin was used for photocatalytic activity. Dilatometric thermal analysis of prepared specimen was performed at different temperatures of 266, 338, 39 , 485, 600 and 700 °C for 2 hours. Using obtained results from XRD and DTA analyses, prepared specimens in 530 °С and during 0.5, 1, 2, 4 and 6 hours underwent heat treatment. The optimized specimen from decomposition point of view was that of 530 °С and 1 hour heat treatment. Additionally the specimen was operating even more efficient than Degussa P25 nanopowder. Ag2Ti4O9 phase was synthesized at room temperature and with regard to decomposition test results, it seems that the specimen has more efficiency than anatase phase. Characterizations of Ag-TiO2 nanoparticles were done by DTA, XRD, PL and SEM.