Journal of Metallurgical and Materials Engineering
Year:2014 | Volume:25 | Issue:2|Papers Count:9

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 structures different grain sizes، the steel samples were annealed and normalized at various temperatures and times. After heat treatment, the microstructures of test samples were analyzed by optical microscope. The grain size was determined using Clemex software. specimens were then exposed to DC plasma nitriding treatment and they were analyzed again using optical and scanning electron microscope as well as through X-ray diffraction technique. The results showed that a power-law equation may be obtained for variations of diffusion depth versus grain boundary density (GBD). According to this equation, the diffusion depth decreases with a decrease in the grain size of the steel.

Recently, mixed-metal oxides with suitable properties such as high chemical resistance and thermal stability, have been used in a wide range of applications as corrosion resistant coatings. In the present study, Aluminum/Magnesium/Titanium mixed-metal oxides was used as a coating on AA1100 aluminum by sol-gel method and by dip coating process and the effect of various molar fractions and heat treatment cycle on properties of this coating was investigated. In order to study the effect of crystallinity of the coated samples, test samples were characterized using X-ray diffraction (XRD) and Vickers microhardness analyses and their microstructures were examined by Scanning Electron Microscope (SEM). The corrosion behavior of samples were also studied by Open Circuit Potential (OCP) and potentiodynamic polarization techniques in 3.5 wt. %NaCl solution. The results showed that the amorphous sol-gel coatings are less porous representing better corrosion resistance when they are compared with the crystalline coatings. The corrosion rates of the crystalline samples with Al/Mg/Ti molar ratios of 5:1:3 and 2.5:3:4 were 5 and 13 times greater, respectively, than those for the amorphous samples and the porosity contents in the former samples with the same molar ratios were 17 and 27 times greater than those of the latter samples, respectively.

The main purpose of this research is to evaluate the performance of strontium-aluminum polyphosphate as an biocompatible zinc free anticorrosion pigment in formulation of the protective primer based on epoxy resin. Comparing with the zinc phosphate, the most effective content of the modified pigment was determined by the means of electrochemical impedance spectroscopy test. According to the results of pull-off experiment, the superior SAPP incorporated formulations resulted from EIS showed enhanced adhesion strength during the 60-day immersion period. Moreover, indentation test results showed that the effective concentrations of SAPP anticorrosion pigment can stop the decrease of coating hardness during the immersion period.

Electrodeposition of composites is a low-cost and low-temperature method, which is used to make metal matrix composite coatings. In this study, various amounts of surfactants of anionic sodium dodecylsulfate and cationic cetyltrimethylammonium bromide were used as additives in composite coating of Ni/TiN. Watts bath was used as the plating bath with the concentration of particles, current density and agitation speed which were considered to be 30g/lit, 4A/dm2 and 450rpm, respectively. The results showed that the anionic surfactant causes more particles to be present in the composite coatings compared with cationic caused. An increase in the SDS concentration to the optimal value led to more uniform dispersion of nanoparticles in the coating. The hardness of pure nickel and optimal composite coating SDS were measured by AFM and the results showed that the hardness of coating, in the presence of particles, increases from 1.86 to 3.23 GPa, and its wear resistance showed an increased value.

In this study, four Cr-Mn austenitic steels (Ni-free) were fabricated by vacuum induction melting. Several plates with 10 mm thickness were produced by hot-rolling. Corrosion behaviour of Cr-Mn austenitic steels and 316L stainless steel in 0.1 M H2SO4 solution was investigated using open-circuit potential, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) test techniques. The results indicated that the open-circuit potentials of four Cr-Mn austenitic steels are shifted towards positive values. In addition, the potentiodynamic polarization curves suggested that four Cr-Mn austenitic steels represent comparable passive behaviour within the 0.1 M H2SO4 solution. Nyquist plots for the Cr- Mn steels in 0.1 M H2SO4 solution also showed a capacitive loop at high and medium frequencies and an inductive loop at low frequencies.

Calcareous precipitates are formed on some parts of steel surface on which cathodic reactions occur. The purpose of this research has been to investigate the effect of potential on crystal form of calcareous deposits and to study the effect of these precipitates on the corrosion resistance of mild steel in natural seawater. The electrochemical tests, i.e. electrochemical 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. In addition, the Scanning electron microscope (SEM) and XRD analyzer were used to study the morphology and type of deposits during the applied cathodic protection. The results of this research showed that a large amount of CaCO3 are formed at the potential of -1.1 V, although a small quantity of Mg (OH)2 precipitate were also formed. On the other hand, the precipitate were mainly Mg (OH)2 with a large amount of porosity at the potential of -1.2 V. The results of electrochemical tests also showed that the corrosion resistance of mild steel in natural seawater increases whit the formation of these precipitates, particularly at the applied cathodic potential of -1.1 V.

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.