Fei Zhao

The complex environment within waste incineration boilers generates large amounts of acidic gases, such as Cl2 and 𝐻𝐶𝑙, which frequently lead to severe corrosion and subsequent failure of boiler components. To solve this problem, a C276 alloy coating was prepared on a 316L stainless steel substrate using high-speed flame spraying technology. Corrosion tests were conducted under a concentration gradient of 0.5% to 3% 𝐻𝐶𝑙 and a time gradient ranging from 300 to 1500 seconds. The corrosion mechanism of C276 coating in 𝐻𝐶𝑙 and steam atmosphere at high temperature (1000 ° C) was investigated. The corrosion kinetics, macroscopic morphology, surface and cross-sectional microstructures, element distribution, and corrosion product types were systematically analyzed. The results demonstrate that the corrosion evolution of the C276 coating is highly dependent on both time and 𝐻𝐶𝑙 concentration. Temporally, the coating undergoes three distinct stages: corrosion initiation, development, and accelerated failure. Gaseous metal chlorides are driven by water vapor as catalysts, undergoing strong high-temperature hydrolysis and secondary oxidation, generating porous oxides and releasing 𝐻𝐶𝑙 gas, thereby constructing a destructive mechanism that accelerates the cyclic corrosion and peeling failure of coatings.

To address the corrosion protection issues for hot components of high-end equipment in extreme service environments, the C276 alloy coating was deposited on the surface of 304 stainless steel via high-velocity air fuel (HVAF) spraying. The extreme conditions of 1000 °C temperature, an atmosphere containing 6% HCl, and a flow rate of 30 m/s were simulated in the study using a high-temperature airflow corrosion erosion device. The C276 coating and the 304 stainless steel substrates were subjected to a corrosion test for 25 min. The surface phase composition, element distribution, corrosion product characteristics, and cross-section structure of the samples before and after corrosion were systematically analyzed by means of a scanning electron microscope, an energy dispersive spectrometer, and an X-ray diffractometer. The mechanism of high-temperature chlorination corrosion was deduced through thermodynamic and kinetic analysis. The results show that compared with 304 stainless steel, the C276 alloy coating exhibits better corrosion resistance in an extremely high-temperature environment containing HCl, and the average weight gain and growth rate of the corrosion layer were lower. The main corrosion products on the C276 coating surface are Fe₂O₃, FeO, FeCl₂, NiO, and Cr₂O₃, among which the oxides of Ni and Cr form a continuous and dense protective oxide layer that effectively inhibits the intrusion of corrosive media. The high-temperature HCl corrosion follows the ‘chlorination–oxidation’ cycle mechanism, and Cl₂ plays a catalytic role in the reaction and accelerates the corrosion process.

The most important segment of the electric arc furnace (EAF) steelmaking process is the stirring and decarburization of the molten bath during the oxidation stage, with the bath temperature typically ranging from 1550 to 1600 °C. The coherent jet is a key factor influencing the stirring and decarburization of the molten bath. The factors affecting the impact capability of coherent jets have been widely studied, including the nozzle flow parameters and arrangement methods. However, there are few studies on the combustion chamber structure of the coherent jet oxygen lance. In order to study the effect of the combustion chamber structure on the characteristics of the coherent jet, a method combining numerical simulation and combustion experiments is used to study the flow fields of the coherent jet for a combustion chamber under different length and inclination angle conditions. The results show that the flow field characteristics of the coherent jet are influenced by the length and inclination angle of the combustion chamber. Compared with the coherent jet oxygen lance without a combustion chamber, the potential core length of the main oxygen jet under the short-distance horizontal combustion chamber condition is longer, but the potential core length of the main oxygen jet with the excessively long horizontal combustion chamber is shorter. The influence of the inclination angle on the potential core length of the main oxygen jet is complex. The influence mode is different depending on the length of the combustion chamber. Finally, it is found that the combined horizontal and inclined combustion chamber can achieve the best effect on prolonging the potential core length of the main oxygen jet.

During the process of electric arc furnace (EAF) steelmaking, the coherent jet plays a vital role in stirring and decarburization of the molten bath. Its flow field characteristics are influenced by the parameters of the shrouding gas. Improving the impact capability of coherent jets has been a hot research topic in recent years, with one method being the use of supersonic shrouding gas, known as supersonic combustion coherent jet technology. However, the mechanism by which a supersonic shrouding gas influences the main oxygen jet remains unclear. To investigate and quantify the effect of the shrouding gas parameters on the main oxygen jet, the flow fields of the SC coherent jet under different shrouding gas parameter conditions are investigated by both numerical simulation and combustion experiment. The results show that the potential core length of the main oxygen jet is negatively correlated with both the shrouding gas temperature and the distance between the shrouding gas and the main oxygen jet. The effect of the shrouding gas Mach number on the potential core length of the main oxygen jet shows a staged variation. Furthermore, a quantitative relationship between the potential core length of the SC coherent jet and the shrouding gas parameters is established.

Autoclaved Aerated Concrete (AAC) is commonly used in lower floors buildings in low seismicity areas due to its lightweight property and high energy absorption capacity. This paper proposes a novel application of AAC as an effective seismic countermeasure in the reduction of vibrational energy for concrete gravity dam. According the vibrating characteristics and failure modes of gravity dam under earthquake excitation, AAC was placed in the upper zone of a gravity dam to reduce the seismic inertia force and consequently to increase the seismic safety of the dam. Dynamic responses of two non-overflow sections of a gravity dam were analyzed through finite element analysis utilizing a damaged plasticity constitutive model. The anti-seismic effect of using AAC in gravity dams is researched by inputting different kind of ground motion records. The comparison of the natural vibration characteristics, dam crest displacement, and dynamic damage of the dam were investigated. The results show that, AAC effectively improves seismic resistance of concrete gravity dams, particularly eliminating cracks in the concrete along reduced damage zones, through inertial force reduction and energy dissipation. The results warrant further considerations for applying AAC to gravity dams.

The high-frequency and high-amplitude pyroshock environment during the service of the spacecraft will cause damage to the equipment. Here, we develop a shock test device based on air cannon to simulate the above pyroshock environment. Then, a finite element model was established by explicit dynamic software ANSYS/LS-DYNA, and the simulation results were proved to be consistent with the test data. Based on the theory of Shock Response Spectrum (SRS), the effects of device parameters such as pressure, bullet material and resonant plate material on SRS were investigated via numerical simulation and shock test. This study shows that the amplitude of SRS increases with the increase of pressure in the range of 0.15–0.60 MPa, and the break frequency amplitude has a square root function relationship with the pressure. Additionally, the high-frequency amplitude of SRS was affected by the energy transfer efficiency of the bullet.

A coherent jet oxygen supply plays a key role in the process of electric arc furnace steelmaking: it provides the necessary oxygen for the smelting of molten steel and promotes the flow of the molten pool. Compared with coherent jets in current use, the supersonic combustion coherent jet shrouded in supersonic methane gas could improve the impact capacity and stirring intensity of the molten pool. In order to reduce the smelting cost, the characteristics of the supersonic combustion coherent jet shrouding the supersonic methane and nitrogen mixtures must be studied. Computational fluid dynamics software is used to simulate the supersonic combustion coherent jet under various methane–nitrogen mixing conditions. The six-component combustion mechanism of methane and the Eddy Dissipation Concept combustion reaction model are selected. In agreement with thermal experiments, the simulation results show that the inclusion of a small amount of nitrogen has little effect on the combustion of supersonic shrouding methane gas. However, as the nitrogen content increases, the combustion region of supersonic shrouding gas becomes shorter in length, resulting in decreases in the lengths of the high-temperature, low-density region, and the high-turbulence-intensity region. These effects weaken the ability of the shrouding gas to envelop the main oxygen jet. The potential core length of the main oxygen jet decreases significantly; this decrease first accelerates and then decelerates. These results demonstrate the feasibility of including a small amount of nitrogen (about 10 wt%) in the supersonic shrouding methane gas without substantial negative impacts on the characteristics of the supersonic combustion coherent jet.

TiAl alloy represents a new class of light and heat-resistant materials. In this study, the effect of temperature, pressure, and grain size on the high-temperature creep properties of nanocrystalline TiAl alloy have been studied through the molecular dynamics method. Based on this, the deformation mechanism of the different creep stages, including crystal structure, dislocation, and diffusion, has been explored. It is observed that the high-temperature creep performance of nanocrystalline TiAl alloy is significantly affected by temperature and stress. The higher is the temperature and stress, the greater the TiAl alloy’s steady-state creep rate and the faster the rapid creep stage. Smaller grain size accelerates the creep process due to the large volume fraction of the grain boundary. In the steady-state deformation stage, two kinds of creep mechanisms are manly noted, i.e., dislocation motion and grain boundary diffusion. At the same temperature, the creep mechanism is dominated by the dislocation motion in a high-stress field, and the creep mechanism is dominated by the diffusion creep in the low-stress field. However, it is observed to be mainly controlled by the grain boundary diffusion and lattice diffusion in the rapid creep stage.

Herein, a supersonic combustion coherent jet is proposed based on current coherent jet technology to improve the impact capacity of a coherent jet and increase the stirring intensity of the electric arc furnace (EAF) bath. Further, numerical simulations and an experimental analysis are combined to study the supersonic combustion coherent jet characteristics, including the Mach number, dynamic pressure, static temperature, vorticity, and turbulence intensity, in the EAF steelmaking environment. The results show that the supersonic combustion coherent jet exhibits stable combustion in a high-temperature EAF steelmaking environment. The supersonic combustion flame generated by the supersonic shrouding fuel gas can envelop the main oxygen jet more effectively than current coherent jets. Furthermore, the velocity attenuation, vorticity, and turbulence intensity performances of the supersonic combustion coherent jet are better when compared with those of the current coherent jet. The velocity core length of the main oxygen jet for the supersonic combustion coherent jet is 30% longer than that of the current coherent jet, resulting in an improved impact capacity and stirring intensity of the molten bath.