Search Results (95)

MIL-STD-1530D and the United States Air Force (USAF) Structures Bulletin EZ-SB-19-01 require an ability to predict the growth of naturally occurring three-dimensional cracks with crack depths equal to what they term an equivalent initial damage size (EIDS) of 0.254 mm. This requirement holds for both additively manufactured and conventionally built parts. The authors have previously presented examples of how to perform such predictions for additively manufactured (AM) Ti-6Al-4V; wire arc additively manufactured (WAAM) 18Ni 250 Maraging steel; and Boeing Space, Intelligence and Weapon Systems laser bed powder fusion (LPBF) Scalmalloy^®, which is an additively manufactured Aluminium-Scandium-Mg alloy, using the Hartman-Schijve crack growth equation. In these studies, the constants used were as determined from ASTM E647 standard tests on long cracks, and the fatigue threshold term in the Hartman-Schijve equation was set to a small value (namely, 0.1 MPa √m). This paper illustrates how this approach can also be used to predict the growth of naturally occurring three-dimensional cracks in WAAM CP-Ti (commercially pure titanium) specimens built by Solvus Global as well as in WAAM-built Inconel 718. As in the prior studies mentioned above, the constants used in this analysis were taken from prior studies into the growth of long cracks in conventionally manufactured CP-Ti and in AM Inconel 718, and the fatigue threshold term in these analyses was set to 0.1 MPa √m. These studies are complemented via a prediction of the growth of naturally occurring three-dimensional cracks in conventionally built M300 steel. Full article

In this article, the structure formation and phase composition of coatings containing Cr₂AlC MAX phase under the conditions of plasma spraying were studied. Mechanical mixtures of commercially available Cr₃C₂ and Al powders were used as a material for spraying. The amount of aluminium in the mixtures was 9 and 18 wt.%. As a result of studying physicochemical processes occurring during plasma spraying of mechanical mixtures of selected compositions, the formation of coatings containing Cr₂AlC MAX phase was established, the synthesis of which occurs both at the stage of the particles flight of initial components in the plasma jet as a result of the collision and coagulation, and at the stage of a coating layer formation as a result of layering particles deformed during the collision–splats. It is shown that for the formation of a denser coating with a higher MAX phase content for spraying, it is rational to use a mixture of chromium carbide powders with 9 wt.% of aluminium. A coating with the composition 91Cr₃C₂-9Al (wt.%) has high corrosion resistance in operation conditions in a chloride-acetate solution, and by its indicators of corrosion resistance, is not inferior to the Cr₃C₂-NiCr coating, which is widely used in industry to protect parts from corrosion and wear. The obtained results show the possibility and feasibility of using mechanical mixtures of commercially available powders for the formation of coatings containing Cr₂AlC MAX phase instead of expensive synthesized MAX-Cr₂AlC powders. Full article

External pressure is often applied during sintering to obtain materials with improved properties. For complex concentrated alloys (CCAs), this processing step is commonly performed in vacuum. However, this can promote the evaporation of elements and increase the oxide content, thereby degrading the properties of the alloy. In this study, we compared the microstructures and properties of AlCrCuFeMnNi CCA samples obtained by hot uniaxial pressing sintering (HPS) and pressureless sintering (PLS) using a helium atmosphere purified by an oxygen getter system. The powders were prepared from mixtures of CrFeMn, AlNi and Cu and sintered by HPS at 900 °C for 1 h with an applied pressure of 30 MPa and by PLS at 1050 °C for 1 h. The samples were characterised using X-ray diffraction, scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron backscattering diffraction, density measurements and hardness tests. It was found that the oxygen getter system promoted oxygen partial pressure values at sintering temperatures similar to those of a mixture of 90% helium and 10% hydrogen. The HPS allowed us to obtain almost fully dense samples with a smaller average grain size and finer distribution of aluminium oxides than PLS. These differences increased the hardness of the samples sintered under pressure. Full article

High-strength aluminium alloys are prone to porosity and cracking during laser-based powder bed fusion of metals (PBF-LB/M) due to the complex solidification behaviour, thus limiting the preparation of high-quality aluminium alloys. In order to effectively reduce the defect formation, this study investigated the influence mechanism of different process parameters on the formation of porosity and cracks in Al-Zn-Mg-Cu alloys in the PBF-LB/M process by combining experimental and numerical simulation. The degree of influence of the process parameters on the temperature field and the temperature field on the defect formation was also quantified using path analysis. The results show that modulation of the process parameters can effectively reduce the formation of cracks and pores, although it is difficult to eliminate them. The melt pool temperature has a significant effect on the formation of porosity, and the temperature gradient has a significant effect on the formation of cracks. The degree of influence of laser power on the melt pool temperature and temperature gradient was greater than that of scanning speed, with values of 0.980 and 0.989, respectively. Therefore, the priority of modulating the laser power is higher than that of scanning speed in order to reduce the formation of defects more effectively. Full article

The detection of defects in aluminium alloys using eddy current testing (ECT) can be restricted by higher electrical conductivity. Considering the occurrence of discontinuities during the selective laser melting (SLM) process, checking the ability of the ECT method for the mentioned purpose could bring simple and fast material identification. The research described here is focused on the application of three ECT probes with different frequency ranges (0.3–100 kHz overall) for the identification of artificial defects in SLM aluminium alloy AlSi10Mg. Standard penetration depth for the mentioned frequency range and identification abilities of used probes expressed through lift-off diagrams precede the main part of the research. Experimental specimens were designed in four groups to check the signal sensitivity to variations in the size and depth of cavities. The signal behavior was evaluated according to notch-type and hole-type artificial defects’ presence on the surface of the material and spherical cavities in subsurface layers, filled and unfilled by unmolten powder. The maximal penetration depth of the identified defect, the smallest detectable notch-type and hole-type artificial defect, the main characteristics of signal curves based on defect properties and circumstances for distinguishing between the application of measurement regime were stated. These conclusions represent baselines for the creation of ECT methodology for the defectoscopy of evaluated material. Full article

Powder metallurgy process has the advantage of optimized material utilization with near net shape, resulting in reduced costs. The densification behavior of sintered aluminium under different loading conditions plays an important role in assessing the performance of parts. The experimental studies to examine the densification behavior are cost intensive and less flexible. Therefore, simulation studies are conducted and results are compared with the experimentation results. The FEA-based DEFORM-2D tool is used for modeling and simulation purposes. The performance curves of load vs. displacement are plotted. A new material is (Al-cr3c2) made and a flow curve is constructed using the disc compression test findings and using software to meet the experimentally observed flow stress. The relationship between stress and strain is studied under different loading conditions of sintered aluminium preforms during densification. Formability stress and strain in plane stress state condition initially rise with the rise in axial strain and then remain constant throughout the process. With a rise in the height reduction percentage, the relative density rises. The final density is higher because there are more pores in the sample when the aspect ratio is lower and the rate of densification is slower. Full article

As a recently developed high-strength aluminium alloy used specifically for laser additive manufacturing, AlMgMnSc alloy possesses superior mechanical properties and excellent processability. Extreme high-speed laser deposition (EHLD) is a novel surface-modification technique, which is characterised by high depositing speed, rapid cooling, rate and minimal dilution rate. To offer a new method for surface repairing high-strength aluminium alloys, an AlMgMnSc alloy coating, containing two deposition layers, is prepared on a 6061 aluminium-alloy axle using the EHLD technique. Meanwhile, the microstructure, composition distribution, and microhardness variation of the fabricated coating are studied. The results reveal that the coating is dense and crack-free, which is well-bonded with the substrate. Additionally, layer 1 is mainly composed of large columnar and equiaxed grains, while layer 2 consists of a fully equiaxed grain structure with an average grain size of about 4.5 μm. Moreover, the microhardness of the coating (about 104~118 HV) is similar to the substrate (about 105 HV), proving the feasibility of repairing high-strength aluminium alloys using AlMgMnSc alloy powders through the EHLD technique. Full article

A gaseous elemental mercury (Hg⁰) sampler was developed for the assessment of mercury (Hg) pollution from the air and utilised aluminium (Al) powder as the accumulation medium. The Hg sampler is presented as an alternative cost-effective sorbent that can be used for the assessment of Hg pollution in atmospheric air in areas where natural bio-indicators such as lichens and moss do not grow, including the urban environments. The chemical treatment of Al materials was necessary to weaken the aluminium oxide (Al₂O₃) layer to increase the adsorption capability of Al material. Treated Al samples were exposed to Hg vapours for one hour to two weeks in a Hg atmosphere chamber. Other Al powder samples were exposed to the ambient air at areas of the Tshwane Metropolitan Municipality for six to ten months. The analysis of samples by an RA-915+ Zeeman mercury analyser showed that the limit of detection (LOD) and limit of quantification (LOQ) for the determination of Hg in Al powder with a mass of 100 mg were found to be 0.31 ng g⁻¹ and 1.0 ng g⁻¹, respectively. The content of Hg that accumulated on Al powder was linear from 0.1 to 25 ng g⁻¹, thus enabling the measurement of Hg accumulation from air at the global average concentration level. Mercury from air that accumulated on Al powder in the Tshwane Metropolitan Municipality ranged between 70 ng g⁻¹ and 155 ng g⁻¹. Full article

This paper presents the results of laboratory tests for new materials made of a carbon fibre-reinforced polymer (CFRP) composite with a single-sided protective coating. The protective coatings were made of five different powders—Al₂O₃, aluminium, quartz sand, crystalline silica and copper—laminated in a single process during curing of the prepreg substrate with an epoxy matrix. The specimens were subjected to flame exposure and solid particle erosion tests, followed by uniaxial tensile tests. A digital image correlation (DIC) system was used to observe the damage location and deformation of the specimens. All coatings subjected to solid particle erosion allowed an increase in tensile failure force ranging from 5% to 31% compared to reference specimens made of purely CFRP. When exposed to flame, only three of the five materials tested, Al₂O₃, aluminium, quartz sand, could be used to protect the surface, which allowed an increase in tensile failure force of 5.6%. Full article

Primary and secondary mill scales (MSs) are waste products produced by the surface oxidation of steel during the hot (800 to 1200 °C) rolling process in downstream steelmaking. While the primary MS is comprised of FeO, Fe₃O₄, and Fe₂O₃ in a range of proportions, the secondary MS primarily contain red ferric oxide (Fe₂O₃) (red MS). We report a novel route for extracting iron from red MS and transforming it into ferro-aluminium alloys using carbothermic reduction in the presence of alumina. The red MS powder was blended with high-purity alumina (Al₂O₃) and synthetic graphite (C) in a range of proportions. The carbothermic reduction of red MS-Al₂O₃-C blends was carried out at 1450 °C and 1550 °C under an argon atmosphere for 30 min and then furnace-cooled. The red MS was completely reduced to iron at these temperatures with reduced iron distributed around the matrix as small droplets. However, the addition of alumina unexpectedly resulted in a significant increase in the number and sizes of iron droplets generated, much higher reactivity, and the formation of ferrous alloys. A small amount of alumina reduction into metallic aluminium was also observed at 1450 °C. There is an urgent need to identify the true potential of industrial waste and the materials within it. This study showed that red MS is a valuable material source that could be transformed into ferro-aluminium alloys. These alloys find application in a range of industrial sectors such as construction, automotive, infrastructure, etc. Full article

In this paper, SiCp aluminium matrix composites were used as the matrix, and AlSi10Mg powder, which has a relatively similar coefficient of thermal expansion to that of the matrix, was used to prepare laser cladding Al-based coatings. The results show that the optimal process parameters are P = 4400 W, V_f = 11.3 g·min⁻¹, and V_S = 1800 mm·min⁻¹, and, although the hardness of the coatings is lower than the hardness of the substrate, it reduces the generation of defects such as cracks and porosity. With the increase in WC reinforced phase and the hardness of the coatings, wear resistance increases, the granular cytocrysts are transformed into rod-like cytocrysts, and at the same time generate the dendritic crystals, and the undergo grain refining and generate the new phases such as Al₄C₃, Al₄SiC₄. There is no obvious defect in AlSi10Mg + 40%WC coatings, the macro morphology of the coatings is good, there is no spalling in the friction wear morphology, and the wear resistance is excellent, but there are obvious cracks and obvious spalling in the coatings of AlSi10Mg + 60%WC. Compared to the matrix hardness of 171.61 HV, the hardness of the 20%WC cladding layer increased by a factor of 1.06, while the hardness of the 40%WC cladding layer increased by a factor of 1.65 and that of the 60%WC cladding layer increased by a factor of 1.8. In terms of wear, compared to a substrate wear amount of 9.36 mg, the wear for the 20%WC cladding layer was reduced to 6.13 mg (34.5% less than the substrate), for the 40%WC cladding layer it was reduced to 4.58 mg (51.06% less than the substrate), and for the 60%WC cladding layer it was reduced to 7.35 mg (21.47% less than the substrate). The quality of the coatings decreases although the hardness is higher than that of AlSi10Mg + 40%WC. The comprehensive performance of AlSi10Mg + 40%WC coatings is optimal. Full article

Regenerated magnesia-calcium brick samples with different aluminium oxide (Al₂O₃) contents were prepared using spent magnesia-calcium bricks and fused magnesia as the main raw materials and Al₂O₃ powders as the additive. The phase compositions, microstructures, room temperature, hot flexural strength, and kiln coating adherence of the regenerated samples were investigated. This indicates that the Al₂O₃ content increased, mainly resulting in the content of tetracalcium aluminoferrite (C₄AF) and tricalcium aluminate (C₃A) increasing in the regenerated samples. The bulk density, room temperature flexural strength, and kiln coating adherence all increased, whereas the hot flexural strength and corrosion resistance to cement clinker both deteriorated with an increase in the Al₂O₃ content. This was because, on the one hand, the low melting point phases of C₄AF and C₃A improved the sinterability of the regenerated samples during the burning stage, and on the other hand, they melted or existed in the liquid phase at the experimental temperature, which degraded the hot flexural strength and corrosion resistance but enhanced the kiln coating adherence as the wettability of the liquid phase. The content of Al₂O₃ in the regenerated magnesia-calcium brick should not be higher than 1.1 wt.%, considering its comprehensive performance for cement rotary kiln. Full article

Although electrocoagulation combined with zeolite (ECZ) shows higher efficiency in wastewater treatment, the actual contribution of zeolite particle size has not been fully explored. In this work, the influence of particle size of synthetic zeolite SZ (<90, 90–160, and 160–600 μm) on ECZ treatment of compost leachate with very high organic load is investigated together with different electrode materials (Fe, Al, and Zn), current densities (0.003, 0.009 and 0.018 A/cm²), and contact times (10, 20 and 30 min). The results positively highlight that the largest particle size should be used in ECZ, as it leads to a lower increase in pH and temperature, a higher decrease of chemical oxygen demand (COD) and turbidity, and a lower electrode consumption, while causing more damage to the electrode surface. The estimated energy costs ranged from 3.960 kW/m³–1313.657 kW/m³. The Taguchi L9 orthogonal configuration showed the highest COD and turbidity decrease under the conditions of 160–600 µm zeolite particles. The powder X-ray diffractometer (PXRD) analysis shows that interplanar spacing decreases when smaller and medium SZ particle sizes are used, while this effect was not observed with larger zeolite particle size. SEM-EDS shows that oxygen, silicon, and aluminium are the predominant elements in electrogenerated sludge coupled with zeolite. Full article

Novel aluminium matrix composites have been fabricated using a powder metallurgy route with reinforcement phase particles of high entropy alloy (HEA) consisting of third transition metals. These new composites are studied as far as their microstructure (SEM, XRD), basic mechanical properties (hardness, elastic modulus) and creep response using nanoindentation techniques are concerned. Wear (sliding wear tests) and corrosion behaviour (in 3.5 wt.% NaCl environment) were also assessed. It was observed that, microstructurally, no secondary intermetallic phases were formed. Hardness and wear resistance seemed to increase with the increase in HEA particles, and in terms of corrosion, the composites exhibited susceptibility to localised forms. Nanoindentation techniques and creep response showed findings that are connected with the deformation nature of both the Al matrix and the HEA reinforcing phase. Full article

This article employed the fused deposition modelling (FDM) method and gas-pressure infiltration to manufacture alumina/AlSi12 composites. Porous ceramic skeletons were prepared by FDM 3D printing of two different alumina powder-filed filaments. The organic component was removed using a combination of solvent and heat debinding, and the materials were then sintered at 1500 °C to complete the process. Thermogravimetric tests and DTA analysis were performed to develop an appropriate degradation and sintering program. Manufactured skeletons were subjected to microstructure analysis, porosity analysis, and bending test. The sintering process produced porous alumina ceramic samples with no residual carbon content. Open porosity could occur due to the binder’s degradation. Liquid metal was infiltrated into the ceramic, efficiently filling any open pores and forming a three-dimensional network of the aluminium phase. The microstructure and characteristics of the fabricated materials were investigated using high-resolution scanning electron microscopy, computer tomography, hardness testing, and bending strength testing. The developed composite materials are characterized by the required structure—low porosity and homogenous distribution of the reinforcing phase, better mechanical properties than their matrix and more than twice as high hardness. Hence, the developed innovative technology of their manufacturing can be used in practice. Full article