The International Journal of Advanced Manufacturing Technology, Dec 30, 2012
Direct metal laser sintering (DMLS) is an additive manufacturing technique for the fabrication of... more Direct metal laser sintering (DMLS) is an additive manufacturing technique for the fabrication of near netshaped parts directly from computer-aided design data by melting together different layers with the help of a laser source. This paper presents an investigation of the surface roughness of aluminum samples produced by DMLS. A model based on an L 18 orthogonal array of Taguchi design was created to perform experimental planning. Some input parameters, namely laser power, scan speed, and hatching distance were selected for the investigation. The upper surfaces of the samples were analyzed before and after shot peening. The morphology was analyzed by means of field emission scanning electron microscope. Scan speed was found to have the greatest influence on the surface roughness. Further, shot peening can effectively reduce the surface roughness.
Metallurgical and Materials Transactions, Feb 14, 2017
Nickel superalloys are typical materials used for the hot parts of engines in aircraft and space ... more Nickel superalloys are typical materials used for the hot parts of engines in aircraft and space vehicles. They are very important in this field as they offer high-temperature mechanical strength together with a good resistance to oxidation and corrosion. Due to high-temperature buckling phenomena, reinforcement of the nickel superalloy might be needed to increase stiffness. For this reason, it was thought to investigate the possibility of producing composite materials that might improve properties of the metal at high temperature. The composite material was produced by using electrochemical deposition method in which a composite with nickel matrix and long silicon carbide fibers was deposited over the nickel superalloy. The substrate was Inconel 718, and monofilament continuous silicon carbide fibers were chosen as reinforcement. Chemical compatibility was studied between Inconel 718 and the reinforcing fibers, with fibers both in an uncoated condition, and coated with carbon or carbon/titanium diboride. Both theoretical calculations and experiments were conducted, which suggested the use of a carbon coating over the fibers and a buffer layer of nickel to avoid unwanted reactions between the substrate and silicon carbide. Deposition was then performed, and this demonstrated the practical feasibility of the process. Yield strength was measured to detect the onset of interface debonding between the substrate and the composite layer.
Journal of Materials Engineering and Performance, Aug 20, 2015
Titanium aluminide alloys are good candidates for structural applications thanks to their low den... more Titanium aluminide alloys are good candidates for structural applications thanks to their low density and good balance of properties up to relatively high temperatures. However, their application is still limited by significant oxidation. Four c-TiAl alloys with different content of aluminum and niobium were produced by electron beam melting: Ti-45Al-2Cr-2Nb, Ti-48Al-2Cr-2Nb, Ti-45Al-2Cr-8Nb, and Ti-46Al-2Cr-8Nb. The behavior of these alloys in response to oxidation in air during constant heating up to 1000°C and isothermal oxidation for 10 h at 850 and 950°C were studied by thermogravimetric analysis. The mass gain due to oxidation of the low Nb-containing alloys was always at least twice that of the high Nbcontaining alloys. Both low and high Nb-containing alloys exhibited on their surface oxidation products of the same nature: oxides TiO 2 and Al 2 O 3 , and nitrides TiN and Ti 2 AlN. Niobium addition up to 8 at.% did not suppress the growth of rutile and promote the formation of a protective alumina layer. However, it efficiently reduced the formation of rutile, mainly responsible for the mass gain due to oxidation of c-TiAl alloys and with tendency to spallation.
Laser Induced Solution Deposition (LISD) is essentially a laser chemical processing with similar ... more Laser Induced Solution Deposition (LISD) is essentially a laser chemical processing with similar mechanism of the counterpart-laser chemical vapor deposition (LCVD). It is a novel method for synthesizing nanocsale particles or thin films with the combined advantages of laser chemical vapor deposition and electroless chemical deposition in solution (electrolyte). It is simple and efficient, and it can produce high quality nanoparticles or patterned uniform thin films. In this paper the nanostructured Co/CoO x particles have been fabricated by LISD technique. We have characterized the deposited materials by using scanning electron microscope (SEM), the high-resolution transmission electron microscope (HRTEM) and X-ray diffraction technique (XRD). We have found that the sizes of the deposited particles are smaller than 5 nm uniformly suspended in the solution used in the LISD deposition, and the sizes are smaller than 500 nm on the silicon substrates inserted in the deposited solution. The results by energy dispersive X-ray analysis (EDX) have indicated that there are Co peaks and O peaks, which meant there were oxygen contamination or the deposited products were cobalt oxide rather than pure cobalt nanoparticles. The X-ray diffraction has shown that we have obtained pure Co nanoparticles in some cases but we have obtained cobalt oxides in other cases, which mainly depended on the experimental conditions such as the selection of solvents and solutes as well as the selection of the lasers including the wavelength and the power of the laser beams. The studies of the magnetic properties, catalytic properties as well as their relationship of pure cobalt nanoparticles and cobalt oxide nanoparticles are in good progress and we will publish the useful results elsewhere.
Powders of alloys Ti-48Al-2Cr-2Nb (48-2-2) and Ti-48Al-2Nb-0.7Cr-0.3Si (RNT650) were used to fabr... more Powders of alloys Ti-48Al-2Cr-2Nb (48-2-2) and Ti-48Al-2Nb-0.7Cr-0.3Si (RNT650) were used to fabricate test samples and turbocharger wheel prototypes, respectively, by electron beam melting. This additive manufacturing technology uses an electron beam to generate parts by selectively melting the powder in a layer-by-layer way based on CAD data. The parts of both alloys were fully densified with only minor percentages of build flaws. For alloy 48-2-2, a loss of Al of about 1.4 wt% is observed, while the levels of impurities are comparable between the powder and the part. Furthermore, the microstructure was investigated after EBM and after EBM + heat treatment for alloy 48-2-2. It is characterized by equiaxed grains after EBM. An additional heat treatment transformed this microstructure into a fully lamellar one showing that the microstructure was homogenized.
Tape casting combined with layer stacking, debinding and sintering proved to be a suitable techni... more Tape casting combined with layer stacking, debinding and sintering proved to be a suitable technique for processing SiC-based multilayers to be used as thermal protection system for space vehicles. In this paper two methods have been evaluated in order to decrease the thermal conductivity through the thickness of the material: the insertion of layers containing a pore forming agent able to leave residual porosity; the deposition of an external insulating coating made of yttria-partially stabilized zirconia (YPSZ). Both techniques contribute to the reduction of thermal conductivity. The insertion into the multilayered structure of porous layers with a high level of residual porosity halves the thermal conductivity but 25% decrease in bending strength is observed. The fracture surface however shows that highly porous layers activates crack deflection mechanism, increasing fracture energy. The use of an YPSZ coating allows for a less evident reduction of thermal conductivity (from 102 to 75 W/(m K) at room temperature) but good mechanical properties are maintained (340 MPa bending strength).
Composites Part A-applied Science and Manufacturing, May 1, 2010
Co-continuous metal/ceramic composites (or C 4) were obtained by Reactive Metal Penetration start... more Co-continuous metal/ceramic composites (or C 4) were obtained by Reactive Metal Penetration starting from commercial cordierite preforms. The infiltrating alloys were chosen to be 1050, 2011 and 7075 standard aluminium alloys, with increasing content of alloying elements The kinetics of infiltration was studied, together with the microstructure and mechanical properties of the obtained composites, which are influenced by the quantity of alloying elements. The higher the alloying elements quantity, the higher the microhardness of the composites.
Concept γ-TiAl materials represent an important class of structural materials which thanks to the... more Concept γ-TiAl materials represent an important class of structural materials which thanks to their excellent physical and mechanical properties, play an important role in the aerospace and automotive industries. In particular, they are considered an attractive alternative to nickel-based superalloys due to a lower density [1]. In this work, realized within the European projects TIALCHARGER and E-BREAK and the Regional Project Great2020 FaseII, three kind of γ-TiAl alloys have been investigated: 48-2-2 alloy (aerospace, E-BREAK), TNM alloy (aerospace, E-Break, Great2020 FaseII) and RNT650 alloy (automotive, TIALCHARGER) [2]. Motivations and Objectives The Electron Beam Melting.(EBM) is an additive manufacturing technology that uses an electron beam to generate parts by selectively melting the powder layer by layer according to CAD data. This technology presents several advantages in terms of costs and energy saving compared to the conventional manufacturing processes. The aims of this work are the evaluation of the powder's recyclability and the optimization of the EBM process parameters using a DOE to obtain the desired microstructure for a specific application after the heat treatment on the well known 48-2-2 alloy, and contemporary the set up of EBM process and the heat treatments on new generation alloys: TNM for turbine blades and RNT650 alloy for turbocharger wheels. Results and Discussion Regarding the recyclability, the analysis performed on powder recycled several times and used for several EBM cycles confirm that, for what concerns particle size distribution, flowability and apparent density, the recycling process adopted doesn't change the powder properties. Regarding the chemistry, is evident that the recycling process generate only a very small amount of oxygen pick-up which will not affect the specimen production. For the TNM alloy, two heat treatment that gives a near lamellar microstructure with the presence of some β-phase have been set. This kind of microstructure is considered the most promising, for the application of this alloy, in terms of tensile properties with sufficient creep properties. For the RNT650 alloy an heat treatment was set up to obtain a near lamellar microstructure both on samples bars that on hollow and full turbocharger wheels
Laser powder bed fusion (LPBF) is an additive manufacturing technology that implies using metal p... more Laser powder bed fusion (LPBF) is an additive manufacturing technology that implies using metal powder as a raw material. The powders suitable for this kind of technology must respect some specific characteristics. Controlled gas atomization and post-processing operations can strongly affect the final properties of the powders, and, as a consequence, the characteristics of the bulk components. In fact, a complete characterization of the powders is mandatory to fully determine their properties. Beyond the most used tests, such as the volume particle size distribution (PSD) and flowability, the PSD number, the Hausner ratio and the oxidation level can give additional information otherwise not detectable. The present work concerns the complete characterization of two AlSi10Mg powders: a commercial-grade gas atomized powder and a laboratory-scale gas atomized counterpart. The laboratory-scale gas atomization allows to better manage the amount of the fine particles and the oxidation leve...
This work deals with the effect of different heat treatments on directed energy deposition (DED)-... more This work deals with the effect of different heat treatments on directed energy deposition (DED)-produced Ti-6Al-4V samples. Annealing treatments at 1050 • C followed by different cooling rates were conducted to allow a complete recrystallization of the microstructure and remove the columnar prior-β grains, thus increasing the overall isotropy of the material. An agine treatment at 540 • C was also performed for further microstructural stabilization. The microstructures, textures and mechanical properties were then assessed. Due to the heat treatments, greatly differing microstructures were achieved in an equiaxed grain morphology. However, a "grain memory" effect was detected which resulted in the grains size increasing along the height of the samples. This effect was correlated to the intrinsic prior-β grain width variation along Z on the as-printed specimens, typical of the DED technology. Electron backscatter diffraction analyses proved that the intensity of the preferential directions increased after the heat treatments, likely due to the crystallographic variant selection mechanisms taking place when the samples cool down from the annealing temperature. This effect is also influenced by the significant difference in terms of prior-β grains sizes between the heat-treated and the as-printed specimens. To sum up, a complete homogenization of the material via heat treatment above the β-transus temperature proved to be challenging. In fact, the data suggest that the intrinsic texture-related anisotropy granted by the manufacturing process is very difficult to be eliminated.
γ-TiAl materials represent an important class of structural materials which already proved to be ... more γ-TiAl materials represent an important class of structural materials which already proved to be extremely promising for both automotive and aerospace applications. At present, the EBM is the most attractive additive manufacturing process for the production of TiAl components. In this study several samples of the alloy Ti-48Al-2Cr-2Nb (at%) were produced varying EBM process parameters such as line offset, speed function, max beam current and focus offset according to a DoE matrix exhibiting differences in terms of residual defects, microstructure, aluminum evaporation, etc. Within this work an FE thermal model of the EBM process was used in order to investigate and explain the above mentioned differences obtained during the process. The FE thermal model of the EBM process gives an idea of the reached temperature and showed that material is subjected to numerous thermal cycles before and after the EB scan, which lead to a first temperature raise before the EB scan, and then several r...
Journal of Materials Engineering and Performance, 2021
Over the last decade, the enormous potential of metal additive manufacturing (AM) processes has l... more Over the last decade, the enormous potential of metal additive manufacturing (AM) processes has led these technologies to establish their position in many industries. Much effort is being made toward their widespread application; however, much remains to be done to achieve full industrialization of these processes. Therefore, many companies, research centers and universities are investing in comprehensive research and development activities in order to further promote the industrialization of metal AM. This review traces the progress of metal AM technologies through an investigation of patents. In the present study, beam-based metal AM patents were searched through the Orbit Intelligence database. First, the number of patents per year was studied, indicating that, as expected, there is strong growth in AM patenting activities. The patents were afterward examined in order to highlight the key players in the field, and it was found that the main players investing in this market are: m...
Conformal cooling coils have been developed during the last decades through the use of additive m... more Conformal cooling coils have been developed during the last decades through the use of additive manufacturing (AM) technologies. The main goal of this study was to analyze how the presence of an internal channel that could act as a conformal cooling coil could affect compressive strength and quasi-elastic gradient of AlSi10Mg lattice structures produced by laser powder bed fusion (LPBF). Three different configurations of samples were tested in compression at 25 °C and 200 °C. The reference structures were body centered cubic (BBC) in the core of the samples with vertical struts alongZ(BCCZ) lattices in the outer perimeter, labelled as NC samples. The main novelty consisted in inserting a straight elliptical channel and a 45° elliptical channel inside the BCCZ lattice structures, labelled as SC and 45C samples respectively. All the samples were then tested in as-built (AB) condition, and after two post process heat treatments, commonly used for AlSi10Mg LPBF industrial components, a ...
In today's business environment, the trend towards more product variety and customization is unbr... more In today's business environment, the trend towards more product variety and customization is unbroken. Due to this development, the need of agile and reconfigurable production systems emerged to cope with various products and product families. To design and optimize production systems as well as to choose the optimal product matches, product analysis methods are needed. Indeed, most of the known methods aim to analyze a product or one product family on the physical level. Different product families, however, may differ largely in terms of the number and nature of components. This fact impedes an efficient comparison and choice of appropriate product family combinations for the production system. A new methodology is proposed to analyze existing products in view of their functional and physical architecture. The aim is to cluster these products in new assembly oriented product families for the optimization of existing assembly lines and the creation of future reconfigurable assembly systems. Based on Datum Flow Chain, the physical structure of the products is analyzed. Functional subassemblies are identified, and a functional analysis is performed. Moreover, a hybrid functional and physical architecture graph (HyFPAG) is the output which depicts the similarity between product families by providing design support to both, production system planners and product designers. An illustrative example of a nail-clipper is used to explain the proposed methodology. An industrial case study on two product families of steering columns of thyssenkrupp Presta France is then carried out to give a first industrial evaluation of the proposed approach.
An investigation on the effect of powder recycling on the microstructure and mechanical propertie... more An investigation on the effect of powder recycling on the microstructure and mechanical properties of AISI 316L produced by
In the circular economy, products, components, and materials are aimed to be kept at the utility ... more In the circular economy, products, components, and materials are aimed to be kept at the utility and value all the lifetime. For this purpose, repair and remanufacturing are highly considered as proper techniques to return the value of the product during its life. Directed Energy Deposition (DED) is a very flexible type of additive manufacturing (AM), and among the AM techniques, it is most suitable for repairing and remanufacturing automotive and aerospace components. Its application allows damaged component to be repaired, and material lost in service to be replaced to restore the part to its original shape. In the past, tungsten inert gas welding was used as the main repair method. However, its heat affected zone is larger, and the quality is inferior. In comparison with the conventional welding processes, repair via DED has more advantages, including lower heat input, warpage and distortion, higher cooling rate, lower dilution rate, excellent metallurgical bonding between the de...
The International Journal of Advanced Manufacturing Technology, Dec 30, 2012
Direct metal laser sintering (DMLS) is an additive manufacturing technique for the fabrication of... more Direct metal laser sintering (DMLS) is an additive manufacturing technique for the fabrication of near netshaped parts directly from computer-aided design data by melting together different layers with the help of a laser source. This paper presents an investigation of the surface roughness of aluminum samples produced by DMLS. A model based on an L 18 orthogonal array of Taguchi design was created to perform experimental planning. Some input parameters, namely laser power, scan speed, and hatching distance were selected for the investigation. The upper surfaces of the samples were analyzed before and after shot peening. The morphology was analyzed by means of field emission scanning electron microscope. Scan speed was found to have the greatest influence on the surface roughness. Further, shot peening can effectively reduce the surface roughness.
Metallurgical and Materials Transactions, Feb 14, 2017
Nickel superalloys are typical materials used for the hot parts of engines in aircraft and space ... more Nickel superalloys are typical materials used for the hot parts of engines in aircraft and space vehicles. They are very important in this field as they offer high-temperature mechanical strength together with a good resistance to oxidation and corrosion. Due to high-temperature buckling phenomena, reinforcement of the nickel superalloy might be needed to increase stiffness. For this reason, it was thought to investigate the possibility of producing composite materials that might improve properties of the metal at high temperature. The composite material was produced by using electrochemical deposition method in which a composite with nickel matrix and long silicon carbide fibers was deposited over the nickel superalloy. The substrate was Inconel 718, and monofilament continuous silicon carbide fibers were chosen as reinforcement. Chemical compatibility was studied between Inconel 718 and the reinforcing fibers, with fibers both in an uncoated condition, and coated with carbon or carbon/titanium diboride. Both theoretical calculations and experiments were conducted, which suggested the use of a carbon coating over the fibers and a buffer layer of nickel to avoid unwanted reactions between the substrate and silicon carbide. Deposition was then performed, and this demonstrated the practical feasibility of the process. Yield strength was measured to detect the onset of interface debonding between the substrate and the composite layer.
Journal of Materials Engineering and Performance, Aug 20, 2015
Titanium aluminide alloys are good candidates for structural applications thanks to their low den... more Titanium aluminide alloys are good candidates for structural applications thanks to their low density and good balance of properties up to relatively high temperatures. However, their application is still limited by significant oxidation. Four c-TiAl alloys with different content of aluminum and niobium were produced by electron beam melting: Ti-45Al-2Cr-2Nb, Ti-48Al-2Cr-2Nb, Ti-45Al-2Cr-8Nb, and Ti-46Al-2Cr-8Nb. The behavior of these alloys in response to oxidation in air during constant heating up to 1000°C and isothermal oxidation for 10 h at 850 and 950°C were studied by thermogravimetric analysis. The mass gain due to oxidation of the low Nb-containing alloys was always at least twice that of the high Nbcontaining alloys. Both low and high Nb-containing alloys exhibited on their surface oxidation products of the same nature: oxides TiO 2 and Al 2 O 3 , and nitrides TiN and Ti 2 AlN. Niobium addition up to 8 at.% did not suppress the growth of rutile and promote the formation of a protective alumina layer. However, it efficiently reduced the formation of rutile, mainly responsible for the mass gain due to oxidation of c-TiAl alloys and with tendency to spallation.
Laser Induced Solution Deposition (LISD) is essentially a laser chemical processing with similar ... more Laser Induced Solution Deposition (LISD) is essentially a laser chemical processing with similar mechanism of the counterpart-laser chemical vapor deposition (LCVD). It is a novel method for synthesizing nanocsale particles or thin films with the combined advantages of laser chemical vapor deposition and electroless chemical deposition in solution (electrolyte). It is simple and efficient, and it can produce high quality nanoparticles or patterned uniform thin films. In this paper the nanostructured Co/CoO x particles have been fabricated by LISD technique. We have characterized the deposited materials by using scanning electron microscope (SEM), the high-resolution transmission electron microscope (HRTEM) and X-ray diffraction technique (XRD). We have found that the sizes of the deposited particles are smaller than 5 nm uniformly suspended in the solution used in the LISD deposition, and the sizes are smaller than 500 nm on the silicon substrates inserted in the deposited solution. The results by energy dispersive X-ray analysis (EDX) have indicated that there are Co peaks and O peaks, which meant there were oxygen contamination or the deposited products were cobalt oxide rather than pure cobalt nanoparticles. The X-ray diffraction has shown that we have obtained pure Co nanoparticles in some cases but we have obtained cobalt oxides in other cases, which mainly depended on the experimental conditions such as the selection of solvents and solutes as well as the selection of the lasers including the wavelength and the power of the laser beams. The studies of the magnetic properties, catalytic properties as well as their relationship of pure cobalt nanoparticles and cobalt oxide nanoparticles are in good progress and we will publish the useful results elsewhere.
Powders of alloys Ti-48Al-2Cr-2Nb (48-2-2) and Ti-48Al-2Nb-0.7Cr-0.3Si (RNT650) were used to fabr... more Powders of alloys Ti-48Al-2Cr-2Nb (48-2-2) and Ti-48Al-2Nb-0.7Cr-0.3Si (RNT650) were used to fabricate test samples and turbocharger wheel prototypes, respectively, by electron beam melting. This additive manufacturing technology uses an electron beam to generate parts by selectively melting the powder in a layer-by-layer way based on CAD data. The parts of both alloys were fully densified with only minor percentages of build flaws. For alloy 48-2-2, a loss of Al of about 1.4 wt% is observed, while the levels of impurities are comparable between the powder and the part. Furthermore, the microstructure was investigated after EBM and after EBM + heat treatment for alloy 48-2-2. It is characterized by equiaxed grains after EBM. An additional heat treatment transformed this microstructure into a fully lamellar one showing that the microstructure was homogenized.
Tape casting combined with layer stacking, debinding and sintering proved to be a suitable techni... more Tape casting combined with layer stacking, debinding and sintering proved to be a suitable technique for processing SiC-based multilayers to be used as thermal protection system for space vehicles. In this paper two methods have been evaluated in order to decrease the thermal conductivity through the thickness of the material: the insertion of layers containing a pore forming agent able to leave residual porosity; the deposition of an external insulating coating made of yttria-partially stabilized zirconia (YPSZ). Both techniques contribute to the reduction of thermal conductivity. The insertion into the multilayered structure of porous layers with a high level of residual porosity halves the thermal conductivity but 25% decrease in bending strength is observed. The fracture surface however shows that highly porous layers activates crack deflection mechanism, increasing fracture energy. The use of an YPSZ coating allows for a less evident reduction of thermal conductivity (from 102 to 75 W/(m K) at room temperature) but good mechanical properties are maintained (340 MPa bending strength).
Composites Part A-applied Science and Manufacturing, May 1, 2010
Co-continuous metal/ceramic composites (or C 4) were obtained by Reactive Metal Penetration start... more Co-continuous metal/ceramic composites (or C 4) were obtained by Reactive Metal Penetration starting from commercial cordierite preforms. The infiltrating alloys were chosen to be 1050, 2011 and 7075 standard aluminium alloys, with increasing content of alloying elements The kinetics of infiltration was studied, together with the microstructure and mechanical properties of the obtained composites, which are influenced by the quantity of alloying elements. The higher the alloying elements quantity, the higher the microhardness of the composites.
Concept γ-TiAl materials represent an important class of structural materials which thanks to the... more Concept γ-TiAl materials represent an important class of structural materials which thanks to their excellent physical and mechanical properties, play an important role in the aerospace and automotive industries. In particular, they are considered an attractive alternative to nickel-based superalloys due to a lower density [1]. In this work, realized within the European projects TIALCHARGER and E-BREAK and the Regional Project Great2020 FaseII, three kind of γ-TiAl alloys have been investigated: 48-2-2 alloy (aerospace, E-BREAK), TNM alloy (aerospace, E-Break, Great2020 FaseII) and RNT650 alloy (automotive, TIALCHARGER) [2]. Motivations and Objectives The Electron Beam Melting.(EBM) is an additive manufacturing technology that uses an electron beam to generate parts by selectively melting the powder layer by layer according to CAD data. This technology presents several advantages in terms of costs and energy saving compared to the conventional manufacturing processes. The aims of this work are the evaluation of the powder's recyclability and the optimization of the EBM process parameters using a DOE to obtain the desired microstructure for a specific application after the heat treatment on the well known 48-2-2 alloy, and contemporary the set up of EBM process and the heat treatments on new generation alloys: TNM for turbine blades and RNT650 alloy for turbocharger wheels. Results and Discussion Regarding the recyclability, the analysis performed on powder recycled several times and used for several EBM cycles confirm that, for what concerns particle size distribution, flowability and apparent density, the recycling process adopted doesn't change the powder properties. Regarding the chemistry, is evident that the recycling process generate only a very small amount of oxygen pick-up which will not affect the specimen production. For the TNM alloy, two heat treatment that gives a near lamellar microstructure with the presence of some β-phase have been set. This kind of microstructure is considered the most promising, for the application of this alloy, in terms of tensile properties with sufficient creep properties. For the RNT650 alloy an heat treatment was set up to obtain a near lamellar microstructure both on samples bars that on hollow and full turbocharger wheels
Laser powder bed fusion (LPBF) is an additive manufacturing technology that implies using metal p... more Laser powder bed fusion (LPBF) is an additive manufacturing technology that implies using metal powder as a raw material. The powders suitable for this kind of technology must respect some specific characteristics. Controlled gas atomization and post-processing operations can strongly affect the final properties of the powders, and, as a consequence, the characteristics of the bulk components. In fact, a complete characterization of the powders is mandatory to fully determine their properties. Beyond the most used tests, such as the volume particle size distribution (PSD) and flowability, the PSD number, the Hausner ratio and the oxidation level can give additional information otherwise not detectable. The present work concerns the complete characterization of two AlSi10Mg powders: a commercial-grade gas atomized powder and a laboratory-scale gas atomized counterpart. The laboratory-scale gas atomization allows to better manage the amount of the fine particles and the oxidation leve...
This work deals with the effect of different heat treatments on directed energy deposition (DED)-... more This work deals with the effect of different heat treatments on directed energy deposition (DED)-produced Ti-6Al-4V samples. Annealing treatments at 1050 • C followed by different cooling rates were conducted to allow a complete recrystallization of the microstructure and remove the columnar prior-β grains, thus increasing the overall isotropy of the material. An agine treatment at 540 • C was also performed for further microstructural stabilization. The microstructures, textures and mechanical properties were then assessed. Due to the heat treatments, greatly differing microstructures were achieved in an equiaxed grain morphology. However, a "grain memory" effect was detected which resulted in the grains size increasing along the height of the samples. This effect was correlated to the intrinsic prior-β grain width variation along Z on the as-printed specimens, typical of the DED technology. Electron backscatter diffraction analyses proved that the intensity of the preferential directions increased after the heat treatments, likely due to the crystallographic variant selection mechanisms taking place when the samples cool down from the annealing temperature. This effect is also influenced by the significant difference in terms of prior-β grains sizes between the heat-treated and the as-printed specimens. To sum up, a complete homogenization of the material via heat treatment above the β-transus temperature proved to be challenging. In fact, the data suggest that the intrinsic texture-related anisotropy granted by the manufacturing process is very difficult to be eliminated.
γ-TiAl materials represent an important class of structural materials which already proved to be ... more γ-TiAl materials represent an important class of structural materials which already proved to be extremely promising for both automotive and aerospace applications. At present, the EBM is the most attractive additive manufacturing process for the production of TiAl components. In this study several samples of the alloy Ti-48Al-2Cr-2Nb (at%) were produced varying EBM process parameters such as line offset, speed function, max beam current and focus offset according to a DoE matrix exhibiting differences in terms of residual defects, microstructure, aluminum evaporation, etc. Within this work an FE thermal model of the EBM process was used in order to investigate and explain the above mentioned differences obtained during the process. The FE thermal model of the EBM process gives an idea of the reached temperature and showed that material is subjected to numerous thermal cycles before and after the EB scan, which lead to a first temperature raise before the EB scan, and then several r...
Journal of Materials Engineering and Performance, 2021
Over the last decade, the enormous potential of metal additive manufacturing (AM) processes has l... more Over the last decade, the enormous potential of metal additive manufacturing (AM) processes has led these technologies to establish their position in many industries. Much effort is being made toward their widespread application; however, much remains to be done to achieve full industrialization of these processes. Therefore, many companies, research centers and universities are investing in comprehensive research and development activities in order to further promote the industrialization of metal AM. This review traces the progress of metal AM technologies through an investigation of patents. In the present study, beam-based metal AM patents were searched through the Orbit Intelligence database. First, the number of patents per year was studied, indicating that, as expected, there is strong growth in AM patenting activities. The patents were afterward examined in order to highlight the key players in the field, and it was found that the main players investing in this market are: m...
Conformal cooling coils have been developed during the last decades through the use of additive m... more Conformal cooling coils have been developed during the last decades through the use of additive manufacturing (AM) technologies. The main goal of this study was to analyze how the presence of an internal channel that could act as a conformal cooling coil could affect compressive strength and quasi-elastic gradient of AlSi10Mg lattice structures produced by laser powder bed fusion (LPBF). Three different configurations of samples were tested in compression at 25 °C and 200 °C. The reference structures were body centered cubic (BBC) in the core of the samples with vertical struts alongZ(BCCZ) lattices in the outer perimeter, labelled as NC samples. The main novelty consisted in inserting a straight elliptical channel and a 45° elliptical channel inside the BCCZ lattice structures, labelled as SC and 45C samples respectively. All the samples were then tested in as-built (AB) condition, and after two post process heat treatments, commonly used for AlSi10Mg LPBF industrial components, a ...
In today's business environment, the trend towards more product variety and customization is unbr... more In today's business environment, the trend towards more product variety and customization is unbroken. Due to this development, the need of agile and reconfigurable production systems emerged to cope with various products and product families. To design and optimize production systems as well as to choose the optimal product matches, product analysis methods are needed. Indeed, most of the known methods aim to analyze a product or one product family on the physical level. Different product families, however, may differ largely in terms of the number and nature of components. This fact impedes an efficient comparison and choice of appropriate product family combinations for the production system. A new methodology is proposed to analyze existing products in view of their functional and physical architecture. The aim is to cluster these products in new assembly oriented product families for the optimization of existing assembly lines and the creation of future reconfigurable assembly systems. Based on Datum Flow Chain, the physical structure of the products is analyzed. Functional subassemblies are identified, and a functional analysis is performed. Moreover, a hybrid functional and physical architecture graph (HyFPAG) is the output which depicts the similarity between product families by providing design support to both, production system planners and product designers. An illustrative example of a nail-clipper is used to explain the proposed methodology. An industrial case study on two product families of steering columns of thyssenkrupp Presta France is then carried out to give a first industrial evaluation of the proposed approach.
An investigation on the effect of powder recycling on the microstructure and mechanical propertie... more An investigation on the effect of powder recycling on the microstructure and mechanical properties of AISI 316L produced by
In the circular economy, products, components, and materials are aimed to be kept at the utility ... more In the circular economy, products, components, and materials are aimed to be kept at the utility and value all the lifetime. For this purpose, repair and remanufacturing are highly considered as proper techniques to return the value of the product during its life. Directed Energy Deposition (DED) is a very flexible type of additive manufacturing (AM), and among the AM techniques, it is most suitable for repairing and remanufacturing automotive and aerospace components. Its application allows damaged component to be repaired, and material lost in service to be replaced to restore the part to its original shape. In the past, tungsten inert gas welding was used as the main repair method. However, its heat affected zone is larger, and the quality is inferior. In comparison with the conventional welding processes, repair via DED has more advantages, including lower heat input, warpage and distortion, higher cooling rate, lower dilution rate, excellent metallurgical bonding between the de...
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