مجله مهندسی متالورژی
پیاپی 84 (زمستان 1400)

In this study, the effects of grain size on the tensile properties and the work-hardening behavior of 304 austenitic stainless steel was investigated. For this purpose, the thermomechanical processing was carried out by applying a 75% thickness reduction to the as-received 304 stainless steel sheet followed by annealing at two different temperatures of 750 and 1000 °C to produce sheets with two different fine- and coarse-grained microstructures. The average grain size decreased from 25 μm in the as-received matrix to 1.93 μm in the sample, which was annealed at 750 °C for 90 min (fine-grained sample). Also, the mean grain size of 35.52 μm (coarse-grained sample) was obtained after annealing at 1000 °C for 90 min. XRD and optical microscopy were used for characterizing the microstructure. The tensile tests were performed in the directions of 0°, 45°, and 90° to the rolling direction of the samples. The yield strength of as-received, fine-grained, and coarse-grained samples were obtained 405, 733, and 305 MPa, respectively. However, the total elongation decreased from 73% in the as-received sample to about 52% in the fine-grained sample. The work hardening behavior of both fine- and coarse-grained samples was observed in three stages: an initial sharp drop until a minimum value was reached, then an increase until a maximum value was reached, and finally a reduction in the work hardening rate until the beginning of necking. The work-hardening rate (dσ/dε) of the coarse-grained sample was higher than that of the fine-grained sample. This was due to the higher martensitic transformation rate in the coarse-grained sample.

The recycling of steel-making dust was investigated using the leaching process in sulfuric acid and the separation of zinc ions by solvent extraction method. Due to the high chloride content of steel-making dust, the spent used in the experiments after the completion of the processes in the first cycle was returned to the beginning of the steel-making furnace dust recycling process to investigate the effect of chloride ions on the extraction of zinc metal. Aqueous solution was prepared by dissolving steel-making dust in sulfuric acid and followed by precipitation of iron in hydroxide form. To separate zinc from aqueous solution, D2EHPA agent was used at a constant temperature of 25 ºC and the ratio of aqueous to organic phase was 1:1. The effect of pH parameter in the range of 1-5 and volume concentration of extractant 5-30% on the extraction of zinc in three cycles of return spent were investigated. According to the results, an increase in pH up to about 3, the extraction of zinc increased enormousely, and the extraction was almost complete at higher than 3. Also, an increment in D2EHPA concentrationenhanced the zinc extraction and the optimum extraction was found to be 30%. Thermodynamic calculations showed that the main active ion of zinc in the leaching solution is Zn2+ and in the first cycles, it controls the absorption mechanism by the D2EHPA extractant. The fitting of thermodynamic data for the 10th cycle also showed that the molar percentage of ZnCl+ species changes from 2.05 % to 12.86%.

The nickel-based superalloys high sensitivity to various types of cracks during fusion welding and post welding heat treatment, leads to limitations in the repair welding of damaged parts of this material. Strain aging crack is a type of prevalent crack in the IN738LC superalloys that occurs during the post-weld heat treatment, which was investigated in few studies. In this study, using numerical modeling, the susceptibility to strain aging cracking in IN738LC superalloy welded by TIG method without filler metal was investigated. The results of thermal-mechanical modeling as well as experimental evaluation of cross-section of the autogenous welded samples after post-heat treatment showed that the transverse plastic strain of (rather than longitudinal) plastic is a suitable preliminary criterion for evaluating the susceptibility of superalloy to the strain aging cracking and it seems that if the plastic transverse strain is more than 4.6%, the probability of this crack occurring after post weld heat treatment will be very high.

In this paper, the structural , electronic and optical  properties of calcium carbonate in hexagonal (calcite) ,orthorhombic (aragonite)  and orthorhombic( waterite)phases are investigated.The calculations have been performed with pseudopotential methodin the framework of the density functional theory with different approximations and using Quantum Espresso package.The band structure results for the calcium carbonate compound in the hexagonal phase indicate an indirect band gap in the  direction and the orthorhombic phase has a direct band gap.The refractive index obtained for the hexagonal phase in the and  directions are 1.45 and 1.27, respectively. The obtained refractive index for orthorhombic phase in and  directions are 1.48, 1.45 and 1.36, respectively. Also, the value of the optical gap for orthorhombic and hexagonal phases in and directions have been calculated. The obtained results are in good agreement with other available data.

Dental implants are one of the most common treatments in dentistry and Titanium is one of the most widely used materials to make a dental implant. Silver is also a good choice because of its antibacterial properties and reduced risk of infection after surgery. But a dental implant should have a lower Young modulus than the jawbone to prevent stress shielding. One way to reduce the Young modulus is to create porosity. The aim of this study was to make a Titanium-Silver dental implant using spark plasma sintering (SPS) method with 20-25% porosity. For this purpose, parts were made with Ti -1wt.% Ag and Ti -3wt.% Ag, under temperatures of 900 °C and 850 °C and pressures of 10 MPa and 30 MPa. Results of XRD and SEM showed that the samples had alpha-Titanium microstructure with pore size of less than 100 microns with spherical morphology. Also, the sample made at 850 °C and 10 MPa is the best sample because it has 20-25% porosity and compressive strength close to the jawbone, compared to other samples. Statistical data and modeling in Design Expert software showed that porosity increases with decreasing temperature and pressure; but decreasing temperature is more effective in creating pores. According to the three-dimensional diagrams, it can be concluded that, the highest porosity, while maintaining the mechanical properties, was obtained at a temperature of 850 °C, pressure of 10 MPa and 1% Silver.

The aim of this study is to provide the characteristics of laser cladding and its application in three areas of coating, repair and prototyping. Among the innovations of this research, we can compare the features and advantages of laser coating with other conventional methods such as tags, etc. by mentioning sample studies. Also, the study of the areas of coating, repair / reconstruction and prototyping of laser coating with mentioning an objective industrial example in order to understand the exact application of other innovations of the present study is considered. In other words, the innovation of this research is the presentation of features and application of laser coating in three areas of coating, reconstruction and prototyping of industrial parts in comparison with other methods that were not addressed in a study. In this regard, the benefits of this technology will be presented first. Details of the laser coating process of the brake discs are given. How to repair the gas turbine fuel nozzle and rebuild the locomotive engine body by laser method will also be introduced. A prominent example of laser prototyping is the production of a helicopter engine combustion chamber. For a better understanding, a comprehensive overview of previous studies will be provided. Finally, the speed and capabilities used in each of the three areas of coating, reconstruction and laser prototyping are introduced.