METALLURGICAL ENGINEERING
Year:2017 | Volume:19 | Issue:4 (64) |Papers Count:8

Cooling waters are used in many industries for lowering the working temperature of the machineries or parts. Corrosion inhibitors are used to mitigate corrosion of such metallic parts in contact with cooling water. In case these machineries are under stress they may fail due to SCC. Therefore it is necessary to check the susceptibility of metallic parts to SCC in cooling water. The inhibition effect of sodium citrate on SCC of carbon steel in SCW is investigated using SSRT. The stress-strain curves and potential changes showed that citrate ions increase time to failure of carbon steel in presence of 500 ppm chloride ions. Moreover it was observed that the presence of citrate ion is not effective at high concentration of chloride ions i.e.1000 ppm. The results showed that in presence of citrate ion the toughness was decreased probably due to the prevention of pitting which may increase the elongation.

Microstructure and low cycle-high temperature fatigue properties of Nimonic 105 superalloys with and without B and Zr is investigated in this article. Fully reversed strain-controlled tests were performed at 750°C, R=0 and strain rate of 3×10-3 s-1. The results show that Zr cause to ZrC formation at the grain boundaries and grain interior. Also Zr is reduced the grain size of the alloys. The carbides at the absence of Zr is of the type of (Cr, Mo)23C6 at the grain boundaries. The g’ size decreased by B additions to the alloys and the number of twins increased. 0.013wt% B improves low cycle-high temperature fatigue of the alloy. At the presence of B, fracture is of the types of intragranular and intergranular but by addition of 0.16wt% Zr the only fracture type is intragranular. Hard and none coherent MC type precipitates by Zr addition are the initiation place for micrcraking and the cause of fatigue life reduction.

NiTi alloys (SMAs) are unique alloys, which have two attractive properties, shape memory effect, super-elasticity and biocompatibility. Each property strongly depends on the composition, temperature and structure. To have shape memory and super elastic behavior at the same time, a bi-layer composite, austenitic (A) /martensitic (M) NiTi alloy was designed and made to investigate the properties. Layers with2: 1 ratio (M: A) were bonded under diffusion bonding process in vacuum tube furnace at 1000⁰C, for 3 hours under 20 MPa compressive stress. To evaluate the effect of interface zone on the properties, specimens were annealed in vacuum tube furnace at1000 ⁰C for 5 and 10 hours. The interface was investigated by optical microscopy, and chemical composition gradient in the interface zone was analyzed using line scan analysis with energy dispersive X-ray spectroscopy. Mechanical properties of the interface zone were studied using micro-hardness measurements. The shape memory and super elastic behavior of bi-layer were investigated using loading-unloading test and in-situ thermal heating by applying electrical current. The results depicted that annealing time has significant effect on the width of interface zone, and thus a microstructural gradient has been developed, within the thickness of the specimen. It was found that the bi-layer specimens could act as a functionally graded material due to their chemical composition gradients that is desirable for better controllability in actuation applications.

During recent years recycling of lithium-ion batteries has attracted a lot of attention due to their extensive apllications in various electric and electronic vehicles. Recycling of these batteries is of a great importance due to environmental issues and metal sources content, so this paper is to review the current status of these batteries’ recycling technologies. Among different recycling methods, hydrometallurgical based route is an optimized method to separate and recover metals and it has three steps as pre-treatment, leaching and deep recovery. In addition to brief description of these batteries’ structure and components, this paper has summarized the chemical and physical processes utilized in all steps of pre-treatment, leaching and metal recovery. Heat treatment, ultrasonic, dissolving and mechanical treatment are the common methods in the pretreatment step and crystallization, solvent extraction, electrochemical deposition and precipitation are accounted most used methods in the recovery step. Finally all investigations operated over the recycling issue also have been summarized in this paper. These categorized studies include both research and optimization into each triple step of hydrometallurgical route and new electrodes synthesis.

Cellular metals and metallic foams as a class of new engineering materials have unique properties and thus, these materials can be successfully used in many industrial applications. In this study, hollow alumina spheres were used to create cells and cell walls in ductile iron. Alumina hollow spheres were manufactured by polystyrene beads as the substrate and using the coating the polystyrene beads by mixture of alumina powder and sodium silicate as binder. Sand casting technique was used to produce ductile iron syntactic foams. In this technique, alumina hollow spheres were placed into the mold cavity and then, the molten metal was poured. Casting specimens were grinded and then, light microscopy, scanning electron microscopy evaluations, and compression testing were carried out. The results were shown that reduced cell sizes, improved compressive behavior of casting foams. The microstructure of casting specimens consisted of pearlite and ferrite surrounded nodular graphite. In the specimens with smaller alumina hollow spheres, the thickness of the cell walls decreases and cooling rate increases. Therefore, carbide phases were formed in microstructure.

Gray cast iron is among the most common and important engineering material that plays a significant role and has many applications in various industries, including the automotive and machinery manufacturing. It still attracts researchers’ interest to improve its properties and maintain its position among the engineering materials. In this research, the microstructure of plain cast iron as well as those containing 4 wt% aluminum with different amounts of silicon, 1 to 4 wt%, was studied. Pin-on disc method was used to evaluate the wear resistance of the cast irons. The results showed that the addition of aluminum to gray cast iron brings about the formation of ferrite phase, which accompanies a decrease in hardness value. In addition, the increase in silicon content in aluminum bearing cast iron up to 2wt% intensifies the formation of ferrite phase, while further increase to 3 wt% results in emerging a Fe-Al-Si intermetallic compound. In gray cast iron with constant 4 wt% aluminum, increasing silicon content to 3 wt% and 4 wt% leads to improve the hardness value due to the increased percentage of intermetallic phase. Confirming microstructure evolution as well as hardness values, the results of wear experiment approved lower wear rate in cast irons containing intermetallic phase. In contrast, the lowest wear resistance was observed in aluminum bearing cast iron containing 2 wt% silicon.