Seasonal variation of low-latitude E-region plasma irregularities studied using Gadanki radar and ionosonde

In this paper, we present seasonal variation of E region field-aligned irregularities (FAIs) observed using the Gadanki radar and compare them with the seasonal variation of Es observed from a nearby location SHAR. During daytime, FAIs occur maximum in summer and throughout the day, as compared to other seasons. During nighttime, FAIs occur equally in both summer and winter, and relatively less in equinoxes. Seasonal variations of Es (i.e. ftEs and fbEs) show that the daytime activity is maximum in summer and the nighttime activity is maximum in equinoxes. No relation is found between FAIs occurrence/SNR and ftEs/fbEs. FAIs occurrence, however, is found to be related well with (ftEs-fbEs ). This aspect is discussed in the light of the present understanding of the mid-latitude Es-FAIs relationship. The seasonal variations of FAIs observed at Gadanki are compared in detail with those of Piura, which show a significant difference in the daytime observations. The observed difference has been discussed considering the factors governing the generation of FAIs

Dissimilar metal joint quality measurement using infrared thermography: Experimental and Numerical approach for the application to CMT welding

Abstract Joining of dissimilar material has become highly popular research subject in the automobile industry due to the reduced weight and thereby increasing the fuel efficiency. Infrared thermography can be used as a natural tool to measure the temperature near the welding region and correlate the distribution of temperature to the weld quality. In the present work the quality of the dissimilar welded sample is identified using the temperature distribution in the vicinity of the weld pool region. A numerical model for CMT continues welding process has been modeled and simulated for the first time and compared with the experimental measurement

Anomalous kinetics, patterns formation in recalescence, and final microstructure of rapidly solidified Al-rich Al-Ni alloys

Copyright © 2022 The Authors. From thermodynamical consideration, rather a monotonically increasing crystal growth velocity with increasing undercooling is expected in the crystallization of liquids, mixtures, and alloys [P.K. Galenko and D. Jou, Physics Reports 818 (2019) 1]. By contrast to this general theoretical statement, Al-rich Al-Ni alloys show an anomalous solidification behavior: the solid-liquid interface velocity slows down as the undercooling increases [R. Lengsdorf, D. Holland-Moritz, D. M. Herlach, Scripta Materialia 62 (2010) 365]. It is also found that besides the anomalous growth behaviour, changes in the shape of the recalescence front as the growth front morphology occur. In the light of recent measurements in microgravity with an Al-25at.% Ni alloy sample onboard the International Space Station (ISS) results confirming this anomalous behavior as an unexpected trend in solidification kinetics are presented. The measurements show multiple nucleation events forming the growth front, a mechanism that has been observed for the first time in Al-Ni alloys [D. Herlach et al., Physical Review Materials 3 (2019) 073402; M. Reinartz et al. JOM 74 (2022) 2420] and summarized with detailed analysis in the present publication over a wider range of concentrations. Particularly, the experimental measurements and obtained data directly demonstrate that the growth front does thus not consist of dendrite tips (as in usual rapid solidifying samples), but of newly forming nuclei propagating along the sample surface in a coordinated manner. Theoretical analysis on intensive nucleation ahead of crystal growth front is made using the previously developed model [D.V. Alexandrov, Journal of Physics A: Mathematical and Theoretical 50 (2017) 345101]. Using equations of this model, quantitative calculations confirm the interpretation of experimentally observed propagation of the recalescence front and obtained data on the microstructure of droplets solidified in electromagnetic levitation facility (EML) on the Ground, under reduced gravity during parabolic flights, and in microgravity conditions onboard the ISS.European Space Agency (ESA) within the project NEQUISOL under contract No. 15236/02/NL/SH for experimental measurements under reduced gravity and by RSF under project No. 21-19-00279 for theoretical modeling; German Space Center - Space Administration under contract No. 50WM1941; German Science Foundation (DFG) under the Project GA 1142/11-1 for experimental measurements on the Ground

Dendritic solidification and fragmentation in undercooled Ni-Zr alloys

Kinetics of dendritic solidification and fragmentation of dendritic crystals in undercooled Ni–Zr samples are studied. Using the capacitance proximity sensor technique and a high-speed-camera system, the dendrite growth velocity has been measured as a function of initial undercooling in solidifying droplets processed by the electromagnetic levitation technique. Analyses of solidified droplets give evidence to a transition from coarse grained dendrites to grain refined dendrites (CG-GR) at small undercooling, a transition from grain refined dendrites to coarse grained dendrites (GR-CG) at moderate undercooling, and to a second transition from coarse grained dendrites to grain refined dendrites (CG-GR) at a higher undercooling. Predictions of a sharp-interface model are compared with the results of experiments on Ni–Zr samples

Dendrite Growth Velocity in Levitated Undercooled Nickel Melts

Model predictions for the dendrite growth velocity at low undercoolings are deviating significantly from experimental data obtained in electromagnetic levitation with a Capacitance Proximity Sensor (CPS) [K. Eckler, D.M. Herlach, Mater. Sci. Eng. A 178 (1994) 159]. In addition to that, previous data sets obtained by different techniques are not in good agreement with each other. For instance, growth velocity data for nickel melts obtained with a high-speed camera system [D.M. Matson, in: Solidification 1998, TMS, Warrendale PA, 1998, p. 233] show higher values at low undercoolings than data obtained with the CPS. Within this work new measurements of dendritic growth velocity in levitated undercooled nickel samples were performed as a function of undercooling DT to investigate this discrepancy. Solidification of the undercooled melt was detected at undercooling levels within the range of 30 K < DT < 300 K. The new data reveal high accuracy and low scattering. These data are compared with two independent growth velocity data sets and discrepancies are discussed. For verification of the new CPS data dendrite growth velocity was also measured by using a high-speed camera where the morphology of the intersection of the solidification front with the sample surface was investigated. The new experimental data are analyzed within the model of dendrite growth obtained on the basis of Brener's theory [E. Brener, J. Cryst. Growth 99 (1990) 165] and the model of dendrite growth with melt convection in a solidifying levitated drop, presently being developed. Special attention is paid to the effects of convection and small amounts of impurities on the growth dynamics at small undercoolings

Solidification microstructure development

In the present article, evolution of microstructure during solidification, as a function of various parameters, is discussed. Macrosegregation is described as being due to insufficient diffusivity of solute in the solid. Pattern formation is discussed in the light of instabilities at the solidification growth front. An overview of the scaling relations for various microstructures is given. Metastable extensions to equilibrium phase diagrams and corrections to equilibrium quantities are described