The Degassing Laws for Railway Wheel Steel in a Vacuum Tank Degasser

The research presents the results of data analysis on degassing of wheel grades of steels in a tank degasser with a capacity of 120 tons, operated at the JSC “Ural Steel”. The volume of the analyzed sample included 754 steels for railway wheels (steel grades “2” and “T” according to State standard GOST 10791-2011) weighing more than 80 thousand tons received in November-December 2019.It was established that in order to guarantee the production of hydrogen content of less than 1.5 ppm and nitrogen before 0.007%, it is necessary to carry out vacuum treatment of metal with overheating of 110-130°C at the residual pressure of up to 3 mbar for 20-25 minutes and argon flow rate of at least 0.05 m3/ton. The regression equation was obtained, which allows to predict the results of degassing, as well as select the values of vacuum treatment parameters in order to achieve a given content of dissolved gases - hydrogen and nitrogen.

Ag-coated cotton fabric as ultrasensitive and flexible SERS substrate

Surface enhanced Raman scattering (SERS) has proven to be increasingly valuable as an analytical tool since this phenomenon was first observed in 1973. However, challenges still exist to ensure their ability to access targeted analytes and adequate levels of sensitivity to them on irregular surfaces. Herein, silver (Ag) nanoparticles are deposited onto cotton fabric through magnetron sputtering to develop a flexible and ultrasensitive SERS-active substrate. To obtain a better enhancement effect, Ag nanoparticles of different sizes are produced by controlling the argon flow rate and the sputtering time. The finite-difference time-domain (FDTD) method and Raman mapping are used to explain the process behind Raman signal enhancement. The cotton fabric sample with Ag nanoparticles deposited at an argon flow rate of 200 sccm (labelled as AC-200) shows a high enhancement factor (EF) of 104 with a Methylene blue (MB) solution of 10−3 M, stability with a related standard deviation (RSD) of 1.03%, excellent reproducibility with an RSD of 1.92% and high sensitivity with 10−9 M of MB solution. Therefore, AC-200 demonstrates exceptional SERS signal reproducibility and stability for different types of chemical analytes and has the potential to be used in future practical applications.

Optimization of the MIG Arc Weld-Brazing Process on Titanium and Aluminum Lap-Joint Welds Using the Taguchi Method, Grey Relational Analysis and Fuzzy Logic

The dissimilar materials lap-joint of Ti-6Al-4V titanium (Ti) and 6061 aluminum (Al) alloys was achieved through a metal inert gas (MIG) arc weld-brazing process. The relationships between the major MIG arc weld-brazing parameters such as travel speed of MIG torch, MIG welding current, argon flow rate of MIG torch, wettability of weld bead and mechanical property of Ti/Al lap-joint specimens were investigated. A proposed approach that integrates the Taguchi method, grey relational analysis (GRA) and fuzzy logic was employed to obtain the optimal MIG arc weld-brazing parameters. The proposed approach was adopted to solve the MIG arc weld-brazing process with multiple quality characteristics (QCs). The experimental procedure of this study not only improves the wettability of weld bead, but also increases the tensile strength of Ti/Al lap-joint specimens. Confirmation experiments revealed that this study could efficiently optimize the MIG arc weld-brazing parameters, and the average tensile strength of Ti/Al lap-joint specimens could reaches 178 MPa. During the MIG weld-brazing, higher argon flow rate of the MIG torch that produces turbulence to the weld pool and brings outside air could create a high amount of porosity over the weld bead.

Effect of Argon Flow on Oxygen and Carbon Coupled Transport in an Industrial Directional Solidification Furnace for Crystalline Silicon Ingots

Transient global simulations were carried out to investigate the effect of argon flow on oxygen and carbon coupled transport in an industrial directional solidification furnace for quasi-single crystalline silicon ingots. Global calculation of impurity transport in the argon gas and silicon melt was based on a fully coupled calculation of the thermal and flow fields. Numerical results show that the argon flow rate affects the flow intensity along the melt–gas surface, but has no significant effect on the flow patterns of silicon melt and argon gas above the melt–gas surface. It was found that the evaporation flux of SiO along the melt–gas surface decreases with the increasing argon flow rate during the solidification process. However, the net flux of oxygen atoms (SiO evaporation flux minus CO dissolution flux) away from the melt–gas surface increases with the increasing argon flow rate, leading to a decrease in the oxygen concentration in the grown ingot. The carbon concentration in the grown ingot shows an exponential decrease with the increase of the argon flow rate, owing to the fact that the dissolution flux of CO significantly decreases with the increasing argon flow rate. The numerical results agree well with the experimental measurements.

Changes in the Coating Composition Due to APS Process Conditions for Al2O3-Cr2O3-TiO2 Ternary Powder Blends

Thermally sprayed coatings from the single oxides and binary compositions of the Al2O3-Cr2O3-TiO2 system show multifunctional properties. Ternary compositions are promising for further improvement in their performance. The stability of the composition during coating formation is an important issue for blended feedstock powders in order to obtain the desired properties. This work focuses on the compositional changes of a ternary blend of Al2O3, Cr2O3 and TiOx powders of equal content by mass in a conventional atmospheric plasma spraying (APS) process using an Ar/H2 plasma gas mixture. By increasing the argon flow rate at constant hydrogen flow rate, the total plasma gas flow rate and the Ar/H2 ratio were varied. For the highest argon flow rate, this resulted in an average particle velocity of 140% and an average particle temperature of 90% of the initial values, respectively. Coating composition and microstructure were studied by optical microscopy, SEM, including EDS analyses, and XRD. In addition, the coating hardness and electrical impedance were also measured. Differences in the “difficulty of melting factor” (DMF) and the thermal diffusivity of the three oxides appear to be responsible for the dramatic change of the coating composition with an increasing argon flow rate. For the highest argon flow rate applied, besides TiO2, the coating contains only 8 wt.% Al2O3, while the Cr2O3 content remained almost constant. At the same time, the change of the Ar/H2 ratio resulted in the formation of stoichiometric TiO2 in the coating by oxidation of TiOx in the feedstock powder. Moreover, a small content of titanium was found in the Cr2O3 splats, showing that there are only limited interactions between the large oxide powder particles. Thus, the study has shown that stability of the chemical composition during spraying of ternary powder blends is strongly influenced by the process conditions.