This study aimed to have a wide-range investigation on changes of optical, structural, mechanical durability and nuclear radiation attenuation properties of barium borosilicate glasses through BaO ...reinforcement. Accordingly, gamma-ray attenuation parameters of a series of glasses with the nominal composition of xBaO-(50-x)B2O3–20NaO–15SiO2–10CaO–5Al2O3 (x= 0, 5, 10, 20 and 30 wt%) were extensively evaluated using experimental, simulation and theoretical methods. The linear attenuation coefficient (LAC) of glasses were experimentally measured using NaI (Tl) (3×3 inch) detector. LAC values of Ba00, Ba05, Ba10, Ba20 and Ba30 glasses were reported as 0.4951, 1.0129, 1.5780, 2.8795 and 4.4203 at 81 keV and 0.1030, 0.1084, 0.1148, 0.1278, and 0.1397 at 2614 keV, respectively. Accordingly, obtained results were compared with the XCOM program and FLUKA general purpose Monte Carlo simulation code at photon energies from 81 to 2614 keV. Furthermore, LAC values were used to calculate other related parameters including MAC, X1/2, and λ. Comparatively higher density (3.652 g/cm3), greater LAC, MAC and lower both X1/2, and λ values achieved for Ba30 glass indicated it as a better gamma shield. The outcomes of mechanical durability investigations showed that replacing B2O3 with BaO resulted in a decrease in the flow movement that leads to an increase in the density of the crosslinking as well as the observed difference in the atomic mass B and the atomic mass of Ba and thus increase the hardness Moreover, the vibrational modes of theses samples are active in four IR spectral peaks related to the compositions. Moreover, the optical parameters of these samples have been calculated. The results also showed that an enhancement of the transmittance was observed since optical band gap increases as BaO content increases.
Nitrile butadiene rubbers (NBR) are widely used in sealing applications, such as O‐rings inside the pneumatic system of the French high‐speed train (TGV). In this application, a strong hardening of ...the NBRs alters the sealing function. Predicting the evolution of the mechanical properties during service life, especially the material hardening, is therefore a strategic issue to optimize time in maintenance operations of the TGV's pneumatic system. The main goal of this study is to reproduce the aging observed on a train's pneumatic system by performing thermo‐oxidative accelerated aging tests with different commercial nitrile rubbers at several temperatures and up to 2016 h. After achieving similar degradation to specimens aged on trains, aging mechanisms and effects have been investigated through different characterization techniques: infrared spectroscopy, swelling tests, X‐ray fluorescence spectrometry, differential scanning calorimetry, thermogravimetric analysis, and micro‐hardness measurements. The results obtained enabled us to identify and to relate aging mechanisms to aging conditions and to precisely determine and quantify the effects of physicochemical state evolution on the mechanical properties of each NBR considered. Extra crosslinks and oxidative functionalities form in the different elastomers, making them hard and brittle, and thus impacting the sealing function.
Aging of nitrile butadiene rubber results in permanent deformation and hardening of O‐rings used in the pneumatic system of the French high‐speed train (TGV). This phenomenon impacts its sealing function. Predicting the evolution of the mechanical properties, such as hardening, is a strategic issue to optimize time in maintenance operations of the TGV's pneumatic system.
In the present study, solid-lubricating surfaces were produced through electrical discharge process using green compact electrodes prepared from tungsten disulphide (WS2) and copper (Cu) powder ...mixture. The effect of experimental parameters such as duty factor, peak current, and powder mixture ratio was investigated on wear behavior and surface integrity of coating. The FESEM images indicated fewer pores with powder mixture ratio WS2:Cu/60:40, peak current 7A and duty factor 50%. The XRD profile of coating showed the various peaks of W, WS2, Cu and Cu2S. Micro-hardness of the solid-lubricating coating reduced from 180HV (workpiece) to a minimum value of 44.11HV (coating). Further, Pin-On-Disc wear test showed significant reduction in wear from 95.75 μm (parent surface) to the least value of 6.71 μm (coated surface).
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•Deposition of the material (WS2 +Cu) from the prepared green compact tool over the mild steel surface.•Analysis of morphology of the deposited layer with respect to the input parameters.•Issue of chemical compatibility and interface phenomenon of the WS2 powder particles and the workpiece material has been discussed.•Evaluation of tribological performance and tribo-mechanical properties of the deposited layer.
•The material removal process between tool and workpiece is studied analytically, which explains the kinematics mechanism and the reduction of milling force in LTUM.•The texture generation process of ...LTUM is firstly analyzed through a theoretical model. It was found that the tool angles are essential to understand the generation of micro dimples structures.•The effects of process parameters on the micro dimpled surface are discussed. It could be concluded that the position and arrangement of the micro dimpled textures can be controlled by changing the values of the parameters λ1 and λ2.•Related experiments of cutting force and surface topography were conducted to study the machining characteristics. It could be found that LTUM significantly enhanced the surface micro hardness compared with CM.
Ultrasonic Machining (UM) is extensively used in processing of difficult to cut materials due to its superior performance. However, the mechanics of this process is still not fully understood when superimposed on other machining operations. In this paper, Longitudinal-Torsional Ultrasonic Assisted Milling (LTUAM) is introduced for machining of a high strength titanium alloy Ti-6Al-4V. The separation geometrical characteristics between the tool and workpiece are studied analytically. Moreover, the texturing generation mechanism of LTUAM is analyzed through a theoretical model. The proposed method considers the influence of 3D tool topography, which can accurately simulate the ultrasonic surface topography. Related experiments of the generated cutting force and the surface topography were conducted to investigate the machining characteristics. The results showed that compared with Conventional Milling (CM), a noticeable decrease of the cutting force was observed in LTUAM. This can be explained from the perspective of tool workpiece contact rate model. Micro dimpled surface textures were successfully fabricated on Ti-Al6-4V using LTUAM technique. The surface test results indicated that the surface micro-hardness was enhanced between 6.34% and 13.22% compared with CM. This research provides guidance for applications of ultrasonic machining to textured surfaces.
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Machining of Ni-based superalloys is a challenging issue, and it may lead to tool deterioration, poor surface quality, and other structural defects. Therefore, the main theme of this study is to ...examine the effect of different sustainable cooling/lubrication conditions on the machining performance, surface integrity, and accompanying tribological aspects of Inconel 718 superalloy. In this context, the milling experiment variables were selected as two feed rates, two cutting speeds, and four cutting environments: dry, air, synthetic oil-based MQL, and LN2-assisted Cryo. Tool wear mechanisms, surface roughness/profile/topography, cutting performance (tool-chip interface temperature and energy consumption), chip shapes, microstructures, and micro-Vickers hardness of the machined surfaces were thoroughly analyzed to assess experimental observations. The Cryo medium reduces tool wear, surface roughness, cutting temperature, and cutting energy by 67 %, 61 %, 85 %, and 33 % in comparison with a dry environment, respectively. Abrasion, adhesion, and diffusion mechanisms were supposed to be the most dominant wear types following SEM observations. Besides, the Cryo environment concluded a reduction of grain size to ⁓ 4 µm in concomitant with an increase of micro-hardness ⁓ % 15. The whole observed outcomes agreed to a great extent with each other, asserting the effectiveness of the LN2 cooling protocol in improving machining characteristics of Inconel 718 superalloy.
This work investigates the influence of multi-step laser polishing on microstructural properties of the remelted surface layer of tool steel H11. Four different sets of process parameters were ...selected for laser polishing of initially annealed samples made from tool steel H11. In a sequential, multi-step process using continuous and pulsed laser radiation (Nd:YAG) a significant reduction of surface roughness was achieved.. The remelted layers were analyzed using roughness measurements, white light interferometry, X-ray diffractometry, electron backscatter diffraction, glow discharge emission spectroscopy, and nanoindentation hardness measurements. Laser polishing leads to a grain refinement and a significant increase in hardness. A minimal surface roughness of Ra = 50 nm was achieved in an Argon process atmosphere with an additional 6 vol% CO2. In particular the carbon concentration was significantly reduced within the remelted layer. The lower carbon concentration is correlated with a decreased maximal surface hardness down to 366 HV. High residual tensile stresses of up to 926 MPa can be introduced by laser polishing. Overall, high temperature gradients and, in particular, decarburization due to carbon diffusion processes were identified to be the major driving force for significant changes in surface roughness and microstructural properties.
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•Multi-step laser polishing of tool steel H11 leads to a minimal surface roughness of Ra = 0.05 μm•High temperature gradients, small interaction times, and multiple tempering cycles result in a fine-grained microstructure•Each laser polishing step results in a characteristic decarburization of the surface boundary layer (carbon fingerprint)•Decarburization due to CO2 and O2 correlates with less martensite formation, lower hardness and smaller surface roughness•Laser polishing can introduce high residual tensile stresses of up to 926 MPa
Properties and serviceability of additively manufactured components are affected by their geometry, microstructure and defects. These important attributes are now optimized by trial and error because ...the essential process variables cannot currently be selected from scientific principles. A recourse is to build and rigorously validate a digital twin of the additive manufacturing process that can provide accurate predictions of the spatial and temporal variations of metallurgical parameters that affect the structure and properties of components. Key building blocks of a computationally efficient first-generation digital twin of laser-based directed energy deposition additive manufacturing utilize a transient, three-dimensional model that calculates temperature and velocity fields, cooling rates, solidification parameters and deposit geometry. The measured profiles of stainless steel 316L and Alloy 800H deposits as well as the secondary dendrite arm spacing (SDAS) and Vickers hardness measurements are used to validate the proposed digital twin. The predicted cooling rates, temperature gradients, solidification rates, SDAS and micro-hardness values are shown to be more accurate than those obtained from a commonly used heat conduction calculation. These metallurgical building blocks serve as a phenomenological framework for the development of a digital twin that will make the expanding knowledge base of additive manufacturing usable in a practical way for all scientists and engineers.
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The aluminium alloys AA5082 and AA7075 were welded using friction stir welding (FSW) and tungsten inert gas (TIG) welding. The effect of these two (FSW and TIG) welding processes on the tensile and ...fatigue properties of dissimilar AA5082-AA7075 butt welded joints were studied. The S-N curve for both, FSW and TIG, joints were established. The results exhibited that the tensile and fatigue properties of dissimilar FSW welded butt joints are better than those of dissimilar TIG welded butt joints. The fatigue strength for FSWed and TIG welded joint is determined as 40 MPa for 106 cycles and 30 MPa for 105 cycles of fatigue life, respectively. The micro-hardness of the joints is also studied for both joints. The hardness for TIG joint is lower than the FSWed joint in the welded zone.
The empirical relationships were developed to predict the tensile strength, percentage elongation, micro-hardness and residual stress of the TIG+FSP welded joint of AA6061 and AA7075 at a 95% ...confidence level. The developed models show that the tool rotational speed and tilt angle are the dominating parameters as compare to others. The decrease in traverse speed and increase the tool rotational speed lead to the increase in heat input to TIG+FSP welded joint. The confidence interval has shown that tensile strength and hardness increased with increasing tool rotation, whereas residual stress decreased with increasing tool rotation. The minimum compressive residual stress of 18 MPa, maximum tensile strength (255 MPa), and hardness (105 HV) were located at the nugget zone of the TIG+FSP weldment at tool rotation 1300 rpm, traverse speed 45 mm/min with tilt angle 1°. The optimized value of tensile strength, percentage elongation, micro-hardness at nugget zone, and residual stress at nugget zone is 216.52 MPa, 23.65%, 89.65 HV, and 43.74 MPa respectively, whereas the optimized input process parameters tool rotation, traverse speed, and tilt angle are 1123.53 rpm, 50.37 mm/min and 0.1424
0
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•A strategy for high integrity laser cladding of stainless steel components with the corrosion resistant Inconel 625 wire is presented.•The mechanism of enhanced corrosion as a result of Fe dilution ...is reported.•Corrosion performance of the typical Inconel 625 wire laser coating is shown to be very similar to the wrought Inconel 625.•The corrosion performance of the coatings degrades with increasing Fe dilution.•Corrosion resistance of Inconel 625 wire laser coating is superior to the wrought 304 stainless steel.
The electrochemical corrosion performance of laser clad Inconel 625 wire in a de-aerated 3.5 wt% NaCl solution was investigated. The microstructure of the clad beads before and after the corrosion testing was examined using a combination of optical microscopy, scanning electron microscopy (with energy dispersive X-ray analysis) and X-ray diffraction. Well bonded, minimally diluted, pore- and crack-free single bead and multiple (overlapped) beads of Inconel 625 wire were successfully deposited. The clad beads comprise dendritic γ-Ni (FCC) matrix and interdendritic precipitates which are Mo- and Nb-rich. The microstructural evolution of a typical clad bead is observed to begin with columnar dendrites, at the clad-substrate interface, growing vertically to the substrate. This blends into horizontal columnar dendrites near the top region. High integrity laser coating (multiple beads) of Inconel 625 wire with a minimal dilution ratio of 4.5% is found in this study. The corrosion performance of the coating, which degrades with increasing Fe dilution, is very close to that of wrought Inconel 625 but superior to the wrought 304L stainless steel. The stainless steel exhibited localised (pitting) corrosion however, it was fully protected by the Inconel 625 wire laser coating in the saline solution.
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