Wear Behavior of AlSi10Mg Alloy Produced by Laser-Based Powder Bed Fusion and Gravity Casting

Herein, the sliding wear behavior of AlSi10Mg samples realized using laser‐based powder bed fusion (LPBF) is investigated via pin‐on‐disc (PoD) tests, before and after T6 heat treatment. The changes in the microstructure, density, and hardness induced by heat treatment are correlated with the tribological behavior of the alloy. Furthermore, short wear tests are conducted and the resulting wear tracks are investigated through scanning electron microscopy (SEM), equipped with an energy‐dispersive spectroscopy (EDS) microprobe to elucidate how the wear mechanisms evolve with sliding distance. For comparison, gravity cast (GC) AlSi10Mg samples are also characterized and tested. The as‐built additive manufacturing (AM) sample exhibits the lowest wear rate and coefficient of friction because of its high hardness and relative density, whereas the heat‐treated sample shows the worst behavior in comparison with the GC samples. The results suggest a significant influence of porosity on the wear behavior of AM alloys

Laser texturing of a multilayer DLC from nano-liquid-diamond precursors via microsecond laser pulses

Diamond Like Carbon (DLC) coatings have well known mechanical properties, including high hardness, chemical stability, optical transparency and biocompatibility. In addition they are frequently used in multilayer coating systems. Laser surface texturing of DLC coatings can be a tailoring solution to optimize the coating functional parameters like roughness, wettability, wear, corrosion resistance, etc. Furthermore, compared to mechanical grinding, local laser removal could be a suitable technology for repairing locally damaged coated parts (i.e. worn surfaces, corroded surfaces, etc.) In the present work, laser surface texturing and controlled laser removal of a multilayer DLC coating obained from nano-liquid-diamond precursors have been studied using a 8W Q-switched laser (λ=532 nm) with microsecond pulses. Textured ablation as well as full planar decoating are shown through proper adjustment of laser texturing parameters

Numerical solution of the problem on the determination of the sizes of fireproof fire in the surface fires

Эта статья посвящена разработке математической модели для изучения распространения лесных низовых пожаров. В работе приводятся результаты расчетов противопожарных разрывов с учетов скорости ветра и влагосодержания лесных горючих материалов. В состав модели входят все важные физико-химические процессы горения: сушка горючего материала, пиролиз, сжигание полукокса, турбулентное сгорание газообразных продуктов. Использование программного обеспечения PHOENICS позволяет тестировать разработанную модель. The paper contemplates to the development of a mathematical model for studying the spread of forest surface fires. The paper presents the results of calculations of fire breaks taking into account wind speed and moisture content of forest combustible materials. The model includes all the important physicochemical combustion processes: drying of combustible material, pyrolysis, burning of char, turbulent combustion of gaseous products. Using software PHOENICS allows you to test the developed model

investigation on fatigue strength of sand blasted dmls alsi10mg alloy

Abstract Fatigue resistance of Direct Metal Laser Sintered (DMLS) AlSi10Mg alloy after sand-blasting was investigated in the present study. A preliminary characterization of the samples was carried out in order to identify material microstructure, surface roughness and superficial residual stresses. It was found that the applied post-processing treatment was responsible for a strong decrease in average surface roughness as compared to the as-built condition and induced compressive residual stresses on the samples surface. Axial fatigue tests were performed in both finite and infinite (i.e. 2x106 cycles) life regimes and the obtained results were compared with literature values for the same alloy after various post-treatments, including heat treatment, machining, polishing and shot peening. A general positive effect of the applied sand-blasting on fatigue resistance was observed. This, coupled with the improvements of surface finishing, encourages the use of sand-blasting as a simple and effective post-treatment. Finally, observations of the fractured surfaces allowed also the identification of porosities located on the surface as the main crack initiation sites. Once the crack has started, it moves along a large flat area, as typical of fatigue propagation, with a small final overload region

Evaluation on the fatigue behavior of sand-blasted AlSi10Mg obtained by DMLS

In the present paper, fatigue tests were performed on sand-blasted AlSi10Mg samples produced by Direct Metal Laser Sintering (DMLS). The effect of sand-blasting on surface properties was evaluated by roughness and residual stresses measurements, together with morphological analysis, in comparison with as-built condition. An evident improvement of surface finishing was observed after sand-blasting, which also leaded to the presence of compressive residual stress on the external surface of samples, as revealed by XRD2 measurements. Furthermore, defects analysis allowed the identification of a uniform distribution of porosities in the cross section in terms of number of defects, while larger porosities seem more abundant close to the surface. It was found that the tested material exhibits good fatigue resistance, supporting the positive role of sand-blasting as a simple post-processing treatment. Superficial defects are the preferential crack initiation sites, as demonstrated by SEM analysis of fracture surfaces

Study of Microstrain and Stress in Non-Planar Palladium Membranes for Hydrogen Separation

Palladiums tubular membranes are developed to operate up to 400 °C, for the synthesis of H2 and for the separation of CO2 in Water Gas Shift (WGS) processes and reforming gas of methane [. Palladium has FCC lattice that allows the separation of hydrogen from carbon dioxide through a solution-diffusion mechanism [. To ensure high selectivity in the separation process, the functional Pd layer on the porous substrate of the membranes must have a microstructure with low defects and free from residual stresses [.MicroXRD measurements were performed to evaluate the effect of the stress-relief heat treatment, carried out for different time and temperatures, on the palladium layer. Microstrains were assessed before and after stress-relief by the Williamson-Hall method [. The use of microdiffraction was mandatory considering the tubular shape of membranes. The data were corrected for elastic anisotropy of palladium and the altered Williamson-Hall method was successfully applied.The XRD two-dimensional (2D) images and the integrated spectra collected from the samples allowed to study also the evolution of Pd microstructure and the reduction of micro-stresses due to stress relief. The results of the study allowed to identify the optimal thermal profile for the heat treatment of palladium membranes

Study of microstrain and stress in non-planar Palladium membranes for hydrogen separation

Palladiums tubular membranes are developed to operate up to 400 °C, for the synthesis of H2 and for the separation of CO2 in Water Gas Shift (WGS) processes and reforming gas of methane [. Palladium has FCC lattice that allows the separation of hydrogen from carbon dioxide through a solution-diffusion mechanism [. To ensure high selectivity in the separation process, the functional Pd layer on the porous substrate of the membranes must have a microstructure with low defects and free from residual stresses [.MicroXRD measurements were performed to evaluate the effect of the stress-relief heat treatment, carried out for different time and temperatures, on the palladium layer. Microstrains were assessed before and after stress-relief by the Williamson-Hall method [. The use of microdiffraction was mandatory considering the tubular shape of membranes. The data were corrected for elastic anisotropy of palladium and the altered Williamson-Hall method was successfully applied.The XRD two-dimensional (2D) images and the integrated spectra collected from the samples allowed to study also the evolution of Pd microstructure and the reduction of micro-stresses due to stress relief. The results of the study allowed to identify the optimal thermal profile for the heat treatment of palladium membranes

Impact behavior of gravity cast AlSi10Mg alloy: Effect of hot isostatic pressing and innovative high pressure T6 heat treatment

In the present study, the impact behavior of gravity casting AlSi10Mg alloy was evaluated with an instrumented Charpy pendulum. The effect of hot isostatic pressing, also followed by a T6 treatment, was analyzed in comparison with samples in the as-cast, annealed and T6 conditions. Furthermore, the effect of the innovative high-pressure T6 was investigated. It was found that the hot isostatic pressing is able to ensure densification of the alloy with an increase in both hardness and energy absorbed during impact. The T6 treatment performed at atmospheric pressure after the hot isostatic pressing is able to increase hardness and peak force. At the same time, the innovative high-pressure T6 is able to ensure similar results than those of hot isostatic pressing followed by T6, leading to a significant decrease in the treatment duration and costs and reducing the carbon footprint of the manufacturing process

Influence of the Manufacturing Process on Defects in the Galvanized Coating of High Carbon Steel Wires

This study is a detailed failure analysis of galvanized high carbon steel wires, which developed coating cracks during the torsion test performed as a quality control at the end of the manufacturing process. Careful visual inspections showed that the cracks are already present in the coating before the torsion test. In order to explain the origin of these cracks, systematic metallographic investigations were performed by means of optical and scanning electron microscope on both the wires and the rods that have been cold drawn to produce the wire. The chemical composition of the galvanized coatings was evaluated by means of energy dispersive spectroscopy. Micro bidimensional X-ray diffraction experiments were also performed to measure the residual stresses in the galvanized coating. The results showed that the failure is related to two main factors: the relatively high content of silicon in the steel and the unsuitable cooling rate of the rods at the exit from the galvanizing bath. The mechanism proposed to explain the origin of the defects was supported by Finite Elements Methods simulations and verified with in-plant tests. The proper countermeasures were then applied and the problem successfully solved