This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
The direct laser deposition (DLD) process has seen rigorous research in the past two decades due ... more The direct laser deposition (DLD) process has seen rigorous research in the past two decades due to its ability to directly manufacture products followed by minimal machining. The process input variables play a vital role in determining the properties achieved in the products manufactured by the DLD method. Inconel 625, a nickel-based superalloy with exceptional mechanical performance and corrosion resistance, has been used in critical applications within the aerospace, process, and marine industry. However, its poor machinability and higher load requirements for plastic deformation have been challenging for manufacturers. Therefore, many studies have explored the additive manufacturing of Inconel 625 to overcome these problems. This article focuses on the DLD of Inconel 625 and its composites, presenting the state-of-the-art, drawing a relation among laser processing parameters and resulting material properties, microstructure and phase evolution, and the high-temperature performan...
Recent Advancements in Aluminum Alloys [Working Title]
This chapter summarizes the recent advances in additive manufacturing of high-strength aluminum a... more This chapter summarizes the recent advances in additive manufacturing of high-strength aluminum alloys, the challenges of printability, and defects in their builds. It further intends to provide an overview of the state of the art by outlining potential strategies for the fabrication of bulk products using these alloys without cracking. These strategies include identifying a suitable processing window of additive manufacturing using metallic powders of conventional high-strength aluminum alloys, pre-alloying the powders, and developing advanced aluminum-based composites with reinforcements introduced either by in situ or ex situ methods. The resulting microstructures and the relationship between these alloys’ microstructure and mechanical properties have been discussed. Since post-processing is inevitable in several critical applications, the chapter concludes with a brief account of post-manufacturing heat treatment processes of additively manufactured aluminum alloys.
Recent Advancements in Aluminum Alloys [Working Title]
Low- pressure casting and high-pressure casting processes are the most common liquid-based techno... more Low- pressure casting and high-pressure casting processes are the most common liquid-based technologies used to produce aluminum components. Processing conditions such as cooling rate and pressure level greatly influence the microstructure, mechanical properties, and heat treatment response of the Al alloys produced through these casting techniques. The performance of heat treatment depends on the alloy’s chemical composition and the casting condition such as the vacuum required for high-pressure casting, thus, highlighting the low-pressure casting application that does not require a vacuum. The level of pressure applied to fill the mold cavity can affect the formation of gas porosities and oxide films in the cast. Moreover, mechanical properties are influenced by the microstructure, i.e., secondary dendritic arm spacing, grain size, and the morphology of the secondary phases in the α-matrix. Thus, the current study evaluates the most current research developments performed to reduc...
Aluminum is a critical element of the circular economy as it can be recycled several times. Moreo... more Aluminum is a critical element of the circular economy as it can be recycled several times. Moreover, Al recycling is a more economically and environmentally efficient procedure than the primary Al production from ores. Secondary aluminum alloys are mostly used in casting applications since it is possible to accommodate their chemical composition through secondary manufacturing processes. However, the quality of the alloys may be considerably altered during the different steps of the recycling process. Inadequate waste sorting might result in excessive contamination. Iron is the most dangerous contaminant because it causes brittle and fragile intermetallic phases, which significantly impacts the mechanical characteristics of alloys. In addition, the microstructure of the alloy changes significantly after multiple cycles of remelting. These issues lead to the downcycling of aluminum, i.e., in other words, the reduction in the overall quality of the alloys. Thus, it has been shown tha...
The mechanical behaviour of as-built DED-produced 18Ni300 Maraging steel was studied by manufactu... more The mechanical behaviour of as-built DED-produced 18Ni300 Maraging steel was studied by manufacturing a wall-like structure from which three different specimen types were obtained: specimens in which the loading direction was the same as the printing direction (vertical), specimens in which these two directions were perpendicular (horizontal), and bimetallic specimens in which the interface between the AISI 1045 substrate and the 18Ni300 steel was tested. The yield strength of the produced samples was 987.9±34.2, 925.9±89.7 and 486.7±47.2 MPa for the vertical, horizontal and bimetallic specimens, respectively, while the elongation to failure was 9.4±1.9, 18.3±2.3 and 14.06±0.6% in the same order. The latter specimen failed within the substrate-comprised portion of the specimen. Additionally, the fracture surfaces were analysed through scanning electron microscopy, concluding that while both surfaces consist of dimples, the horizontal specimen presented microporosities with a reduced...
Aluminum structural composites through the infiltration process can be performed by vacuum, centr... more Aluminum structural composites through the infiltration process can be performed by vacuum, centrifugal, or squeeze casting, involving the infiltration of molten Al into fibers, particles, foams, or even porous preforms. This methodology creates hybrid structures of two distinct metal alloys that can be used to locally strengthen components or even to improve the properties of bulk materials, such as ultimate tensile strength and thermal conductivity. New approaches involve the infiltration of liquid Al into a three‐dimensional (3D)‐printed structure of the more rigid metal, such as steel, that the Al matrix. In the current study, stainless steel and copper inserts were produced by fused filament fabrication techniques with various geometries. Moreover, some 3D inserts were electrochemically coated with pure copper to enhance the wettability of the steel insert by Al. Then, the infiltration of these inserts was evaluated by gravity casting, centrifugal casting, and low‐pressure sand...
The quality of metallic additive manufacturing outputs is heavily dependent on the employed proce... more The quality of metallic additive manufacturing outputs is heavily dependent on the employed processing parameters. Hence, the assessment and definition of the input variables appropriate to the material in question is of vital importance, in order to optimise the attainable properties and minimise wasted feed stock in failed trials. In this work, optimal parameters for 18Ni300 Maraging steel are found for deposition in an H13 substrate. Additinally, the influence of pre-heating in depositions on a DIN CK45 steel are analysed by optical microscopy (OM) and microhardness measurements along the interface, and mechanical characterisation of DED-produced 18Ni300 is performed, as well as a bi-metallic alloy comprised of 18Ni300 and CK45, through the production and testing of tensile specimens.
The application of maraging steels such as 18Ni300 alloy is noteworthy for mould industries, appl... more The application of maraging steels such as 18Ni300 alloy is noteworthy for mould industries, applying repair purposes through direct energy deposition process. This objective requires microstructural characterizations and the evaluation of mechanical behaviour such as hardness. The state of substrate material, including the heat-affected zone (HAZ) and the interface between the HAZ and deposited layer, is essential, the formation of hard phases and abrupt transitions. Thus, the influence of the number of deposited layers or the pre-heating condition appears noteworthy. In the current study, microscopy observations did not reveal the presence of any crack in the cross-sections of deposited 18Ni300 alloy powder on AISI 1045 sheet steel; however, pores were observed in deposited layers. Besides, microscopic analyses revealed the achievement of a smooth HAZ in the deposited layers composed of three-layered depositions or that received preheating, confirmed by hardness measurements as we...
The development of biomaterials, particularly metallic ones, is one of the focuses of the scienti... more The development of biomaterials, particularly metallic ones, is one of the focuses of the scientific community, mainly due to an increase of average life expectancy and an improvement of the casted materials combined with better mechanical properties and defect-free products. The use of cobalt alloys in applications, such as knee, hip, and dental prostheses, is the result of their good ability to maintain mechanical properties and biocompatibility over long periods of use. Numerical methods are becoming more important, as they help product improvement in a faster and economic way. This work focuses on the development of a numerical model in ProCAST®, comparing the shrinkage porosity and cooling curves with real castings. When correlating simulation results with available experimental data, it is possible to understand that the formulated model demonstrates an acceptable solution in terms of precision (shrinkage porosity and cooling curve). The alloy’s thermal properties and heat con...
The joining of zirconia (ZrO2) to Ti6Al4V using Ag-Cu sputter-coated Ti brazing filler foil was i... more The joining of zirconia (ZrO2) to Ti6Al4V using Ag-Cu sputter-coated Ti brazing filler foil was investigated. Brazing experiments were performed at 900, 950, and 980 °C for 30 min under vacuum. The microstructural features of the brazed interfaces were evaluated by optical microscopy (OM) and by scanning electron microscopy (SEM). The chemical composition of the brazed interfaces was analyzed by energy dispersive X-ray spectroscopy (EDS). Room temperature shear tests and Vickers microhardness tests performed across the interfaces were used to evaluate the mechanical strength of the joints. Multilayered interfaces were produced for all brazing temperatures, consisting essentially in α-Ti + Ti2(Ag, Cu), TiAg. Joining to ZrO2 was promoted by the formation of a hard layer, reaching a maximum of 1715 HV0.01, possibly consisting mainly in α-Ti and Ti oxide(s). Joining to the Ti6Al4V was established by a layer composed of a mixture of α-Ti and Ti2(Ag, Cu). The highest shear strength (152 ±...
The joining of alumina (Al2O3) to γ-TiAl and Ti6Al4V alloys, using Ag-Cu sputter-coated Ti brazin... more The joining of alumina (Al2O3) to γ-TiAl and Ti6Al4V alloys, using Ag-Cu sputter-coated Ti brazing filler foil, was investigated. Brazing experiments were performed at 980 °C for 30 min in vacuum. The microstructure and chemical composition of the brazed interfaces were analyzed by scanning electron microscopy and by energy dispersive X-ray spectroscopy, respectively. A microstructural characterization of joints revealed that sound multilayered interfaces were produced using this novel brazing filler. Both interfaces are composed mainly of α-Ti, along with Ti2(Ag,Cu) and TiAg intermetallics. In the case of the brazing of γ-TiAl alloys, α2-Ti3Al and γ-TiAl intermetallics are also detected at the interface. Bonding to Al2O3 is promoted by the formation of a quite hard Ti-rich layer, which may reach a hardness up to 1872 HV 0.01 and is possibly composed of a mixture of α-Ti and Ti oxides. Hardness distribution maps indicate that no segregation of either soft or brittle phases occurs at...
Functionally graded material (FGM) based on Inconel 625 and AISI 431 stainless steel powders was ... more Functionally graded material (FGM) based on Inconel 625 and AISI 431 stainless steel powders was produced by applying the direct laser deposition (DLD) process. The FGM starts with layers of Inconel 625 and ends with layers of 431 stainless steel having three intermediate zones with the composition (100-X)% Inconel 625-X% 431 stainless steel, X = 25, 50, and 75, in that order. This FGM was deposited on a 42CrMo4 steel substrate, with and without preheating. Microstructures of these FGMs were evaluated, while considering the distribution of chemical composition and grain structure. Microstructures mainly consisted of columnar grains independent of preheating condition; epitaxial growth was observed. The application of a non-preheated substrate caused the formation of planar grains in the vicinity of the substrate. In addition, hardness maps were produced. The hardness distribution across these FGMs confirmed a smooth transition between deposited layers; however, the heat-affected zon...
The International Journal of Advanced Manufacturing Technology, 2021
Metal powder hot embossing (MPHE) is a low-cost micromanufacturing technique that can produce met... more Metal powder hot embossing (MPHE) is a low-cost micromanufacturing technique that can produce metallic parts with aspects in micron scale. In this study, scanning electron microscopy (SEM) is employed for evaluating the shape retention and the homogeneity of microstructure of replicated geometries into AISI 316L powder feedstock by the secondary electron imaging (SEI) and the backscattered electron imaging modes, the distribution of chemical composition by the electron-dispersive spectroscopy (EDS) mapping, and grain structures by the electron backscatter diffraction technique. Moreover, the SEI and EDS techniques completed the failure analysis of tensile tests. Nanoindentations were also performed to assist phase identification analysis in the densified microstructure. Different geometries in the micron scale (micro wall half-reservoirs, micro channel half-flanges, convex and concave micro gear configurations, and micro tensile specimens) were selected for replication. Shaping limitations were attributed to the geometry, convex or concave, and the stiffness of the die. Micro gear and micro wall configurations were shaped using a stiffer elastomer (T = 230 °C and P = 11.3 to 14 MPa for 45 min) and a metallic die (T = 170 °C and P = 11.3 MPa for 10 min), respectively. The shaping of concave geometries was achieved regardless of the metal powder concentration, 60 and 65 vol.%. Densified parts retained the replicated micro configurations after long periods of thermal debinding and sintering, with densification above 95%. The chemical composition in sintered parts was homogeneous. The microstructure was principally composed of austenitic grains. The 316L stainless steel sintered part produced through MPHE presented an ultimate tensile strength of 458 ± 15 MPa, similar to that of a wrought AISI 316L alloy; the fracture type in the micro tensile specimen was ductile.
Journal of Materials Engineering and Performance, 2020
The current research focuses on the shaping of aluminum feedstock by micro powder hot embossing. ... more The current research focuses on the shaping of aluminum feedstock by micro powder hot embossing. This method includes a mixture of powder with binder material for feedstock preparation. Then, shaping is accomplished by embossing, debinding and sintering. Micro powder hot embossing can be interested in the fabrication of parts when small series production is intended. The embossing step, to provide the designed configuration, is challenging and carried out using an elastomer die and uniaxial compaction. We evaluated the shaping process using aluminum feedstock and two geometries with similar aspect ratios (micro-channel half-flanges and micro-wall half-reservoirs). The micro-channel, half-flanges and half-reservoirs configurations were shaped using elastomer die; the micro-wall configuration was attained by the application of metallic die. For each die, the processing conditions (temperature, compaction and holding time) and shaping steps were selected to ensure the replicability and homogeneity of the green parts. The green parts were thermally debound and successfully sintered at a relatively high sintering temperature in a low-pressure atmosphere. The sintered parts retained their shapes and showed shrinkage.
The strengthening effect on aluminium (Al) by ultrafine particles of tungsten carbide (WC) after ... more The strengthening effect on aluminium (Al) by ultrafine particles of tungsten carbide (WC) after compacting and sintering was evaluated. The Al-1 vol.% WC mixture was prepared through a high-speed stirring technique, called assisted sonication. In this study, the effects of compacting, sintering temperature and holding time were evaluated by composite microstructural characterization and by mechanical tests. The characterizations involved electron dispersive spectroscopy and X-ray diffraction techniques for phase identification; electron backscattered diffraction for crystallographic analysis; backscattered electrons and secondary electrons imaging for failure and wear studies. In all composites, hardness was determined; for the hardest composite, the tensile strength, flexural strength and ball scattering wear resistance were also evaluated. The Al-1 vol.% WC composite produced by assisted sonication, densified by cold compacting at 152 MPa and sintered at 640 °C for 2 h at 5 × 10−...
Magnetic pulse welding can be considered as an advanced joining technique because it does not req... more Magnetic pulse welding can be considered as an advanced joining technique because it does not require any shielding atmosphere and input heat similar to conventional welding techniques. However, it requires comprehensive evaluations for bonding dissimilar materials. In addition to processing parameters, the surface preparation of the components, such as target material, needs to be evaluated. Different surface conditions were tested (machined, sand-blasted, polished, lubricated, chemically attacked, and threaded) using a fixed gap and standoff distance for welding. Microstructural observations and tensile testing revealed that the weld quality is dependent on surface preparation. The formation of waviness microstructure and intermetallic compounds were verified at the interface of some joints. However, these conditions did not guarantee the strength.
Hot embossing is a small-scale, low-cost processing technology that can deliver products to the m... more Hot embossing is a small-scale, low-cost processing technology that can deliver products to the market in a short time. This microreplication technology is well established to produce polymeric components and has applications in several industrial sectors. The use of micropowder hot embossing in the production of metal components is an emerging and challenging process that, when compared to other typical technologies, brings some economic advantages in a volatile market with an increasing tendency to manufacture customized products. The main objective of this review is to analyze the potential of powder hot embossing and its developments in the production of metallic microparts/components. This technology requires four distinct steps: (1) production feedstock (preparation of mixtures), (2) hot embossing (shape forming), (3) debinding and (4) sintering. These steps are interrelated and influence the characteristics of the final metallic microparts. This study summarizes the approache...
The homogeneity of dispersion and reinforcing of pure aluminium by multi-walled carbon nanotubes ... more The homogeneity of dispersion and reinforcing of pure aluminium by multi-walled carbon nanotubes (MWCNT) through the application of a high speed sonication (340 Hz) assisted by ultrasonication (35 kHz) was evaluated, this method was termed “assisted sonication”. Other reinforcements (graphene, nanoalumina, and ultrafine tungsten carbide) were used for comparison with the MWCNT. The hardness measurement enabled us to evaluate the strengthening effect of the reinforcements. Raman analysis was the technique selected to evaluate the integrity of MWCNTs during dispersion. The scanning and transmission electron microscopies revealed the dispersion and microstructure of the nanoreinforcements and nanocomposites. After applying the assisted sonication, the MWCNTs were detangled without exfoliation. The integrity of MWCNTs was strongly influenced by the presence of the aluminum powder during dispersion. The application of the assisted sonication method reduced the size of the aggregates in t...
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
The direct laser deposition (DLD) process has seen rigorous research in the past two decades due ... more The direct laser deposition (DLD) process has seen rigorous research in the past two decades due to its ability to directly manufacture products followed by minimal machining. The process input variables play a vital role in determining the properties achieved in the products manufactured by the DLD method. Inconel 625, a nickel-based superalloy with exceptional mechanical performance and corrosion resistance, has been used in critical applications within the aerospace, process, and marine industry. However, its poor machinability and higher load requirements for plastic deformation have been challenging for manufacturers. Therefore, many studies have explored the additive manufacturing of Inconel 625 to overcome these problems. This article focuses on the DLD of Inconel 625 and its composites, presenting the state-of-the-art, drawing a relation among laser processing parameters and resulting material properties, microstructure and phase evolution, and the high-temperature performan...
Recent Advancements in Aluminum Alloys [Working Title]
This chapter summarizes the recent advances in additive manufacturing of high-strength aluminum a... more This chapter summarizes the recent advances in additive manufacturing of high-strength aluminum alloys, the challenges of printability, and defects in their builds. It further intends to provide an overview of the state of the art by outlining potential strategies for the fabrication of bulk products using these alloys without cracking. These strategies include identifying a suitable processing window of additive manufacturing using metallic powders of conventional high-strength aluminum alloys, pre-alloying the powders, and developing advanced aluminum-based composites with reinforcements introduced either by in situ or ex situ methods. The resulting microstructures and the relationship between these alloys’ microstructure and mechanical properties have been discussed. Since post-processing is inevitable in several critical applications, the chapter concludes with a brief account of post-manufacturing heat treatment processes of additively manufactured aluminum alloys.
Recent Advancements in Aluminum Alloys [Working Title]
Low- pressure casting and high-pressure casting processes are the most common liquid-based techno... more Low- pressure casting and high-pressure casting processes are the most common liquid-based technologies used to produce aluminum components. Processing conditions such as cooling rate and pressure level greatly influence the microstructure, mechanical properties, and heat treatment response of the Al alloys produced through these casting techniques. The performance of heat treatment depends on the alloy’s chemical composition and the casting condition such as the vacuum required for high-pressure casting, thus, highlighting the low-pressure casting application that does not require a vacuum. The level of pressure applied to fill the mold cavity can affect the formation of gas porosities and oxide films in the cast. Moreover, mechanical properties are influenced by the microstructure, i.e., secondary dendritic arm spacing, grain size, and the morphology of the secondary phases in the α-matrix. Thus, the current study evaluates the most current research developments performed to reduc...
Aluminum is a critical element of the circular economy as it can be recycled several times. Moreo... more Aluminum is a critical element of the circular economy as it can be recycled several times. Moreover, Al recycling is a more economically and environmentally efficient procedure than the primary Al production from ores. Secondary aluminum alloys are mostly used in casting applications since it is possible to accommodate their chemical composition through secondary manufacturing processes. However, the quality of the alloys may be considerably altered during the different steps of the recycling process. Inadequate waste sorting might result in excessive contamination. Iron is the most dangerous contaminant because it causes brittle and fragile intermetallic phases, which significantly impacts the mechanical characteristics of alloys. In addition, the microstructure of the alloy changes significantly after multiple cycles of remelting. These issues lead to the downcycling of aluminum, i.e., in other words, the reduction in the overall quality of the alloys. Thus, it has been shown tha...
The mechanical behaviour of as-built DED-produced 18Ni300 Maraging steel was studied by manufactu... more The mechanical behaviour of as-built DED-produced 18Ni300 Maraging steel was studied by manufacturing a wall-like structure from which three different specimen types were obtained: specimens in which the loading direction was the same as the printing direction (vertical), specimens in which these two directions were perpendicular (horizontal), and bimetallic specimens in which the interface between the AISI 1045 substrate and the 18Ni300 steel was tested. The yield strength of the produced samples was 987.9±34.2, 925.9±89.7 and 486.7±47.2 MPa for the vertical, horizontal and bimetallic specimens, respectively, while the elongation to failure was 9.4±1.9, 18.3±2.3 and 14.06±0.6% in the same order. The latter specimen failed within the substrate-comprised portion of the specimen. Additionally, the fracture surfaces were analysed through scanning electron microscopy, concluding that while both surfaces consist of dimples, the horizontal specimen presented microporosities with a reduced...
Aluminum structural composites through the infiltration process can be performed by vacuum, centr... more Aluminum structural composites through the infiltration process can be performed by vacuum, centrifugal, or squeeze casting, involving the infiltration of molten Al into fibers, particles, foams, or even porous preforms. This methodology creates hybrid structures of two distinct metal alloys that can be used to locally strengthen components or even to improve the properties of bulk materials, such as ultimate tensile strength and thermal conductivity. New approaches involve the infiltration of liquid Al into a three‐dimensional (3D)‐printed structure of the more rigid metal, such as steel, that the Al matrix. In the current study, stainless steel and copper inserts were produced by fused filament fabrication techniques with various geometries. Moreover, some 3D inserts were electrochemically coated with pure copper to enhance the wettability of the steel insert by Al. Then, the infiltration of these inserts was evaluated by gravity casting, centrifugal casting, and low‐pressure sand...
The quality of metallic additive manufacturing outputs is heavily dependent on the employed proce... more The quality of metallic additive manufacturing outputs is heavily dependent on the employed processing parameters. Hence, the assessment and definition of the input variables appropriate to the material in question is of vital importance, in order to optimise the attainable properties and minimise wasted feed stock in failed trials. In this work, optimal parameters for 18Ni300 Maraging steel are found for deposition in an H13 substrate. Additinally, the influence of pre-heating in depositions on a DIN CK45 steel are analysed by optical microscopy (OM) and microhardness measurements along the interface, and mechanical characterisation of DED-produced 18Ni300 is performed, as well as a bi-metallic alloy comprised of 18Ni300 and CK45, through the production and testing of tensile specimens.
The application of maraging steels such as 18Ni300 alloy is noteworthy for mould industries, appl... more The application of maraging steels such as 18Ni300 alloy is noteworthy for mould industries, applying repair purposes through direct energy deposition process. This objective requires microstructural characterizations and the evaluation of mechanical behaviour such as hardness. The state of substrate material, including the heat-affected zone (HAZ) and the interface between the HAZ and deposited layer, is essential, the formation of hard phases and abrupt transitions. Thus, the influence of the number of deposited layers or the pre-heating condition appears noteworthy. In the current study, microscopy observations did not reveal the presence of any crack in the cross-sections of deposited 18Ni300 alloy powder on AISI 1045 sheet steel; however, pores were observed in deposited layers. Besides, microscopic analyses revealed the achievement of a smooth HAZ in the deposited layers composed of three-layered depositions or that received preheating, confirmed by hardness measurements as we...
The development of biomaterials, particularly metallic ones, is one of the focuses of the scienti... more The development of biomaterials, particularly metallic ones, is one of the focuses of the scientific community, mainly due to an increase of average life expectancy and an improvement of the casted materials combined with better mechanical properties and defect-free products. The use of cobalt alloys in applications, such as knee, hip, and dental prostheses, is the result of their good ability to maintain mechanical properties and biocompatibility over long periods of use. Numerical methods are becoming more important, as they help product improvement in a faster and economic way. This work focuses on the development of a numerical model in ProCAST®, comparing the shrinkage porosity and cooling curves with real castings. When correlating simulation results with available experimental data, it is possible to understand that the formulated model demonstrates an acceptable solution in terms of precision (shrinkage porosity and cooling curve). The alloy’s thermal properties and heat con...
The joining of zirconia (ZrO2) to Ti6Al4V using Ag-Cu sputter-coated Ti brazing filler foil was i... more The joining of zirconia (ZrO2) to Ti6Al4V using Ag-Cu sputter-coated Ti brazing filler foil was investigated. Brazing experiments were performed at 900, 950, and 980 °C for 30 min under vacuum. The microstructural features of the brazed interfaces were evaluated by optical microscopy (OM) and by scanning electron microscopy (SEM). The chemical composition of the brazed interfaces was analyzed by energy dispersive X-ray spectroscopy (EDS). Room temperature shear tests and Vickers microhardness tests performed across the interfaces were used to evaluate the mechanical strength of the joints. Multilayered interfaces were produced for all brazing temperatures, consisting essentially in α-Ti + Ti2(Ag, Cu), TiAg. Joining to ZrO2 was promoted by the formation of a hard layer, reaching a maximum of 1715 HV0.01, possibly consisting mainly in α-Ti and Ti oxide(s). Joining to the Ti6Al4V was established by a layer composed of a mixture of α-Ti and Ti2(Ag, Cu). The highest shear strength (152 ±...
The joining of alumina (Al2O3) to γ-TiAl and Ti6Al4V alloys, using Ag-Cu sputter-coated Ti brazin... more The joining of alumina (Al2O3) to γ-TiAl and Ti6Al4V alloys, using Ag-Cu sputter-coated Ti brazing filler foil, was investigated. Brazing experiments were performed at 980 °C for 30 min in vacuum. The microstructure and chemical composition of the brazed interfaces were analyzed by scanning electron microscopy and by energy dispersive X-ray spectroscopy, respectively. A microstructural characterization of joints revealed that sound multilayered interfaces were produced using this novel brazing filler. Both interfaces are composed mainly of α-Ti, along with Ti2(Ag,Cu) and TiAg intermetallics. In the case of the brazing of γ-TiAl alloys, α2-Ti3Al and γ-TiAl intermetallics are also detected at the interface. Bonding to Al2O3 is promoted by the formation of a quite hard Ti-rich layer, which may reach a hardness up to 1872 HV 0.01 and is possibly composed of a mixture of α-Ti and Ti oxides. Hardness distribution maps indicate that no segregation of either soft or brittle phases occurs at...
Functionally graded material (FGM) based on Inconel 625 and AISI 431 stainless steel powders was ... more Functionally graded material (FGM) based on Inconel 625 and AISI 431 stainless steel powders was produced by applying the direct laser deposition (DLD) process. The FGM starts with layers of Inconel 625 and ends with layers of 431 stainless steel having three intermediate zones with the composition (100-X)% Inconel 625-X% 431 stainless steel, X = 25, 50, and 75, in that order. This FGM was deposited on a 42CrMo4 steel substrate, with and without preheating. Microstructures of these FGMs were evaluated, while considering the distribution of chemical composition and grain structure. Microstructures mainly consisted of columnar grains independent of preheating condition; epitaxial growth was observed. The application of a non-preheated substrate caused the formation of planar grains in the vicinity of the substrate. In addition, hardness maps were produced. The hardness distribution across these FGMs confirmed a smooth transition between deposited layers; however, the heat-affected zon...
The International Journal of Advanced Manufacturing Technology, 2021
Metal powder hot embossing (MPHE) is a low-cost micromanufacturing technique that can produce met... more Metal powder hot embossing (MPHE) is a low-cost micromanufacturing technique that can produce metallic parts with aspects in micron scale. In this study, scanning electron microscopy (SEM) is employed for evaluating the shape retention and the homogeneity of microstructure of replicated geometries into AISI 316L powder feedstock by the secondary electron imaging (SEI) and the backscattered electron imaging modes, the distribution of chemical composition by the electron-dispersive spectroscopy (EDS) mapping, and grain structures by the electron backscatter diffraction technique. Moreover, the SEI and EDS techniques completed the failure analysis of tensile tests. Nanoindentations were also performed to assist phase identification analysis in the densified microstructure. Different geometries in the micron scale (micro wall half-reservoirs, micro channel half-flanges, convex and concave micro gear configurations, and micro tensile specimens) were selected for replication. Shaping limitations were attributed to the geometry, convex or concave, and the stiffness of the die. Micro gear and micro wall configurations were shaped using a stiffer elastomer (T = 230 °C and P = 11.3 to 14 MPa for 45 min) and a metallic die (T = 170 °C and P = 11.3 MPa for 10 min), respectively. The shaping of concave geometries was achieved regardless of the metal powder concentration, 60 and 65 vol.%. Densified parts retained the replicated micro configurations after long periods of thermal debinding and sintering, with densification above 95%. The chemical composition in sintered parts was homogeneous. The microstructure was principally composed of austenitic grains. The 316L stainless steel sintered part produced through MPHE presented an ultimate tensile strength of 458 ± 15 MPa, similar to that of a wrought AISI 316L alloy; the fracture type in the micro tensile specimen was ductile.
Journal of Materials Engineering and Performance, 2020
The current research focuses on the shaping of aluminum feedstock by micro powder hot embossing. ... more The current research focuses on the shaping of aluminum feedstock by micro powder hot embossing. This method includes a mixture of powder with binder material for feedstock preparation. Then, shaping is accomplished by embossing, debinding and sintering. Micro powder hot embossing can be interested in the fabrication of parts when small series production is intended. The embossing step, to provide the designed configuration, is challenging and carried out using an elastomer die and uniaxial compaction. We evaluated the shaping process using aluminum feedstock and two geometries with similar aspect ratios (micro-channel half-flanges and micro-wall half-reservoirs). The micro-channel, half-flanges and half-reservoirs configurations were shaped using elastomer die; the micro-wall configuration was attained by the application of metallic die. For each die, the processing conditions (temperature, compaction and holding time) and shaping steps were selected to ensure the replicability and homogeneity of the green parts. The green parts were thermally debound and successfully sintered at a relatively high sintering temperature in a low-pressure atmosphere. The sintered parts retained their shapes and showed shrinkage.
The strengthening effect on aluminium (Al) by ultrafine particles of tungsten carbide (WC) after ... more The strengthening effect on aluminium (Al) by ultrafine particles of tungsten carbide (WC) after compacting and sintering was evaluated. The Al-1 vol.% WC mixture was prepared through a high-speed stirring technique, called assisted sonication. In this study, the effects of compacting, sintering temperature and holding time were evaluated by composite microstructural characterization and by mechanical tests. The characterizations involved electron dispersive spectroscopy and X-ray diffraction techniques for phase identification; electron backscattered diffraction for crystallographic analysis; backscattered electrons and secondary electrons imaging for failure and wear studies. In all composites, hardness was determined; for the hardest composite, the tensile strength, flexural strength and ball scattering wear resistance were also evaluated. The Al-1 vol.% WC composite produced by assisted sonication, densified by cold compacting at 152 MPa and sintered at 640 °C for 2 h at 5 × 10−...
Magnetic pulse welding can be considered as an advanced joining technique because it does not req... more Magnetic pulse welding can be considered as an advanced joining technique because it does not require any shielding atmosphere and input heat similar to conventional welding techniques. However, it requires comprehensive evaluations for bonding dissimilar materials. In addition to processing parameters, the surface preparation of the components, such as target material, needs to be evaluated. Different surface conditions were tested (machined, sand-blasted, polished, lubricated, chemically attacked, and threaded) using a fixed gap and standoff distance for welding. Microstructural observations and tensile testing revealed that the weld quality is dependent on surface preparation. The formation of waviness microstructure and intermetallic compounds were verified at the interface of some joints. However, these conditions did not guarantee the strength.
Hot embossing is a small-scale, low-cost processing technology that can deliver products to the m... more Hot embossing is a small-scale, low-cost processing technology that can deliver products to the market in a short time. This microreplication technology is well established to produce polymeric components and has applications in several industrial sectors. The use of micropowder hot embossing in the production of metal components is an emerging and challenging process that, when compared to other typical technologies, brings some economic advantages in a volatile market with an increasing tendency to manufacture customized products. The main objective of this review is to analyze the potential of powder hot embossing and its developments in the production of metallic microparts/components. This technology requires four distinct steps: (1) production feedstock (preparation of mixtures), (2) hot embossing (shape forming), (3) debinding and (4) sintering. These steps are interrelated and influence the characteristics of the final metallic microparts. This study summarizes the approache...
The homogeneity of dispersion and reinforcing of pure aluminium by multi-walled carbon nanotubes ... more The homogeneity of dispersion and reinforcing of pure aluminium by multi-walled carbon nanotubes (MWCNT) through the application of a high speed sonication (340 Hz) assisted by ultrasonication (35 kHz) was evaluated, this method was termed “assisted sonication”. Other reinforcements (graphene, nanoalumina, and ultrafine tungsten carbide) were used for comparison with the MWCNT. The hardness measurement enabled us to evaluate the strengthening effect of the reinforcements. Raman analysis was the technique selected to evaluate the integrity of MWCNTs during dispersion. The scanning and transmission electron microscopies revealed the dispersion and microstructure of the nanoreinforcements and nanocomposites. After applying the assisted sonication, the MWCNTs were detangled without exfoliation. The integrity of MWCNTs was strongly influenced by the presence of the aluminum powder during dispersion. The application of the assisted sonication method reduced the size of the aggregates in t...
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Papers by Omid Emadinia