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  • Open access
  • 48 Reads
Electromagnetic processing during directional solidification of particle strengthened Aluminum alloys for additive manufacturing

Rise of metal additive manufacturing technology has increased the demand for high performance alloys such as metal matrix composites (MMC). Metallurgical production of MMC remains a challenge. The nano-powder of dielectric particles does not mix well into the liquid metal because of several reasons. On a macroscopic level, the powder is rejected by the molten metal through buoyancy and surface tension forces. On a microscopic level, the particles are held together by Van der Waals forces forming particle agglomerates. Our research strategy is to address these issues separately in two steps. We are investigating electromagnetically assisted MMC casting method for production of particle strengthened directionally solidified aluminum alloys. In the first step, nanoparticles are mixed into melt while it is in a semi-solid state by efficient permanent magnet stirrers. Then the alloy is subjected to ultrasound treatment for fine particle dispersion. Semi-continuous casting of MMC is used to obtain material for additive manufacturing process. Material is casted in 6-20 mm rod by direct chill casting method, which can be made into wire with the application in wire-feed additive manufacturing. We investigate the possibility to improve Al alloy SiC composite material properties by applying electromagnetic interaction during solidification. Electric current and moderate static magnetic field (0.1-0.5 T) creates melt convection in mushy zone. Such interaction enhances heat and mass transfer near the solidification interface and hinders the reagglomeration of the added particles.

  • Open access
  • 55 Reads
The multifunctional roles of chitosan in the formation of flower-shaped palladium nanoparticles

The chemical and physical routes are usually used to synthesis the metal nanoparticles. However, the harmful effects on the environment and human health turn the scientists on finding greener methods. We have developed the novel green method for the synthesis of the flower-shape palladium nanoparticles (FPNPs) based on the chitosan (CS) polymer. In this method, CS can work as a stabilizer, a shape-directing agent, and a size-controllable agent for the synthesis of these nanoparticles. We proposed the growth model of FPNPs in the presence of CS to interpret mechanistic understanding. This study provided pioneer evidence about the multifunctional roles of natural polymer in the preparation of metal nanoparticles. Deep and extensive studies should be conducted to explore the great benefits of natural polymers in the green synthesis of metal nanoparticles

  • Open access
  • 139 Reads
Reliability Design Of Mechanical Systems Such Subjected To Repetitive Stresses

The basic reliability concepts - parametric ALT plan, failure mechanism and design, acceleration factor, and sample size equation were used in the development of a parametric accelerated life testing (ALT) method to assess the reliability quantitative test specifications (RQ) of mechanical systems subjected to repetitive stresses. To calculate the acceleration factor of the mechanical system, a generalized life-stress failure model with a new effort concept was derived and recommended. The new sample size equation with the acceleration factor also enabled the parametric ALT to quickly evaluate the expected lifetime. This new parametric ALT should help an engineer uncover the design parameters affecting reliability during the design process of the mechanical system. Consequently, it should help companies improve product reliability and avoid recalls due to the product failures in the field. As the improper design parameters in the design phase are experimentally identified by this new reliability design method, the mechanical system should improve in reliability as measured by the increase in lifetime, LB, and the reduction in failure rate.

  • Open access
  • 145 Reads
Investigation on Viscosity of Lime-Alumina Based Mould Powders during Continuous Casting of High-Aluminium Steels

High-aluminium steels contain a significant amount of aluminium. The reaction between Al in the liquid steel and SiO2 in lime-silica-based mould powders during the continuous casting process of high Al steel causes chemical compositional changes in the mould powders, subsequently affecting the surface quality of slabs. In order to solve the aforementioned problem, lime-alumina based mould powders have been developed which can lead to an increase in the surface quality of cast slabs by inhibiting molten steel/slag interaction. However, the mould slag tends to crystallise easily, which leads to a deterioration of the mould lubrication. In this study, viscosity of lime-alumina-based mould powders with the addition of B2O3 and the effects of increasing the CaO/Al2O3 ratio have been observed through IPT (Inclined Plate Test) and rotational viscometry. Additionally, FactSage software and empirical models were used to calculate viscosity of the mould powders. The results show that the viscosity of mould powders decreases dramatically while CaO/Al2O3 ratio changed from 1 to 1.5. The viscosity of designed mould powder shows that with the increase in CaO/Al2O3 ratio ranged from 1.5 to 2.5, viscosity slightly decreases, then when the CaO/Al2O3 ratio over 2.5, viscosity nearly levels off.

  • Open access
  • 70 Reads
Investigation of factors influencing on the autoclave tests results of internal anticorrosive polymer coatings

In the oil and gas industry the majority of equipment failure incidents are caused by corrosion. One of the effective methods for corrosion protection is usage of different coatings systems. The article presents the results of polymer powder coatings properties research that used to protect the inner wall of field pipelines.

Autoclave tests were used for researching coatings properties. Autoclave studies consisted of decompression tests and HT/HP immersion tests in simulated environments. The studies were carried out in solutions containing CO2, H2S in the gas phase, as well as in the phases of combined composition. The liquid phase was 5% NaCl with different pH levels. The influence of pressure release time, exposure time, pressure release cyclicity and composition of test solution on the functional properties of the coating was studied. Systems based on polymer powder coatings were used as test samples.

The work result is the clarification of the autoclave tests methodological features and the identification of factors affecting the results repeatability. Identical coating systems have been tested over a wide temperature range, showing signs of coating degradation as test temperatures increase. Also given an example of autoclave test usage as a method for detecting low quality application of paint system. The results of the work will be useful in planning a test program for the development of new anticorrosive internal pipe coatings.

  • Open access
  • 100 Reads
The Effects of Cyclic Close Die Forging on Microstructure and Mechanical Properties of Ti – 5Al – 3Mo – 1.5V Alloy

Superplastic behaviour of certain metals and alloys having very fine grains, very large tensile elongations are obtained within certain temperature ranges at low strain rates. In this work, Ti – 5Al – 3Mo – 1.5V alloy was produced and studied. This paper aims to study the effects of cyclic close die forging on microstructure and mechanical properties of this alloy by considering variable parameters such as deformation temperature (Td) from 8500C, 9000C and 9500C and the number of cycles performed while forging in closed die (n) of 3, 6 and 9 times. The response is average grain size (dtb) and tensile stress (σb). The results indicated that the smallest average grain size 1 μm could be obtained at Td = 9000C, n = 9 times and the tensile stresses are enhanced. The experimental results we obtained also suggest that the microstructure of Ti – 5Al – 3Mo – 1.5V alloy is accordant for for superplastic deformation. The superplastic forming can show maximum elongation of 1000% or more.

  • Open access
  • 125 Reads
Numerical and Analytical Analysis of the Low Cycle Fatigue Behavior of Notched and Un-notched 316 L (N) Austenitic Stainless Steel Samples at Ambient and Elevated Temperatures

Smooth and notched mechanical components made of metals frequently experience repeated cyclic loads at different temperatures. Thus, low cycle fatigue (LCF) is considered the dominant failure mode for these components. The stainless steel (SS) is the most widely selected materials by engineers, owing to its outstanding mechanical and LCF properties and anti-corrosion properties. Moreover, a reliable estimation of the fatigue life is essential in order to preserve people’s safety in industries. In the present study, an evaluation of some of the commonly known low cycle fatigue life methodologies is performed for notched and un­-notched samples made of 316L (N) SS, at ambient and higher temperatures. For the notched ones, the elastic-plastic strains were firstly determined and then the fatigue lives were estimated for constant nominal strain amplitudes, varying from ± 0.4 to ± 0.8%. A comparison between the calculated fatigue lives and those obtained experimentally from the literature was made. Overall, some of the widely used fatigue life prediction methods for smooth specimens have resulted in unsafe estimations for applied strain amplitudes ranging from ± 0.3% to ±1.0%. And those of notched specimens were generally found to give strongly conservative predictions. To overcome this problem, attempts have been made to suggest new parameters that can precisely assess the lifetimes of smooth samples, and a new equation was suggested for notched ones, under both room and high temperatures.

  • Open access
  • 160 Reads

The quest for suitable reductants for the extraction of iron from ores at minimal energy requirements and maximum degree of metallization is attracting growing researchers’ attention. In the present work, an attempt is made to use non-contact charcoal in the reduction of run-off mine goethite ore at heating temperatures above 570oC. The reduction mechanism adopted is in accordance with Levenspiel’s relations for the shrinking core model. The first stage is concerned with the diffusion of gaseous reactant through the film surrounding the particle to the surface of the solid where Goethite hematite is reduced by CO from wood charcoal to magnetite (3Fe2O3 + CO → 2Fe2O3 + CO2). The second stage involves the penetration of a gaseous reactant through the blanket of ash to the surface of the unreacted core where magnetite is reduced to wustite (Fe3O4 + CO → 3FeO + CO2). The final stage is the reaction of the gaseous reactant with solid at the reaction surface, which is described by the stoichiometry equation where the product consists of fluid and solid (FeO + CO → Fe + CO2). This non-contact charcoal reduction approach is adopted to maximize the benefit of using CO/CO2 gases from charcoal for reduction without the need for beneficiation and concentration. The rate-controlling steps for the reduction kinetics of average particle size 5, 10, 15, and 20 mm at 570, 700, 800, 900, and 1000oC are studied after heat treatment of the ore-wood charcoal in activated carbon reactor at total reduction time of 40 minutes based on literature. Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) analysis are done to investigate the spectrometric phase change and metallic components of the ore sample after reduction, respectively. The average percentage metallic iron content of 56.6, 60.8, and 61.7% and degree of metallization of 91.62, 75.96, and 93.6% are achieved from the SEM/EDX analysis of the reduced ore sample at reduction temperature of 570, 800 and 1000oC, respectively. The sharp drop in the degree of metallization of the reduced ore samples is observed at intermediate temperatures 700, 800, 900oC of the reduction. This indicates the tendency of high carbon deposit at the wustite stage of the reduction process at the least temperature and residence time of 5700C and 10 minutes, respectively. This study demonstrates that diffusion through the ash layer is the controlling resistance of the overall reduction process.

  • Open access
  • 33 Reads
Influence of structural heterogeneity of high-strength OCTG tubes on sulfide corrosion cracking resistance

High-strength OCTG tubes like C110, according to API 5CT (yield strength at least 758 MPa), are subject to requirements in terms of mechanical and corrosion properties. Steels of that group must combine high strength characteristics and resistance to a process of general corrosion and sulfide corrosion cracking (SSC). Extreme operating conditions require the high quality of the steels and determine the requirements for the level of alloying and purity for detrimental impurities, as well as for the chemical and structural homogeneity of the fabricated tubes. The production of these tubes is complicated because of influence on final structure by all parts of manufacturing from smelting and casting, to rolling and final heat treatment.

In this work, we studied the influence of seamless tubes microstructure with a 177.8 mm diameter and 10.36 mm wall thickness of high-strength steel (yield strength more than 758 MPa) to sulfide stress corrosion cracking (SSC) and sulfide stress corrosion cracking with low strain rates (SSRT). Tubes were obtained from continuous billets by screw piercing with preliminary quenching and tempering.

It was established that cracking during the tests always begins from the inner surface of the tube. Rough segregation bands were found on the inner tube surface, which occupies about a third of the thickness. The segregation bands consist of bainite varying degrees of tempering with a hardness from 280 (light band) to 320 HV (dark band). In the dark band, in comparison with the soft light ones, the content of chromium, molybdenum and niobium is increased. In addition to dispersed niobium, molybdenum, and chromium carbides formed during rolling and heat treatment, coarse niobium and titanium carbonitrides formed in the solidifying metal were found in the band. Thus, it has been shown that zonal segregations formed in continuous casting are not eliminated during rolling but are transformed in the region of banding of the inner pipe surface, which cannot be eliminated by heat treatment. Recommendations for the ladle treatment and casting of these steels are proposed, as well as modes of heat treatment to minimize the harmful effect of the segregated banding found on the pipe properties.

SSRT method helps more accurately and faster study the performance of steels in the development of technology for their production. But to verify of SSRT methods and the development of criteria for evaluating materials, a large statistics of two parallel tests is needed - standard tests according NACE TM 0177 (SSC) and SSRT methods.

  • Open access
  • 30 Reads
Quantitative description of the microstructure of duplex stainless steels using selective etching

The properties of duplex stainless steels (DSSs) depend on the ferrite-austenite ratio and on the amount of secondary phases. The actual phase content depends on the chemical composition of the steel and the technology of rolling and heat treatment of the final product. Therefore, it is necessary to control the volume fractions of all phases, their size and the distribution pattern. The existing physical methods for assessing the volume fraction of phases, for example, magnetometry or X-ray diffraction (XRD) quantitative phase analysis, work either with reference to certain databases to interpret the results, or in very narrow determination ranges. These methods also require the manufacture of additional samples, while metallographic assessment can be carried out on samples after mechanical tests. Therefore, in this work, a metallographic technique for assessing the phases in DSSs, based on selective etching and subsequent analysis according to ASTM E 1234, was developed.

Using thermodynamic modeling and scanning electron microscopy, the phases in the samples were identified. Studied samples were obtained after different heat treatments, including solution annealing and quenching from 1050-1200°C to obtain different amounts of ferrite, and annealing at 600-800°C to precipitate sigma-phase. By selecting reagents and etching technique, images of microstructure were obtained. The obtained images are suitable for measuring the volume fraction of ferrite and sigma-phase in the manual mode using the grid intercept method according to ASTM E 562 and in the automatic mode according to the ASTM E 1245. It is shown that chemical etching makes it possible to obtain more contrasting images for automatic analysis; however, the chemical method is very sensitive to changes in the conditions of sample preparation. Electrolytic etching makes it possible to obtain a stable high etching quality, but it requires selection of techniques for each sample using expensive equipment.

It was shown that the developed methodology for quantitative analysis based on selective etching and metallographic assessment according to ASTM E 1245 allows obtaining a much more accurate result compared to the proposed ASTM E 562 method, which well correlates with the XRD quantitative phase analysis. The accumulation of the results of a quantitative assessment the DSS’s structure according to the developed methodology will be a reliable basis for creating new and improved production technology of existing steels.

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