Ultra-Narrow Gap Fiber Laser Conduction Welding Technology for 304 Stainless Steel Thick Plates and the Mechanical Properties of Welding Joints

The application of thick metal plates is increasing, and the welding problem is becoming more and more prominent. Narrow gap laser welding is one of the important methods, and it is also a research hotspot. The stainless steel thick plates were welded using the ultra-narrow gap fiber laser conduction welding with filler wire. Results show that the ranges of technological parameters for the achievement of the weld seam with no defects are smaller when the gap width is comparatively larger. Using the optimized technological parameters, the butt welding with no defects on the 3 mm gap between two 304 stainless steel plates with 60 mm thickness was achieved through the filling 20 times. This welding method of 304 metal with large thickness is rare in the literature. The tensile strength of the welding joint can be up to 87% of that of the base metal, and the micro-hardness and yield strength of the joint are comparable with those of the base metal.

Межзонный двухфотонный линейно-циркулярный дихроизм в полупроводниках в приближении Кейна

Interband two-photon optical transitions are classified and expressions are obtained for the matrix elements in a narrow-gap semiconductor depending on the band parameters, degree of polarization, and light frequency. It is shown that the main contribution to two-photon linear-circular dichroism in narrow-gap semiconductors is made by optical transitions proceeding from the subband of light holes to the conduction band. The dependences of the partial coefficients of interband two-photon absorption of light, which differ from each other by the types of optical transitions, are analyzed depending on the degree of polarization of the light, and a quantitative analysis of the coefficient of linear-circular dichroism of two-photon absorption of light is carried out. Expressions are obtained for the spectral dependence of the coefficient of interband two-photon absorption of light in narrow-gap semiconductors in the Kane model.

Исследование плазмонного резонанса в Bi-=SUB=-2-=/SUB=-Se-=SUB=-3-=/SUB=- и Sb-=SUB=-2-=/SUB=-Te-=SUB=-3-=/SUB=- методом инфракрасной спектральной эллипсометрии

In the infrared region of the spectrum (IR), the optical properties of single-crystal samples of narrow-gap degenerate semiconductors Bi2Se3 and Sb2Te3 are investigated by infrared spectral ellipsometry (SE). The transport properties of the Drude fitting of dielectric functions obtained by spectroscopic ellipsometry are studied. The behavior of the bulk and surface plasmon polaritons is investigated in detail. The dispersion and mean free path of the plasmon, the depth of the skin layer for the conducting and dielectric surfaces are calculated. The contribution of the plasmon to the optical properties is estimated from the spectral density for the Bi2Se3 and Sb2Te3 samples.

Narrow Gap MAG Welding and Joint Performance Analysis of 25Cr2NiMo1V Thick Plate

The narrow gap MAG welding system was used to successfully weld the 50mm thick butt joint of 25Cr2NiMo1V rotor steel. After 15-layer bead welding, heat treatment is performed on the welded joint. Compare the changes in the microstructure, tensile strength and impact energy of the welded joints and the heat-treated joints at 580°C (20h). The results show that after the heat treatment of the structure, the side lath ferrite in the coarse-grained region grows up, and the eutectoid ferrite grows up in the fine-grained region first. The strength of the welded joint is about 605MPa, and the fracture is characterized by ductile fracture. After heat treatment at 580°C (20h), the strength is about 543MPa, the fracture is characterized by ductile fracture, and there are also a large number of discontinuous small surface platforms, and the characteristic of brittle fracture appears slightly. The impact energy of the weld center of the welded joint is about 141J, the fusion line area is about 113J, and the toughness of the fusion line is slightly lower than that of the weld center. After heat treatment, the impact energy at the center of the weld is about 183J, the fusion line area is about 95J, the toughness of the weld center increases, and the toughness of the fusion line decreases.