Effect Of Thermal State Research Articles

Effect of thermal state on the chemical composition of the mantle and the sizes of the moon’s core

Based on the joint inversion of seismic and gravity data in combination with the Gibbs free energy minimization method for calculating phase equilibria in the framework of the Na2O-TiO2-CaO-FeO-MgO-Al2O3-SiO2 system, the influence of the thermal state on the chemical composition models of the mantle and the sizes of the Fe-S core of the Moon has been studied. The boundary conditions used are seismic models from Apollo experiments, mass and moment of inertia from the GRAIL mission. As a result of solving the inverse problem, constraints on the chemical composition (concentration of rock-forming oxides) and the mineralogy of a three-layer mantle are obtained. It is shown that regardless of the temperature distribution, the FeO content of 11–14 wt.% and magnesian number MG# 80–83 are approximately the same in the upper, middle and lower mantle of the Moon, but differ sharply from that for the bulk composition of the silicate Earth (Bulk Silicate Earth = BSE, FeO ~8 wt% and MG# 89). On the contrary, estimates of the Al2O3 content in the mantle rather noticeably depend on the temperature distribution. For the considered scenarios of the thermal state with a difference in temperature of 100–200°C at different depths, Al2O3 concentrations increase from 1–5% in the upper and middle mantles to 4–7 wt.% in the lower mantle with garnet amounts up to 20 wt.%. For the “cold” models, the bulk abundance of aluminum oxide in the Moonis Al2O3 ~1–1.2 × BSE, and for the “hot” models it can be in the range of 1.3–1.7 × BSE. Concentrations of SiO2 to a lesser extent depend on the temperature distribution and constitute 50–55% in the upper and 45–50 wt.% in the lower mantle; orthopyroxene, rather than olivine, is the dominant mineral of the upper mantle. Based on the modeling of the density of Fe-S melts at high Р-Т parameters, the sizes of the lunar core are estimated. The Fe-S core radii with an average density of 7.1 g/cm3 and a sulfur content of 3.5–6 wt.% are in the range of 50–350 km with a most likely value of about 300 km and rather weakly depend on the thermal regime of the Moon. The simulation results suggest that a lunar mantle is stratified by chemical composition and indicate significant differences in the compositions of the Earth and its satellite.

Effect of Thermal State on the Mantle Composition and Core Sizes of the Moon

Based on the joint inversion of seismic and gravity data in combination with phase equilibrium calculations within the Na2O–TiO2–CaO–FeO–MgO–Al2O3–SiO2 system using the method of Gibbs free energy minimization, we estimated the influence of the thermal state on the model chemical composition of the lunar mantle and the size of the Fe–S lunar core. Models based on the Apollo seismic data and mass and moment of inertia estimates from the data of the GRAIL mission were used as boundary conditions. The solution of the inverse problem provided constraints on the chemical composition (major oxide abundances) and mineralogy of the three-layer mantle. It was shown that, independent of temperature distribution, the FeO contents (~11–14 wt %) and MG# values (80–83) of the upper, middle, and lower mantle of the Moon are approximately equal and strongly different from those of the bulk silicate Earth (BSE): FeO ~ 8% and MG# ~ 89. In contrast, the estimates of Al2O3 content in the mantle are sensitive to temperature distribution. The analysis of thermal state models with temperature differences of 100–200°C at different depths showed that the Al2O3 content increases from 1–5 wt % in the upper and middle mantle to 4–7 wt % in the lower mantle containing up to 20 wt % garnet. The lunar abundance of Al2O3 is ~(1.0–1.2) × BSE for “cold” models and may be as high as (1.3–1.7) × BSE for “hot” models. The abundance of SiO2 is less sensitive to temperature distribution and is 50–55 wt % in the upper mantle and 45–50 wt % in the lower mantle. Orthopyroxene rather than olivine is the dominant mineral of the upper mantle. Based on the modeling of Fe–S melt density at high P and T, the size of the lunar core was estimated. The radius of the Fe–S core having a mean density of 7.1 g/cm3 and a sulfur content of 3.5–6.0 wt % lies within the range 50–350 km with the most probable value of approximately 300 km and depends weakly on the thermal regime of the Moon. The results of modeling imply that the lunar mantle is chemically stratified and the compositions of the Earth and its satellite are significantly different.

Experimental and Computational Investigation of Structural Integrity of Dissimilar Metal Weld Between Ferritic and Austenitic Steel

The structural integrity of dissimilar metal welded (DMW) joint consisting of low-alloy steel and 304LN austenitic stainless steel was examined by evaluating mechanical properties and metallurgical characteristics. INCONEL 82 and 182 were used as buttering and filler materials, respectively. Experimental findings were substantiated through thermomechanical simulation of the weld. During simulation, the effect of thermal state and stress distribution was pondered based on the real-time nuclear power plant environment. The simulation results were co-related with mechanical and microstructural characteristics. Material properties were varied significantly at different fusion boundaries across the weld line and associated with complex microstructure. During in-situ deformation testing in a scanning electron microscope, failure occurred through the buttering material. This indicated that microstructure and material properties synergistically contributed to altering the strength of DMW joints. Simulation results also depicted that the stress was maximum within the buttering material and made its weakest zone across the welded joint during service exposure. Various factors for the failure of dissimilar metal weld were analyzed. It was found that the use of IN 82 alloy as the buttering material provided a significant improvement in the joint strength and became a promising material for the fabrication of DMW joint.

Quantification of Microtexture at Weld Nugget of Friction Stir-Welded Carbon Steel

Friction stir welding of C-Mn steel was carried out under ~800-1400 rpm tool rotation. Tool traversing speed of ~50 mm/min remained same for all joints. Effect of thermal state and deformation on texture and microstructure at weld nugget was investigated. Weld nugget consisted of ferrite + bainite/Widmanstatten ferrite with different matrix grain sizes depending on peak temperature. A texture around (ϕ2 = 0°, φ = 30°, ϕ2 = 45°) was developed at weld nugget. Grain boundary misorientation at weld nugget indicated that continuous dynamic recrystallization influenced the development of fine equiaxed grain structure. Pole figures and orientation distribution function were used to determine crystallographic texture at weld nugget and base metal. Shear texture components D1, D2 and F were present at weld nugget. D1 shear texture was more prominent among all. Large number of high-angle grain boundaries (~60-70%) was observed at weld nugget and was the resultant of accumulation of high amount of dislocation, followed by subgrain formation.

Three-Dimensional Thermomechanical Simulation and Experimental Validation on Failure of Dissimilar Material Welds

Dissimilar material weld joints, consisting of low-alloy steel and 304LN austenitic stainless steel (SS), have critical application in boiling water reactors in the nuclear industry. It was predicted that phase transformation adjacent to the fusion boundary and stress distribution across the transition joint play a key role in the structural degeneration of these welds. Quantitatively, to evaluate their contribution, two different joints were considered. One was fabricated with buttering material 309L SS (M/S Mishra Dhatu Nigam Limited, Hyderabad, India), and the other was produced with buttering material IN182 (M/S Mishra Dhatu Nigam Limited, Hyderabad, India). Base materials remained the same for both. Thermomechanical simulation on dissimilar material welds was performed using finite-element modeling to predict the thermal effect and stress prone area. Temperature-dependent thermal and structural properties were considered for simulation. Simulation results were compared with microstructural characteristics, and data were obtained from the in-situ tensile test. Simulation results exhibited that stress was at maximum in the buttering material and made the zone weaker with respect to adjacent areas. During the validation of results, it was observed that failure occurred through buttering material and endorsed the inference. The variation in mechanical properties of the two welds was explained considering the effect of thermal state and stress distribution.

The effect of thermal state of materials on their erosion stability in a dust-laden gaseous flow

The effect of thermal state of materials on their erosion stability in a dust-laden gaseous flow