Performance of BaZrO3/Y2O3 dual-phase refractory applied to TiAl alloy melting

Vacuum induction melting is a potential process for the preparation of TiAl alloys with good homogeneity and low cost. But the crucial problem is a selection of high stability refractory. In this study, a BaZrO₃/Y₂O₃ dual-phase refractory was prepared and its performance for melting TiAl alloys was studied and compared with that of a Y₂O₃ refractory. The results showed the dual-phase refractory consisted of BaZr_1-xY_xO_3-δ and Y₂O₃(ZrO₂), exhibited a thinner interaction layer (30 μm) than the Y₂O₃ refractory (90 μm) after melting the TiAl alloy. Although the TiAl alloys melted in the dual-phase and Y₂O₃ refractory exhibited similar oxygen contamination (<0.1 wt%), the alloy melted in the dual-phase refractory had smaller Y₂O₃ inclusion content and size than that in the Y₂O₃ refractory, indicating that the dual-phase refractory exhibited a better melting performance than the Y₂O₃ refractory. This study provides insights into the process of designing highly stable refractory for melting TiAl alloys.     

SLM printing of cermet powders: Inhomogeneity from atomic scale to microstructure

It is very challenging for 3D printing based on the selective laser melting (SLM) technology to obtain cermet bulk materials with high density and homogeneous microstructures. In this work, the SLM process of the cermet powders was studied by both simulations and experiments using the WC-Co cemented carbides as an example. The results indicated that the evolution of the ceramic and metallic phases in the cermet particle during the heating, melting and solidification processes were all significantly inhomogeneous from atomic scale to mesoscale microstructures. As a consequence, the microstructural defects were caused intrinsically in the printed bulk material. The formation and growth of the bonding necks between the particles were mainly completed at the later stage of laser heating and the early stage of solidification. Both simulations and experiments demonstrated that thin amorphous layers formed at the ceramics/metal interfaces. This work disclosed the mechanisms for the evolution from the atomic scale to microstructure during the SLM printing of cermet powders, and discovered the origin of the defects in the printed cermet bulk materials.     

Study on ice-melting performance of gradient gas diffusion layer in proton exchange membrane fuel cell

In this study, a three-dimensional model was established using the lattice Boltzmann method (LBM) to study the internal ice melting process of the gas diffusion layer (GDL) of the proton exchange membrane fuel cell (PEMFC). The single-point second-order curved boundary condition was adopted. The effects of GDL carbon fiber number, growth slope of the number of carbon fibers and carbon fiber diameter on ice melting were studied. The results were revealed that the temperature in the middle and lower part of the gradient distribution GDL is significantly higher than that of the no-gradient GDL. With the increase of the growth slope of the number of carbon fiber, the temperature and melting rate gradually increase, and the position of the solid-liquid interface gradually decreases. The decrease in the number of carbon fibers has a similar effect as the increase in the growth slope of the number of carbon fibers. In addition, as the diameter of the carbon fiber increases, the position of the solid-liquid interface gradually decreases first and then increases.     

Complex study of protective Cr3C2–NiAl coatings deposited by vacuum electro-spark alloying,pulsed cathodic arc evaporation,magnetron sputtering,and hybrid technology

Coatings were obtained by vacuum electro-spark alloying (VESA), pulsed cathodic arc evaporation (PCAE), magnetron sputtering (MS) techniques and VESA-PCAE-MS hybrid technology using Cr₃C₂–NiAl electrodes. The structure of the coatings was analyzed using scanning and transmission electron microscopy, X-ray diffraction and energy-dispersive spectroscopy. Mechanical properties were determined by nanoindentation, while tribological properties were assessed using pin-on-disk tribometer. Corrosion resistance was estimated by voltammetry in 1 N H₂SO₄ and 3.5%NaCl solutions. Oxidation resistance tests were performed at 800°С in air. The VESA coating had the highest thickness, low friction coefficient and high wear resistance. PCAE coating demonstrated the highest hardness (24 GPa) and elastic recovery (59%), oxidation resistance and superior corrosion resistance both in 1 N H₂SO₄ (i_corr = 70 μА/cm²) and 3.5%NaCl (i_corr = 0.74 μА/cm²) solutions. The MS coating had average mechanical properties and low corrosion current density (71 μА/cm²) in 1 N H₂SO₄. Deposition of coatings using VESA-PCAE-MS hybrid technology led to an increase in corrosion and oxidation resistance at least by 1.5 times in comparison with the VESA coating.     

An automated treatment planning strategy for highly noncoplanar radiotherapy arc trajectories

Radiation therapy is a technology-driven cancer treatment modality that has experienced significant advances over the last decades, due to multidisciplinary contributions that include engineering and computing. Recent technological developments allow the use of noncoplanar volumetric modulated arc therapy (VMAT), one of the most recent photon treatment techniques, in clinical practice. In this work, an automated noncoplanar arc trajectory optimization framework designed in two modular phases is presented. First, a noncoplanar beam angle optimization algorithm is used to obtain a set of noncoplanar irradiation directions. Then, anchored in these directions, an optimization strategy is proposed to compute an optimal arc trajectory. The computational experiments considered a pool of twelve difficult head-and-neck tumor cases. It was possible to observe that, for some of these cases, the optimized noncoplanar arc trajectories led to significant treatment planning quality improvements, when compared with coplanar VMAT treatment plans. Although these experiments were done in a research environment treatment planning software (matRad), the conclusions can be of interest for a clinical setting: automated procedures can simplify the current treatment workflow, produce high-quality treatment plans, making better use of human resources and allowing for unbiased comparisons between different treatment techniques.     

Contribution of metal vapor mass at periphery part of pulsed arc to electromagnetic force in weld pool

The arc welding has been used in various welding methods because it is inexpensive and high in strength after welding. However, it is a problem that accidents such as collapse of the bridge occur because of the welding defects. The welding of low cost and high productivity is required without the welding defects. The pulsed TIG welding is inexpensive and capable of high‐quality welding. The electromagnetic force contributing to penetration changes because the transient response of arc temperature and iron vapor generated from anode occurs. However, the analysis of pulsed TIG welding with metal vapor has been elucidated only metal vapor concentration near anode with transient phenomenon and heat flux. Thus, the theoretical elucidation of penetration depth with control factor has not been researched. In this paper, the contribution of metal vapor mass at the periphery part of pulsed arc to the electromagnetic force in the weld pool is elucidated. As a result, the iron vapor mass at periphery part decreased with increasing the frequency. The iron vapor was stagnated at axial center within one cycle. The electromagnetic force to the penetration depth direction in weld pool increased at axial center. Therefore, the metal vapor mass at periphery part plays an important role for the electromagnetic force increment at axial center.     

二氧化碳气体保护焊在厚板上的应用

板厚为 5 5mm的 16Mn钢采用CO2 半自动气保焊建造大型转炉炉体的可能性和可靠性如何 ?目前尚缺少足够的试验数据。为了给转炉工程的施工焊接提供可靠数据 ,确保焊接质量 ,对板厚 5 5mm16Mn钢CO2 半自动的焊接性能进行了一系列的试验研究     

Simplification of the Plasma Load of Negative-Pulse-Bias Source Used in Arc Ion Plating

Based on the voltage and current fluctuating phenomenon in the arc plasma load under the negative-pulse-bias, usingthe plasma physics theory and analysis of computer simulation expatiates that the nature of plasma load in vacuumarc plasma is a capacitance     

烟机结垢的成因分析及防范措施

通过对烟机垢物的元素和晶体组成进行表征，分析其形成条件，计算验证并探讨垢物的形成过程，并提出应对防范措施。烟机结垢过程为：极少数原料油滴在反应汽化段内未完全汽化，未汽化油黏附在催化剂细粉表面并缩合生焦；部分焦炭颗粒未在再生器内烧尽，进入烟道后继续燃烧达到细粉的熔融温度，转化为液相黏性物质；携带微量高温熔融粉尘的烟气在三级旋风分离器下料口、烟机叶片等部位受高速离心作用，黏附到易结垢部位，形成无定形垢物。可通过提升原料油喷嘴雾化效果，调整合适的剂油比和系统细粉含量来减少烟机结垢。