Papers by Keyword: Gas Pressure

Abstract: Conventional plasma nitriding can induce defects due to direct plasma formation on the surface of the treated material. To address this issue, the screen-assisted direct current plasma nitriding (S-DCPN) method was developed, which generates plasma on both the sample and a surrounding screen, thereby reducing such defects. In this study, S-DCPN was applied to ferritic stainless steel (SUS430) using austenitic stainless steel (SUS304) as the screen material. Treatments were performed at 633 K for 15 hours under gas pressures of 200 and 600 Pa, with varying gas compositions of 75 % N₂ – 25 % H₂, 50 % N₂ – 50 % H₂, and 25 % N₂ – 75 % H₂. To evaluate the effects of gas composition and pressure, a range of analyses was conducted, including X-ray diffraction (XRD), cross-sectional microstructural observations, glow discharge optical emission spectrometry (GD-OES), hardness testing, and corrosion testing. The results revealed the formation of the α_N phase, a supersaturated solid solution of nitrogen in ferrite, under all conditions. Nitrogen diffusion and surface hardness increased with higher hydrogen content, and corrosion resistance was notably enhanced under the 25 % N₂ – 75 % H₂ condition. These findings demonstrate the effectiveness of S-DCPN in improving the surface properties of ferritic stainless steel while maintaining or enhancing corrosion resistance.

Abstract: This study investigates the relationship between core gas pressure, solid phase fraction in the sand core, and gas porosity formation in casting processes. The experiments were conducted using EN AC-45500 aluminium alloy, varying casting temperatures and casting diameters. The maximum core gas pressure was measured and correlated closely with the solid phase fraction at the sand core-metal interface. Notably, the study reveals that gas breakthroughs can occur even at core gas pressures lower than the metallostatic pressure. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used to analyse the blow-holes imprints and their chemical composition, confirming that the observed porosity originates from core gas. The results underline the importance of the solid phase fraction in controlling gas porosity formation and provide new insights into the mechanisms of blow-holes formation in aluminium alloy casting.

Abstract: This article is devoted to expanding the technological capabilities of the gas-forming stamping method by increasing the pressure of combustion products acting on the surface of a workpiece stamped. Therefore, a scheme of a two-chamber device and a method for compressing the fuel mixture is proposed. The essence of the method is that of carrying out the stamping products under the high gas pressure, which is created by compression and subsequent combustion of the gaseous fuel mixture. To ensure the compression of the fuel mixture, the device is equipped with two combustion chambers separated by a piston. Due to this method, the pressure rises sharply. Under the influence of the combustion products' pressure, the workpiece is intensely deformed and fills the cavity of the matrix. This method of sheet stamping, implemented on a two-chamber device, will increase the gas pressure on the surface of the forged workpiece to 70-80 MPa at a fuel mixture pressure of 1 MPa, which ensures stamping of a variety range of parts in almost all branches of small-scale production related to metalworking.

Abstract: Metal powder is used in the Powder Metallurgy (PM) application process. Most of the metals used in the PM are stainless steel made by the gas atomization process. This study uses the free fall gas atomizer. The material was used to produce the metal powder from various forms of stainless steel 304 raw material, which is melted in an electric induction furnace. This method is very practical to be applied in the large-scale metal processing industries. While the gas pressure variation results show that metal powder with a smaller size will be produced more using high gas pressure. The free fall gas atomizer has successfully produced stainless steel 304 metal powder with the size <40 μm and have a spherical shape. The well-rounded sphericity for 8 bar pressure, 10 bar pressure, and 12 bar pressure are 61.1%, 41.7%, and 37.5% respectively. It can be concluded that 12 bar pressure produces the smallest size range of powder about <40 µm with the most quantity about 1.11%wt, followed by 10 bar pressure about 0.41%wt and 8 bar pressure about 0.07%wt.

Abstract: Plasma nitriding has attracted much interest to improve the hardness of aluminium alloys. However, the contradictive properties can be produced on the metal surface due to the saturated condition of the diffused nitrogen atom in the metal surface layer. The objective of this work was to investigate the effect of nitriding time and gas pressure to improve the hardness of aluminium using plasma nitriding. The nitriding processes were conducted in a DC glow discharge with nitrogen gas flowing inside the vacuum chamber. Firstly, the sample was nitrided using a fixed gas pressure of 1.2 mbar with the varied nitriding times of 3, 4, 5 and 6 hours. The optimum time producing the highest hardness of the surface was then used in the next nitriding process with varied gas pressure of 1.2, 1.4, 1.6 and 1.8 mbar (1 bar = 10⁵ Pa). The optimum gas pressure producing the highest hardness was then used again in the last nitriding process using varied nitriding time of 3, 4, 5 and 6 hours. The result showed that the highest hardness was achieved using the gas pressure and nitriding time of 1.6 mbar and 4 hours, respectively. The formed AlN phase on the aluminium surface was identified by XRD, whereas the surface morphology was observed by SEM image. Compared to the untreated sample, the hardness of the treated samples was significantly high.

Abstract: Based on definition of porosity, permeability model of gas-bearing coal was build which took porosity gas pressure, gas adsorption expansion, temperature and crustal stress into account, and the factors affecting the permeability of gas-bearing coal has been analyzed theoretically. The results show that permeability decreased exponentially with crustal stress increasing, permeability decreased linearly with temperature increasing and permeability decreased first and then increased with gas pressure increasing; crustal stress had the strongest effect than gas pressure and temperature, decreasing crustal stress was the most effective way to increase permeability and to improve extraction; the results verified by experiments data show that the smaller error and the higher prediction accuracy can meet production practical requirement, which could provide some guidance to gas extraction.

Abstract: This paper demonstrates the deposition of barrier layers and seed layers in TSV for 3D package. The high aspect ratio through silicon via sputtering process uses the magnetron-sputtering of Au. In order to achieve the continuous coverage of thin film on the sidewall and bottom of vertical microvias, the sputtering and anti-sputtering process was optimized. The impact of thickness of the seed layer and the gas pressure of the chamber on the coverage of the seed layers are discussed. The continuous seed layers and barrier layers on in the micro-vias with aspect ratio 3.5 can be achieved at low cost.

Abstract: To analyze the mining effect to gas permeability of tectonic soft coal seam, we choose typical sample from tectonic soft coal, study the gas permeability and microstructure. The results suggest that tectonic soft coal has been badly destroyed, and its micro fracture pore develops. Confining pressure has a great influence on the permeability of tectonic soft coal. When gas pressure remains constant, with the increase of confining pressure of tectonic soft coal permeability began to decrease very fast. But when decreasing to a certain degree, it changes slowly; when confining pressure remains constant, with the increase of gas pressure, permeability of tectonic soft coal first decreases and then increases. Under the condition of low gas pressure, tectonic soft coal permeability shows a significant Klinkenberg effect.

Abstract: To further explore the impact of gas pressure on gas desorption and flowing law, the gas desorption experimental system designed autonomously is used to carry out studies on gas desorption experiment under different gas pressures. By data fitting, the relationship between gas desorption quantity and time is obtained and also established the model for gas desorption. The results show that: the gas desorption quantity curves is "The first half rises sharply, the latter half segment is gently rising and eventually becomes stabilized", and when the gas adsorption equilibrium pressure is the greater, the gas desorption amount is greater. And the formula can describe the gas desorption law well, the correlation coefficient R2 is above 0.97. The study provides an important theory reference to coal and gas outburst prediction, coal seam gas content prediction and its exploitation and utilization.

Abstract: The dependence of the layer growth rate on a gas (argon, nitrogen) pressure inside the reactor has been examined in order to analyze the conditions of growth of AlN thick layers and bulk crystals by the sublimation sandwich-method. It is shown that the layer growth rate steadily increases as the pressure in the reactor decreases in a wide pressure interval 1–0.02 bar. This suggests that a key role in the layer growth kinetics is played by the source-to-substrate transfer of the components (Al, N), rather than the adsorption - desorption processes on the source and substrate surface. In addition the growth rate in argon atmosphere is much higher than in nitrogen one for the high pressures and is practically the same for the lowest (0.05 – 0.02 bar).