نشریه مهندسی متالورژی و مواد
سال سی و سوم شماره 3 (پاییز 1401)

The aim of this work is the study of the argon implantation on the corrosion resistance behavior of AISI 304 stainless steel substrates. The effect of ion implantation dose on morphology and corrosion properties of AISI 304 SS has been investigated.In this work, argon ions of 30 keV energy have been implanted into  AISI 304 stainless steel at different fluences ranging from to Ar/cm2.The AFM analysis of implanted samples clearly shows significant change in surface. In order to evaluate the effect of the ion bombardment on the corrosion behavior, otentiodynamic tests were performed. The results show that the corrosion resistance of the samples strongly depends on the implantation fluences.The Corrosion potential and roughness curves obviously indicate that corrosion Potential variations caused by argon ion bombardment are inversely proportional to surface roughness. Corrosion current variations show an optimal dose at ions/ cm2 in which the corrosion resistivity is 12 times higher than un-implanted sample.

Grain growth during sintering of nanomaterial is one of the main drawback is this process. Since the nanomaterials maintain their unique performance as long as their size dos not exceed a specific size range, various strategies, including the addition of oxide particles, are adopted to prevent this phenomenon and to slow down grain growth. In this research, titanium oxide particles were used to prevent the growth of NiTi nanostructured alloy grains during sintering operations due to their suitable thermal stability with amount of 10 wt.%. The effect of titanium oxide particles was investigated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses. For this purpose, two groups of samples including with and without presence of titanium oxide were prepared and studied. The results of kinetic analysis on both sample groups showed that grain growth occurred after the process, in the presence of this oxide, up to twice the initial size and before sintering. But the growth rate in the absence of titanium oxide increased up to five times. The reason for this is the amount of activation energy required for grain growth. This energy was 31.85 kJ in the sample without titanium oxide and 47.96 kJ in the sample with the presence of 10% of this oxide. Also, based on DSC data, the barrier energy were calculated as 9.93 and 7.75 kJ, and the grain growth activation energy were calculated as 13.4 and 14.4 kJ, for the samples with out and with titanium oxide respectively.

Ferritic-Martensitic dual-phase steels are widely used in car manufacturing industries because of their attractive mechanical properties like significant tensile strength and good formability. It is clear that the mechanical properties of these steels are dependent on their microstructural characteristics like the fraction of different phases and the dislocation density of each phase, and these characteristics are affected by the thermomechanical history.  The aim of this work is to investigate the effect of the microstructure of the Ferritic-Martensitic SAPH440 steel on its tensile behavior like the tensile strength and the strain rate sensitivity of flow stress. For this purpose, the steel is subjected to inter-critical annealing at different temperatures between 750 ºC to 790 ºC and then, it is subjected to the tension test at room temperature using two different strain rates. Also, the microstructure evolutions of this steel are studied using optical microscopy, scanning electron microscopy, and X-ray diffraction. Results show that the increase of the intercritical annealing temperature from 750 ºC to 790 ºC causes an increase of the martensite fraction from 31% to 45% and the increase of dislocation density of ferrite from 5×1014 to 1.54×1016. These variations cause the increase of the tensile strength from 800 MPa to 1100 MPa while the strain rate sensitivity of the flow stress decreases to a negligible amount.

Reactive composites are a new group of composite materials consisting of two or more metal materials that can not ignite or explode in the environment but can release a lot of energy due to shock and severe impact loads. This study aimed to investigate the effect of the ratio of constituent particles on the microstructure and thermal and mechanical properties of the Al-Ni composite. For this purpose, the Al-Ni compound with 2:1, 1:1 and 3:1 molar ratios was milled and mixed. Then the samples were cold pressed and sintered at 400 ˚C under argon atmosphere for one hour. The microstructure of samples was analyzed by microstructure field emission scanning electron microscopy (FESEM) and XRD. For the investigation of thermal and mechanical properties, DTA and ignition tests and compression and Hopkinson tests were used respectively. In the ignition test, due to the AlNi product, the highest value of heat released was related to a sample with 1:1 Al:Ni molar ratio. In the compression and Hopkinson tests, the highest values of compressive strength were 208.7 and 309.7 Mpa respectively, which belong to a 1:1 Al:Ni molar ratio. Also, the results showed that the compressive strength increased by changing the strain rate from 0.01 s-1 (in the pressure test) to 1000 s-1 (in the Hopkinson test).

The fabrication of the most similar structure to the bone with appropriate mechanical, physical, and biological characteristics is challenging. The main aim of the present research is to design, fabricate, and characterize the gelatin-calcium phosphate composite scaffolds. First, calcium phosphate particles (SCP) were synthesized through the sol-gel process. Accordingly, the prepared particles were synthesized via the sol-gel route and heat-treated at 1100℃. Then, the gelatin-calcium phosphate composite scaffolds were fabricated through solvent casting and freeze-drying methods. According to the pycnometer and particle size (PSA) analyses, the density and the particle size of the SCP particles were 4.06 g/cm3 and 37±5 nm, respectively. Based on the XRD and DTA-TG results of the particles, crystallization of the calcium phosphate phases has been started at 800℃. The functional groups of the particles have been also studied through FTIR analysis. The roughness of the particles was 17.32nm based on the AFM microscopy results. According to the three-point flexural test, the final strength of the scaffolds was 15 MPa. Field emission scanning electron microscopy (FESEM) showed that the scaffolds had a completely porous structure with interconnected pores. Resazurin Red Assay confirmed the viability of 78% of stem cells on the scaffolds after 5 days of seeding. Immersion of the scaffolds in the simulated body fluid (SBF) caused the controlled release of the Ca2+, Si4+, and PO43- ions. Altogether, the gelatin-calcium phosphate composite scaffolds have a promising role in tissue engineering applications.

U-500 is a nickel-based superalloy which has significant amounts of some precious elements such as cobalt and chromium. Due to the economic and strategic value of these metals, their recovery from the used superalloys is of great importance. Hydrometallurgy is an economical and effective method for recovering these valuable metals from the superalloy scraps. So in this investigation, the dissolution behavior of nickel, cobalt and chromium elements from the used U-500 superalloy in the electro leaching process as well as the effect of different process parameters (such as: sulfuric acid concentration, applied voltage, process temperature, stirring and cathode-anode distance) on the dissolution of these elements are studied in details. The results show clearly that by increasing the concentration of sulfuric acid in the electrolyte, the applied voltage, and temperature, as well as decreasing the cathode-anode distance, the anodic dissolution of the superalloy U-500 is improved. Electrolyte stirring has no significant effect on increasing the anodic dissolution of the superalloy. The optimum conditions for the anodic dissolution of superalloy U-500 in sulfuric acid electrolyte was determined as acid concentration of 125 g/L, applied voltage of 4 V, stirring speed of 300 rpm, and cathode-anode distance of 3 cm without temperature control (starting with ambient temperature as the initial temperature(. Under these conditions, about 75% nickel, 84% cobalt and 67% chromium were durnig 25 minutes.