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Directed energy deposition (DED), as an additive manufacturing technology, has shown unique advantages in multi-material additive manufacturing and remanufacturing. In this study, two types in-situ alloyed CrCoNi medium entropy alloys that have thin-walled structures with different thicknesses (T1 and T2) were manufactured by the DED process, and the mechanisms of differences in relative density, microstructure, and mechanical properties at different heights were systematically analyzed. In terms of microstructure, the T1 and T2 samples along the building direction exhibit significant differences in crystallographic orientation, grain size, and dislocation density, which are related to the local temperature gradient differences caused by the scanning path and heat accumulation. In terms of mechanical properties at different heights of the two types of thin-walled structures, the yield strength is higher but the elongation is lower at the bottom position of sample, while the yield strength is lower but the elongation is higher at the middle and top positions. The differences of mechanical properties at different heights of the T1 and T2 samples are related to the microstructure and relative density. This finding provides new insights for the design and performance analysis of complex thin-walled structures formed by additive manufacturing. [ABSTRACT FROM AUTHOR]

This study explores the effect of in-situ alloying and volumetric energy density (VED) on the microstructure of Laser Powder Bed Fusion (L-PBF) fabricated Ti alloys. Pure Ti, Ti–5Cu, and Ti–5Cu–1Si (wt%) samples were printed using elemental powders with varying VEDs. This study investigates the influence of VED and Cu/Si additions on the growth restriction factor (Q) and columnar-to-equiaxed transition of the β phase. Pure Ti samples exhibited coarse, prior columnar β grains with an average diameter of 106 μm, and a grain shape factor greater than 3.0. In contrast, both Ti–Cu and Ti–Cu–Si samples displayed a significant fraction of equiaxed prior β grains with a near-spherical morphology. Additionally, Cu/Si addition refined the prior β columnar grains, reducing their average diameter to 37 μm and 25 μm in Ti–Cu and Ti–Cu–Si, respectively. Furthermore, the study reveals a strong dependence of microstructure on VED in the Ti–5Cu–1Si alloy. Higher VED promotes a more uniform distribution of solute elements and a lower thermal gradient, resulting in finer equiaxed β grains with an average diameter of 4.9 μm, compared to samples printed at lower VEDs. The addition of Cu and Si also significantly refined the lath-like α phase and decreased the c/a ratio of the Ti HCP lattice, introducing lattice microstrains in the Ti–Cu and Ti–Cu–Si alloys. These findings demonstrate the potential of in-situ alloying and VED optimization for tailoring microstructures in novel Ti alloys fabricated via L-PBF, paving the way for achieving superior mechanical properties.

Titanium aluminide (TiAl) alloy is deemed to possess desirable properties but exhibits significant drawbacks such as poor fracture toughness, wear and ductility that impedes its structural application and limit workability and production. Hence, it is crucial to accomplish a sufficient stability in relation to strength and ductility without losing other attractive material properties of the TiAl alloy. Therefore, this work is aimed at studying a novel TiAl-based alloy synthesized using direct energy deposition (DED) technique. The alloy was developed through in-situ alloying with Al, Si, Ti, Mo and V elemental powders to fabricate quintenary alloy of Ti-Al-Si-Mo-V. From the results obtained, it was observed that the microstructural and phase analysis of the Ti-Al-Si-Mo-V alloys exhibited varying amount of β0 and ζ-Ti5Si3 phases along the grain interfaces reliant on the amount of Mo and V present with the formation of fully lamellar (FL) and duplex phase (DP) microstructures for 1400 °C and 1200 °C heat treatment temperatures, respectively. The Ti-Al-Si-Mo-V alloy ultimate tensile strength (UTS) was about 6.6–49.3 % greater than Ti-48Al-2 Nb-2Cr (GE-4822) alloy; while the yield strength (YS) was up to 34 % greater than GE alloy based on the nanoindentation results. Consequently, the Ti-Al-Si-Mo-V alloy would perform very well as material for aero-engines parts. The simulation result shows that cracking could be avoided by increasing the processing temperature. It was inferred that the processing temperature does not affect the maximum stress experienced by the TiAl alloy but the minimum stress level changes with processing temperatures.

TC11 alloy is an important high temperate Ti alloy. Its laser in-situ alloying by powder bed fusion-laser beam (PBF-LB) has been explored in this study. Results show that it is feasible to print the TC11 alloy using elemental powders rather than pre-alloyed powder, in terms of high density and good combination of strength and ductility at both room and elevated temperatures, along with minor loss of composing elements. Interestingly, it is noticed that an unusual nanocrystalline microstructure has formed due to the use of ZrH2 powder feedstock, partially explaining the reason for the good mechanical properties achieved. Finite element analysis has been employed to understand the in-situ alloying. Furthermore, a post processing by micro-arc oxidation (MAO) has been employed to the alloy, aiming to enhance its high-temperature oxidation resistance. The results make an implication that hydrides such as ZrH2 may hold the promise to develop nanosized, advanced Ti materials through laser in-situ alloying, and MAO can be considered for PBF-LB prepared TC11 alloy. [ABSTRACT FROM AUTHOR]

A blend of only commercial powders, including Ni625, CoCrF75, and 316L, were used as the raw material for fabricating non-equiatomic CoCrFeNiMoxNby high entropy alloys (HEAs) through laser powder bed fusion (PBF-LB/M) via in situ alloying, instead of using pure elemental powders, thus reducing the raw materials cost. The rapid cooling inherent in the PBF-LB/M process facilitated the dissolution of Mo and Nb, resulting in a single FCC phase characterized by high relative densities. High-temperature tensile tests were conducted at room temperature, 700 °C, 800 °C, and 900 °C, revealing mechanical properties that surpassed those reported in existing HEA literature. The remarkable strength of the HEAs developed in this study primarily stemmed from the incorporation of Mo and Nb, leading to the precipitation of Mo and Nb-rich lave phases at elevated temperatures. While constraining elongation when confined to grain boundaries, these precipitates enhanced strength without compromising elongation when distributed throughout the matrix. This work is a feasibility study to explore the usage of commodity compositions from the market to develop HEAs using PBF-LB/M, which opens the possibility of using scraps to further the development of new materials. Consequently, this study presents a rapid and cost-effective approach for HEA development, improving efficiency and sidestepping the direct utilization of critical raw metals for sustainable manufacturing. Moreover, this work also underscores the outstanding mechanical performance of these HEAs at high temperatures, paving the way for the design of innovative alloys for future high-temperature applications. [ABSTRACT FROM AUTHOR]

The oxidation behavior of copper-silver (Cu–Ag) alloy with the structure of triply periodic minimal surfaces (TPMS) processed by laser powder bed fusion (LPBF) was investigated at 300 °C and 600 °C. The lightweight TPMSs increase surface area, boosting measurement sensitivity in oxidation studies. The presence of silver enhances oxidation resistance of Cu–Ag alloy compared to that of pure copper by slowing down the oxidation process and thinning the oxide layer. This suggests that silver in the alloy potentially suppresses the outward diffusion of copper from the substrate to the oxide layer. This effect is evident in the oxidation rate curves, where the introduction of silver changes the oxidation kinetics from a linear rate in Cu to a parabolic rate in Cu–2 wt.% Ag at 300 °C. Moreover, at 600 °C, silver induces a slower parabolic rate in Cu–2 wt.% Ag compared to Cu.

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The binary Fe–Ni system offers alloys with notably low linear coefficients of thermal expansion (CTE), contingent upon their Ni content. In this respect twin-wire arc additive manufacturing (T-WAAM) presents the opportunity of in-situ alloying through the simultaneous feeding of two metal wires into a weld pool to obtain desired alloy compositions. This study aims to deposit a graded wall with Ni contents targeted at 42, 46, and 52 wt% in the building direction of the wall, along with a block comprising of 46 wt% Ni, employing the T-WAAM approach. The results show effective incorporation of additional Ni into the weld pool and geometrically stable weld beads in the continuous metal transfer mode during the T-WAAM process. This mode led to the defect-free and chemically stable deposition of the graded wall and the block with average Ni contents of 42.3 ± 1.1, 45.8 ± 1.4, 52.6 ± 0.8 wt%, and 46.4 ± 0.9 wt%, respectively. The measured Curie temperatures of the as-deposited alloys and the mean CTE values of alloy 46 were found to be comparable to the commercial alloys. In summary, this study validates the feasibility of in-situ deposition of low thermal expansion alloy compositions, thereby enabling the possibility of on-demand thermal expansion properties.

The further developments of additive manufacturing (AM) provides a possibility for Ti6Al4V and its functionally graded materials (FGMs), but limits further applications due to its low ductility, low microhardness and poor wear resistance. The key lies in the presence of microstructures such as epitaxial columnar β-grain orientation and heterogeneous phase distribution in AM Ti6Al4V, as well as the interfacial bonding problems (intermetallic phases, delamination, cracking) in AM Ti6Al4V FGMs. In order to address these fundamental intra and inter-layer problems, firstly the microstructure and phase evolution process of AM Ti6Al4V columnar-to-equiaxed transformation (CET) promoted by some alloying strategies was summarized in this paper according to alloying elements and reinforcing particle types. Subsequently, controlled changes in the composition and microstructure of AM Ti6Al4V FGMs were achieved by adding interlayers/introducing gradient interfaces, and the metallurgical reactions and phase transformation mechanisms that inhibit the formation of intermetallic compounds and interfacial defects were explored. Finally, the difficulties and future research directions for alloying strategies to achieve high strength and ductility of AM Ti6Al4V were presented. This review aims to improve the reliability of AM Ti6Al4V and its FGMs for applications in critical load-bearing structures through in-situ alloying and multi-material for the microstructure design of AM Ti6Al4V.

This study investigated cracking phenomena in 316L stainless steel (SS316L) and Inconel 718 (IN718) composition-graded material (CGM) additively manufactured by the direct energy deposition (DED) process. In order to prevent cracking in the CGM, thermodynamic analysis was performed to avoid the critical concentration for crack formation. Based on the local compositional detouring (LCD) method suggested by new approach, a crack-free CGM with a nonlinear combination of SS316L and IN718 was successfully fabricated with local additional elemental powder in the CGM defective region obtained using a multi-powder feeding system during the DED process.

Formation of strong texture, columnar grains, and chemical inhomogeneity are some of the serious challenges associated with SLM of metallic alloys. This paper deals with in-situ SLM manufacturing of Ti-5Cu (wt.%) samples from pure Ti and Cu powders at a constant volumetric energy density (VED) of 50.26 J/mm3. The heat treatment of samples was carried out by heating at 1050 °C (above the ß-transus temperature) for 3hr followed by furnace cooling. Then the effects of Cu addition to pure Ti and heat treatment on ß-columnar to equiaxed transition (CET) morphology and size of the a phase as well as microhardness of pure Ti and Ti-5Cu samples were investigated. The results showed that the ß columnar grains with an average equivalent diameter (deq) of 80 µm in SLMed pure Ti were effectively converted to equiaxed grains with an average deq of ~15 µm in the SLMed Ti-5Cu samples. The Cu addition increased the average microhardness from ~290 HV for pure Ti to ~415 HV for Ti-5Cu samples. This was attributed to the formation of equiaxed grains, increased lattice micro-strain resulting from Cu addition and decreased size of the lath-like a phase. The applied heat treatment led to the formation of equiaxed ß grains with an average diameter of ~125 µm, dissolution of unmelted titanium particles and the non-dissolution zones of Cu and Ti, and a rather homogeneous structure in Ti-5Cu samples. It also resulted in the decomposition of a' martensitic structure and the formation of different morphologies of Ti2Cu precipitates. Reduction of the average microhardness of the Ti-5Cu samples to ~312 HV after heat treatment was also related to the increase in deq of the equiaxed ß grains, in addition to the increase in the size of the a laths phase and decrease in micro-strain. [ABSTRACT FROM AUTHOR]

The application of commercially pure titanium (CP–Ti) has long been limited by its insufficient strength and plastic instability. However, strength enhancement typically comes at the expense of ductility since the two important mechanical properties are often mutually exclusive. In the present work, multi-element Fe–Cr–Ni–Mo in the form of 316L steel was added into CP-Ti by additive manufacturing (AM), so as to realize the simultaneous enhancement of strength and uniform ductility. The localized homogenization of CP-Ti and 316L alloy melts during laser melting deposition produced the microstructure comprised of basket-weave ɑ laths, discontinuous ɑGB, and retained β phases, which endowed Ti-1.35Fe-0.36Cr-0.24Ni-0.05Mo alloy with related higher ultimate tensile strength (635 MPa) and larger uniform ductility (12%). This approach could provide guidance for designing high-performance metal materials starting with elements powder through additive manufacturing.

A blend of only commercial powders, including Ni625, CoCrF75, and 316L, were used as the raw material for fabricating non-equiatomic CoCrFeNiMoxNby high entropy alloys (HEAs) through laser powder bed fusion (PBF-LB/M) via in situ alloying, instead of using pure elemental powders, thus reducing the raw materials cost. The rapid cooling inherent in the PBF-LB/M process facilitated the dissolution of Mo and Nb, resulting in a single FCC phase characterized by high relative densities. High-temperature tensile tests were conducted at room temperature, 700 °C, 800 °C, and 900 °C, revealing mechanical properties that surpassed those reported in existing HEA literature. The remarkable strength of the HEAs developed in this study primarily stemmed from the incorporation of Mo and Nb, leading to the precipitation of Mo and Nb-rich lave phases at elevated temperatures. While constraining elongation when confined to grain boundaries, these precipitates enhanced strength without compromising elongation when distributed throughout the matrix. This work is a feasibility study to explore the usage of commodity compositions from the market to develop HEAs using PBF-LB/M, which opens the possibility of using scraps to further the development of new materials. Consequently, this study presents a rapid and cost-effective approach for HEA development, improving efficiency and sidestepping the direct utilization of critical raw metals for sustainable manufacturing. Moreover, this work also underscores the outstanding mechanical performance of these HEAs at high temperatures, paving the way for the design of innovative alloys for future high-temperature applications.

This study investigated cracking phenomena in 316L stainless steel (SS316L) and Inconel 718 (IN718) composition-graded material (CGM) additively manufactured by the direct energy deposition (DED) process. In order to prevent cracking in the CGM, thermodynamic analysis was performed to avoid the critical concentration for crack formation. Based on the local compositional detouring (LCD) method suggested by new approach, a crack-free CGM with a nonlinear combination of SS316L and IN718 was successfully fabricated with local additional elemental powder in the CGM defective region obtained using a multi-powder feeding system during the DED process. We aim to avoid the cracks of functionally graded materials fabricated by local in-situ alloying technique using the result of thermodynamically analyzing. [ABSTRACT FROM AUTHOR]

Additive manufacturing has become increasingly important in the production of magnetic materials in recent years due to the great demands for miniaturization and complex-shaped magnet parts. In this study, the laser beam-powder bed fusion process (LPBF) has been used to develop an in-situ alloying process for the additive manufacturing of a permanent magnet material of the Fe–Cr–Co system. This novel method allows for the production of complex alloys with a chemical composition suited to each specific case of application, achieved by using elemental powders or simpler commercial alloy powders as base materials. The core focus of this study has been on the development and characterization of the printing process using a Fe-30.5Cr-15Co-1.5Mo alloy. The in-situ alloying process has been developed by performing melt pool tests on the two main component powders Fe and Cr and by conducting parameter studies using two different powder mixtures with different sphericity of their components. The influence of different printing parameters and post-printing treatments on the chemical homogeneity and magnetic properties has been studied for selected samples. In addition, magnetic measurements at different temperatures have been performed to investigate the temperature stability of the magnetic properties of the 3D printed material. Impact Statement As by today, the current amount of research done on the additive manufacturing of magnetic materials is rather low. Most of research is focused on rare- earth containing magnetic materials. In this work therefore, we are taking another direction in which we will show that LPBF combined with in- situ alloying is an ideal method for the production of a great variety of different rare- earth free magnetic materials. The positive results of our work can both have an influence on the the scientific community, as further research in the field on different promising rare- earth free magnetic materials is to be expected. Furthermore, a positiv economic impact may occur since the production of rare- earth free magnetic materials is dependent on different raw material sources which are both more cost- effectiv and less critical in terms of their supply chain. This effect is also accompanied by a positive environmental impact, since the mining of rare- earth metals usually comes with considerable environmental pollution.

Post-heat treatment is commonly employed to improve the microstructural homogeneity and enhance the mechanical performances of the additively manufactured metallic materials. In this work, a ternary (NiTi) _91 Nb _9 (at.%) shape memory alloy was produced by laser powder bed fusion (L-PBF) using pre-alloyed NiTi and elemental Nb powders. The effect of solution treatment on the microstructure, phase transformation behavior and mechanical/functional performances was investigated. The in-situ alloyed (NiTi) _91 Nb _9 alloy exhibits a submicron cellular-dendritic structure surrounding the supersaturated B2-NiTi matrix. Upon high-temperature (1273 K) solution treatment, Nb-rich precipitates were precipitated from the supersaturated matrix. The fragmentation and spheroidization of the NiTi/Nb eutectics occurred during solution treatment, leading to a morphological transition from mesh-like into rod-like and sphere-like. Coarsening of the β -Nb phases occurred with increasing holding time. The martensite transformation temperature increases after solution treatment, mainly attributed to: ( i ) reduced lattice distortion due to the Nb expulsion from the supersaturated B2-NiTi, and ( ii ) the Ti expulsion from the β -Nb phases that lowers the ratio Ni/Ti in the B2-NiTi matrix, which resulted from the microstructure changes from non-equilibrium to equilibrium state. The thermal hysteresis of the solutionized alloys is around 145 K after 20% pre-deformation, which is comparable to the conventional NiTiNb alloys. A short-term solution treatment (i.e. at 1 273 K for 30 min) enhances the ductility and strength of the as-printed specimen, with the increase of fracture stress from (613 ± 19) MPa to (781 ± 20) MPa and the increase of fracture strain from (7.6 ± 0.1)% to (9.5 ± 0.4)%. Both the as-printed and solutionized samples exhibit good tensile shape memory effects with recovery rates >90%. This work suggests that post-process heat treatment is essential to optimize the microstructure and improve the mechanical performances of the L-PBF in-situ alloyed parts.

Hypereutectic Al-high Si alloys are of immense interest for applications in the automotive, space or electronic industries, due their low weight, low thermal expansion, and excellent mechanical and tribological properties. Additionally, their production by laser powder bed fusion (LPBF) technology provides high flexibility in geometrical design and alloy composition. Since, most of the alloy properties could be improved by increasing the Si content, there is much interest in discovering the maximum that could be realized in LBPF Al-high Si alloys, without the appearance of any material failure. For this reason, in this work the production of Al-high Si alloys with extremely high silicon content of up to 70 wt.% was fundamentally investigated with respect to microstructure and mechanical properties. Highly dense (99.3%) and crack-free AlSi50 samples (5 × 5 × 5 mm3), with excellent hardness (225 HV5) and compressive strength (742 MPa), were successfully produced. Further, for the first time, AlSi70 LBPF samples of high density (98.8%) without cracks were demonstrated, using moderate scanning velocities. Simultaneously, the hardness and the compressive strength in the AlSi70 alloys were significantly improved to 350 HV5 and 935 MPa, as a result of the formation of a continuous Si network in the microstructure of the alloy. With respect to the powder source, it was found that the application of powder blends resulted in similar alloy properties as if pre-alloyed powders were used, enabling higher flexibility in prospective application-oriented alloy development. [ABSTRACT FROM AUTHOR]

In-situ alloying is a facile method for exploring high-performance metallic materials for additive manufacturing. However, composition inhomogeneity is inevitable, and it is a double-edged sword for the properties of in-situ alloyed parts. Appropriately controlling the composition inhomogeneity benefits the applications of in-situ alloying in specific microstructural and properties design. In this work, the Al20Cu alloy was selected as the benchmark alloy to investigate the tailoring of composition inhomogeneity. The morphology and area percentage of composition inhomogeneity in the as-built samples were firstly analyzed. These results provided evidence for the formation of composition inhomogeneity and indicate that its content is tightly dependent on processing parameters. The characteristics of the molten pool under various processing parameters were investigated by modeling the laser remelting process. Based on these, a processing map was established to guide the tailoring of composition inhomogeneity. This study expands the understanding of the formation mechanism of composition inhomogeneity in in-situ alloyed parts and sheds light on employing laser powder bed fusion in-situ alloying for new materials development. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (L-PBF) has garnered significant interest since its inception as it offers unparalleled advantages to fabricate complex-shaped metallic components. Due to its unique forming characteristics in terms of point-by-point, line-by-line, and layer-by-layer scanning manner, it enables the precise tailoring of site-specific microstructure and corresponding mechanical properties to meet the specific demanding applications. The present review aims to retrospect the recent advancements in microstructure manipulation strategies implemented during L-PBF, including multi-material, in-situ alloying, and processing (modifying the printing parameters/strategy and introducing the auxiliary fields). The evolution of microstructure and associated mechanical properties of L-PBF alloys derived from these strategies is thoroughly reviewed and discussed. Finally, the review presents perspectives on current challenges and outlines the future research directions. This comprehensive analysis aims to establish fundamental knowledge for manipulating microstructure and mechanical properties during L-PBF to fabricate alloys with desired microstructure and exceptional mechanical properties. [ABSTRACT FROM AUTHOR]

This study addresses the challenge of breaking the trade-off dilemma between strength and ductility in additively manufactured Titanium (Ti) products. By leveraging concentration non-uniformity and controlled diffusion during in-situ alloying of unalloyed titanium (CP-Ti) and 316L stainless steel (SS316) powders via laser powder bed fusion (LPBF), we formulated a novel Fe-containing alloy with improved printability and enhanced mechanical performance. The microstructure of the as-built Ti alloy comprises a heterostructure of nano-scaled martensitic α′ within the micro-scaled equiaxed prior-β grains, resulting from rapid solidification inherent in LPBF. Since the modified laser-powder bed fusion in this work lacks a pre-heating function, a stress-relief annealing process was conducted to enhance the mechanical properties of the as-built parts. The annealed in-situ alloyed Ti-Fe achieves a superb balance between strength and ductility, with an ultimate tensile strength (UTS) of approximately 1118.0 MPa and an elongation of ∼9.0 %. This study provides insights for designing high-performance Ti alloys with heterostructures using a mixture of elemental powder and alloyed powders via LPBF. The significance of concentration non-uniformity and diffusion during solidification is highlighted, demonstrating how these factors contribute to the formation of superior heterostructures through additive manufacturing. [ABSTRACT FROM AUTHOR]

Babbitt alloy, a commonly used wear-resistant coating material, has a low hardness. This causes severe plastic deformation, detachment or heavy wear to easily occur under low speed and heavy-load service conditions, reducing its service life. To solve these problems and improve the bonding strength and wear resistance of the tin-based Babbitt alloy coating, a higher laser cladding power was adopted to achieve in-situ alloying of the cladding layer and enhance the strength of the coating. The increase in strength was verified through the Fleischer theory and Orowan empirical formula to mainly result from the enhancement of solid solution strengthening and dispersion strengthening. Meanwhile, due to dispersion strengthening and the presence of dendritic FeSn, the occurrence of delamination wear was effectively prevented. The bonding strength of the final sample reached 147 MPa, and the wear rate was as low as 4.24 × 10–5 mm3/N・m. Thus, a high-strength and wear-resistant Babbitt alloy cladding layer was obtained. • The in-situ alloying of cladding layer was achieved by dissolution and diffusion of Fe from substrate. • FeSn affects the diffusion of Sb and Cu, and refining Cu 6 Sn 5 and SnSb. • Dendritic FeSn inhibits Sn plastic flow during wear, alleviating delamination wear. [ABSTRACT FROM AUTHOR]

The demand for high-strength aluminum alloys for the laser powder bed fusion (LPBF) process is still growing. However, to date, the crack susceptibility of conventional alloys as well as the high prices for specially developed alloys are the main obstacles for the use of high-strength aluminum alloys for LPBF. In this paper, crack-free LPBF samples with a relative density >99.9% were processed from AlMgSi1Zr (6182 series alloy) powder, to which 0.5 wt.-% Zr and 0.5 wt.-% Ti were added via mechanical mixing. No hot cracks were found in the µCT scans. Moreover, a fully equiaxed microstructure with a mean size of the α-Al grains of 1.2 µm was observed in the as-built parts. Al3(Zr,Ti) particles were observed, acting as efficient heterogeneous grain refiners for α-Al by building a semi-coherent interface. Unmolten Ti and Zr particles with sizes up to 80 µm were found in the α-Al phase. The resulting fine-grained microstructure led to a tensile strength of 329 ± 4 MPa and a total elongation at a break of 11.4 ± 0.9% after solution heat treatment, quenching in water, and subsequent artificial ageing. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) of Ti-based biomedical implants is a pivotal research topic because of its ability to produce implants with complicated geometries. Despite desirable mechanical properties and biocompatibility of Ti alloys, one major drawback is their lack of inherent antibacterial properties, increasing the risk of postoperative infections. Hence, this research focuses on the Ti536 (Ti5Al3V6Cu) alloy, developed through Electron Beam Powder Bed Fusion (EB-PBF), exploring bio-corrosion, antibacterial features, and cell biocompatibility. The microstructural characterization revealed grain refinement and the formation of Ti 2 Cu precipitates with different morphologies and sizes in the Ti matrix. Electrochemical tests showed that Cu content minimally influenced the corrosion current density, while it slightly affected the stability, defect density, and chemical composition of the passive film. According to the findings, the Ti536 alloy demonstrated enhanced antibacterial properties without compromising its cell biocompatibility and corrosion behavior, thanks to Ti 2 Cu precipitates. This can be attributed to both the release of Cu ions and the Ti 2 Cu precipitates. The current study suggests that the EB-PBF fabricated Ti536 sample is well-suited for use in load-bearing applications within the medical industry. This research also offers an alloy design roadmap for novel biomedical Ti-based alloys with superior biological performance using AM methods., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

• ZrCuAlNb metallic glass composite is in-situ alloyed using laser additive manufacturing. • A blend of elemental powders is used to prepare the ZrCuAlNb precursor. • Various processing parameters and multiple laser remelting cycles are applied. This study investigates the feasibility of synthesizing a ZrCuAlNb bulk metallic glass composite through in-situ alloying of pure elemental powder blend using powder-fed laser-directed energy deposition. The process parameters are carefully optimized and multiple laser remelting is applied to address the chemical inhomogeneity and elemental micro-segregation. A detailed microstructural examination confirms the successful discovery and development of an amorphous-crystalline composite structure. [ABSTRACT FROM AUTHOR]

Maraging steels are known for their exceptional strength derived from the martensite matrix and nano-precipitate strengthening. However, the trade-off to the high strength is often a loss of ductility and minimal strain hardening. Introducing metastable austenite to the matrix to activate transformation-induced plasticity (TRIP) is an effective approach to achieve high strength and ductility synergy. Existing methods to introduce TRIP into additively manufactured maraging steels are limited by the compositions of pre-alloyed powder or additional heat treatment steps. In-situ alloying via the laser directed energy deposition (L-DED) process allows flexibility in tailoring the alloying composition to achieve an austenite–martensite microstructure. Herein, we develop a TRIP–maraging steel by in-situ alloying of M789 with 316L (4–8 wt%) during the L-DED process. The addition of 316L facilitates austenite reversion in solution-treated maraging steel. As a result, the TRIP–maraging steel exhibits a 76 % increase in uniform elongation at the expense of a minimal sacrifice of strength. Furthermore, the corrosion resistance of the TRIP–maraging steel is enhanced. This work showcases a pathway to developing superior alloys by in-situ alloying via additive manufacturing. [Display omitted] [ABSTRACT FROM AUTHOR]

Elemental powders or pre-alloyed powders can be blended to form a powder stock with new compositions. In-situ alloying of blended powder mixtures during LPBF processing speeds up the alloy development process as it allows composition adjustment. Pre-alloyed powder is typically used in industrial settings to ensure consistency of the built material, whereas blended powders are used to experiment with new alloy compositions. In this research, we compare a range of binary alloy compositions built from blended elemental powder and pre-alloyed powder to evaluate how the feedstock powder affects the built material. The alloy is a lightweight alloy with a low coefficient of thermal expansion, comprised of Al and Si. The following compositions were formed by mixing pure Al and Si powder: AlSi38, AlSi40 and AlSi42, and pre-alloyed AlSi40 powder was also used.Parametric studies were performed for both the blended and pre-alloyed powders. It was found that the optimum process parameters for the blended and pre-alloyed powder were different. The line energy for pre-alloyed powder was selected to be 0.150 J/mm (300 W, and 2000 mm/s) which yielded a density of 99.5% of the theoretical density. The optimal density for the blended powders was 99.07-99.16% which was also achieved with 0.150 J/mm (375 W, 2500 mm/s). The alloys are brittle, with Young's modulus 86-99 GPa. Coefficient of thermal expansion (CTE) reduced with increasing Si content, material built from pre-alloyed powder had 5% higher CTE than material built from blended powder.

High Entropy Alloys are a class of alloys which have been shown to largely exhibit stable microstructures, as well as frequently good mechanical properties, particularly when manufactured by additive manufacturing. Due to the large number of potential compositions that their multi-component nature introduces, high throughput alloy development methods are desirable to speed up the investigation of novel alloys. Here, we explore once such method, in-situ alloying during Additive Manufacture, where a powder of a certain pre-alloyed composition is mixed with the required composition of powder of an additional element, such that alloying takes place when powders are melted during the process. To test the effectiveness and capability of the approach, selective laser melting has been used to manufacture pre-alloyed CoCrFeNi, and also CoCrFeNiCu and CoCrFeNiTi alloys by combining pre-alloyed CoCrFeNi powder with elemental powders of Cu and Ti. Processing parameter variations are used to find the highest relative density for each alloy, and samples were then characterised for microstructure and phase composition. The CoCrFeNi alloy shows a single phase face centred cubic (FCC) microstructure, as found with other processing methods. The CoCrFeNiCu alloy has a two phase FCC microstructure with clear partitioning of the Cu, while the CoCrFeNiTi alloy has an FCC matrix phase with NiTi intermetallics and a hexagonal close packed (HCP) phase, as well as unmelted Ti particles. The microstructures therefore differ from those observed in the same alloys manufactured by other methods, mainly due to the presence of areas with higher concentrations than usually encountered of Cu and Ti respectively. Successful in-situ alloying in this process seems to be improved by the added elemental powder having a lower melting point than the base alloy, as well as a low inherent tendency to segregate. While not producing directly comparable microstructures however, the approach does seem to offer advantages for the rapid screening of alloys for AM processability, identifying, for example, extensive solid-state cracking in the CoCrFeNiTi alloy. [ABSTRACT FROM AUTHOR]

In this work, twin wire arc additive manufacturing (T-WAAM) combined with in-situ alloying method was developed to fabricate multi-element alloys, and biomedical Ti-6Al-7Nb alloy with a good combination of strength and ductility was successfully fabricated for the first time. The modification of microstructure and the improvement of mechanical properties of the deposited Ti-6Al-7Nb alloy caused by Nb addition were investigated. Although demonstrated here for Ti-6Al-7Nb alloy, the combined method of T-WAAM and in-situ alloying is in principle applicable to fabricate other multi-element alloys by composition design, which is conductive to expanding the application fields of WAAM. IMPACT STATEMENT Twin wire arc additive manufacturing combined with in-situ alloying was developed to fabricate multi-element alloys, and biomedical Ti-6Al-7Nb alloy with a good combination of strength and ductility was first fabricated.

In-situ alloying is a facile method for exploring high-performance metallic materials for additive manufacturing. However, composition inhomogeneity is inevitable, and it is a double-edged sword for the properties of in-situ alloyed parts. Appropriately controlling the composition inhomogeneity benefits the applications of in-situ alloying in specific microstructural and properties design. In this work, the Al20Cu alloy was selected as the benchmark alloy to investigate the tailoring of composition inhomogeneity. The morphology and area percentage of composition inhomogeneity in the as-built samples were firstly analyzed. These results provided evidence for the formation of composition inhomogeneity and indicate that its content is tightly dependent on processing parameters. The characteristics of the molten pool under various processing parameters were investigated by modeling the laser remelting process. Based on these, a processing map was established to guide the tailoring of composition inhomogeneity. This study expands the understanding of the formation mechanism of composition inhomogeneity in in-situ alloyed parts and sheds light on employing laser powder bed fusion in-situ alloying for new materials development.

In this work, a high strength Al alloy was successfully processed via in-situ alloying of AlSi10Mg and Cu elemental powders during Laser Powder Bed Fusion. To get superior strength, 4 wt% of Cu was added to AlSi10Mg composition to benefit from the additional solid solution and precipitation strengthening mechanisms induced by Cu atoms. Microstructure, chemical composition, hardness, and tensile properties of as-built samples were firstly determined. The microstructure showed a dual eutectic formed by Si precipitates intermixed with θ-Al2Cu phase. The average Cu concentration was 3.96 ± 0.26 wt% in line with the theoretical one. Hardness and yield strength of AlSi10Mg + 4Cu alloy showed an increase of respectively 8.8 % and 35.6 % compared to the as-built AlSi10Mg, owing to the highly super-saturated solid solution of Si and Cu atoms upon rapid solidification. After that, a direct aging heat-treatment strategy was pursued to fully exploit the potential alloy precipitation by heating as-built samples at temperatures between 160 and 190 °C. A maximum hardness response was achieved after 1 h at 175 °C. The high hardening was primarily attributed to a mix of θ''/θ'+θ-Al2Cu and Si phases coupled with a still high solid solution content. Nevertheless, direct aging slightly decreased the alloy ductility due to the prominent precipitation of brittle Si particles during aging and the presence of Cu inhomogeneities formed after in-situ alloying.

The design of metal matrix composites predominantly focusses on synergistically integrating the intrinsic properties of matrix and reinforcing phase aiming to achieve outstanding strength and ductility simultaneously. In metal matrix composites, the reinforcing phase invariably faces challenges such as agglomeration and non-uniform distribution, resulting in a significant reduction in mechanical properties. Here, we propose a method to overcome this barrier through an in-situ alloying of laser powder bed fusion i.e., redistributing the reinforcing phase (Cr 2 B boride) in medium entropy alloy matrix (CoCrNi). The in-situ alloying can be achieved by a mixture of CoCrNi powders and B 4 C particles. After remelting, a nano-sized core-shell structure is developed by establishing "soft core" of CoCrNi matrix embedded with "hard shell" of Cr 2 B boride. Such nano-sized core-shell structure mainly contributes to a yield strength (867 ± 1.6 MPa), a high tensile strength (1200 ± 13 MPa) and a decent ductility (17 ± 0.5%) of the CoCrNi/Cr 2 B composite due to the load bearing strengthening and hetero-deformation induced hardening. Additionally, the crack propagation can be suppressed by the CoCrNi matrix/Cr 2 B interface. The insights provide a new design strategy of in-situ formation of the nano-sized core-shell structure to develop the metal matrix composites with high strength and ductility. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • The feasibility of obtaining low thermal expansion (LTE) Fe-Ni alloys using T-WAAM is investigated. • Deposition mode affects the stability of the melt pool and the resulting chemical composition. • Stability in deposition and composition is achieved with the continuous metal transfer mode during the T-WAAM process. • The as-deposited LTE alloys exhibit thermal properties comparable to the conventionally produced alloys. The binary Fe–Ni system offers alloys with notably low linear coefficients of thermal expansion (CTE), contingent upon their Ni content. In this respect twin-wire arc additive manufacturing (T-WAAM) presents the opportunity of in-situ alloying through the simultaneous feeding of two metal wires into a weld pool to obtain desired alloy compositions. This study aims to deposit a graded wall with Ni contents targeted at 42, 46, and 52 wt% in the building direction of the wall, along with a block comprising of 46 wt% Ni, employing the T-WAAM approach. The results show effective incorporation of additional Ni into the weld pool and geometrically stable weld beads in the continuous metal transfer mode during the T-WAAM process. This mode led to the defect-free and chemically stable deposition of the graded wall and the block with average Ni contents of 42.3 ± 1.1, 45.8 ± 1.4, 52.6 ± 0.8 wt%, and 46.4 ± 0.9 wt%, respectively. The measured Curie temperatures of the as-deposited alloys and the mean CTE values of alloy 46 were found to be comparable to the commercial alloys. In summary, this study validates the feasibility of in-situ deposition of low thermal expansion alloy compositions, thereby enabling the possibility of on-demand thermal expansion properties. [ABSTRACT FROM AUTHOR]

High Entropy Alloys are a class of alloys which have been shown to largely exhibit stable microstructures, as well as frequently good mechanical properties, particularly when manufactured by additive manufacturing. Due to the large number of potential compositions that their multi-component nature introduces, high throughput alloy development methods are desirable to speed up the investigation of novel alloys. Here, we explore once such method, in-situ alloying during Additive Manufacture, where a powder of a certain pre-alloyed composition is mixed with the required composition of powder of an additional element, such that alloying takes place when powders are melted during the process. To test the effectiveness and capability of the approach, selective laser melting has been used to manufacture pre-alloyed CoCrFeNi, and also CoCrFeNiCu and CoCrFeNiTi alloys by combining pre-alloyed CoCrFeNi powder with elemental powders of Cu and Ti. Processing parameter variations are used to find the highest relative density for each alloy, and samples were then characterised for microstructure and phase composition. The CoCrFeNi alloy shows a single phase face centred cubic (FCC) microstructure, as found with other processing methods. The CoCrFeNiCu alloy has a two phase FCC microstructure with clear partitioning of the Cu, while the CoCrFeNiTi alloy has an FCC matrix phase with NiTi intermetallics and a hexagonal close packed (HCP) phase, as well as unmelted Ti particles. The microstructures therefore differ from those observed in the same alloys manufactured by other methods, mainly due to the presence of areas with higher concentrations than usually encountered of Cu and Ti respectively. Successful in-situ alloying in this process seems to be improved by the added elemental powder having a lower melting point than the base alloy, as well as a low inherent tendency to segregate. While not producing directly comparable microstructures however, the approach does seem to offer advantages for the rapid screening of alloys for AM processability, identifying, for example, extensive solid-state cracking in the CoCrFeNiTi alloy.

In this work, twin wire arc additive manufacturing (T-WAAM) combined with in-situ alloying method was developed to fabricate multi-element alloys, and biomedical Ti-6Al-7Nb alloy with a good combination of strength and ductility was successfully fabricated for the first time. The modification of microstructure and the improvement of mechanical properties of the deposited Ti-6Al-7Nb alloy caused by Nb addition were investigated. Although demonstrated here for Ti-6Al-7Nb alloy, the combined method of T-WAAM and in-situ alloying is in principle applicable to fabricate other multi-element alloys by composition design, which is conductive to expanding the application fields of WAAM. IMPACT STATEMENT Twin wire arc additive manufacturing combined with in-situ alloying was developed to fabricate multi-element alloys, and biomedical Ti-6Al-7Nb alloy with a good combination of strength and ductility was first fabricated. [ABSTRACT FROM AUTHOR]

Since selective laser melting (SLM) is a master forming technology, the material properties of the SLM components are defined during the manufacturing process. The idea is then to use SLM for micro metallurgy, which means that powders of different composition can easily be mixed to give a small amount of a desired alloy, which is useful if only small amounts of a special alloy are required. In this study, the binary shape memory alloy (SMA) Nitinol is processed accordingly. The entire process chain is analysed. The powder blending leads to a particle size distribution (PSD) with D 10 = 15.57 µm and D 90 = 48.24 µm, which is well processable. With the developed SLM process parameter set and the corresponding manufacturing strategy crack free components with relative densities ρ rel > 98.6 % are produced. For these samples, the homogeneity of the alloy components after SLM processing as well as the phase change temperatures required for the shape memory effect (SME) are investigated in dependence on the processing parameters. The best-suited parameter set is further used for the manufacturing of specimens for compression tests, in which the presence of the SME is proven with a mean recoverable strain ε pp = 0.884 % after 10 test cycles. [ABSTRACT FROM AUTHOR]

This study aimed to modulate the magnetic properties of selective laser melting NiFeMo alloy. This was achieved via the controlled addition of Mo elemental in-situ alloying content to change the tissue morphology and crystal structure of SLM-formed (NiFeMo) 100−x Mo x alloy (x = 0 wt%, 0.25 wt%, 0.5 wt%, 0.75 wt%, 1.0 wt%, 1.25 wt%, 1.5 wt%, 2.0 wt%). The results of scanning electron microscopy (SEM), X-ray diffraction, electron backscatter diffraction (EBSD), DC B-H hysteresis tester, and transmission electron microscopy (Titan-G2) indicate that all samples are predominantly face-centered-cubic (FCC) γ- (Ni, Fe) solid solutions and typical soft-magnetic hysteresis line features. However, the lattice parameter a of γ- (Ni, Fe) decreased and then increased with increasing Mo content. When the added Mo content is 0–1.25 wt%, the Mo particles inside the (NiFeMo) 100−x Mo x alloy become nucleation sites, creating a diffusive metallurgical behavior with the Ni and Fe elements, and preventing the growth of columnar crystals, leading to the reduction of LAGBs density and the enhancement of the { 111 } texture orientation in the easy magnetization direction, increasing B s and the decrease of H c of the NiFeMo alloy. At the Mo content of 1.25 wt%, the soft magnetic properties were optimal, with B s and H c being 0.704 T and 17.31 A/m, respectively. Conversely, when the added Mo content was 1.5–2.0 wt%, the solubility of Mo elements in the γ- (Ni, Fe) solid solution was limited, which resulted in the occurrence of metallurgical defects within the organization such as unfused Mo particles, unfused areas, and porosity. Moreover, when the added Mo content increased to 2.0 wt%, the { 111 } lattice spacing in the easy magnetization direction increased by 0.2261 nm compared to the NiFeMo alloy, and the average lattice distortion Δ ε increased to 0.16%, causing a decrease in the soft magnetic performance of the (NiFeMo) 98 Mo 2 alloy, with B s reducing to 0.6666 T and H c increasing to 23.44 A/m. • The microstructure evolution of NiFeMo alloy formed by in-situ alloy-SLM was analyzed and described in detail. • The crystallographic relationship of NiFeMo alloy with Mo element was analyzed on an atomic scale by HETEM. • Analyzed the changes in soft magnetic properties of NiFeMo alloy with different Mo additions. • Clarified the influencing mechanism of Mo element in-situ alloying on the magnetic properties of NiFeMo alloy. [ABSTRACT FROM AUTHOR]

• ά+ β structure was found and width of ά needles varying from 50 to 100 nm. • The optimal parameters combination is achieved with higher VED. • Graded composition micro/nanostructure was found depending on LBPF parameters. • Low Young's modulus of about 64 GPa was found for denser Ti-15Nb alloy. The novelty of the present work lies in applying an in-situ alloying procedure to obtain a metastable Ti-15Nb (wt.%) alloy through laser powder bed fusion (LPBF). Mixing elemental powders of c.p. Ti and c.p. Nb were subjected to different parameter combinations through LPBF and these conditions led to different results regarding microstructure homogeneity, porosity, and properties as a composite of Ti-15Nb matrix with unmelted Nb powder particles. The phases found in the LPBF samples were ά martensite (hcp) and β-Ti matrix (bcc). The lowest hardness of 262 HV was obtained by microhardness test while the highest was 318 HV. However, porosity and unmelted Nb exhibit notable variations and show a distinct trend based on energy density, scanning speed, and laser power. TEM analysis together with ASTAR mapping showed α' martensite needles of 50 to 100 nm width dispersed through the β-Ti matrix. Processing of elemental powders such as Ti and Nb to form an in-situ alloying of Ti-15Nb alloy through laser powder bed fusion with a low Young's modulus of 64 GPa opens new perspectives for biomedical applications. [ABSTRACT FROM AUTHOR]

Creation of new alloys through in-situ alloying in additive manufacturing is being actively explored to improve the properties and performance of manufactured parts. Multiphysics models are often used to investigate the underlying physics controlling AM processes using high-fidelity simulations of individual powder particle melting within the meltpool. In this paper, we present a novel multiphysics-multiphase model for simulating multicomponent powder beds during the AM process. A convection–diffusion formulation for component mass fraction, in conjunction with the Navier–Stokes equations and enthalpy form of the energy equation, enable us to predict the phase evolution in multicomponent beds and the dispersion of solute metals in the melt pool during the process. A non-equilibrium phase diagram (NEPD) model that incorporates the associated phase diagram is introduced to obtain the mass fraction in both solid and liquid phases as well as local temperature and liquid fraction by efficiently solving a set of nonlinear equations locally at each computational cell. This work introduces a numerical method for multicomponent Al-Zr binary material system for light-weight aluminum alloys, specifically demonstrating its efficacy and accuracy for eutectic solidification of this multicomponent. [ABSTRACT FROM AUTHOR]

• A novel SS316L-Cu successfully developed via laser powder bed fusion process. • Adding Cu to steels offers a new path to curb the spread of bacterial infections. • In-situ alloying presents new opportunities to produce cost-effective biomaterials. Developing antibacterial metal implants is an innovative approach to reducing the risk of implant-related infections. In order to clarify the in-situ effect of copper contents on the microstructure and antibacterial properties of AISI316L stainless steel for advanced applications, Cu-bearing stainless steel was developed by the mean of the laser powder bed fusion process. This work demonstrates that using in-situ alloying with Cu addition can significantly promote antimicrobial activity against Escherichia coli and Staphylococcus aureus without significantly affecting microstructures. This methodology would apply to developing novel metallic materials towards new engineering applications of multi-function. [ABSTRACT FROM AUTHOR]

• A welding strategy exploiting laser beam oscillation and in-situ alloying was proposed to obtain ultra-fine equiaxed grains. • The periodical fluctuation of molten metal induced by the oscillating laser beam facilitated diffusion of Zr elements. • The tensile strength of the welded joints increased by 66 %, from 228 to 379 MPa The formation of weld cracking in high-strength Al-Li alloys has been a longstanding challenge attributed to undesirable coarse columnar grains and inhomogeneous microstructure distribution in the fusion zone of welds. At present, grain refining has been recognized as the most effective approach to inhibit cracking and enhance the mechanical properties of welded joint. Herein, a novel welding strategy exploiting laser beam oscillation and in-situ alloying with Zr was proposed to obtain ultra-fine equiaxed grains in all-weld metal for medium-thick Al-Li alloy. Macro-scale simulation for heat-mass transfer and micro-scale simulation for microstructure evolution were conducted to investigate the formation of ultra-fine equiaxed grains. Firstly, the oscillating laser beam causes the periodical fluctuation of molten metal in the molten pool, which promotes adequate diffusion of Zr elements during welding. Secondly, the homogeneous Zr element scattering in the molten pool has sufficient cooling conditions to precipitate the L1 2 -Al 3 Zr phase in all-weld metal. The cooling rate during solidification is less than the critical temperature calculated by the time-dependent nucleation theory, which creates favorable conditions for forming primary Al 3 Zr. Finally, dense efficient nucleation sites prompt the formation of ultra-fine grains in all-weld metal. Compared with the single laser welding joint, the grain size decreases from 106.7 to 7.7 μm, and the tensile strength increases from 228 to 379 MPa. The microhardness of the fusion zone is equivalent to that of heat affected zone. These findings suggest that further improvements in mechanical properties cannot achieved by improving the process of fusion welding. [ABSTRACT FROM AUTHOR]