1,721,001 research outputs found
Effect of laser remelting on surface roughness and microstructure of AlSi10Mg selective laser melting manufactured parts
No full textSelective laser melting (SLM) allows to obtain components by a careful selection of process parameters. This technology is becoming more and more attractive because it is capable of producing dense and complex metallic parts. Considering that one of the main drawbacks of this technology is the high surface roughness, this research aims at reducing it by means of skin laser remelting performed during the fabrication process. Since the remelting strategy affects only the external skin, the building time is slightly affected by this additional operation and the infill part properties remain unchanged. In this work, the effect of process parameters on the surface morphology and alloy microstructure has been analyzed. The obtained results highlighted that the remelting process allows to improve the surface morphology but it affects the subsurface defect formation. The obtainable surface roughness for different surface slopes was modelled as a function of the process parameters
Effect of dispersed particles on TiAl alloys fracture behavior
Full text linkγTiAl based alloys are very attractive for structural applications at high temperatures. The addition to the selected alloy of dispersed alumina particles increases the yield strength and the elastic modulus of γTiAl alloys but affects their fracture behavior by favoring the propagation of brittle fracture. The analysis of the fracture surface revealed that the addition to oxide particle, during component production by means of investment casting, favors brittle fracture propagation by intensifying stresses and by increasing the quantity of shrinkage cavities inside the casting
Comparison between mechanical properties and structures of a rolled and a 3D-printed stainless steel
Full text linkIn this work selective laser melting was successfully utilized to produce 316 stainless steel bulk specimens. Although this technology provides many advantages compared to conventional shaping processes, little residual porosity may be a problem for some applications where high strength is required. The objective of this work was to determine, through data analysis, a mechanical and metallographic comparison between thin sheets made by using different manufacturing technologies: Cold rolling and additive manufacturing. This comparison was useful to understand whether it could be more advantageous to use the prototyping for new mechanical components. The results show that the additive manufactured steel, due to its microstructure, is characterized by a higher yield strength and by a lower elongation and ultimate tensile strength
Additively manufactured CuCrZr alloy: improvement of mechanical properties by heat treatment
Full text linkCuCrZr alloy plays a fundamental role for the production of critical components because it is characterized by good thermal and electrical conductivity and by high mechanical strength after precipitation hardening treatment. In the framework of a wider research on the mechanical behaviour of additively manufactured CuCrZr alloy, this study focuses on the effects of heat treatment parameters on the alloy strength. The additive manufacturing process, characterized by very high cooling rates, determines the formation, in the as-built condition, of a supersaturated solid solution. The results obtained reveal that aging temperature and time are critical parameters for improving the mechanical behaviour of CuCrZr alloy which behaves differently than the alloy produced through the use of traditional techniques
Novel lead battery recycling process combining pyrometallurgical anode preparation and electrorefining
No full textLead acid batteries are processed mainly by using pyrometallurgical operations with problems related to SO2 evolution. Many efforts have been devoted to solving this concern. In this work, where only the anode preparation was a pyrometallurgical process, this problem has been overcome by limiting the process temperature. Several tests have been carried out in order to determine the starting mix composition that allows to reduce the process temperature and then SO2 emissions. Three different anode types were cast and tested. Independently on the anode type, the complex composition of the anode requires to design a special electrolytic cell composed by two different compartments. Preliminary electrorefining tests highlighted that the best results were obtainable by using the anode cast in a titanium holder that allowed to obtain high-purity lead, high anode durability, and low quantity of anodic mud. By using this anode, the specific energy consumption varied over the 0.04–0.17 kWh/kg range. Graphic Abstract: [Figure not available: see fulltext.
Mechanical testing of metallic foams for 3D model and simulation of cell distribution effects
No full textCellular materials have a bulk matrix with a larger number of voids named also cells. Metallic foams made by powder technology represent stochastic closed cells. The related inhomogeneity leads to a scattering of results both in terms of stress-strain curves and maximum strength. Scattering is attributed to relative density variations and local cell discontinuities and it is confirmed also in case of dynamic loading. Finite element simulations through geometrical models that are able to capture the void morphology (named “mesoscale models”), confirm these results and some efforts have been already done to quantify the relationship between shape irregularities and mechanical behavior. The aim of this paper is to present the dynamic characterization of an AA7075 closed cell material and to calibrate its mesoscale finite element model according to the related cell shape distribution. Specimens have been derived from a small ingot (45x45x100 mm) divided along sections so that morphological analysis and experimental tests have been carried out. Specimens extracted from a half of the ingot have been used for dynamic compression tests by means of a split Hopkinson bar, meanwhile specimens extracted from the other half of the ingot have been dissected for porosity distribution analyses carried out by means of image analysis. Stress-strain curves obtained from the mechanical tests have been discussed in terms of strain rate and statistical descriptors of the porosity. Successively a 3D-model of the specimen has been generated starting from the Voronoi algorithm, assigning as input the above-mentioned statistical distribution of the porosity. Due to the peculiarity of the cell morphology (e.g. single larger cells), stress-strain localization has been demonstrated as one of the reasons of the scattering found during the experiments. A material model, to reproduce the investigated foam mechanical behavior, has been calibrated. Despite the difference among experiments the material model is able to reproduce all of them. Difference between the model coefficients quantifies roughly the difference due to the local geometry of the cells
Joining Dissimilar Steels by Means of Selective Laser Melting: Material Microstructure and Interfacial Characteristics
No full textThe increasing demand for designing complex structures using Functionally Graded Material boosts the research on reliable joining processes. For several industrial applications in the automotive, tooling, and petrochemical industries, the joining of a stainless steel with a low-alloy steel is often required to obtain a variation of mechanical and corrosion properties when different parts of the same structure are subjected to different working conditions. Welding a stainless steel with a low-alloy steel is a challenging operation because it is not easy to control the microstructure of the welded joint and to avoid metallurgical defects such as hot cracks. Moreover, traditional welding methods can only be applied to relatively simple geometries. To design and produce multi-material components, characterised by complex geometries, Selective Laser Melting process capabilities can be exploited. In this paper, an AISI 316L stainless steel is joined to 16MnCr5 steel by carefully tuning the process parameters. Metallurgical investigations coupled with Energy Dispersion Spectroscopy analyses allowed to evaluate the soundness of the joint and the effect of the process thermal cycle on the alloy microstructures and properties. The results are very promising and show that a careful selection of process parameters allows to obtain a continuous joint
Strain rate and density-dependent strength of AlSi7 alloy foams
No full textFoams are able to absorb energy and bear stress more uniformly and efficiently than the correspondent bulk materials. This makes them ideal candidates to increase the specific structure's absorption efficiency.Concerning their characterisation, there are still some open issues needing further investigations, such as the experimental analysis of their dynamic behaviour with alloy types, strain rates and foam density changes.This paper focuses on the above mentioned issues presenting the results of a dynamic characterisation by means of a direct tension-compression Hopkinson bar. Tests are carried out on AlSi7 alloy foam specimens obtained from a large ingot made by compact powder technology. The results are discussed mainly in terms of strength and energy absorption efficiency, considering the effects of strain rate and of the variation of foam density, due to the manufacturing process
Effect of heat treatment on mechanical properties of FeMnAlC alloys
Full text linkFeMnAlC alloys exhibit an attractive strength/ductility combination, low density and some of them show good oxidation behavior at high temperatures. In this paper the effect of a solubilization treatment at 1030 °C followed by aging at 550 °C on the mechanical properties of two alloys belonging to this system, has been evaluated. The results of the investigation revealed that the steel characterized by the higher quantity of Mn and Al shows, after heat treatment, the formation of intermetallic phases that make the alloy very brittle. Considering the obtained results, it is evident that optimizing the alloy chemical composition is of paramount importance to guarantee a high fracture toughness if the steel works for limited time intervals at high temperature
Fracture behaviour of alloys for a new laser ranged satellite
Full text linkA new laser-ranged satellite called LARES 2 (Laser Relativity Satellite 2) has been recently designed for accurate tests of Einsten's theory of General Relativity and space geodesy. Some high density alloys (8.6-9.3 g/dm3) have been studied and characterised for producing the LARES 2 passive satellite. The considered materials were Copper and Nickel based alloys that have been produced and characterised. Aim of this work was to analyse their fracture behaviour that is a requirement for materials to be used for space applications. Fracture tests have been carried out on several specimens and fracture surfaces have been analysed
- …
