Quantitative tests revealing hydrogen enhanced dislocation motion in α-iron

Hydrogen embrittlement jeopardizes the use of high-strength steels as critical load-bearing components in energy, transportation, and infrastructure applications. However, our understanding of hydrogen embrittlement mechanism is still obstructed by the uncertain knowledge of how hydrogen affects dislocation motion, due to the lack of quantitative experimental evidence. Here, by studying the well-controlled, cyclic, bow-out movements of individual screw dislocations, the key to plastic deformation in α-iron, we find that the critical stress for initiating dislocation motion in a 2 Pa electron-beam-excited H2 atmosphere is 27~43% lower than that under vacuum conditions, proving that hydrogen lubricates screw dislocation motion. Moreover, we find that aside from vacuum degassing, dislocation motion facilitates the de-trapping of hydrogen, allowing the dislocation to regain its hydrogen-free behavior. Atomistic simulations reveal that the observed hydrogen-enhanced dislocation motion arises from the hydrogen-reduced kink nucleation barrier. These findings at individual dislocation level can help hydrogen embrittlement modelling in steels.

Degassing and layers variation effect on composite processing by vacuum assisted resin transfer moulding

Vacuum assisted resin transfer molding (VARTM) is a fiber reinforced composite (FRC) making process in which resin is impregnated to fabric by application of vacuum. This process is also known as vacuum infusion process. The critical issue in VARTM process is void generation. Voids form due to variety of reasons, most of which can be avoided. Vacuum degassing is one of the solutions which will reduce air entrapped inside resin during impregnation. In this work six laminates from jute and polyester resin were prepared, three with degassing and three without degassing with variation in number of jute layers 5, 10 and 15 respectively. Microscopic examination and mechanical properties have been observed before and after degassing. It was observed that degassing improves mechanical properties of composite laminates and reduce void content. It was observed that the thickness variation in laminate increased as number of layer increased.

Void Content Minimization in Vacuum Infusion (VI) via Effective Degassing

This paper addresses the major concern which component porosity represents in Vacuum Infusion (VI) manufacturing due to resin gelation at pressures close to absolute vacuum. Degassing is a fundamental step to minimize or even avoid resin outgassing and enhance dissolution of voids created during preform impregnation. The efficacy of different degassing procedures based on vacuum degassing, and assisted by adding a nucleation medium, High Speed (HS) resin stirring and/or later pressurization during different time intervals have been analyzed in terms of final void content is studied. Through a rigorous and careful design of the manufacturing process, outgassing effects on final void content were isolated from the rest of porosity causes and specimens with two clearly identifiable regions in terms of porosity were manufactured to facilitate its analysis. Maximum void content was kept under 4% and porous area size was reduced by 72% with respect to conventional vacuum degassing when resin was stirred at HS; therefore, highlighting the importance of enhancing bubble formation during degassing.

Removal of Dissolved Oxygen from Water by Nitrogen Stripping Coupled with Vacuum Degassing in a Rotor–Stator Reactor

Oxygen is a harmful substance in many processes because it can bring out corrosion and oxidation of food. This study aimed to enhance the removal of dissolved oxygen (DO) from water by employing a novel rotor–stator reactor (RSR). The effectiveness of the nitrogen stripping coupled with vacuum degassing technique for the removal of DO from water in the RSR was investigated. The deoxygenation efficiency (η) and the mass transfer coefficient (KLa) were determined under various operating conditions for the rotational speed, liquid volumetric flow rate, gas volumetric flow rate, and vacuum degree. The nitrogen stripping coupled with vacuum degassing technique achieved values for η and KLa of 97.34% and 0.0882 s−1, respectively, which are much higher than those achieved with the vacuum degassing technique alone (η = 89.95% and KLa = 0.0585 s−1). A correlation to predict the KLa was established and the predicted KLa values were in agreement with the experimental values, with deviations generally within 20%. The results indicate that RSR is a promising deaerator thanks to its intensification of gas–liquid contact.

Formation and Evolution of DS-Type Inclusions in 15-5PH Stainless Steel

15-5PH stainless steel castings are key components in fracturing trucks. However, DS-type inclusions can lead to fatigue failure of the material. To elucidate the formation mechanism of large-size DS-type inclusions, the evolution, growth, and aggregation of inclusions during vacuum oxygen decarburization, ladle refining, and vacuum casting were studied. The results show that the DS-type inclusions with sizes larger than 20 μm were CaO–Al2O3–SiO2–MgO–CaS composite inclusions. After Si–Al additions in vacuum degassing, typical inclusions were spinel or Al2O3. After Ca–Si additions during ladle treatment, typical inclusions were liquid or dual-phase Al2O3–CaO–SiO2–MgO. During the solidification process, due to the segregation of S and the decrease in solubility, the typical inclusions in the final casting became Al2O3–CaO–SiO2–MgO–CaS. For optimal fatigue performance of stainless steel castings, slag and refractory composition control were also necessary because the [Mg] contents mainly come from the slag and lining.

Thermophysical Properties of Pipe Steel in the Liquid State

The temperature dependences of the kinematic viscosity and surface tension of liquid pipe steel with different modes of melt preparation were investigated. A transition zone was found on the temperature dependences of the thermophysical properties, which separates the regions with different activation energies of viscous flow and surface tension. At the heating stage in the transition zone, the thermal decomposition of clusters based on cementite Fe3C occurs. As a result of the decomposition, free carbon atoms appear which tend to give a uniform distribution in liquid iron with increasing temperature. At a low content of alloying elements and impurities, a high-temperature melt should have a large-scale cluster structure, which provides a more uniform distribution of chemical elements. The melt after vacuum degassing has a narrow transition zone near 1920 K, in contrast to the wide transition zone of the melt without vacuum degassing. The wider transition zone is shifted to high-temperature and this shift is associated with the thermal decomposition of carbides and oxides. Studies have shown that heating liquid pipe steel above the temperature of the liquid–liquid structural transition makes it possible to obtain a more homogeneous structure with a more uniform distribution of alloying and impurity elements in the melt. The sharp drop in surface tension at temperatures above 1920 K in the melt without vacuum degassing is associated with the diffusion of free S and O atoms, which are released after thermal decomposition of sulfides and oxides.

Degassing Process Influence on Tensile Strength of Neat E132 Epoxy Polymeric Materials

During the composite’s fabrication process, one of the most common defect occurs is void. Numerous literatures have suggested that the presence of void negatively affect its mechanical properties and effective degassing process is one the solutions for such issue. In this study, experiments were carried out using neat E132 epoxy to investigate the effects of different degassing process (hot water, ultrasonic bath, and vacuum) on its tensile strength. The duration of its process was carried out from 5 – 9 minutes for hot water and ultrasonic bath where vacuum process was extended until 10 minutes to observed limiting behavior. It is found that the vacuum degassing method is the most effective. Vacuum degassing process displayed the least formation of bubble and micro voids even for 10 minutes. It is also revealed that vacuum degassing process resulted the highest average tensile strength at 48.8MPa. Such findings would facilitate the well bonded effective nanocomposite fabrication process.