Key Engineering Materials Vol. 902

Abstract: The temperature dependence of the kinematic viscosity was determined in the Fe_84.5Cu_0.6Nb_0.5Si_1.5B_8.6P₄C_0.3 melt, which has an anomaly in the temperature range 1700–1900 K. The cluster sizes participating in the viscous flow were calculated using the transition state theory. It is shown that the activation energy E_a is directly proportional to the natural logarithm of the cluster size d, and the melt viscosity decreases with increasing cluster size. In the anomalous region at heating, the activation energy first decreases and then increases. This behavior was associated with the cluster dissolution and the subsequent formation of new clusters with a different size and chemical composition. Upon cooling, the viscosity corresponds to the melt structure formed at the maximum heating temperature.

Abstract: An interconnected copper network or copper foam was successfully fabricated by electrochemical deposition using polyethylene glycol (PEG) and sodium bromide (NaBr) as additives. Both the amount of PEG and the current density were varied to obtain a Cu foam with the smallest pore diameter and wall thickness. The increasing amount of PEG resulted in a decrease in pore diameter. However, the wall thickness of the Cu network was increased. At 800 mg/L PEG and 20 mM NaBr, the average pore size of the foam was about 11.03 µm. Dendritic formation was also observed on the walls of the Cu foam. Further, higher current density resulted in increased dendritic growth. X-ray diffraction confirms that the Cu foam was spontaneously oxidized in air, leading to the formation of cuprous oxide (Cu₂O).

Abstract: The compressive behavior of ME20M alloy along rolling direction (RD) at a wide strain rates under low temperatures is investigated in this paper. Compressive stress-strain results reveal that the effect of strain rate on yield strength and flow stress is not obvious, especially at low temperatures. Moreover, the temperature plays an important role in compressive responses. SEM observations indicate that brittle fracture is the main fracture mode at low strain rate, and ductile fracture occurs in the failure of the alloy at high strain rate.

Abstract: In modern scientific and engineering expertise there are a few methods for graphical computational analysis related to decision making. However, few of them are devoted to materials science and the determination of the complex of properties separately and simultaneously. This research proposes a decision analysis approach tested for the basic properties of BH11 steel. With the help of the approach the tendencies as technological regimes in the change of the microhardness Hv, the relative wear resistance Kv and the connected nitride zone δnz are established. A model for the phase composition is derived, which interprets all observed trends and technological regimes for the relatively minimal and relatively maximal studied values. Thus, the efficiency of the technology in processing the considered steel is associated with the structure and properties of ion nitrided layers, which as a research is the main task of materials science.

Abstract: This paper demonstrates the results of the study of microstructure and physical-mechanical properties of the high-strength economically alloyed Fe-Cr-Mo steel, developed by RosNITI JSC for the production of the oil country tubular goods (OCTG) (casing and tubing). The main requirement for this steel is to provide simultaneous increased strength and resistance to sulfide stress cracking (SSC). It was shown that this problem could be solved by special heat treatment. As a result, the structure of this steel consists of a secondary sorbite with a lower dislocation density. Hardening is provided by dispersion-strengthened V, Nb carbides.

Abstract: In this paper, a new metastable Titanium alloy in the Ti-Nb-Ta-Mo system has been successfully produced using both the d-electron and Mo_eq concept. The influence of cold rolling on the microstructure and hardness was investigated. The alloy was fabricated by arc melting, cold rolled up to 90% reduction in thickness and characterized using X-ray diffraction (XRD), optical microscope and Vickers microhardness. The XRD peaks depicted both β and α′′ phases in all the cold rolled specimens. The hardness of the alloy increased with increasing cold rolling reduction thickness. An excellent plasticity (≥ 65%) and compressive strength up to (2.9 GPa) was achieved with low Young’s modulus (31 GPa) and no failure or crack on the alloy. Also, the alloy demonstrated a high compressive true strength coefficient (k ≈1426 MPa) along with improved strain hardening index (n ≈ 0.41). Based on the XRD, optical microscope and microhardness indentation micrographs, the deformation mechanism of Ti-13Nb-1.5Ta-3Mo was found to be a combination of stress induced transformation, mechanical twinning and slipping.

Abstract: The influences of moisture corruption and drying considerations on diffusible hydrogen were examined in this study. Two trials were carried out on an arc welding procedure, with the first being an assessment of the results of moisture contamination and the second being a test of the impact of welding constraints on diffusible hydrogen content. For example, the dispersible hydrogen found in welds was likened to the hydrogen levels of different unused electrodes. To calculate the proper drying constraints (Time and Temperature) for an applicable moisture contamination level in the weld electrode, an empirical equation was devised. For electrodes with a small diameter and welding parameter limits typically used for out-of-position welding, the equation is appropriate.

Abstract: This paper presented an investigation result of single layer and bilayer of PTA coating of two different Fe-Cr-V powder commercially available and an improvement of the surface hardness by adding 35% of WC. In case of single layer, the microstructure was uniform across the thickness and also the hardness, while microstructure of the bilayer was obviously separated between interlayer and topcoat. The bilayer coating microstructure was changed, and approaching the topcoat, the microstructure was similar to single layer. The hardness of bilayer was decreased due to the dilution. After adding WC into the powder, the microstructure was changed and it could be seen that WC particles distributed across the coating. The hardness was increased due to dilution of some WC. Moreover, in all cases, PTA process offered coating with no crack and no re-precipitated with only small pores. However, adding WC could result in bigger pore size.

Abstract: Generally, power transformers have been using mineral oil as a liquid insulator due to its availability and excellent dielectric property. However, petroleum sources are depleting, which implies that mineral oil is going to be limited in availability. So, this research is to investigate on vegetable oil with nanographene filler as a substitution. Vegetable insulating oil is considered as environment-friendly insulating oil due to their superiority of biodegradable, nature-friendly, high fire-point, and good level of breakdown voltage (BV). Nevertheless, vegetable insulating oil have high viscosity, leading to a slow flow rate on the cooling performance of power transformers. To solve this problem, a process of transesterification was used to produce palm oil methyl ester (POME) from a refined bleached deodorized palm olein (RBDPO) to reduce its viscosity. RBDPO and POME were used as two kinds of fluid-based to combine with graphene nanoparticles (GNPs). Electrical breakdown voltage tests were performed by the IEC60156 standard. The results shown that POME have higher BV than RBDPO but adding GNPs may lead to lower BV even with a small amount of concentration. Nevertheless, every nanofluid has a higher BV than 30 kV.