نشریه مهندسی متالورژی و مواد
سال بیست و پنجم شماره 2 (پاییز و زمستان 1393)

In this paper، the correlation between the surface rumpling and cracking phenomena with twinning mechanism during plastic deformation of Hadfield steel has been investigated. The effect of stacking fault energy and the amount of strain are evaluated. The experimental samples with specific amounts of carbon، manganese and aluminum resulting in different stacking fault energies، were produced using investment casting process. The tensile tests were conducted at ambient temperature. The microscopic and macroscopic investigations were done using optical and scanning electron microscopes. The observations have shown that surface crinkling of austenitic manganese steels is related to twining mechanism during plastic deformation. This plastic deformation mechanism causes rotation and inhomogeneous deformation of the grains and therefore، surface grains with free surfaces were becoming more crinkled and cracked. It was observed that crinkling and cracking phenomena takes place more and coarser with an increase in the strain.

Techniques of severe plastic deformation have been successfully used for the production of novel metallic microstructures. Among different types of these techniques، accumulative roll bonding (ARB) has been extensively used to produce multi-layered composites. In the present study، a new manufacturing process for Cu/Ni- 1vol% Fe3O4 composites was developed by using Copper and Nickel sheets together with micron sized Fe3O4 particles as the starting materials. It was observed that as the number of ARB passes increased، the Nickel layers were necked and fractured. After five ARB passes، a multi-layer Cu/Ni-Fe3O4 composite including homogeneously distributed fragmented Nickel layers with the Fe3O4 particles in the Copper matrix was achieved. The structure as well as the mechanical properties of this composite were studied at different stages of ARB process. With an increase in the applied strain during ARB passes، the strength of composite samples increased، but the elongation decreased. In addition، the magnetic behavior by magnetic device detector (VSM) and tensile tests were performed in order to investigate the mechanical behavior of ARB products. Finally، the scanning electron microscope (SEM) was used to study the microstructure of layers in composites samples.

In this study، the effect of grain size on nitrogen diffusion into CK45 has been investigated. In order to obtain different grain sizes، samples were annealed and normalized at various temperatures and durations. The grain size was determined with Clemex Vision software. Then، the specimens were exposed to DC plasma nitriding treatment and again analyzed by optical microscope، scanning electron microscope and X-ray diffraction analysis. Results propose power equation for variations of diffusion depth versus grain boundary density (GBD).

In this study، mixed metal oxides Al2O3/MgO/TiO2 coatings with Al/Mg/Ti ratio of 5:1: 3 and 2. 5:3: 4 were coated on aluminum by sol-gel method. The surface morphology، Phase analysis، thermal behavior and the corrosion behavior of the Al2O3/MgO/TiO2 coatings were characterized by (SEM)، (XRD)، (TG-DTA) and Potentiodynamic Polarization test in 3. 5 wt. % NaCl solution. The results demonstrated that heat treatment at 450 °C caused the decrease of corrosion resistance of coating so that after heat treatment، corrosion rate of the samples coated with Al/Mg/Ti molar ratio of 5:1: 3 and 2. 5:3: 4 were 5 and 13 times respectively.

The research mainly intends to evaluate performance of strontium aluminum polyphosphate as an eco friendly zinc free anticorrosion pigment in formulation of the protective primer based on epoxy resin. Comparing to zinc phosphate، the most effective content of the modified pigment was determined through electrochemical impedance spectroscopy. According to pull-off، the superior SAPP incorporated formulations resulted from EIS showed enhanced adhesion strength during 60-d immersion period. Moreover، indentation test results revealed that the effective concentrations of SAPP anticorrosion pigment could stop coating hardness drop within the exposure.

Composite Electrodeposition is a low-cost and low-temperature method، which is used to make metal matrix composite coatings. In This study the surfactant of anionic (SDS) and cationic (CTAB) is used as additive in composite coating of Ni/TiN. The results showed that the anionic surfactant caused more particles in the composite coatings. Increasing SDS concentration to the optimal value leads to more uniform dispersion of nanoparticles in the coating. The hardness of pure nickel and optimal composite coating is measured by AFM and the results showed that the hardness of the coating increases from 1. 86Gpa to 3. 23Gpa، in the presence of particles.

In this study، the four Cr-Mn- (Ni-free) austenitic steels were fabricated by vacuum induction furnace. Then plates with 10 mm thickness were fabricated by hot-rolling. Corrosion behaviour of the four Cr-Mn steels in 0. 1 M H2SO4 solution was investigated using by open-circuit potential، potentiodynamic polarization، and electrochemical impedance spectroscopy (EIS). The results indicated that the open-circuit potentials of the four Cr-Mn austenitic steels were found to shift towards positive direction. Also، the potentiodynamic polarization curves suggested that the four Cr-Mn austenitic steels showed comparable passive behaviour in sulfuric solutions.

Calcareous deposits formed on the part of steel that cathodic reactions occur on their surface. The purpose of this research is an investigation of the effect of potential on crystal form of the calcareous deposits and effect of them on the corrosion resistance of the mild steel in natural seawater. The electrochemical tests such as impedance and polarization tofel tests were used in order to investigate the effect of applied cathodic potential on the corrosion resistance of mild steel in Persian gulf seawater. Also، scanning electron microscopy (SEM) and XRD analyzer were used to investigate the morphology and the type of deposits under applied cathodic protection.

In this paper، the evidences and remnants of archaeometallurgical activities in Elamite site of Haft Tappeh (14th century BC) have investigated and identification of archaeometallurgical materials have been done based on analytical investigations. SEM-EDS analysis and metallography were used to identify the chemical composition and microstructural features of archaeometallurgical materials in Haft Tappeh. The results showed that the metallurgical process in Haft Tappeh has been copper smelting from sulfidic ores. This process has been done by matte production and the mixture of matte and copper has been roasted for the purpose of purification in order to produce objects. The metallic objects in Haft Tappeh have been manufactured by copper-lead as well as bronze alloys. In some cases، some metallic elements such as Ni and Zn were observed in composition. Based on the microstructural studies، it could be concluded that an alternating cold working and annealing operation has been used after casting to shape the metallic artifacts.