Study on the Solidification Behavior of Inconel617 Electron Beam Cladding NiCoCrAlY: Numerical and Experimental Simulation

To better control the Inconel617 electron beam cladding solidification process, a three-dimensional temperature field model was built to simulate the temperature gradient, cooling rate, and solidification rate in the solidification process and take a deep dive into the solidification behavior, as well as the calculation of the solidification characteristic parameters at the edge of the molten pool and then predict the solidification tissue structure. The study shows that the largest temperature gradient occurred in the material thickness direction. The self-cooling effect of the material dominated the solidification of the alloy layer; the cooling rate depended on the high-temperature thermal conductivity of the material and the self-cooling effect of the matrix, and the maximum cooling rate in the bonding zone was 1380 °C/s. The steady-state solidification rate was equal to the moving speed of the heat source; the solidification characteristics of the solidification process at the edge of the molten pool increased with the distance from the surface: the cooling rate decreased from 1421.61 to 623 °C/s, the temperature gradient increased from 0.0723 × 106 to 0.417 × 106, and the solidification rate decreased from 0.01 to 0 m/s. The prediction was made that the small and thin equiaxed crystals are on the top, a thin and short dendritic transition structure in the middle, and relatively coarse dendrites at the bottom. Experiments confirmed that the solidification tissue structure is basically consistent with the simulation law.

Effect of layer thickness on the overhanging surface quality manufactured by selective laser melting

With the increasing demand for the precision of lightweight part, overhanging surface quality has attracted more and more attentions in recent years. In this work, the relationship between overhanging surface quality and layer thickness was studied. The testing results revealed that with the increasing of the layer thickness, surface quality, especially the surface flatness, showed a significant decreasing trend due to the decreasing of the bending deformation. When layer thickness was ranged from 0.15 to 0.18, it reached a relative optimal condition while the sinking distance and flatness within 0.095 mm–0.1 mm and 0.076 mm–0.078 mm, respectively. With the further increasing of the layer thickness, both sinking distance and surface flatness had a quite significant decreasing due to the increasing gravity of the overhanging layer powder and bonded powder caused by the molten pool sinking. Combined to the experimental data and the analysis given above, the structure of the overhanging surface was optimized and the surface quality showed a further increase.

Numerical simulation method of submerged arc surfacing process of rollers

The submerged arc surfacing process involves complex behaviors such as metal heat transfer, melting, flow, phase transformation, and solidification and involves the interaction of electric field, thermal field, magnetic field, and flow field. At present, it is impossible to reveal the transient mechanism of multi-field coupling in submerged arc surfacing by experience or trial and error, which is not conducive to shorten the development cycle and save the cost. Moreover, it is difficult to measure the molten pool velocity, von Mises stress, and phase transformation zone in real-time. However, these factors are the key to obtain a high-quality surfacing layer. Therefore, a three-dimensional mathematical model of heat force flow multi-field coupling for roller submerged arc surfacing is established in this article. The distribution and variation of welding temperature, von Mises stress, molten pool flow field, and phase transformation zone are revealed by solving the model. The maximum von Mises stress of the rollers during submerged arc surfacing is 432 MPa. The depth of the phase transformation is 2.50 mm, and the width is 1.98 mm. Zeiss-IGMA HD FESEM was used to observe the welding microstructure. The results show that the main microstructure is martensite and a small amount of ferrite.

Experimental Study on Stratification Morphology of the Molten Pool During Severe Accident

Stratification morphology of a molten pool under severe reactor accident was investigated by the CESEF experimental facility. The experimental scale was 5,000 g, the atomic ratio of U/Zr was 1.5, the content of stainless steel was 10%, and the oxidation degree of Zr was 40–100%. It was shown that the molten pool was obviously stratified within the range of experimental parameters; one was a metal layer, and the other was an oxide layer. The layered morphology of the molten pool was different with the composition of different corium. With the decrease in the Zr oxidation degree, the metal layer moved downward in the molten pool, and the molten pool would overturn. The main elements in the oxide layer were U, Zr, and O, and the content of stainless steel was low. The main element in the metal layer was stainless steel and contained a certain amount of U and Zr.