Research on Residual Stress Distribution in Different Areas of Laser-MAG Arc Hybrid Welding by Numerical Simulation

In this research, through experiments and numerical simulations, the residual stress distribution of the top and bottom surfaces of the laser (TruDisk16002)-arc (MAG) hybrid welding seam and the weld cross-section are studied. The results show that when the arc power is 6.5KW and the laser power is 7.5KW, the weld is formed well. The residual stress on the bottom surface near the weld is higher than that on the top surface. The laser zone in the center of the weld has the largest residual stress, the arc zone is smaller, and the mixed zone is the smallest. The laser zone has the largest residual stress at the fusion line and the heat-affected zone, followed by the mixed zone, and the arc zone is the smallest. followed by the mixed zone, and the arc zone has the smallest.

Study on MnS Inclusion Aggregation along Continuous Casting Slab Thickness of Medium Carbon Structural Steel

Precipitation of MnS inclusions in steel affects the mechanical properties of the material significantly. The evolution of MnS inclusions along the continuous casting slab thickness and its influencing factors has not been clearly established and comprehensively studied. In this paper, solidification macrostructure, sulfur segregation and MnS inclusions in the continuous casting slab of medium carbon structural steel 45# were studied by various methods, including the metallographic observations, elemental analysis, scanning electron microscope (SEM) with Energy Dispersive Spectrometer (EDS) observation, automatic particle analysis, and thermodynamic calculations. The 2D/3D morphologies of MnS inclusions suggest that the sulfides turn from globular to rodlike, and further to dendritic shape along the slab thickness progressively. Furthermore, it was found that MnS inclusions are remarkably aggregated in the columnar crystals and the equiaxed crystals mixed zone, where the sulfides have the largest average diameter of 6.35 μm and the second maximum area fraction of 0.025% along the slab thickness. In order to reveal the mechanism of this phenomenon, the precipitation temperature of MnS inclusion in the 45# steel was clarified by thermodynamic calculation and experimental observation, and the quantitative relationships among the distribution of sulfur content, secondary dendrite arm spacing (SDAS), and precipitation area fraction of MnS inclusions were discussed. Moreover, the inclusion size was numerically predicted to compare with the measured value. The results indicate that the large SDAS, high sulfur content and low cooling rate accounting for the large-size aggregated MnS inclusions in the mixed zone. Unfortunately, the dendritic MnS inclusions, even if the average diameter exceeds 52 μm, can act as the nucleation sites for ferrites, and the distribution of the sulfides promotes uneven microstructure in the steel.

Hydraulic resistances of suspended flows in bedrooms with a moving bottom

The results of some existing theoretical and experimental studies of hydraulic resistances of open flows in moving channels are considered. Possible reasons for the inconsistency of the results of various studies of hydraulic resistance in open channels with increased roughness are indicated. The analysis of mass field data on the Darcy (Shezi) coefficient of canals in alluvial soils and a sandy mobile bed is carried out. It was confirmed that the channels of these categories are characterized by a mixed zone of hydraulic resistance, and regularities were revealed that take into account the features of the real resistance zone of earthen channels. Based on the analysis of the smoothly varying flow of open flows and the corresponding theory of the boundary layer and the law of the logarithmic distribution of velocities, the calculated dependencies are obtained, making it possible to determine the resistance of open flows concerning natural conditions.

Grenzland als Synergie- und Dysergiezone

The author discusses reasons for the scientific interest on the definition of “border / borderland / boundary” in many research-fields, various types of which are described in the article. It is suggested that at least two of them – “threshold” and “mixed zone” – are significantly marked by processes of syn-/ and dysergy. For this reason, the category of “border / borderland / boundary” should be included into the terminological instrumentarium of synergetics and systems theory.

Микроструктура переходных границ в многослойных Мо/Ве-системах

The microstructure of Mo / Be multilayer periodic systems was studied by X-ray reflectivity and diffractometry and EXAFS spectroscopy. It was found that in the Mo / Be system, mixed zones of different compositions form at the boundaries. At the Mo-on-Be border, there is a mixed zone, similar in composition to MoBe22, and at the Be-on-Mo border, with MoBe2. As a result of thermal annealing for one hour, the structure of the transition boundaries in the multilayer system remains stable. With further annealing, diffusion processes occur that lead to the formation of another compound at the interface — MoBe2, instead of MoBe22, however, the period of the structure remains unchanged. This behavior explains the increase in the reflection coefficient of Mo / Be mirrors after annealing for one hour and a further decrease in the reflection coefficient with a longer annealing time.

Functionally Graded SS 316L to Ni-Based Structures Produced by 3D Plasma Metal Deposition

In this investigation, the fabrication of functionally graded structures of SS316L to Ni-based alloys were studied, using the novel technique 3D plasma metal deposition. Two Ni-based alloys were used, a heat resistance alloy Ni80-20 and the solid-solution strengthened Ni625. Different configurations were analyzed, for the Ni80-20 a hard transition and a smooth transition with a region of 50% SS316L/50% Ni80-20. Regarding the structures with Ni625, a smooth transition configuration and variations in the heat input were applied. The effect of the process parameters on the geometry of the structures and the microstructures was studied. Microstructure examinations were carried out using optical and scanning electron microscopy. In addition, microhardness analysis were made on the interfaces. In general, the smooth transition of both systems showed a gradual change in the properties. The microstructural results for the SS316L (both systems) showed an austenite matrix with δ-phase. For the mixed zone and the Ni80-20 an austenite (γ) matrix with some M7C3 precipitates and laves phase were recognized. The as-built Ni625 microstructure was composed of an austenite (γ) matrix with secondary phases laves and δ-Ni3Nb, and precipitates M7C3. The mixed zone exhibited the same phases but with changes in the morphology.