Unmelted Powder Research Articles

Effect of Volumetric Energy Density on the Evolution of the Microstructure and the Degradation Behavior of 3D-Printed Fe-Mn-C Alloys from Water-Atomized Powders

Additive manufacturing of metals opens new doors for innovation in custom-based productions in a wide range of fields, including medicine, even if it introduces new challenges that need to be addressed to guarantee the properties are equal to or superior to those of conventional fabrication processes. In this research, porous, biodegradable Fe-Mn-C alloys were fabricated using a 3D printing technique with four different printing energy densities ranging from 62.5 to 125.0 J/mm3. The effect of printing energy density on the microstructure and degradation behavior was investigated. Lower energy densities resulted in higher pore density and the presence of unmelted powder particles, while the alloy printed at 104.2 J/mm3 exhibited the lowest pore density and the smallest grain size. Degradation tests revealed that the highest pore density in the sample printed at 62.5 J/mm3, and the lowest grain size in the sample printed at 104.2 J/mm3 contributed to faster degradation rates. The alloy printed at the highest energy density, 125.0 J/mm3, demonstrated the largest grain size and the slowest degradation rate. Energy-dispersive spectroscopy and Fourier transform infrared spectroscopy analyses identified manganese carbonate as the primary degradation product, with calcium phosphate forming as a secondary product. These findings provide a significant understanding of the relationship between printing parameters, microstructure, and degradation behavior, which are essential for optimizing the performance of Fe-Mn-C alloys in biodegradable material applications.

Improved Mechanical Performances of Hastelloy C276 Composite Coatings Reinforced with SiC by Laser Cladding.

Composite coatings reinforced with varying mass fractions of SiC particles were successfully fabricated on 316 stainless steel substrates via laser cladding. The phase compositions, elemental distribution, microstructural characteristics, hardness, wear resistance and corrosion resistance of the composite coatings were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Vickers hardness testing, friction-wear testing and electrochemical methods. The coatings have no obvious pores, cracks or other defects. The phase compositions of the Hastelloy C276 coating includes γ-(Ni, Fe), Ni2C, M6C, M2(C, N) and M23C6. SiC addition resulted in the formation of high-hardness phases, such as Cr3Si and S5C3, with their peak intensity increasing with SiC content. The dendrites extend from the bonding zone towards the top of the coatings, and the crystal direction diffuses from the bottom to each area. Compared with the dendritic crystals formed at the bottom, the microstructure at the top is mostly equiaxed crystals and cellular crystals with smaller volume. When SiC powder particles are present around the crystals, the microstructure of the cladding layer grows acicular crystals containing Si and C. These acicular crystals tend to extend away from the residual SiC powder particles, and the grain size in this region is smaller and more densely distributed. This indicates that both melted and unmelted SiC powder particles can contribute to refining the grain structure of the cladding layer. The optimal SiC addition was determined to be 9 wt%, yielding an average microhardness of 670.1 HV0.5, which is 3.05 times that of the substrate and 1.19 times that of the 0 wt% SiC coating. The wear resistance was significantly enhanced, reflected by a friction coefficient of 0.17 (43.59% of the substrate, 68% of 0 wt%) and a wear rate of 14.32 × 10-6 mm3N-1·m-1 (27.35% of the substrate, 40.74% of 0 wt%). The self-corrosion potential measured at 315 mV, with a self-corrosion current density of 6.884 × 10⁻6 A/cm2, and the electrochemical charge-transfer resistance was approximately 25 times that of the substrate and 1.26 times that of the 0 wt%. In this work, SiC-reinforced Hastelloy-SiC composite coating was studied, which provides a new solution to improve the hardness, wear resistance and corrosion resistance of 316L stainless steel.

Nanograin-enhanced surface-layer strengthening of 3D printed intervertebral cage induced by sandblasting.

3D-printed customized titanium alloy (Ti6Al4V, TC4) as load-bearing prostheses and implants, such as intervertebral cages, have been widely used in clinical practice. Native biological inertia and inadequate bone in-growth of porous titanium alloy scaffolds hampered their clinical application efficiency and then extended the healing period. To improve the osseointegration capacity of 3D-printed intervertebral cages, sandblasting was selected to execute their surface treatment. On the one hand, sandblasting treatment can efficiently eliminate incomplete unmelted powder that adheres to struts in intervertebral cages during the manufacture of 3D printing, resulting in high surface area and low surface flatness induced by the rough surface could favor osseointegration. On the other hand, sandblasting can also induce ultrafine grains and nanograins in the near-surface layer that are conductive to mechanical strength enhancement. This can be verified by both microhardness and residual compressive stress reaching peak values (404.2 HV, 539.1 MPa) in the transverse section of its near-surface layer along the depth from the surface. This is attributed to the fact that more grain boundaries can impede dislocation movement. Sandblasting surfaces in intervertebral cages could favor osseointegration and in-growth, providing a foundation for sandblasting treatment of 3D-printed intervertebral cages in clinical applications.

Clarifying the formation of equiaxed grains and microstructural refinement in the additive manufacturing of Ti-Cu

Controlling microstructural evolution in metallic additive manufacturing (AM) is difficult, especially in producing refined as-built grains instead of coarse, directional grains. Traditional solutions involve adding inoculants to AM feedstocks, but titanium (Ti) alloys cannot employ this approach without producing detrimental secondary phases. Ti-Cu (Ti-copper) alloys offer a solution through constitutional supercooling and/or solid state thermal cycling under AM conditions. This work analyzes a compositionally graded directed energy deposition (DED) Ti-Cu build, single-melt laser tracks, and dilatometric heat treatments to evaluate if, when, and by what mechanism(s) microstructural refinement occurs. Refinement by inoculation of unmelted powder particles was also considered. Constitutional supercooling produced no net microstructural refinement as any equiaxed dendrites which form are remelted with new deposition. This finding agreed with solidification modeling of powder bed fusion-laser beam (PBF-LB) and DED builds. Solid state thermal cycling refined microstructures only during ex-situ dilatometric heat treatments, suggesting build parameter optimization is needed to achieve refinement in-situ. Accidental heterogeneous nucleation on unmelted Ti powder, originating from the different thermophysical properties of Ti and Cu, provided the most significant microstructural refinement. This work systematically assesses the microstructural refinement mechanisms of Ti-Cu in AM builds and offers insights into microstructural control in eutectoid alloys.

Surface finishing of 3D-printed Ti–6Al–4 V alloy by electrolyte plasma polishing: Process optimization and microstructure

The electrolyte plasma polishing (EPP) technology is proposed to remove the unmelted powder particles and oxide film for high-quality surface finishing of 3D-printed Ti–6Al–4 V alloy. An orthogonal experiment is conducted to investigate multiple factors that contribute to the surface quality of the alloy during the polishing process. The optimal parameters determined for the EPP process are a voltage of 300 V, a polishing time of 12 min, a polishing depth of 12 cm, and a temperature of 75 °C. Based on the extent of the effect, the factors influencing surface roughness were ranked: voltage > time > depth > temperature. The surface crest and trough area of the alloy is substantially reduced after polishing, while the average roughness experienced a reduction of 76 %. The improvement in surface quality is attributed to the corrosion of the oxide layer by F ions in the electrolytic solution, and the melting of surface protrusions due to the impact of high-energy electrons under high-temperature and high-pressure conditions during plasma discharge. Additionally, the surface hardness of the material decreases slightly, but its corrosion resistance and hydrophobicity are enhanced, and the calibration rate of the EBSD sample can reach 92.51 %, demonstrating that it is an excellent surface finishing technique. Hence, EPP is a promising approach for smoothening 3D-printed metals, especially for alloy parts with complex geometry and porous structure.

Formation mechanism of defects in Invar 36/MnCu functionally graded material fabricated by directed energy deposition

The fabrication of Invar/MnCu functionally graded material (FGM) through directed energy deposition (DED) can satisfy the demands for precision devices in aerospace, providing lightweight properties and integrating thermal stability and vibration damping capabilities. However, basic research on Invar/MnCu FGM is still lacking, hindering its potential applications. To address this gap, this study was conducted using mixed powders and consistent process parameters to print experiments for Invar/MnCu FGM and homogeneous samples. Phases, microstructures, compositions, and thermal expansion properties were thoroughly examined. Three types of defects were detected in the Invar/MnCu FGM sample: unmelted Invar 36 powders, cracks, and pores. The mechanism of unmelted powders was deeply discussed, attributing it to material properties influencing laser absorptivity, the required time for melting powder, and effects on solidus temperature. The mechanism of cracks was also discussed, attributing it to the γ-Fe dendritic structure causing low melting point metal to form an intergranular liquid film, harmful secondary phases mismatched with the terminal alloy, and obvious tensile stresses during the DED process. Additionally, an effective strategy was proposed to reduce defects in Invar/MnCu FGM. After optimization, the specimens exhibited excellent tensile properties, with a yield strength of 262 ± 5 MPa, an ultimate tensile strength of 316 ± 7 MPa, and an elongation of 3 % ± 1 %. This research provides valuable references and insights for subsequent work, offering robust support for better understanding and designing other FGM.

Impact of design strategy favoring powder removal on mechanical performance of bio-inspired porous architectures for laser-based powder-bed fusion additive manufacturing

Mass reduction is a concern both in mechanical engineering and living organisms to reduce energy and materials consumption. Lately, transfer of knowledge from biology to engineering has become easier thanks to additive manufacturing. Trabecular bone for example optimally adapts to the mechanical stress it undergoes. Mass reduction methods bio-inspired from trabecular architecture, proposed in the literature, are not always applicable for laser-based powder-bed fusion. In particular, bio-inspired mass reduction methods based on a material removal principle generate porosities throughout a solid initial part which can result in enclosed porosities that trap un-melted powders. Here, we propose a 3D depowderable bio-inspired mass reduction method. Powder removal was controlled in different samples through weighing and X-ray computed microtomography and the impact of the design strategy that ensures correct powder removal on mechanical performance (stiffness) was quantified. Mean performance difference is 10.35 % (between 1.82 % and 26.47 %). For stiff and light parts loaded in bending, the proposed method outperforms parts made of bulk steel alloy by leveraging an architecture bio-inspired from trabecular bone.

Optimized control of laser processing parameter on microstructural evolution and mechanical behavior in CoCrNi medium entropy alloy

In this study, the processing parameters of a laser powder bed fusion (LPBF)-fabricated CoCrNi alloy were systematically investigated for their impact on mechanical properties, microstructure, and fracture characteristics when the relative density exceeds 99%. The maximum relative density of 99.89% was attained at a laser power of 225 W, and scan speed of 1000 mm/s, accompanied by a hardness value of 276.83 HV. However, it is important to note that the highest relative density did not correspond to the maximum σUTS. Tensile testing revealed that increasing the laser power at the same scan speeds led to a decrease in elongation. The LPBF-fabricated CoCrNi alloy exhibited enhanced defect tolerance due to its cellular microstructure, which confined ductile dimple sizes to the nanoscale and impeded crack propagation through pinning effects. At scan speeds of 1000 mm/s and energy densities below 83 J/mm³, an increased presence of unmelted powder and pores was observed. Besides, it was confirmed that the <110> crystallographic texture displayed the strongest orientation within the sample. Theoretical calculations indicated that over 50% of the yield strength is attributed to the dislocation structure. These findings contribute to the process optimization of LPBF, providing a valuable reference for adjusting process parameters to enhance material mechanical properties, particularly when targeting relative densities above 99%.

Computationally guided alloy design and microstructure-property relationships for non-equiatomic Ti–Zr–Nb–Ta–V–Cr alloys with tensile ductility made by laser powder bed fusion

Single-phase body-centered cubic refractory complex concentrated alloys (RCCAs), exhibit strength retention at temperatures above the melting points of conventional Ni-based superalloys. However, their lack of room temperature tensile ductility leads to cracks during processing and/or premature failure under mechanical loading when fabricated by laser-based metals additive manufacturing (AM). We present an alloy design framework for tensile ductility in non-equimolar RCCAs amenable to AM processing within the Ti–V–Cr–Nb–Zr–Ta system. First, density functional theory (DFT) and machine learning informed screening of alloy compositions were used to down-select ∼106 alloys with potential for tensile ductility. Next, Scheil solidification modeling was used to eliminate compositions most at risk for micro-segregation and solidification cracking based on the estimated freezing range of each alloy. This led to the design of two new, representative alloys: Ti0.4Zr0.4Nb0.1Ta0.1 and Ti0.486V0.375Ta0.028Cr0.111. These alloys were evaluated for rapid solidification defect formation using in-situ synchrotron melt pool imaging, fabricated via laser powder bed fusion (L-PBF) AM, and then characterized for processing defects, microstructure, and mechanical properties. Overall, both alloys achieved tensile yield strengths >800 MPa and failure strains >5 %. However, the occurrence of un-melted powders of high melting point elements likely resulted in premature failure during tensile straining. Considerations about mitigating this defect source are discussed and the role of local micro-segregation on ductility are elucidated. Overall, these results highlight the success of our framework, and show potential for laser-based AM-RCCAs with tensile ductility.

Dynamics of pore formation and evolution during multi-layer directed energy deposition additive manufacturing via in-situ synchrotron X-ray imaging: A case study on high-entropy Cantor alloy

Blown-powder directed energy deposition (DED) additive manufacturing is impeded for novel alloys processing by perceivable and detrimental porosity. During multi-layer depositions, however, mechanisms of pore formation and evolution remain elusive for developing pore mitigation strategies. Here, conduction-mode multi-layer DED process of an exemplary high-entropy Cantor alloy have been investigated in-situ by high-energy high-speed synchrotron X-ray imaging. Three new pore formation mechanisms are unveiled when depositing first layer and successive layers: gas pore induced by high-velocity powder injection into melt pool, pore generated from swirl shear of turbulent melt flow, and pore trapped by surface wave. Three pore formation mechanisms are reconfirmed: pore inheritance from feedstock powder, pore generation when laser remelting defect-sensitive locations of existing pore from previous layer or unmelted powder attached on the melt pool surface, and pore formation as cooling of melt pool. A unique mechanism for pore elimination is proposed: a counter-Marangoni melt flow is experimentally found in the stable melt pool and contributes to the prolonged pore lifetime at tens of milliseconds scale; pores are prone to coalesce into larger sizes in laser interaction zone and the adjacent location with circulation zone; coalesced larger pores driven by combined effect of Marangoni and buoyant forces easily get eliminated from melt pool. The results of pore formation and evolution dynamics revealed in Cantor alloy provide quantified experimental data for high-fidelity computational modeling and in-depth insights of porosity control for high-entropy alloy printing down to melt pool scale.

Surface integrity of consecutive shot-peened additively manufactured 316L stainless steel

ABSTRACT The shot peening procedure enhances the mechanical characteristics with the transformation of compressive residual stresses which helps in the increment of operational lifespan of the product. The study comprehensively analyzed the effect of consecutive shot peening procedures up to four peening passes with the coverage increases 100% on each peening pass up to 400% on the laser powder bed fused austenitic stainless steel and compared with the as-built condition focusing on surface characteristics, mechanical characteristics, and corrosion potential. Surface damage of the peened samples was found very minimal with the absence of visible scan tracks and unmelted powder particles due to the controlled peening parameters. The inducement of compressive residual stresses (−625 MPa) was observed to be higher at the fourth consecutive peening passes without strain-induced martensite, with an increment of hardness proportion of 29.12% with a depth of 1 mm, and increment of corrosion resistance across each peening pass.

Research on the effect of remelting on the epitaxial growth process of single crystal superalloy

In this paper, the remelting process is applied to Laser Directed Energy Deposition (L-DED) to repair single crystal superalloys. The main formation modes of stray grains in single crystal epitaxial growth were analyzed, and the inhibitory effect of remelting process on stray grains in single crystal epitaxial growth using L-DED was studied. Comparative experiments between remelting and non-remelting processes have been conducted. Three process parameters in the remelting process: power, z-axis lift and cladding-remelting interval time were studied. The impact of different remelting process parameters on single crystal epitaxial growth and the formation of stray grains has been studied. Remelting has been shown to effectively prevent the formation of stray grains during the solidification of the melt pool, which are otherwise caused by the presence of unmelted powder during the powder feeding phase of the L-DED process. A cladding layer without stray grains on both sides is obtained. After remelting, the epitaxial growth structure can achieve larger cellular and columnar dendritic zones and smaller primary dendrite arms. A favorable epitaxial growth structure was obtained in this paper, under the optimized remelting process window.

Laser-Induced Controllable Porosity in Additive Manufacturing Boosts Efficiency of Electrocatalytic Water Splitting.

In laser-based additive manufacturing (AM), porosity and unmelted metal powder are typically considered undesirable and harmful. Nevertheless in this work, precisely controlling laser parameters during printing can intentionally introduce controllable porosity, yielding a porous electrode with enhanced catalytic activity for the oxygen evolution reaction (OER). This study demonstrates that deliberate introduction of porosity, typically considered a defect, leads to improved gas molecule desorption, enhanced mass transfer, and increased catalytically active sites. The optimized P-93% electrode displays superior OER performance with an overpotential of 270 mV at 20 mA cm-2. Furthermore, it exhibits remarkable long-term stability, operating continuously for over 1000 h at 10 mA cm-2 and more than 500 h at 500 mA cm-2. This study not only provides a straightforward and mass-producible method for efficient, binder-free OER catalysts but also, if optimized, underscores the potential of laser-based AM driven defect engineering as a promising strategy for industrial water splitting.

A comparative analysis of compressive and wear failure of laser-powder bed fused Stainless Steel 316L produced with different hatch spacing in stripe and contour patterns

The selection of hatch spacing is crucial in additive manufacturing processes to produce a defect free Stainless Steel 316L (SS) components, especially in laser powder bed fusion (LPBF) process. Improper selection of hatch spacing could lead to various failure regimes (like vertical cracking, porosity, and un-melted particles) in Stainless Steel 316L (SS) component produced through laser powder bed fusion (LPBF). Further, the failure regimes have a direct impact on the hardness, compression strength, friction, and wear properties of LPBF SS components. The present study has taken substantial efforts to analyse the impact of various hatch spacing (0.08 mm, 0.10 mm. and 0.12 mm) in stripe and contour patterns, in terms of morphology, mechanical, and tribological properties of LPBF SS components. Also, the present study elucidates how variations in hatch spacing influences the features like particle fusion, crack formation, density, hardness, surface roughness, compression, and wear properties. The stripe pattern with low hatch spacing of 0.08 mm showed better particle fusion and high surface roughness; whereas the high hatch spacing has produced voids, un-melted powder particles, and cracks in the stripe and contour pattern. High densities and hardness values were attributed to the stripe patterns with more effective melting and fusing of powder particles. XRD analysis revealed the stable phase compositions across various hatch spacing with a predominant FCC crystal structure. Residual stress distribution was significantly influenced by the hatch spacing for both stripe and contour patterns. Importantly, the low hatch space leads has promoted the tensile residual stress formation and vice versa for the higher hatch spacing. Stripe patterns showed higher compression strengths with buckling and shear mode as a compression failure. The stripe pattern demonstrated a low specific wear rate (SWR) and coefficient of friction (COF) compared to the contour pattern, with respect to the various hatch spacing. Furthermore, the simulated body fluid (SBF) lubrication regime played a significant role in reducing the COF. Patches, groves, furrows, and craters demonstrated the abrasive and adhesive failure for both stripe and contour pattern, which is further detailed in the article.

Directly depositing highly densified and uniform Cu-Cr pseudobinary alloy

Cu-Cr pseudobinary alloys have excellent electrical properties and are widely used in many industries. Laser additive manufacturing can effectively avoid the shortcomings of traditional methods for preparing Cu-Cr alloys. However, the high reflection of Cu powder to laser energy brings difficulties to industrial practice. The assembled Cu powder is used as raw material to absorb more laser energy through the outer layer of Cr powder, thereby improving the melting efficiency of the powder and the quality of the molten pool. Laser remelting of unmelted Cr powder can inhibit the uneven nucleation and growth of precipitated Cr, and improve the uniformity of electrical conductivity and element distribution. This study provides a new idea for the preparation of high-performance Cu alloys.

Effect of post-processing and variation of the building angle of Ti-6Al-4 V disks obtained by selective laser melting: A comparison of physical, chemical and mechanical properties to machined disks

Additive Manufacturing (AM) is driving the development of dental implants with freedom of design, material savings, and predictable properties. The modification of a single parameter, and post-processing treatments affects the final macro and microstructure. The aim was to evaluate the effect of changing the building angle, using the Selective Laser Melting (SLM) technique, on the physical, chemical, and mechanical properties and to compare them with sanded manufacturing surfaces and machined surfaces, with and without chemical surface treatment. There were 8 groups of Ti-6Al-4 V discs (Ø 10 mm×2 mm), classified as machined (M), machined with acid-alkali treatment (TM), SLM 0° (AM0), SLM 0° with sanding (SAM0), SLM 45° (AM45), SLM 45° with sanding (SAM45), SLM 90° (AM90), and SLM 90° with sanding (SAM90). The tests used were Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), roughness, wettability, surface free energy, X-ray diffraction (XRD), and Vickers hardness. The normality of the data was checked using the Shapiro-Wilk test followed by Kruskal-Wallis and ANOVA, with Dunn and Tukey post-tests, with a significance level of 5%. SEM revealed angle dependence in the number of unmelted powder particles and topographical heterogeneity, and EDS reported the elemental composition of the base alloy. AM90 showed the highest wettability among the manufactured groups, and the chemical surface treatment increased the wettability of the machined sample (p<0.001). In the roughness analysis, the higher the building angle, the higher the surface roughness . Sanding provided homogeneity in roughness, wettability, surface free energy, and microhardness. It was concluded that the production routes, change in angle, sanding and surface treatment affect the macro and microstructure of titanium surfaces. Changing the building angle influenced all of the topographical characteristics of the material, a parameter that can be changed and improved that is important for determining properties.

A methodology for the 3D characterization of surfaces using X-ray computed tomography: Application to additively manufactured parts

Many studies highlight the significance of three-dimensional surface topography characterization in assessing its effect on the mechanical or functional properties of materials. This is especially obvious for parts made by additive manufacturing (AM), known for their complex shape and surface topographies. However, a vast majority of 3D characterizations have constraints regarding the macroscopic geometry of the parts they can probe. At the microscale, they are also unable to account for hidden surface features, e.g. notches hidden by unmelted powder particles. Even with the use of X-ray Computed Tomography (XCT) - a tool with the potential to circumvent these issues -data is often reduced to 2D or 2.5D formats for easier analysis, but this leads to a loss of information. This underscores the need for XCT data post-treatment tools to perform thorough 3D surface characterizations. Herein, we introduce a methodology for local roughness and curvature characterization of surfaces of complex shapes using XCT. This method has been designed to be user-friendly, especially for those without extensive data analysis expertise. It provides a comprehensive 3D characterization and efficiently tackles the issues caused by hidden features. After a detailed description of our methodology, we give a first illustrative example based on architected structures fabricated by Electron Powder Bed Fusion (E-PBF). By integrating roughness and curvature metrics, we also derive a parameter indicative of the stress concentrations caused by surface irregularities.

Additive manufacturing of defect-free TiZrNbTa refractory high-entropy alloy with enhanced elastic isotropy via in-situ alloying of elemental powders

Laser powder-bed fusion (L-PBF) additive manufacturing presents ample opportunities to produce net-shape parts. The complex laser-powder interactions result in high cooling rates that often lead to unique microstructures and excellent mechanical properties. Refractory high-entropy alloys show great potential for high-temperature applications but are notoriously difficult to process by additive processes due to their sensitivity to cracking and defects, such as un-melted powders and keyholes. Here, we present a method based on a normalized model-based processing diagram to achieve a nearly defect-free TiZrNbTa alloy via in-situ alloying of elemental powders during L-PBF. Compared to its as-cast counterpart, the as-printed TiZrNbTa exhibits comparable mechanical properties but with enhanced elastic isotropy. This method has good potential for other refractory alloy systems based on in-situ alloying of elemental powders, thereby creating new opportunities to rapidly expand the collection of processable refractory materials via L-PBF.

Effect of processing parameters on the defects, microstructure, and property evaluation of Ti-6Al-4V titanium alloy processed by laser powder bed fusion

In this study, we designed the processing windows for laser powder bed fusion (LPBF) of Ti-6Al-4V (Ti-64) alloy by using central composite design and made a detailed investigation into the influence of processing parameters on the defects. The purpose is to investigate the effect of defects on mechanical properties. It was found that insufficient energy density could lead to the formation of lack of fusion (LOF) defects and produce non-melted powders on the surface, while excessive energy density could lead to cracks that were detrimental to mechanical performance. In addition, the microstructural evaluation found that relatively low energy density could lead to shorter columnar prior-β grains, while prior-β grains in the sample processed by the high energy density extended almost the entire height of the cross-section, which could lead to the strong mechanical property anisotropy. The prior β grains are formed by heterogeneous nucleation on the partially melted material powder. As the energy input increases, all the powder powders in the molten pool can be melted so that these particles do not act as nucleation sites and the prior β grain can grow through more layers without forming new grains being able to nucleate. The prior β-grain in as-built Ti-64 samples consisted of acicular α’ martensite with myriads of lattice distortions, as a precursor to a phase transition, which lead to strong tensile strength and poor ductility. Annealing heat treatment promoted the improvement of the ductile performance of LPBF Ti-64. Overall, this study provides comprehensive views on the effects of processing parameters (laser power, scanning speed, and hatch distance) on the internal (pores and LOF) and external (unmelted powder, sintering neck, and crack), defects, microstructure, and tensile property evaluation of LPBF Ti-64, which offer insights for the development of additive manufactured titanium alloys with excellent mechanical property.

Forming quality analysis of TC4 titanium alloy based on SLM orthogonal process

The TC4 titanium alloy bulk and irregular porous structures were prepared using Selective Laser Melting (SLM). This study systematically investigated the effects of laser power, scanning speed, scanning spacing, and laser energy density on the forming quality of TC4 titanium alloy specimens, through orthogonal experimental design. The research results indicate that laser power is the primary factor affecting the density of TC4 titanium alloy bulk during the SLM process. With the increase of laser energy density, the density of the specimens shows an initial increase followed by a decrease, while Vickers hardness and surface roughness exhibit a decreasing trend followed by an increasing trend. Moreover, the surface of the specimens transforms from a rough surface with a significant presence of pores, voids, or unmelted powder particles to a relatively smooth and flat surface, accompanied by a reduction in the size and quantity of pore defects.