Additive manufacturing(AM)has emerged as one of the most utilized processes in manufacturing due to its ability to produce complex geometries with minimal material waste and greater design freedom.Laser-based AM(LAM)t...Additive manufacturing(AM)has emerged as one of the most utilized processes in manufacturing due to its ability to produce complex geometries with minimal material waste and greater design freedom.Laser-based AM(LAM)technologies use high-power lasers to melt metallic materials,which then solidify to form parts.However,it inherently induces self-equilibrating residual stress during fabrication due to thermal loads and plastic deformation.These residual stresses can cause defects such as delamination,cracking,and distortion,as well as premature failure under service conditions,necessitating mitigation.While post-treatment methods can reduce residual stresses,they are often costly and time-consuming.Therefore,tuning the fabrication process parameters presents a more feasible approach.Accordingly,in addition to providing a comprehensive view of residual stress by their classification,formation mechanisms,measurement methods,and common post-treatment,this paper reviews and compares the studies conducted on the effect of key parameters of the LAM process on the resulting residual stresses.This review focuses on proactively adjusting LAM process parameters as a strategic approach to mitigate residual stress formation.It provides a result of the various parameters influencing residual stress outcomes,such as laser power,scanning speed,beam diameter,hatch spacing,and scanning strategies.Finally,the paper identifies existing research gaps and proposes future studies needed to deepen understanding of the relationship between process parameters and residual stress mitigation in LAM.展开更多
Indirect additive manufacturing(AM)methods have recently attracted attention from researchers thanks to their great potential for cheap,straightforward,and small-scale production of metallic components.Atomic diffusio...Indirect additive manufacturing(AM)methods have recently attracted attention from researchers thanks to their great potential for cheap,straightforward,and small-scale production of metallic components.Atomic diffusion additive manufacturing(ADAM),a variant of indirect AM methods,is a layer-wise indirect AM process recently developed based on fused deposition modeling and metal injection molding.However,there is still limited knowledge of the process conditions and material properties fabricated through this process,where sintering plays a crucial role in the final consolidation of parts.Therefore,this research,for the first time,systematically investigates the impact of various sintering conditions on the shrinkage,relative density,microstructure,and hardness of the 17-4PH ADAM samples.For this reason,as-washed samples were sintered under different time-temperature combinations.The sample density was evaluated using Archimedes,computed tomography,and image analysis methods.The outcomes revealed that sintering variables significantly impacted the density of brown 17-4PH Stainless Steel samples.The results indicated more than 99% relative densities,higher than the value reported by Markforged Inc.(~96%).Based on parallel porosities observed in the computed tomography results,it can be suggested that by modifying the infill pattern during printing,it would be possible to increase the final relative density.The microhardness of the sintered samples in this study was higher than that of the standard sample provided by Markforged Inc.Sintering at 1330℃ for 4 h increased the density of the printed sample without compromising its mechanical properties.According to X-ray diffraction analysis,the standard sample provided by Markforged Inc.and“1330℃—4 h”one had similar stable phases,although copper-rich intermetallics were more abundant in the microstructure of reference samples.This study is expected to facilitate the adoption of indirect metal AM methods by different sectors,thanks to the high achievable relative densities reported here.展开更多
Additive manufacturing(AM),as an advanced manufacturing technology,enables the production of personalized orthopedic implant devices with complex geometries that closely resemble bone structures.Titanium and its alloy...Additive manufacturing(AM),as an advanced manufacturing technology,enables the production of personalized orthopedic implant devices with complex geometries that closely resemble bone structures.Titanium and its alloys are extensively employed in biomedical fields like orthopedics and dentistry,thanks to the excellent compatibility with the human body and high corrosion resistance due to the existence of a thin protective oxide layer known as TiO_(2) upon exposure to oxygen on the surface.However,in joint inflammation,reactive oxygen species like hydrogen peroxide and radicals can damage the passive film on Ti implants,leading to their deterioration.Although AM technology for metallic implants is still developing,advancements in printing and new alloys are crucial for widespread use.This work aims to investigate the corrosion resistance of in-situ alloyed Ti536(Ti5Al3V6Cu)alloy produced through electron beam powder bed fusion(EB-PBF)under simulated peri-implant inflammatory conditions.The corrosion resistance was evaluated using electrochemical experiments conducted in the presence of 0.1%H_(2)O_(2) in a physiological saline solution(0.9%NaCl)to replicate the conditions that may occur during post-operative inflammation.The findings demonstrate that the micro-environment surrounding the implant during peri-implant inflammation is highly corrosive and can lead to the degradation of the TiO_(2) passive layer.Physiological saline with H_(2)O_(2) significantly increased biomaterial open circuit potential up to 0.36 mV vs.Ag/AgCl compared to physiological saline only.Potentiodynamic polarization(PDP)plots confirm this increase,as well.The PDP and electrochemical impedance spectroscopy(EIS)tests indicated that adding Cu does not impact the corrosion resistance of the Ti536 alloy initially under simulated inflammatory conditions,but prolonged immersion leads to enhanced corrosion resistance for all biomaterials tested,indicating the formation of an oxide layer after the reduction of the solution oxidizing power.These results suggest that modifying custom alloys by adding appropriate elements significantly enhances corrosion resistance,particularly in inflammatory conditions.展开更多
Multi-pass ultrasonic impact treatment(UIT)was applied to modify the microstructure and improve the mechanical and tribological characteristics at the near-surface region of commercially pure Ti(CP-Ti)specimens produc...Multi-pass ultrasonic impact treatment(UIT)was applied to modify the microstructure and improve the mechanical and tribological characteristics at the near-surface region of commercially pure Ti(CP-Ti)specimens produced by the laser powder bed fusion(L-PBF)method.UIT considerably refined the L-PBF process-related acicular martensites(α′-M)and produced a well-homogenized and dense surface microstructure,where the porosity content of 1-,3-,and 5-pass UITed samples was reduced by 43,60,and 67%,respectively.The UITed samples showed an enhancement in their near-surface mechanical properties up to a depth of about 300μm.The nanoindentation results for the 3-pass UITed sample revealed an increase of about 53,45,and 220%in its nanohardness,H/E_(r),and H_(3)/E_(r)^(2)indices,respectively.The stylus profilometry results showed that performing the UIT removed the L-PBF-related features/defects and offered a smooth surface.The roughness average(R_(a))and the skewness(R_(sk))of the 3-pass UITed sample were found to be lower than those of the L-PBFed sample by 95 and 223%,respectively.Applying the UIT also enhanced the material ratio,where the maximum load-bearing capacity(~100%)in as-L-PBFed(as-built)and 3-pass UITed samples was obtained at 60-and 10-µm depths,respectively.The tribological investigations showed that applying the UIT resulted in a significant reduction of wear rate and average coefficient of friction(COF)of CP-Ti.For instance,under the normal pressures of 0.05 and 0.2 MPa,the wear rate and COF of the 3-pass UITed sample were lower than those of the L-PBFed sample by 65 and 58%,and 20 and 17%,respectively.展开更多
Electron beam melting(EBM) process is an additive manufacturing process largely used to produce complex metallic components made of high-performance materials for aerospace and medical applications.Especially,lattice ...Electron beam melting(EBM) process is an additive manufacturing process largely used to produce complex metallic components made of high-performance materials for aerospace and medical applications.Especially,lattice structures made by Ti-6A1-4V have represented a hot topic for the industrial sectors because of having a great potential to combine lower weights and higher performances that can also be tailored by subsequent heat treatments.However,the little knowledge about the mechanical behaviour of the lattice structures is limiting their applications.The present work aims to provide a comprehensive review of the studies on the mechanical behaviour of the lattice structures made of Ti-6A1-4V.The main steps to produce an EBM part were considered as guidelines to review the literature on the lattice performance:(1) design,(2) process and(3) post-heat treatment.Thereafter,the correlation between the geometrical features of the lattice structure and their mechanical behaviour is discussed.In addition,the correlation among the mechanical performance of the lattice structures and the process precision,surface roughness and working temperature are also reviewed.An investigation on the studies about the properties of heat-treated lattice structure is also conducted.展开更多
This study investigated dry sliding wear properties of AZ31 magnesium alloy and B_(4)C-reinforced AZ31 composites containing 5,10,and 20 wt.%B_(4)C with bimodal sizes under different loadings(10-80 N)at various slidin...This study investigated dry sliding wear properties of AZ31 magnesium alloy and B_(4)C-reinforced AZ31 composites containing 5,10,and 20 wt.%B_(4)C with bimodal sizes under different loadings(10-80 N)at various sliding speeds(0.1-1 m/s)via the pin-on-disc configuration.Microhardness evaluations showed that when the distribution of B_(4)C particles was uniform the hardness of the composites increased by enhancing the reinforcement content.The unreinforced alloy and the composite samples were examined to determine the wear mechanism maps and identify the dominant wear mechanisms in each wear condition and reinforcement content.For this purpose,wear rates and friction coefficients were recorded during the wear tests and worn surfaces were characterized by scanning electron microscopy and energy dispersive X-ray spectrometry analyses.The determined wear mechanisms were abrasion,oxidation,delamination,adhesion,and plastic deformation as a result of thermal softening and melting.The wear evaluations revealed that the composites containing 5 and 10 wt.%B_(4)C had a significantly higher wear resistance in all the conditions.However,20 wt.%B_(4)C/AZ31 composite had a lower resistance at high sliding speeds(0.5-1 m/s)and high loadings(40-80 N)in comparison with the unreinforced alloy.The highest wear resistance was obtained at high sliding speeds and low loadings with the domination of oxidative wear.展开更多
文摘Additive manufacturing(AM)has emerged as one of the most utilized processes in manufacturing due to its ability to produce complex geometries with minimal material waste and greater design freedom.Laser-based AM(LAM)technologies use high-power lasers to melt metallic materials,which then solidify to form parts.However,it inherently induces self-equilibrating residual stress during fabrication due to thermal loads and plastic deformation.These residual stresses can cause defects such as delamination,cracking,and distortion,as well as premature failure under service conditions,necessitating mitigation.While post-treatment methods can reduce residual stresses,they are often costly and time-consuming.Therefore,tuning the fabrication process parameters presents a more feasible approach.Accordingly,in addition to providing a comprehensive view of residual stress by their classification,formation mechanisms,measurement methods,and common post-treatment,this paper reviews and compares the studies conducted on the effect of key parameters of the LAM process on the resulting residual stresses.This review focuses on proactively adjusting LAM process parameters as a strategic approach to mitigate residual stress formation.It provides a result of the various parameters influencing residual stress outcomes,such as laser power,scanning speed,beam diameter,hatch spacing,and scanning strategies.Finally,the paper identifies existing research gaps and proposes future studies needed to deepen understanding of the relationship between process parameters and residual stress mitigation in LAM.
文摘Indirect additive manufacturing(AM)methods have recently attracted attention from researchers thanks to their great potential for cheap,straightforward,and small-scale production of metallic components.Atomic diffusion additive manufacturing(ADAM),a variant of indirect AM methods,is a layer-wise indirect AM process recently developed based on fused deposition modeling and metal injection molding.However,there is still limited knowledge of the process conditions and material properties fabricated through this process,where sintering plays a crucial role in the final consolidation of parts.Therefore,this research,for the first time,systematically investigates the impact of various sintering conditions on the shrinkage,relative density,microstructure,and hardness of the 17-4PH ADAM samples.For this reason,as-washed samples were sintered under different time-temperature combinations.The sample density was evaluated using Archimedes,computed tomography,and image analysis methods.The outcomes revealed that sintering variables significantly impacted the density of brown 17-4PH Stainless Steel samples.The results indicated more than 99% relative densities,higher than the value reported by Markforged Inc.(~96%).Based on parallel porosities observed in the computed tomography results,it can be suggested that by modifying the infill pattern during printing,it would be possible to increase the final relative density.The microhardness of the sintered samples in this study was higher than that of the standard sample provided by Markforged Inc.Sintering at 1330℃ for 4 h increased the density of the printed sample without compromising its mechanical properties.According to X-ray diffraction analysis,the standard sample provided by Markforged Inc.and“1330℃—4 h”one had similar stable phases,although copper-rich intermetallics were more abundant in the microstructure of reference samples.This study is expected to facilitate the adoption of indirect metal AM methods by different sectors,thanks to the high achievable relative densities reported here.
基金Open access funding provided by Politecnico di Torino within the CRUI-CARE Agreement.
文摘Additive manufacturing(AM),as an advanced manufacturing technology,enables the production of personalized orthopedic implant devices with complex geometries that closely resemble bone structures.Titanium and its alloys are extensively employed in biomedical fields like orthopedics and dentistry,thanks to the excellent compatibility with the human body and high corrosion resistance due to the existence of a thin protective oxide layer known as TiO_(2) upon exposure to oxygen on the surface.However,in joint inflammation,reactive oxygen species like hydrogen peroxide and radicals can damage the passive film on Ti implants,leading to their deterioration.Although AM technology for metallic implants is still developing,advancements in printing and new alloys are crucial for widespread use.This work aims to investigate the corrosion resistance of in-situ alloyed Ti536(Ti5Al3V6Cu)alloy produced through electron beam powder bed fusion(EB-PBF)under simulated peri-implant inflammatory conditions.The corrosion resistance was evaluated using electrochemical experiments conducted in the presence of 0.1%H_(2)O_(2) in a physiological saline solution(0.9%NaCl)to replicate the conditions that may occur during post-operative inflammation.The findings demonstrate that the micro-environment surrounding the implant during peri-implant inflammation is highly corrosive and can lead to the degradation of the TiO_(2) passive layer.Physiological saline with H_(2)O_(2) significantly increased biomaterial open circuit potential up to 0.36 mV vs.Ag/AgCl compared to physiological saline only.Potentiodynamic polarization(PDP)plots confirm this increase,as well.The PDP and electrochemical impedance spectroscopy(EIS)tests indicated that adding Cu does not impact the corrosion resistance of the Ti536 alloy initially under simulated inflammatory conditions,but prolonged immersion leads to enhanced corrosion resistance for all biomaterials tested,indicating the formation of an oxide layer after the reduction of the solution oxidizing power.These results suggest that modifying custom alloys by adding appropriate elements significantly enhances corrosion resistance,particularly in inflammatory conditions.
文摘Multi-pass ultrasonic impact treatment(UIT)was applied to modify the microstructure and improve the mechanical and tribological characteristics at the near-surface region of commercially pure Ti(CP-Ti)specimens produced by the laser powder bed fusion(L-PBF)method.UIT considerably refined the L-PBF process-related acicular martensites(α′-M)and produced a well-homogenized and dense surface microstructure,where the porosity content of 1-,3-,and 5-pass UITed samples was reduced by 43,60,and 67%,respectively.The UITed samples showed an enhancement in their near-surface mechanical properties up to a depth of about 300μm.The nanoindentation results for the 3-pass UITed sample revealed an increase of about 53,45,and 220%in its nanohardness,H/E_(r),and H_(3)/E_(r)^(2)indices,respectively.The stylus profilometry results showed that performing the UIT removed the L-PBF-related features/defects and offered a smooth surface.The roughness average(R_(a))and the skewness(R_(sk))of the 3-pass UITed sample were found to be lower than those of the L-PBFed sample by 95 and 223%,respectively.Applying the UIT also enhanced the material ratio,where the maximum load-bearing capacity(~100%)in as-L-PBFed(as-built)and 3-pass UITed samples was obtained at 60-and 10-µm depths,respectively.The tribological investigations showed that applying the UIT resulted in a significant reduction of wear rate and average coefficient of friction(COF)of CP-Ti.For instance,under the normal pressures of 0.05 and 0.2 MPa,the wear rate and COF of the 3-pass UITed sample were lower than those of the L-PBFed sample by 65 and 58%,and 20 and 17%,respectively.
文摘Electron beam melting(EBM) process is an additive manufacturing process largely used to produce complex metallic components made of high-performance materials for aerospace and medical applications.Especially,lattice structures made by Ti-6A1-4V have represented a hot topic for the industrial sectors because of having a great potential to combine lower weights and higher performances that can also be tailored by subsequent heat treatments.However,the little knowledge about the mechanical behaviour of the lattice structures is limiting their applications.The present work aims to provide a comprehensive review of the studies on the mechanical behaviour of the lattice structures made of Ti-6A1-4V.The main steps to produce an EBM part were considered as guidelines to review the literature on the lattice performance:(1) design,(2) process and(3) post-heat treatment.Thereafter,the correlation between the geometrical features of the lattice structure and their mechanical behaviour is discussed.In addition,the correlation among the mechanical performance of the lattice structures and the process precision,surface roughness and working temperature are also reviewed.An investigation on the studies about the properties of heat-treated lattice structure is also conducted.
文摘This study investigated dry sliding wear properties of AZ31 magnesium alloy and B_(4)C-reinforced AZ31 composites containing 5,10,and 20 wt.%B_(4)C with bimodal sizes under different loadings(10-80 N)at various sliding speeds(0.1-1 m/s)via the pin-on-disc configuration.Microhardness evaluations showed that when the distribution of B_(4)C particles was uniform the hardness of the composites increased by enhancing the reinforcement content.The unreinforced alloy and the composite samples were examined to determine the wear mechanism maps and identify the dominant wear mechanisms in each wear condition and reinforcement content.For this purpose,wear rates and friction coefficients were recorded during the wear tests and worn surfaces were characterized by scanning electron microscopy and energy dispersive X-ray spectrometry analyses.The determined wear mechanisms were abrasion,oxidation,delamination,adhesion,and plastic deformation as a result of thermal softening and melting.The wear evaluations revealed that the composites containing 5 and 10 wt.%B_(4)C had a significantly higher wear resistance in all the conditions.However,20 wt.%B_(4)C/AZ31 composite had a lower resistance at high sliding speeds(0.5-1 m/s)and high loadings(40-80 N)in comparison with the unreinforced alloy.The highest wear resistance was obtained at high sliding speeds and low loadings with the domination of oxidative wear.
