Martina Riccio - Academia.edu (original) (raw)

Papers by Martina Riccio

Research paper thumbnail of Cold spray deposition for additive manufacturing of freeform structural components compared to selective laser melting

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, Apr 1, 2018

Recent advances in the field of cold spray have put forward the potential of this deposition tech... more Recent advances in the field of cold spray have put forward the potential of this deposition technique to be used as a non-thermal additive manufacturing process with significantly high deposition rates. In this study, we use the additive manufacturing potential of cold spray for fabrication of freestanding three-dimensional Inconel 718 samples, which is a challenging material for cold spray due to its high hardness and limited deformability. Additionally, we fabricated samples with similar geometry using one of the most common additive manufacturing methods, i.e. selective laser melting. Microstructural characteristics, distribution of residual stresses, porosity and structural integrity of the cold spray deposited samples were compared with those obtained by selective laser melting before and after different heat treatments. The results of the first time study of axial fatigue strength of cold spray deposited freeform samples indicate the notable efficiency of cold spray for fabrication of freestanding objects for structural components, with similar characteristics to those obtained from laser based additive manufacturing technique and even comparable to bulk material properties. The low working temperature of the cold spray method, suggests it as a promising additive manufacturing technique with a high potential to address many challenges regarding laser based approaches.

Research paper thumbnail of Fatigue strength assessment of “as built” AlSi10Mg manufactured by SLM with different build orientations

International Journal of Fatigue, Oct 1, 2020

Abstract This study investigated the effects of the ‘as-built’ condition on the fatigue propertie... more Abstract This study investigated the effects of the ‘as-built’ condition on the fatigue properties of an AlSi 10 Mg aluminium alloy manufactured by Selective Laser Melting (SLM) in different orientations. The results showed a moderate correlation between defects/surface features at the fracture origin and the roughness measurements. On the other hand, a fatigue strength analysis based on the size of features at fracture origin and residual stress just below the surface proved to be successful. Although considering the synergistic effect of different variables increased the scatter in fatigue life data points, a fatigue strength model including short crack effect and residual stresses made it possible to estimate the EIFS close to the real critical features. Results for life prediction models based on EIFS showed that 87% of the estimated number of cycles to failure are within a factor of 0.5–2 with respect to the experimental number of cycles to failure.

Research paper thumbnail of Experimental evaluation of selective laser melting process for optimized lattice structures

Proceedings Of The Institution Of Mechanical Engineers, Part E: Journal Of Process Mechanical Engineering, Sep 27, 2018

Lattice structures fabricated with micromelting of metal powders are promising solutions for ligh... more Lattice structures fabricated with micromelting of metal powders are promising solutions for lightweight applications. Additive manufacturing processes as selective laser melting are largely used to build bulk components, but the influence of laser settings on lattice struts morphology is not jet fully investigated. Previous studies demonstrate the effect of laser speed and layers thickness on the material density and lattice struts dimensions. In this paper, the effects of the laser volume energy density associated with the process setup parameters are analyzed in relation to the dimensional accuracy of lattice struts. The statistical approach based on design of experiments used in this paper allows getting appreciable reduction of the average errors of struts dimensions (from 48% to 16% and from 22% to 7% in horizontal and vertical orientations, respectively).

Research paper thumbnail of Development of a high strength Al–Zn–Si–Mg–Cu alloy for selective laser melting

Journal of Alloys and Compounds, Sep 1, 2019

Despite additive manufacturing processes are already widely used in several industrial applicatio... more Despite additive manufacturing processes are already widely used in several industrial applications, there are few materials that are specifically designed and optimized for these technologies. Currently, only few Al alloys are available on the market and employed for 3D printing of structural parts. In particular, Si-Mg bearing alloys are the most common Al alloys for additive manufacturing, featuring high processability but moderate mechanical properties. By this work, we studied the effect of Si addition on the hot cracking susceptibility of a high strength Al-Zn-Mg-Cu alloy. A preliminary activity has been carried out by blending Al-Zn-Mg-Cu and Al-Si-Mg powders and analysing their microstructure and properties achieved after selective laser melting. Eventually a new Al-Zn-Si-Mg-Cu alloy has been designed, produced as powder alloy by gas atomization and tested. The microstructure and phase transformations of the new alloy has been investigated by synchrotron X-ray diffraction, differential scanning calorimetry and microscope analysis. The Al-Zn-Si-Mg-Cu alloy processed by selective laser melting featured a relative density of 99.8 %, no hot cracks were noticed within the investigated microstructures. The ability of the new alloy to respond to aging starting from both as built and solution annealed conditions has been also evaluated. A good response to direct aging (directly from as built condition) was demonstrated, featuring yield strength and ultimate tensile strength of 402 and 449 MPa, respectively, and hardness of 174 HV after optimized aging at 165°C for 2 hours.

Research paper thumbnail of Fatigue behaviour of notched laser powder bed fusion AlSi10Mg after thermal and mechanical surface post-processing

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2022

Research paper thumbnail of Effects of Powder Atomisation on Microstructural and Mechanical Behaviour of L-PBF Processed Steels

Metals, Nov 5, 2020

In this research, steel alloys based on the Fe-Cr-Mo, Fe-Cr-Mn and Fe-Cr-Mo-Mn-Ni systems have be... more In this research, steel alloys based on the Fe-Cr-Mo, Fe-Cr-Mn and Fe-Cr-Mo-Mn-Ni systems have been designed, produced by different atomisation techniques, and processed by laser powder bed fusion (L-PBF) to investigate their microstructural and mechanical behaviour. Both gas atomisation and water atomisation were considered for powder preparation. The resulting different flowability of powders, hence a different densification behaviour during processing, could be compensated by tuning the L-PBF parameters and by the application of a post treatment to improve flowability of the water atomised powders. In agreement with thermodynamic calculations, small-size oxide-based nonmetallic inclusions of the type SiO 2 , MnO-SiO 2 , Cr 2 O 3-SiO 2 were found within the steel matrix and on the fracture surfaces of the water atomised L-PBF alloys, featuring higher amounts of oxygen than the gas-atomised steels. Analyses on microstructure and hardness of the hardenable as-built steels suggested that during laser processing, the multilayer L-PBF structure undergoes an in-situ tempering treatment. Furthermore, the mechanical properties of the L-PBF steels could be widely tuned depending on the post-thermal treatment conditions.

Research paper thumbnail of Experimental Characterization of SLM and EBM Cubic Lattice Structures for Lightweight Applications

Experimental Mechanics, Feb 20, 2019

This study carries out an experimental characterization of lattice structures that are based on c... more This study carries out an experimental characterization of lattice structures that are based on cubic cells fabricated through selective laser melting (SLM) and electron beam melting (EBM). The lattice failure under compressive load is studied as a function of the process typology, material properties, and dimensional parameters of the unit cell. The bulk material is first characterized to evaluate the process stability. Three main failure modes of the lattice are identified, depending on the response of ductile/brittle material and the direction of crack propagation. The relationship between lattice geometrical parameters and mechanical strength is observed. The results of the modeling and experiments are suitable to validate the design of lightweight components built with AM processes. The structural performances related to geometrical features, material properties and technological constraints are well explained for further applications in structural design. The equivalent Young's module of lattice samples with different cell size has been measured and compared with numerical simulations based on the homogenization method.

Research paper thumbnail of Strategies to design high-strength Al alloys with improved L-PBF processability

Research paper thumbnail of Development of a Novel High-Temperature Al Alloy for Laser Powder Bed Fusion

Metals, Dec 26, 2020

The number of available materials for Laser Powder Bed Fusion is still limited due to the poor pr... more The number of available materials for Laser Powder Bed Fusion is still limited due to the poor processability of many standard alloys. In particular, the lack of high-strength aluminium alloys, widely used in aerospace and automotive industries, remains a big issue for the spread of beam-based additive manufacturing technologies. In this study, a novel high-strength aluminium alloy for high temperature applications having good processability was developed. The design of the alloy was done based on the chemical composition of the widely used EN AW 2618. This Al-Cu-Mg-Ni-Fe alloy was modified with Ti and B in order to promote the formation of TiB 2 nuclei in the liquid phase able to stimulate heterogeneous nucleation of grains and to decrease the hot cracking susceptibility of the material. The new Al alloy was manufactured by gas atomisation and processed by Laser Powder Bed Fusion. Samples produced with optimised parameters featured relative density of 99.91%, with no solidification cracks within their microstructure. After aging, the material revealed upper yield strength and ultimate tensile strength of 495 MPa and 460 MPa, respectively. In addition, the alloy showed tensile strength higher than wrought EN AW 2618 at elevated temperatures.

Research paper thumbnail of Design of structural low-alloy steels for Laser-powder bed fusion

Research paper thumbnail of Effects of the scanning strategy on the microstructure and mechanical properties of a TiAl6V4 alloy produced by electron beam additive manufacturing

The International Journal of Advanced Manufacturing Technology, Apr 1, 2020

Ti6Al4V specimens were produced using electron beam melting (EBM) with the goal of studying the e... more Ti6Al4V specimens were produced using electron beam melting (EBM) with the goal of studying the effects of the scanning strategies on the surface morphology, microstructure, and mechanical properties. As the factory condition consists in the use of different parameters for scanning the hatch and the contour, additional processing conditions were investigated using the hatch and contour strategies separately, oriented from the center to the border, and vice versa. Due to material anisotropy, the samples were fabricated in both the vertical and planar directions. This work demonstrates that the scanning strategies affect several features of EBMed TiAl4V samples, like the relative density of the specimens, the surface morphology, and the microstructure and mechanical properties. In details, pure contour can increase the relative density, due to the use of pulses instead of continuous electron beam emission, while the hatch scanning produces smoother and more uniform surface morphology. As different thermal histories can be associated with the variation of the scanning strategy, the microstructure can be varied in terms of grain growth. Finally, the tensile behavior of the specimens, evaluated in both the principal orientations, can be correlated to the relative density and surface irregularity.

Research paper thumbnail of On the fatigue strength enhancement of additive manufactured AlSi10Mg parts by mechanical and thermal post-processing

Materials & Design, May 1, 2018

In this paper we have used laser powder bed fusion (PBF) to manufacture and characterize metal mi... more In this paper we have used laser powder bed fusion (PBF) to manufacture and characterize metal microwave components. Here we focus on a 2.5 GHz microwave cavity resonator, manufactured by PBF from the alloy AlSi10Mg. Of particular interest is its thermal expansion coefficient, especially since many microwave applications for PBF produced components will be in satellite systems where extreme ranges of temperature are experienced. We exploit the inherent resonant frequency dependence on cavity geometry, using a number of TM cavity modes, to determine the thermal expansion coefficient over the temperature range 6-450 K. Our results compare well with literature values and show that the material under test exhibits lower thermal expansion when compared with a bulk aluminium alloy alternative (6063).

Research paper thumbnail of Investigation on two Ti–B-reinforced Al alloys for Laser Powder Bed Fusion

Materials Science and Engineering: A, 2021

Abstract Only few medium and high-strength aluminium alloys can be processed by Laser Powder Bed ... more Abstract Only few medium and high-strength aluminium alloys can be processed by Laser Powder Bed Fusion without forming solidification cracks. This constraint limits the diffusion of this technology in many industrial fields, including aerospace and motorsport sectors. In this study, a novel high-strength aluminium alloy for Laser Powder Bed Fusion was designed and its solidification behavior, microstructure and mechanical performance were investigated. The results were compared with those achieved by processing the high-strength A20X alloy processed with the same technology. The alloy was designed based on the chemical composition of the widely used 2618 Al alloy, a conventional high strength Al–Cu–Mg alloy for high temperature applications. The chemical composition of the 2618 alloy was modified by adding Ti and B, which form TiB2 particles that act as nuclei for the solidification of primary α-Al grains. The resulting microstructure made of equiaxed grains revealed resistant to hot cracking. A20X and 2618-modified alloys produced with optimized parameters featured relative densities higher than 99,7% and crack-free microstructures. The A20X-T6 showed yield strength and ultimate tensile strength of 428 MPa and 485 MPa, respectively, while the modified 2618-T6 revealed upper yield strength and ultimate tensile strength of 370 MPa and 468 MPa, respectively. The two alloys also showed a remarkably high strength at 150 °C and 250 °C, exceeding the typical strength values of the 2618 alloy produced by forging.

Research paper thumbnail of A Novel High Strength Al Alloy with Improved SLM Processability

Research paper thumbnail of Sull’utilizzo dell’energia cinetica per produzione additiva: primi risultati di prove di fatica e confronto con lavorazioni SLM

Cold spray (CS) is a cold coating technique where powder deposition occurs due to the high impact... more Cold spray (CS) is a cold coating technique where powder deposition occurs due to the high impact velocity of the particles against a substrate and the resulting high plastic deformation with the generation of adiabatic shear instability conditions. In this paper, series of In718 specimens produced with the cold-spray and SLM have been considered and subjected to various thermal treatments, after machining the specimens. The characterization of the specimens includes microstructural analysis, residual stress measurement, porosity; static tensile and axial fatigue tests were done for the mechanical characterization. The results show comparable characteristics and resistance to those of SLM specimens, suggesting that CS, due to lower process temperature and reduced energy consumption, can be an alternative or complementary additive technology compared to wellestablished laser technologies. Parole chiave: cold spray, SLM, additive manufacturing, fatica, Inconel 718.

Research paper thumbnail of Development of a Novel High-Temperature Al Alloy for Laser Powder Bed Fusion

Metals

The number of available materials for Laser Powder Bed Fusion is still limited due to the poor pr... more The number of available materials for Laser Powder Bed Fusion is still limited due to the poor processability of many standard alloys. In particular, the lack of high-strength aluminium alloys, widely used in aerospace and automotive industries, remains a big issue for the spread of beam-based additive manufacturing technologies. In this study, a novel high-strength aluminium alloy for high temperature applications having good processability was developed. The design of the alloy was done based on the chemical composition of the widely used EN AW 2618. This Al-Cu-Mg-Ni-Fe alloy was modified with Ti and B in order to promote the formation of TiB2 nuclei in the liquid phase able to stimulate heterogeneous nucleation of grains and to decrease the hot cracking susceptibility of the material. The new Al alloy was manufactured by gas atomisation and processed by Laser Powder Bed Fusion. Samples produced with optimised parameters featured relative density of 99.91%, with no solidification ...

Research paper thumbnail of Empowering metal additive manufacturing

Research paper thumbnail of Fatigue behaviour of notched laser powder bed fusion AlSi10Mg after thermal and mechanical surface post-processing

Materials Science and Engineering: A

Research paper thumbnail of Effects of Powder Atomisation on Microstructural and Mechanical Behaviour of L-PBF Processed Steels

Metals

In this research, steel alloys based on the Fe-Cr-Mo, Fe-Cr-Mn and Fe-Cr-Mo-Mn-Ni systems have be... more In this research, steel alloys based on the Fe-Cr-Mo, Fe-Cr-Mn and Fe-Cr-Mo-Mn-Ni systems have been designed, produced by different atomisation techniques, and processed by laser powder bed fusion (L-PBF) to investigate their microstructural and mechanical behaviour. Both gas atomisation and water atomisation were considered for powder preparation. The resulting different flowability of powders, hence a different densification behaviour during processing, could be compensated by tuning the L-PBF parameters and by the application of a post treatment to improve flowability of the water atomised powders. In agreement with thermodynamic calculations, small-size oxide-based nonmetallic inclusions of the type SiO2, MnO-SiO2, Cr2O3-SiO2 were found within the steel matrix and on the fracture surfaces of the water atomised L-PBF alloys, featuring higher amounts of oxygen than the gas-atomised steels. Analyses on microstructure and hardness of the hardenable as-built steels suggested that dur...

Research paper thumbnail of Effects of the scanning strategy on the microstructure and mechanical properties of a TiAl6V4 alloy produced by electron beam additive manufacturing

The International Journal of Advanced Manufacturing Technology

Research paper thumbnail of Cold spray deposition for additive manufacturing of freeform structural components compared to selective laser melting

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, Apr 1, 2018

Recent advances in the field of cold spray have put forward the potential of this deposition tech... more Recent advances in the field of cold spray have put forward the potential of this deposition technique to be used as a non-thermal additive manufacturing process with significantly high deposition rates. In this study, we use the additive manufacturing potential of cold spray for fabrication of freestanding three-dimensional Inconel 718 samples, which is a challenging material for cold spray due to its high hardness and limited deformability. Additionally, we fabricated samples with similar geometry using one of the most common additive manufacturing methods, i.e. selective laser melting. Microstructural characteristics, distribution of residual stresses, porosity and structural integrity of the cold spray deposited samples were compared with those obtained by selective laser melting before and after different heat treatments. The results of the first time study of axial fatigue strength of cold spray deposited freeform samples indicate the notable efficiency of cold spray for fabrication of freestanding objects for structural components, with similar characteristics to those obtained from laser based additive manufacturing technique and even comparable to bulk material properties. The low working temperature of the cold spray method, suggests it as a promising additive manufacturing technique with a high potential to address many challenges regarding laser based approaches.

Research paper thumbnail of Fatigue strength assessment of “as built” AlSi10Mg manufactured by SLM with different build orientations

International Journal of Fatigue, Oct 1, 2020

Abstract This study investigated the effects of the ‘as-built’ condition on the fatigue propertie... more Abstract This study investigated the effects of the ‘as-built’ condition on the fatigue properties of an AlSi 10 Mg aluminium alloy manufactured by Selective Laser Melting (SLM) in different orientations. The results showed a moderate correlation between defects/surface features at the fracture origin and the roughness measurements. On the other hand, a fatigue strength analysis based on the size of features at fracture origin and residual stress just below the surface proved to be successful. Although considering the synergistic effect of different variables increased the scatter in fatigue life data points, a fatigue strength model including short crack effect and residual stresses made it possible to estimate the EIFS close to the real critical features. Results for life prediction models based on EIFS showed that 87% of the estimated number of cycles to failure are within a factor of 0.5–2 with respect to the experimental number of cycles to failure.

Research paper thumbnail of Experimental evaluation of selective laser melting process for optimized lattice structures

Proceedings Of The Institution Of Mechanical Engineers, Part E: Journal Of Process Mechanical Engineering, Sep 27, 2018

Lattice structures fabricated with micromelting of metal powders are promising solutions for ligh... more Lattice structures fabricated with micromelting of metal powders are promising solutions for lightweight applications. Additive manufacturing processes as selective laser melting are largely used to build bulk components, but the influence of laser settings on lattice struts morphology is not jet fully investigated. Previous studies demonstrate the effect of laser speed and layers thickness on the material density and lattice struts dimensions. In this paper, the effects of the laser volume energy density associated with the process setup parameters are analyzed in relation to the dimensional accuracy of lattice struts. The statistical approach based on design of experiments used in this paper allows getting appreciable reduction of the average errors of struts dimensions (from 48% to 16% and from 22% to 7% in horizontal and vertical orientations, respectively).

Research paper thumbnail of Development of a high strength Al–Zn–Si–Mg–Cu alloy for selective laser melting

Journal of Alloys and Compounds, Sep 1, 2019

Despite additive manufacturing processes are already widely used in several industrial applicatio... more Despite additive manufacturing processes are already widely used in several industrial applications, there are few materials that are specifically designed and optimized for these technologies. Currently, only few Al alloys are available on the market and employed for 3D printing of structural parts. In particular, Si-Mg bearing alloys are the most common Al alloys for additive manufacturing, featuring high processability but moderate mechanical properties. By this work, we studied the effect of Si addition on the hot cracking susceptibility of a high strength Al-Zn-Mg-Cu alloy. A preliminary activity has been carried out by blending Al-Zn-Mg-Cu and Al-Si-Mg powders and analysing their microstructure and properties achieved after selective laser melting. Eventually a new Al-Zn-Si-Mg-Cu alloy has been designed, produced as powder alloy by gas atomization and tested. The microstructure and phase transformations of the new alloy has been investigated by synchrotron X-ray diffraction, differential scanning calorimetry and microscope analysis. The Al-Zn-Si-Mg-Cu alloy processed by selective laser melting featured a relative density of 99.8 %, no hot cracks were noticed within the investigated microstructures. The ability of the new alloy to respond to aging starting from both as built and solution annealed conditions has been also evaluated. A good response to direct aging (directly from as built condition) was demonstrated, featuring yield strength and ultimate tensile strength of 402 and 449 MPa, respectively, and hardness of 174 HV after optimized aging at 165°C for 2 hours.

Research paper thumbnail of Fatigue behaviour of notched laser powder bed fusion AlSi10Mg after thermal and mechanical surface post-processing

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2022

Research paper thumbnail of Effects of Powder Atomisation on Microstructural and Mechanical Behaviour of L-PBF Processed Steels

Metals, Nov 5, 2020

In this research, steel alloys based on the Fe-Cr-Mo, Fe-Cr-Mn and Fe-Cr-Mo-Mn-Ni systems have be... more In this research, steel alloys based on the Fe-Cr-Mo, Fe-Cr-Mn and Fe-Cr-Mo-Mn-Ni systems have been designed, produced by different atomisation techniques, and processed by laser powder bed fusion (L-PBF) to investigate their microstructural and mechanical behaviour. Both gas atomisation and water atomisation were considered for powder preparation. The resulting different flowability of powders, hence a different densification behaviour during processing, could be compensated by tuning the L-PBF parameters and by the application of a post treatment to improve flowability of the water atomised powders. In agreement with thermodynamic calculations, small-size oxide-based nonmetallic inclusions of the type SiO 2 , MnO-SiO 2 , Cr 2 O 3-SiO 2 were found within the steel matrix and on the fracture surfaces of the water atomised L-PBF alloys, featuring higher amounts of oxygen than the gas-atomised steels. Analyses on microstructure and hardness of the hardenable as-built steels suggested that during laser processing, the multilayer L-PBF structure undergoes an in-situ tempering treatment. Furthermore, the mechanical properties of the L-PBF steels could be widely tuned depending on the post-thermal treatment conditions.

Research paper thumbnail of Experimental Characterization of SLM and EBM Cubic Lattice Structures for Lightweight Applications

Experimental Mechanics, Feb 20, 2019

This study carries out an experimental characterization of lattice structures that are based on c... more This study carries out an experimental characterization of lattice structures that are based on cubic cells fabricated through selective laser melting (SLM) and electron beam melting (EBM). The lattice failure under compressive load is studied as a function of the process typology, material properties, and dimensional parameters of the unit cell. The bulk material is first characterized to evaluate the process stability. Three main failure modes of the lattice are identified, depending on the response of ductile/brittle material and the direction of crack propagation. The relationship between lattice geometrical parameters and mechanical strength is observed. The results of the modeling and experiments are suitable to validate the design of lightweight components built with AM processes. The structural performances related to geometrical features, material properties and technological constraints are well explained for further applications in structural design. The equivalent Young's module of lattice samples with different cell size has been measured and compared with numerical simulations based on the homogenization method.

Research paper thumbnail of Strategies to design high-strength Al alloys with improved L-PBF processability

Research paper thumbnail of Development of a Novel High-Temperature Al Alloy for Laser Powder Bed Fusion

Metals, Dec 26, 2020

The number of available materials for Laser Powder Bed Fusion is still limited due to the poor pr... more The number of available materials for Laser Powder Bed Fusion is still limited due to the poor processability of many standard alloys. In particular, the lack of high-strength aluminium alloys, widely used in aerospace and automotive industries, remains a big issue for the spread of beam-based additive manufacturing technologies. In this study, a novel high-strength aluminium alloy for high temperature applications having good processability was developed. The design of the alloy was done based on the chemical composition of the widely used EN AW 2618. This Al-Cu-Mg-Ni-Fe alloy was modified with Ti and B in order to promote the formation of TiB 2 nuclei in the liquid phase able to stimulate heterogeneous nucleation of grains and to decrease the hot cracking susceptibility of the material. The new Al alloy was manufactured by gas atomisation and processed by Laser Powder Bed Fusion. Samples produced with optimised parameters featured relative density of 99.91%, with no solidification cracks within their microstructure. After aging, the material revealed upper yield strength and ultimate tensile strength of 495 MPa and 460 MPa, respectively. In addition, the alloy showed tensile strength higher than wrought EN AW 2618 at elevated temperatures.

Research paper thumbnail of Design of structural low-alloy steels for Laser-powder bed fusion

Research paper thumbnail of Effects of the scanning strategy on the microstructure and mechanical properties of a TiAl6V4 alloy produced by electron beam additive manufacturing

The International Journal of Advanced Manufacturing Technology, Apr 1, 2020

Ti6Al4V specimens were produced using electron beam melting (EBM) with the goal of studying the e... more Ti6Al4V specimens were produced using electron beam melting (EBM) with the goal of studying the effects of the scanning strategies on the surface morphology, microstructure, and mechanical properties. As the factory condition consists in the use of different parameters for scanning the hatch and the contour, additional processing conditions were investigated using the hatch and contour strategies separately, oriented from the center to the border, and vice versa. Due to material anisotropy, the samples were fabricated in both the vertical and planar directions. This work demonstrates that the scanning strategies affect several features of EBMed TiAl4V samples, like the relative density of the specimens, the surface morphology, and the microstructure and mechanical properties. In details, pure contour can increase the relative density, due to the use of pulses instead of continuous electron beam emission, while the hatch scanning produces smoother and more uniform surface morphology. As different thermal histories can be associated with the variation of the scanning strategy, the microstructure can be varied in terms of grain growth. Finally, the tensile behavior of the specimens, evaluated in both the principal orientations, can be correlated to the relative density and surface irregularity.

Research paper thumbnail of On the fatigue strength enhancement of additive manufactured AlSi10Mg parts by mechanical and thermal post-processing

Materials & Design, May 1, 2018

In this paper we have used laser powder bed fusion (PBF) to manufacture and characterize metal mi... more In this paper we have used laser powder bed fusion (PBF) to manufacture and characterize metal microwave components. Here we focus on a 2.5 GHz microwave cavity resonator, manufactured by PBF from the alloy AlSi10Mg. Of particular interest is its thermal expansion coefficient, especially since many microwave applications for PBF produced components will be in satellite systems where extreme ranges of temperature are experienced. We exploit the inherent resonant frequency dependence on cavity geometry, using a number of TM cavity modes, to determine the thermal expansion coefficient over the temperature range 6-450 K. Our results compare well with literature values and show that the material under test exhibits lower thermal expansion when compared with a bulk aluminium alloy alternative (6063).

Research paper thumbnail of Investigation on two Ti–B-reinforced Al alloys for Laser Powder Bed Fusion

Materials Science and Engineering: A, 2021

Abstract Only few medium and high-strength aluminium alloys can be processed by Laser Powder Bed ... more Abstract Only few medium and high-strength aluminium alloys can be processed by Laser Powder Bed Fusion without forming solidification cracks. This constraint limits the diffusion of this technology in many industrial fields, including aerospace and motorsport sectors. In this study, a novel high-strength aluminium alloy for Laser Powder Bed Fusion was designed and its solidification behavior, microstructure and mechanical performance were investigated. The results were compared with those achieved by processing the high-strength A20X alloy processed with the same technology. The alloy was designed based on the chemical composition of the widely used 2618 Al alloy, a conventional high strength Al–Cu–Mg alloy for high temperature applications. The chemical composition of the 2618 alloy was modified by adding Ti and B, which form TiB2 particles that act as nuclei for the solidification of primary α-Al grains. The resulting microstructure made of equiaxed grains revealed resistant to hot cracking. A20X and 2618-modified alloys produced with optimized parameters featured relative densities higher than 99,7% and crack-free microstructures. The A20X-T6 showed yield strength and ultimate tensile strength of 428 MPa and 485 MPa, respectively, while the modified 2618-T6 revealed upper yield strength and ultimate tensile strength of 370 MPa and 468 MPa, respectively. The two alloys also showed a remarkably high strength at 150 °C and 250 °C, exceeding the typical strength values of the 2618 alloy produced by forging.

Research paper thumbnail of A Novel High Strength Al Alloy with Improved SLM Processability

Research paper thumbnail of Sull’utilizzo dell’energia cinetica per produzione additiva: primi risultati di prove di fatica e confronto con lavorazioni SLM

Cold spray (CS) is a cold coating technique where powder deposition occurs due to the high impact... more Cold spray (CS) is a cold coating technique where powder deposition occurs due to the high impact velocity of the particles against a substrate and the resulting high plastic deformation with the generation of adiabatic shear instability conditions. In this paper, series of In718 specimens produced with the cold-spray and SLM have been considered and subjected to various thermal treatments, after machining the specimens. The characterization of the specimens includes microstructural analysis, residual stress measurement, porosity; static tensile and axial fatigue tests were done for the mechanical characterization. The results show comparable characteristics and resistance to those of SLM specimens, suggesting that CS, due to lower process temperature and reduced energy consumption, can be an alternative or complementary additive technology compared to wellestablished laser technologies. Parole chiave: cold spray, SLM, additive manufacturing, fatica, Inconel 718.

Research paper thumbnail of Development of a Novel High-Temperature Al Alloy for Laser Powder Bed Fusion

Metals

The number of available materials for Laser Powder Bed Fusion is still limited due to the poor pr... more The number of available materials for Laser Powder Bed Fusion is still limited due to the poor processability of many standard alloys. In particular, the lack of high-strength aluminium alloys, widely used in aerospace and automotive industries, remains a big issue for the spread of beam-based additive manufacturing technologies. In this study, a novel high-strength aluminium alloy for high temperature applications having good processability was developed. The design of the alloy was done based on the chemical composition of the widely used EN AW 2618. This Al-Cu-Mg-Ni-Fe alloy was modified with Ti and B in order to promote the formation of TiB2 nuclei in the liquid phase able to stimulate heterogeneous nucleation of grains and to decrease the hot cracking susceptibility of the material. The new Al alloy was manufactured by gas atomisation and processed by Laser Powder Bed Fusion. Samples produced with optimised parameters featured relative density of 99.91%, with no solidification ...

Research paper thumbnail of Empowering metal additive manufacturing

Research paper thumbnail of Fatigue behaviour of notched laser powder bed fusion AlSi10Mg after thermal and mechanical surface post-processing

Materials Science and Engineering: A

Research paper thumbnail of Effects of Powder Atomisation on Microstructural and Mechanical Behaviour of L-PBF Processed Steels

Metals

In this research, steel alloys based on the Fe-Cr-Mo, Fe-Cr-Mn and Fe-Cr-Mo-Mn-Ni systems have be... more In this research, steel alloys based on the Fe-Cr-Mo, Fe-Cr-Mn and Fe-Cr-Mo-Mn-Ni systems have been designed, produced by different atomisation techniques, and processed by laser powder bed fusion (L-PBF) to investigate their microstructural and mechanical behaviour. Both gas atomisation and water atomisation were considered for powder preparation. The resulting different flowability of powders, hence a different densification behaviour during processing, could be compensated by tuning the L-PBF parameters and by the application of a post treatment to improve flowability of the water atomised powders. In agreement with thermodynamic calculations, small-size oxide-based nonmetallic inclusions of the type SiO2, MnO-SiO2, Cr2O3-SiO2 were found within the steel matrix and on the fracture surfaces of the water atomised L-PBF alloys, featuring higher amounts of oxygen than the gas-atomised steels. Analyses on microstructure and hardness of the hardenable as-built steels suggested that dur...

Research paper thumbnail of Effects of the scanning strategy on the microstructure and mechanical properties of a TiAl6V4 alloy produced by electron beam additive manufacturing

The International Journal of Advanced Manufacturing Technology