Chen-Nan Sun - Academia.edu (original) (raw)

Papers by Chen-Nan Sun

Journal of Materials Processing Technology, 2013

ABSTRACT In this paper, the process monitoring and control in laser aided additive manufacturing ... more ABSTRACT In this paper, the process monitoring and control in laser aided additive manufacturing (LAAM) were studied. Some key issues which affect the process monitoring and control were revealed and discussed in detail. The results show that the geometry of the parts affects the melt-pool temperature, especially where the heat dissipation is strongly limited. The power density distribution plays an important role for controlled LAAM process. The laser beam can only be defocused to a certain extent to avoid the insufficient power density due to the excessively enlarged beam size. This can cause defects on the clad surface and in the clad layer. Surface oxidation must be avoided during the process control, because surface oxidation can deteriorate the LAAM process, as indicated by the disturbances of the measured melt pool temperature. With the path-dependant process control, the dimensional accuracy of the deposition can be significantly improved.

Materials Science and Engineering: A, 2014

ABSTRACT The fabrication of nano-composites is quite challenging because the uniform dispersion o... more ABSTRACT The fabrication of nano-composites is quite challenging because the uniform dispersion of nano-sized reinforcements in metallic substrates is difficult to achieve using powder metallurgy or liquid processing methods. In the present study, Al-based nano-composites reinforced with Al2O3 particles have been successfully fabricated using friction stir processing. The effects nano-Al2O3 particle addition on the evolution of the grain structure and mechanical behaviour of a friction-stir-processed Al matrix were studied and discussed in detail. It was revealed that the pinning effect of Al2O3 particles retarded grain growth following recrystallisation during FSP and led to a more pronounced reduction in grain size. Significant increases in the microhardness and tensile strength relative to Al under the same conditions were obtained by adding Al2O3 particles. A microstructural examination suggested that the voids initiated from the Al/Al2O3 interfaces during testing of the tensile strength of the nano-composites.

Asian Society for Precision Engineering and Nanotechnology (ASPEN 2022)

Materials & Design, 2022

Smart Manufacturing, 2022

Hexachiral auxetic metamaterials can exhibit unconventional behaviors of negative Poisson’s ratio... more Hexachiral auxetic metamaterials can exhibit unconventional behaviors of negative Poisson’s ratio that can achieve superior mechanical properties including energy absorption and indentation resistance. The thickness ratio between the wavy ligament and center ring, which is denoted as [Formula: see text], has a critical influence on the isotropic mechanical properties of the hexachiral structures. This work aims to investigate the effect of [Formula: see text] on the isotropic auxeticity of wavy hexachiral structures under tensile and compressive loadings through simulations and experiments. A parametric study on hexachiral unit cells with [Formula: see text] values ranging from 0.25 to 1.5 was conducted with finite element analysis. With a decrease in [Formula: see text] values, the deformation mechanism showed improved coiling of the wavy hexachiral structure with thinner ligaments and thicker center rings, which exhibits better bending and rotational deformations, respectively. Th...

Additive manufacturing, 2020

Titanium matrix composites reinforced with titanium boride (TiB) and titanium carbide (TiC) were ... more Titanium matrix composites reinforced with titanium boride (TiB) and titanium carbide (TiC) were fabricated in situ via selective laser melting (SLM). Varying contents of boron carbide (B4C) from 0 to 5 wt% were added to pure Ti to prepare blended powders for SLM. The influence of the B4C content on the printability, microstructure and mechanical properties of SLM-printed (TiB + TiC)/Ti composites was studied. The relative densities of all the fabricated composites were greater than 97.8 %; an increase in the B4C content resulted in a decrease in their relative density. The microstructure of the composites varied from a lath-shaped structure (0 wt%) to a dendritic structure (1 wt%) and to a cellular + dendritic structure (2–5 wt%), which was determined by the change of thermal convection within melt pools. Both the dendritic and cellular structures were arranged by coalescent clusters composed of TiB whiskers and TiC particles, while the clusters were formed through a self-joining b...

Surface and Coatings Technology, 2002

Batch-type hot-dip zinc and 5% Al–Zn coatings were investigated for comparison of their corrosion... more Batch-type hot-dip zinc and 5% Al–Zn coatings were investigated for comparison of their corrosion resistance, electrochemical behavior and microstructures. The 5% Al–Zn coatings possess prominent electrochemical passivation behavior. Intermetallics formed mainly between iron, aluminum and zinc adhering to the substrate were identified with energy-dispersive X-ray analysis and are believed to be responsible for the passivation phenomena observed in the electrochemical

Materials & Design, 2016

Selective laser melting (SLM) was used for additive manufacturing multi-wall carbon nanotube (MWC... more Selective laser melting (SLM) was used for additive manufacturing multi-wall carbon nanotube (MWCNT) reinforced Inconel 625 composites. The MWCNTs were coated on Inconel 625 powder through molecular-level mixing. Compared to the SLM fabricated Inconel 625 sample, the composite sample showed significant improvement in ultimate tensile and yield strength with less elongation. Heat-treatment on the composite sample recovered its elongation to the level of pure Inconel 625 while maintaining its ultimate tensile strength but reducing its yield strength. The microstructures of the composite sample had a slightly faster cooling rate than the pure metallic sample during SLM fabrication. The electron backscatter diffraction graphs revealed the grain refinement induced by MWCNTS in the alloy matrix. The Raman spectra and TEM micrographs revealed the presence of MWCNT in the metal matrix after SLM fabrication.

Key Engineering Materials

Polymer extrusion is one of the largest material manufacturing processes, which is deployed subst... more Polymer extrusion is one of the largest material manufacturing processes, which is deployed substantially in productions. The variety of the output product types is greatly attributed to the die part of the extruder because it is one of the essential components that shapes the material. The main purpose of this paper is to create a feasible and efficient design of the extrusion die, which would meet the design requirements and would be more convenient to use as well as have better performance compared to the existing design. In order to obtain adequate results, CAD model of the die bodies were created and simulated in the SolidWorks Plastics and COMSOL software. It is found from the results of the simulation that, proposed design demonstrated better performance in terms of uniformity of the flow at the outlet as well as pressure and temperature distributions.

International Journal of Fatigue

International Journal of Fatigue. Changes resulting from the publishing process, such as peer rev... more International Journal of Fatigue. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently

International Journal of Precision Engineering and Manufacturing-Green Technology

A simple and effective technique to reduce the overall fuel cell polarization resistance was intr... more A simple and effective technique to reduce the overall fuel cell polarization resistance was introduced on a conventionally sintered YSZ electrolyte by creating a hybrid microstructure using low-intensity CO2 laser scanning methods. After laser modification of the YSZ electrolyte surface on the cathode side, the overall polarization resistance was reduced from 513 to 124 Ω cm2, and the maximum power density was increased by 28% from 1.86 to 2.38 mW/cm2 at 450 °C. This improvement was due to the enhanced surface kinetics by higher grain boundary density on the YSZ surface from recrystallization after laser scanning.

Additive Manufacturing

Abstract Lattice structures have been intensively researched for their light-weight properties an... more Abstract Lattice structures have been intensively researched for their light-weight properties and unique functions in specific applications such as for impact protection and biomedical-implant. The advancement of additive manufacturing simplifies the fabrication of lattice structures as opposed to conventional manufacturing and this opens doors to create more designs. There are ample research opportunities to explore the mechanical performance of the lattice structures fabricated by this technology specific to each design. This study filled the research gap by investigating the deformation behaviour and compressive properties of Ti-6Al-4V lattice structures fabricated by a powder bed fusion method from the aspects of design, orientation and density. The results were compared between cubic and honeycomb unit designs, between two orientations and across five different densities. Results showed that both cubic and honeycomb lattice deformed in a layer-by-layer manner for the first tested orientation, where vertical struts were parallel to the compression direction. In the second tested orientation, where lattice struts were angled with respect to the direction of compression, the deformation behaviour was observed as a single diagonal shear band. As the density of the structure increased, the deformation pattern shifted towards diagonal crack similar to a solid part. Honeycomb lattice structure had the highest density efficiency for energy absorption in both orientations and for first maximum compressive strength in the second orientation. Change of orientation significantly affected the efficiency in plateau stress for cubic lattice structure, and compressive property values for honeycomb lattice structure. Comparative studies showed that the first maximum compressive strength and energy absorption of the lattice structures in the first orientation were higher than most of the lattice designs from other literature.

Optics & Laser Technology, 2016

Abstract In this study, micron-size TiB 2 particles were utilized to reinforce Inconel 625 produc... more Abstract In this study, micron-size TiB 2 particles were utilized to reinforce Inconel 625 produced by selective laser melting. Exceptional microhardness 600–700 HV 0.3 of the composite was obtained. In further investigation, the microstructure and mechanical properties of Inconel 625/TiB 2 composite can be significantly influenced by addition of TiB 2 particles during SLM. It was found that the long directional columnar grains observed from SLM-processed Inconel 625 were totally changed to fine dendritic matrix due to the addition of TiB 2 particles. Moreover, with laser energy density (LED) of 1200 J/m, a Ti, Mo rich interface around TiB 2 particles with fine thickness can be observed by FESEM and EDS. The microstructure evolution can be determined by different laser energy density (LED): under 1200 J/m, γ phase in dendrite grains; under 600 J/m, γ phase in combination of dendritic and acicular grains; under 400 J/m, γ phase acicular grains. Under optimized LED 1200 J/m, the dynamic nanohardness (8.62 GPa) and elastic modulus (167 GPa) of SLM-processed Inconel 625/TiB 2 composite are higher compared with those of SLM-processed Inconel 625 (3.97 GPa and 135 GPa, respectively).

Materials & Design

Abstract Additive manufacturing provides great geometrical freedom for fabricating structures wit... more Abstract Additive manufacturing provides great geometrical freedom for fabricating structures with complex or customized architecture. One of the applications benefiting from this technology is the fabrication of functionally graded materials with high degree of control of internal architecture which can be strategic application in advanced energy absorption. This study aims to explore the mechanical properties of functionally graded lattice structures fabricated by an additive manufacturing technique namely, selective laser melting (SLM), with Ti-6Al-4V as the building material. Both cubic lattice and honeycomb lattice structures with varied strut diameter and density were designed and manufactured, and their physical characteristics, deformation behavior and compressive properties were investigated. The collapse of structure always started from least dense layer to the denser layers. In contrast, samples with uniform density showed abrupt shear failure with diagonal cracking across the whole structure. The plateau stress and specific energy absorption of density graded samples were higher than for uniform density samples for three out of four designs by up to 67% and 72%, respectively. In addition, density graded lattices showed distinct energy absorption behavior with cumulative energy absorption increasing as a power of strain function while uniform density lattices showed a near-linear relationship.

Crack initiation constitutes a large portion of the total life for parts under high cycle fatigue... more Crack initiation constitutes a large portion of the total life for parts under high cycle fatigue loading. Materials made by the laser powder bed fusion (L-PBF) process contain unavoidable process-induced porosity whose effect on the mechanical properties needs to be considered for fatigue applications. Results from this work show that not all pores in L-PBF parts promote fatigue crack initiation. The length scale of local microstructure defects, i.e. grain boundary, could be larger than the pores and in such cases they are the primary cause for crack initiation. Samples were produced in this work to demonstrate the critical defect size responsible for the transition between the porosity-driven and microstructure-driven failure modes.

Additive Manufacturing

Abstract Mo2C/Ti64 composites with nearly full densification and enhanced tensile strength were d... more Abstract Mo2C/Ti64 composites with nearly full densification and enhanced tensile strength were developed by using laser powder bed fusion (LPBF). The addition of 1–3 wt% Mo2C particles with an average particle size of ~ 1 µm enabled the LPBF-printed composites with an alternately laminated α′-Ti/β-Ti microstructure along with Mo2C and in-situ synthesized M23C6 (M was Ti, Al, V, and Mo). During LPBF, most of the Mo2C particles were incorporated into the Ti64 matrix, resulting in the α′-Ti and β-Ti solid solutions. The segregation of Mo contributed to the generation of the β-Ti phase at the melt pool boundaries of the composites, leading to the alternating hard α′-Ti/soft β-Ti phases. Remarkable improvements of 22.8% and 19.5% in the hardness and tensile strength of the Ti64 matrix were achieved, respectively. The strengthening of the LPBF-printed composites was associated with the formation of the laminated α′-Ti/β-Ti structure, solid solution behavior of Mo and C, and presence of the remaining Mo2C and precipitated M23C6. The findings are anticipated to provide insights into the selection of reinforcement materials for additively manufactured composites with nearly full densities and greater mechanical strength.

Selective laser melting (SLM) is one of many 3D additive manufacturing (AM) techniques that uses ... more Selective laser melting (SLM) is one of many 3D additive manufacturing (AM) techniques that uses a laser beam to fuse and melt powder materials together in the creation of metal parts. Although SLM offers greater design flexibility as compared to conventional manufacturing methods, fabrication of fine features and thin-wall structures is still challenging. This is because the rapid heating and cooling cycles inherent to the SLM process tend to generate large residual stresses, which may lead to severe plastic deformation in the part. The degree of distortion may be alleviated by tuning the processes, but there is a limit to how much the process parameters can be adjusted before the part density and/or integrity are compromised. In this research, we investigated the effect of four major process parameters – laser power, scan speed, hatch spacing, and layer thickness on thin-wall distortion. The amount of distortion in the thin wall was measured and analyzed against the original flat ...

Journal of Materials Processing Technology, 2013

ABSTRACT In this paper, the process monitoring and control in laser aided additive manufacturing ... more ABSTRACT In this paper, the process monitoring and control in laser aided additive manufacturing (LAAM) were studied. Some key issues which affect the process monitoring and control were revealed and discussed in detail. The results show that the geometry of the parts affects the melt-pool temperature, especially where the heat dissipation is strongly limited. The power density distribution plays an important role for controlled LAAM process. The laser beam can only be defocused to a certain extent to avoid the insufficient power density due to the excessively enlarged beam size. This can cause defects on the clad surface and in the clad layer. Surface oxidation must be avoided during the process control, because surface oxidation can deteriorate the LAAM process, as indicated by the disturbances of the measured melt pool temperature. With the path-dependant process control, the dimensional accuracy of the deposition can be significantly improved.

Materials Science and Engineering: A, 2014

ABSTRACT The fabrication of nano-composites is quite challenging because the uniform dispersion o... more ABSTRACT The fabrication of nano-composites is quite challenging because the uniform dispersion of nano-sized reinforcements in metallic substrates is difficult to achieve using powder metallurgy or liquid processing methods. In the present study, Al-based nano-composites reinforced with Al2O3 particles have been successfully fabricated using friction stir processing. The effects nano-Al2O3 particle addition on the evolution of the grain structure and mechanical behaviour of a friction-stir-processed Al matrix were studied and discussed in detail. It was revealed that the pinning effect of Al2O3 particles retarded grain growth following recrystallisation during FSP and led to a more pronounced reduction in grain size. Significant increases in the microhardness and tensile strength relative to Al under the same conditions were obtained by adding Al2O3 particles. A microstructural examination suggested that the voids initiated from the Al/Al2O3 interfaces during testing of the tensile strength of the nano-composites.

Asian Society for Precision Engineering and Nanotechnology (ASPEN 2022)

Materials & Design, 2022

Smart Manufacturing, 2022

Hexachiral auxetic metamaterials can exhibit unconventional behaviors of negative Poisson’s ratio... more Hexachiral auxetic metamaterials can exhibit unconventional behaviors of negative Poisson’s ratio that can achieve superior mechanical properties including energy absorption and indentation resistance. The thickness ratio between the wavy ligament and center ring, which is denoted as [Formula: see text], has a critical influence on the isotropic mechanical properties of the hexachiral structures. This work aims to investigate the effect of [Formula: see text] on the isotropic auxeticity of wavy hexachiral structures under tensile and compressive loadings through simulations and experiments. A parametric study on hexachiral unit cells with [Formula: see text] values ranging from 0.25 to 1.5 was conducted with finite element analysis. With a decrease in [Formula: see text] values, the deformation mechanism showed improved coiling of the wavy hexachiral structure with thinner ligaments and thicker center rings, which exhibits better bending and rotational deformations, respectively. Th...

Additive manufacturing, 2020

Titanium matrix composites reinforced with titanium boride (TiB) and titanium carbide (TiC) were ... more Titanium matrix composites reinforced with titanium boride (TiB) and titanium carbide (TiC) were fabricated in situ via selective laser melting (SLM). Varying contents of boron carbide (B4C) from 0 to 5 wt% were added to pure Ti to prepare blended powders for SLM. The influence of the B4C content on the printability, microstructure and mechanical properties of SLM-printed (TiB + TiC)/Ti composites was studied. The relative densities of all the fabricated composites were greater than 97.8 %; an increase in the B4C content resulted in a decrease in their relative density. The microstructure of the composites varied from a lath-shaped structure (0 wt%) to a dendritic structure (1 wt%) and to a cellular + dendritic structure (2–5 wt%), which was determined by the change of thermal convection within melt pools. Both the dendritic and cellular structures were arranged by coalescent clusters composed of TiB whiskers and TiC particles, while the clusters were formed through a self-joining b...

Surface and Coatings Technology, 2002

Batch-type hot-dip zinc and 5% Al–Zn coatings were investigated for comparison of their corrosion... more Batch-type hot-dip zinc and 5% Al–Zn coatings were investigated for comparison of their corrosion resistance, electrochemical behavior and microstructures. The 5% Al–Zn coatings possess prominent electrochemical passivation behavior. Intermetallics formed mainly between iron, aluminum and zinc adhering to the substrate were identified with energy-dispersive X-ray analysis and are believed to be responsible for the passivation phenomena observed in the electrochemical

Materials & Design, 2016

Selective laser melting (SLM) was used for additive manufacturing multi-wall carbon nanotube (MWC... more Selective laser melting (SLM) was used for additive manufacturing multi-wall carbon nanotube (MWCNT) reinforced Inconel 625 composites. The MWCNTs were coated on Inconel 625 powder through molecular-level mixing. Compared to the SLM fabricated Inconel 625 sample, the composite sample showed significant improvement in ultimate tensile and yield strength with less elongation. Heat-treatment on the composite sample recovered its elongation to the level of pure Inconel 625 while maintaining its ultimate tensile strength but reducing its yield strength. The microstructures of the composite sample had a slightly faster cooling rate than the pure metallic sample during SLM fabrication. The electron backscatter diffraction graphs revealed the grain refinement induced by MWCNTS in the alloy matrix. The Raman spectra and TEM micrographs revealed the presence of MWCNT in the metal matrix after SLM fabrication.

Key Engineering Materials

Polymer extrusion is one of the largest material manufacturing processes, which is deployed subst... more Polymer extrusion is one of the largest material manufacturing processes, which is deployed substantially in productions. The variety of the output product types is greatly attributed to the die part of the extruder because it is one of the essential components that shapes the material. The main purpose of this paper is to create a feasible and efficient design of the extrusion die, which would meet the design requirements and would be more convenient to use as well as have better performance compared to the existing design. In order to obtain adequate results, CAD model of the die bodies were created and simulated in the SolidWorks Plastics and COMSOL software. It is found from the results of the simulation that, proposed design demonstrated better performance in terms of uniformity of the flow at the outlet as well as pressure and temperature distributions.

International Journal of Fatigue

International Journal of Fatigue. Changes resulting from the publishing process, such as peer rev... more International Journal of Fatigue. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently

International Journal of Precision Engineering and Manufacturing-Green Technology

A simple and effective technique to reduce the overall fuel cell polarization resistance was intr... more A simple and effective technique to reduce the overall fuel cell polarization resistance was introduced on a conventionally sintered YSZ electrolyte by creating a hybrid microstructure using low-intensity CO2 laser scanning methods. After laser modification of the YSZ electrolyte surface on the cathode side, the overall polarization resistance was reduced from 513 to 124 Ω cm2, and the maximum power density was increased by 28% from 1.86 to 2.38 mW/cm2 at 450 °C. This improvement was due to the enhanced surface kinetics by higher grain boundary density on the YSZ surface from recrystallization after laser scanning.

Additive Manufacturing

Abstract Lattice structures have been intensively researched for their light-weight properties an... more Abstract Lattice structures have been intensively researched for their light-weight properties and unique functions in specific applications such as for impact protection and biomedical-implant. The advancement of additive manufacturing simplifies the fabrication of lattice structures as opposed to conventional manufacturing and this opens doors to create more designs. There are ample research opportunities to explore the mechanical performance of the lattice structures fabricated by this technology specific to each design. This study filled the research gap by investigating the deformation behaviour and compressive properties of Ti-6Al-4V lattice structures fabricated by a powder bed fusion method from the aspects of design, orientation and density. The results were compared between cubic and honeycomb unit designs, between two orientations and across five different densities. Results showed that both cubic and honeycomb lattice deformed in a layer-by-layer manner for the first tested orientation, where vertical struts were parallel to the compression direction. In the second tested orientation, where lattice struts were angled with respect to the direction of compression, the deformation behaviour was observed as a single diagonal shear band. As the density of the structure increased, the deformation pattern shifted towards diagonal crack similar to a solid part. Honeycomb lattice structure had the highest density efficiency for energy absorption in both orientations and for first maximum compressive strength in the second orientation. Change of orientation significantly affected the efficiency in plateau stress for cubic lattice structure, and compressive property values for honeycomb lattice structure. Comparative studies showed that the first maximum compressive strength and energy absorption of the lattice structures in the first orientation were higher than most of the lattice designs from other literature.

Optics & Laser Technology, 2016

Abstract In this study, micron-size TiB 2 particles were utilized to reinforce Inconel 625 produc... more Abstract In this study, micron-size TiB 2 particles were utilized to reinforce Inconel 625 produced by selective laser melting. Exceptional microhardness 600–700 HV 0.3 of the composite was obtained. In further investigation, the microstructure and mechanical properties of Inconel 625/TiB 2 composite can be significantly influenced by addition of TiB 2 particles during SLM. It was found that the long directional columnar grains observed from SLM-processed Inconel 625 were totally changed to fine dendritic matrix due to the addition of TiB 2 particles. Moreover, with laser energy density (LED) of 1200 J/m, a Ti, Mo rich interface around TiB 2 particles with fine thickness can be observed by FESEM and EDS. The microstructure evolution can be determined by different laser energy density (LED): under 1200 J/m, γ phase in dendrite grains; under 600 J/m, γ phase in combination of dendritic and acicular grains; under 400 J/m, γ phase acicular grains. Under optimized LED 1200 J/m, the dynamic nanohardness (8.62 GPa) and elastic modulus (167 GPa) of SLM-processed Inconel 625/TiB 2 composite are higher compared with those of SLM-processed Inconel 625 (3.97 GPa and 135 GPa, respectively).

Materials & Design

Abstract Additive manufacturing provides great geometrical freedom for fabricating structures wit... more Abstract Additive manufacturing provides great geometrical freedom for fabricating structures with complex or customized architecture. One of the applications benefiting from this technology is the fabrication of functionally graded materials with high degree of control of internal architecture which can be strategic application in advanced energy absorption. This study aims to explore the mechanical properties of functionally graded lattice structures fabricated by an additive manufacturing technique namely, selective laser melting (SLM), with Ti-6Al-4V as the building material. Both cubic lattice and honeycomb lattice structures with varied strut diameter and density were designed and manufactured, and their physical characteristics, deformation behavior and compressive properties were investigated. The collapse of structure always started from least dense layer to the denser layers. In contrast, samples with uniform density showed abrupt shear failure with diagonal cracking across the whole structure. The plateau stress and specific energy absorption of density graded samples were higher than for uniform density samples for three out of four designs by up to 67% and 72%, respectively. In addition, density graded lattices showed distinct energy absorption behavior with cumulative energy absorption increasing as a power of strain function while uniform density lattices showed a near-linear relationship.

Crack initiation constitutes a large portion of the total life for parts under high cycle fatigue... more Crack initiation constitutes a large portion of the total life for parts under high cycle fatigue loading. Materials made by the laser powder bed fusion (L-PBF) process contain unavoidable process-induced porosity whose effect on the mechanical properties needs to be considered for fatigue applications. Results from this work show that not all pores in L-PBF parts promote fatigue crack initiation. The length scale of local microstructure defects, i.e. grain boundary, could be larger than the pores and in such cases they are the primary cause for crack initiation. Samples were produced in this work to demonstrate the critical defect size responsible for the transition between the porosity-driven and microstructure-driven failure modes.

Additive Manufacturing

Abstract Mo2C/Ti64 composites with nearly full densification and enhanced tensile strength were d... more Abstract Mo2C/Ti64 composites with nearly full densification and enhanced tensile strength were developed by using laser powder bed fusion (LPBF). The addition of 1–3 wt% Mo2C particles with an average particle size of ~ 1 µm enabled the LPBF-printed composites with an alternately laminated α′-Ti/β-Ti microstructure along with Mo2C and in-situ synthesized M23C6 (M was Ti, Al, V, and Mo). During LPBF, most of the Mo2C particles were incorporated into the Ti64 matrix, resulting in the α′-Ti and β-Ti solid solutions. The segregation of Mo contributed to the generation of the β-Ti phase at the melt pool boundaries of the composites, leading to the alternating hard α′-Ti/soft β-Ti phases. Remarkable improvements of 22.8% and 19.5% in the hardness and tensile strength of the Ti64 matrix were achieved, respectively. The strengthening of the LPBF-printed composites was associated with the formation of the laminated α′-Ti/β-Ti structure, solid solution behavior of Mo and C, and presence of the remaining Mo2C and precipitated M23C6. The findings are anticipated to provide insights into the selection of reinforcement materials for additively manufactured composites with nearly full densities and greater mechanical strength.

Selective laser melting (SLM) is one of many 3D additive manufacturing (AM) techniques that uses ... more Selective laser melting (SLM) is one of many 3D additive manufacturing (AM) techniques that uses a laser beam to fuse and melt powder materials together in the creation of metal parts. Although SLM offers greater design flexibility as compared to conventional manufacturing methods, fabrication of fine features and thin-wall structures is still challenging. This is because the rapid heating and cooling cycles inherent to the SLM process tend to generate large residual stresses, which may lead to severe plastic deformation in the part. The degree of distortion may be alleviated by tuning the processes, but there is a limit to how much the process parameters can be adjusted before the part density and/or integrity are compromised. In this research, we investigated the effect of four major process parameters – laser power, scan speed, hatch spacing, and layer thickness on thin-wall distortion. The amount of distortion in the thin wall was measured and analyzed against the original flat ...