Additive Manufactured Alloy Research Articles

A novel high-strength Al-La-Mg-Mn alloy for selective laser melting

• A novel Al-La-Mg-Mn alloy was designed for selective laser melting. • The formation of hierarchical intermetallic was investigated. • The SLM-printed Al-La-Mg-Mn alloy exhibits an excellent tensile strength and appreciable failure strain. • The effect of hierarchical intermetallic on ductility was investigated. Developing high-strength Al-(La, Ce) alloys for additive manufacturing (AM) would entail considerable economic benefits. In this work, a novel near-eutectic Al-La alloy containing 5.50 wt.% Mg and 0.60 wt.% Mn was designed and fabricated via selective laser melting (SLM). Submicron Al 11 La 3 intermetallics with 3D continuous cellular-dendritic and granular morphologies were observed at the interior and boundary of the melt pool, respectively. Interestingly, these intermetallics are hierarchical and contained numerous Al 6 Mn and Mg 2 Si secondary nanoprecipitates. The as-fabricated alloy exhibited a tensile yield strength (YS) of 334 MPa and ultimate tensile strength (UTS) of 588 MPa at room temperature, which is the highest UTS reported for Al-(La, Ce) alloys with an appreciable failure strain of ∼6.4%. The 3D continuous cellular dendritic intermetallic and high Mg content afford significant strengthening and work hardening ability. In addition, the hierarchical feature of the intermetallics generated additional microcracks to coordinate the deformation.

Investigation on the spallation properties and failure mechanism of selective laser melted Ti-6Al-4V alloy with heat treatment under shock load

In this study, the effect of heat treatment on the microstructure of selective laser-melted Ti-6Al-4V alloy and the corresponding spalling performances and damage mechanism at ultra-high-speed (UHS) of 730 m/s are studied. Results show that the acicular martensite in the as-built sample is transformed into large grain basket-weave and Widmanstatten structures with solution treatment at 950 ℃ and 1050 ℃, respectively. The spallation damage mechanism is characterized by the aspects of grain refinement ratio (GRR) and damage porosity (DP). The HT-1050 sample has the highest GRR and DP, while the HT-950 sample has the lowest values, indicating that the HT-950 sample has the highest resistance of spallation. Due to the difference in microstructure morphology and grain size of the three samples, the spalling damage mode of the original sample is characterized by brittle fracture, and then it changes to pore growth and coalescence after heat treatment, larger grains have strong guiding effects on the coalescence of pores. The coalescence of the pores is always accompanied by dynamic recrystallization, thus reducing the local dislocation density and optimizing the development path of cracks. Based on the above work, can provide theoretical support for promoting the application of additive manufacturing alloys in defense industry and aerospace fields.

Creep Analysis and Microstructural Evaluation of a Novel Additively Manufactured Nickel-Base Superalloy (ABD®-900AM)

Abstract Nickel-base superalloys containing 30 to 50% gamma prime (γ') volume fraction are typically used in hot section components (e.g., guide vanes or blades) for power generating gas turbines, and suitable time-dependent properties are required for long-term elevated temperature operation. Additive manufacturing (AM) has recently been used to develop complex hot-section parts utilizing innovative designs with enhanced cooling features which improve efficiencies by reducing cooling air consumption. To further explore the opportunity to improve time-dependent AM superalloys, this paper focuses on a fundamental creep study and characterization of a novel nickel-base superalloy (ABD-900AM) that was manufactured using a laser-based powder bed fusion (LBPBF) AM process. The material was subjected to a subsolvus solution anneal and multistep aging heat treatment (HT) to produce a bi-modal distribution with ∼35% volume fraction of gamma prime without postprocessing hot isostatic pressing (HIP). Microstructural characterization was carried out for the as-built and fully heat-treated structures, and a creep-rupture test program was conducted to study the resultant creep properties. Activation energies and stress exponents in addition to rupture strength and deformation resistance were compared to traditionally cast IN939 and IN738 materials. After testing, specimens were evaluated using a variety of microscopy tools to determine location and features associated with creep damage. The optimized chemistry for ABD-900AM was printed crack free and fully dense in contrast to studies on similar alloys where significant process development and postbuild heat treatments were required. High-temperature mechanical properties in the heat-treated material showed some decrease in creep strength when compared to traditional casting. This strength and rupture life debit was dependent on build orientation, but a considerable increase in creep ductility was observed due to differences in the microstructure when compared with similar AM alloys. Analysis of creep data showed differences in creep mechanisms compared to traditional cast alloys. The relationship between microstructure and creep mechanisms is discussed, and ongoing work to further improve rupture strength through heat-treatment optimization will be highlighted.

The Effect of B4C Powder on Properties of the WAAM 2319 Al Alloy

With ER2319 and B4C powder as feedstocks and additives, respectively, a wire arc additive manufacturing (WAAM) system based on double-pulse melting electrode inert gas shielded welding (DP-MIG) was used to fabricate single-pass multilayer 2319 aluminum alloy. The results showed that, compared with additive manufacturing component without B4C, the addition of which can effectively reduce the grain size (from 43 μm to 25 μm) of the tissue in the deposited layer area and improve its mechanical properties (from 231 MPa to 286 MPa). Meanwhile, the mechanical properties are better in the transverse than in the longitudinal direction. Moreover, the strengthening mechanism of B4C on the mechanical properties of aluminum alloy additive manufacturing mainly includes dispersion strengthening from fine and uniform B4C granular reinforcing phases and fine grain strengthening from the grain refinement of B4C. These findings shed light on the B4C induced grain refinement mechanism and improvement of WAAM 2319 Al alloy.

Effects of cryogenic gas jet cooling on milling surface roughness and tool life for GH4169 alloy additive manufacturing parts

Hybrid additive and subtractive manufacturing is development in metal additive manufacturing techniques, wherein the dry cutting cooling method for subtractive cutting is one of the key technologies. To improve the milling performance of GH4169 alloy (namely Inconel 718 nickel-based superalloy) additive manufacturing parts, a dry cutting cooling method with a cryogenic gas jet and its effects on the cutting performance were investigated in this study. The theoretical model of the cryogenic gas jet flow was established, and the geometric characteristics, motion characteristics, and temperature distribution of the jet flow were analyzed. Meanwhile, considering the design of the nozzle outlet, the jet flow core length with a single nozzle and jet flow field envelope effect on the cooling heat transfer process with multiple nozzles were analyzed using a finite element simulation. Then, milling experiments on GH4169 alloy additive manufacturing parts with different cryogenic gas jet flow parameters were carried out. To reduce tool wear and the machined surface roughness of various parts, the jet flow parameters were optimized using the response surface analysis method. The effects of the milling feed direction on the tool wear and machined surface roughness were investigated. Furthermore, the tool wear morphologies were observed under different continuous milling times. The chemical compositions of the worn zone and tool wear mechanism were analyzed. The results show that cryogenic gas jet cooling can significantly improve the tool life and machined surface roughness of parts for GH4169 alloy additive-manufacturing-part milling, and the continuous cutting time within the tool wear allowance can reach approximately 50 min.

Effects of preheating-ultrasonic synergistic on the microstructure and strength-ductility of 24CrNiMoY alloy steel by laser directed energy deposition

Laser additive manufacturing alloy steel with good strength-ductility has important application prospects in the manufacturing of critical equipment parts. However, the poor matching of strength-ductility caused by high tensile strength and low elongation is a bottleneck problem that restricts the laser directed energy deposition (LDED) technology application. In this paper, based on the previous research on single physical field treatment, a new method to prepare alloy steel samples with better strength-ductility match by using compound physical field treatment (preheating/ultrasonic dual-field) to assist LDED alloy steel is proposed, thus solving the technical bottleneck problem of poor strength-ductility. The results show that the dual-field synergy has a more significant modulating effect on the densities, phase composition ratio, grain size, and strength-ductility matching properties of 24CrNiMoY alloy steel than the single field assistance by LDED. The density of the sample prepared with dual-field assistance was as high as 99.9%, and the phase compositions were ultra-fine crystalline lower bainite, granular bainite and residual austenite, with the average grain size refined from 0.46 μm to 0.26 μm. The ultimate tensile strength, elongation and strength-plastic product at break of the sample prepared by 360 W and 100 °C were (1058 ± 4.2) MPa, (13.8 ± 0.9)% and (14.6 ± 3.7) GPa%, respectively. A remarkable improvement of 12.3% in the strength-plastic product at break was achieved compared with the single ultrasonicated sample. The dual-field synergistic mechanism is the sufficient heterogeneous nucleation and cooling rate, which promoted the transformation of bainite morphology from lath to granular. The combined effect of the two aspects resulted in a satisfactory strength-ductility matching of the prepared alloy steel. This study will provide a promising theoretical and practical reference for the preparation of better strength-ductility matching alloy steel by dual-field-assisted LDED.

On the origin of grain refinement and twin boundaries in as-fabricated austenitic stainless steels produced by laser powder bed fusion

316 L austenitic stainless steel samples have been fabricated by laser powder bed fusion using two powder batches of slightly different compositions but keeping the same processing parameters. Compared to the first powder batch, the second powder batch led to a finer grain structure, a more random texture, and an extremely high density of Σ3 twin boundaries. A review of the literature shows that these two kinds of microstructures had been observed in previous works, but separately and not connected to changes in composition. Several hypotheses are reviewed to explain these microstructure differences. We conclude that local liquid ordering, also described as icosahedral short range order (ISRO) can have an effect on the microstructure formation during solidification. ISRO in the liquid is thought to be stronger in the second powder batch. Finding ways to enhance the influence of the ISRO in the liquid on the microstructure formation can be seen as a promising strategy to design alloys for additive manufacturing.

Development of an additively manufactured metastable beta titanium alloy with a fully equiaxed grain structure and ultrahigh yield strength

Metastable β titanium alloys usually suffer from relatively low yield strengths, which restricts their applications as a structural material. Additive manufacturing (AM), due to its extremely high cooling rates, can generate a refined microstructure that is beneficial to yield strength. However, the intrinsic steep thermal gradients within melt pools often lead to development of columnar grains that can result in mechanical anisotropy. To address these issues, we propose to use potent β-stabilizing elements with large growth restriction factors as the main solute elements in Ti, specifically Fe and Co. d-electron theory is also used to design the detailed compositions of the new titanium alloys for AM. A novel metastable titanium alloy, Ti-xFe-xCo-1Mo (1.5< x <3.5 at%), is thus developed by laser powder bed fusion (L-PBF). With process optimization, the L-PBF-processed alloy was found to contain fully equiaxed β grains embedded with α laths and ω precipitates and the grain boundaries decorated by Ti 2 Co precipitates. The matrix consists of a certain number of micro-sized β flecks and a high density of Fe and Mo atomic clusters. Upon solution treatment (ST), the microstructure turned into equiaxed β grains embedded with ultrafine ω precipitates and Mo atomic clusters. While the L-PBF-processed alloy shows poor tensile properties probably due to the presence of isothermal ω precipitates, the L-PBF-ST-processed alloy demonstrates an unprecedented yield strength of 1.2 GPa and a decent elongation of 10~12%. The alloy deformed by dislocation slipping and failed in a ductile fracture mode.

Influence of microstructural heterogeneities on small-scale mechanical properties of an additively manufactured Al-Ce-Ni-Mn alloy

• Revealed the influence of local microstructural heterogeneity at melt-pool-boundaries in additively manufactured Al-rare earth alloy on nanomechanical properties • In situ nanoindentation and micropillar compression identified melt pool boundaries as weak spots • Identified the reasoning for creep void coalescence and failure initiation from melt pool boundaries Laser powder bed fusion-based additive manufacturing (AM) is a promising method to fabricate creep-resistant Al-rare earth alloys (Al-Ce-Ni-Mn) with stable microstructures at up to 400°C. However, creep testing of these alloys at high temperatures shows that void coalescence and failure initiation occurs along the melt pool boundaries in the microstructure. Hence it is crucial to understand how the local mechanical behavior of the melt pool boundaries would influence the global properties of the AM produced alloy. In this study, in situ nanoindentation conducted at room temperature and 300°C revealed a reduced hardness at the melt pool boundaries. Similarly, micro-pillar compression showed a slight decline in yield strength at these boundaries, indicating that they are the weak spots in the microstructure. Such multimodal local mechanical property studies are necessary for understanding the influence of melt pool boundaries on the bulk response of fusion-based AM alloys.

Towards an alloy design strategy by tuning liquid local ordering: What solidification of an Al-alloy designed for laser powder bed fusion teaches us

High-strength aluminium alloys from the 2XXX, 6XXX, and 7XXX series suffer from severe hot cracking issues during 3D printing. Thus, there is a need to design new alloys with an improved hot cracking resistance while taking advantage of the non-equilibrium processing conditions of laser powder bed fusion to achieve optimized properties. Here, we report the successful fabrication of a new Al-Mn-Ni-Cu-Zr alloy designed for L-PBF. The as-built microstructure was characterized at different scales using synchrotron X-ray nano-tomography and microscopy with a special focus on automated crystallographic orientation mapping (ACOM) in transmission electron microscopy. Based on this multiscale microstructural investigation, we identify various mechanisms involving the presence of a locally ordered liquid during solidification under conditions typical of additive manufacturing. This local liquid ordering is often defined as Icosahedral Short Range Order (ISRO). The multiple consequences of ISRO in the liquid on the hierarchical microstructure inherited from additive manufacturing are discussed. ISRO enables refinement of the grain size thus improving the processability via an increase of the hot cracking resistance, producing equiaxed grains and twinned dendrites contributing to randomizing the crystallographic texture, and possibly extending supersaturated solid solutions through a cage effect. It is concluded that promoting ISRO should be considered a promising pathway to design alloys for additive manufacturing with good processability and optimized properties.

Methods of Additive Manufacturing for Dental Co-Cr Alloys: Systematic Review

Additive manufacturing is a popular method of producing items directly from digital models through a layer-by-layer material build-up process. To evaluate the Current State of Knowledge on Dental Co-Cr Alloy Additive Manufacturing Techniques. Innovative additive printing technologies have made it possible to produce intricate dental components customized for each patient. This study investigated the manufacturing method (build orientation and process parameters), post-processing techniques, and metallic powders utilized in dental applications (stress relieving, surface finishing). The databases PubMed, Science Direct, Mendeley, and Google Scholar were used to carry out an electronic search. A manual search of pertinent article citations was also carried out; inclination angle, stress relieving, heat treatment, cobalt-chromium, selective laser melting, selective laser sintering, and powder bed fusion, dentistry were some of the keywords utilized. Although this publication tries to contain the most recent study from the previous eleven years (2010–2021), and to explain the materials powders and metal used in dental applications. A cutting-edge technique called additive manufacturing uses a layer-by-layer approach to material build-up to produce things directly from digital models. It is missing a tool, a manufacturing process that produces fully thick metallic components quickly and with good precision. Qualities of additive aspects of production such component design flexibility, part complexity, light- weighting, component consolidation, and functional design are generating specific interest in the additive fabrication of metal for use in automotive, marine, oil &amp; gas, and aerospace industries during powder bed fusion, each layer of the powder bed is only partially fused employing a laser or electron beam as an energy source, the recent and most promising additive manufacturing technologies utilized to produce intricate, low-volume, tiny metallic parts. By using computer-aided design (CAD) technology, recent developments in digital dentistry have changed dental offices and dental laboratories, by utilizing 3D printing because precise metal framework fitting and technique faster.

Towards 3-D texture control in a β titanium alloy via laser powder bed fusion and its implications on mechanical properties

Fusion-based additive manufacturing (AM) offers a new opportunity to design metallic materials with complex, direction-dependent mechanical properties by controlling the orientation distribution of the constituent grains—also known as texture. Texture control may be achieved site-specifically by varying the processing variables and tailoring the local melt pool geometry and solidification kinetics. However, the type and direction of textures currently achievable in AM alloys are limited by the melt pool geometry itself. In this work, we advance the capabilities of controlling crystallographic texture in laser powder bed fusion (LPBF) by producing specimens of β titanium-niobium alloy with textures aligned along three different directions: the laser scan direction (SD), the build direction (BD), and—for the first time—the direction perpendicular to both BD and SD (i.e., PD). We achieve this three-dimensional (3-D) texture control by fine tuning the keyhole melt pool geometry and amount of overlap throughout the build. We test the tensile properties of the three different specimens along their respective texture axes and elucidate the relationships between crystallographic orientation, mesostructure, and mechanical behavior. We find that the novel PD texture exhibits the best combination of strength, strain hardenability, and ductility. We ascribe these results to the unique mesostructure of this specimen. This work opens new opportunities for designing novel materials with directional properties by achieving three-dimensional (3-D) texture control during fusion-based AM.

Copper alloys for additive manufacturing: Laser powder bed fusion of CuCr1Zr by using a green qcw-laser

Copper alloys for additive manufacturing: Laser powder bed fusion of CuCr1Zr by using a green qcw-laser

Acoustics for in-process melt pool monitoring during metal additive manufacturing

Intrinsic to most metal additive manufacturing (AM) processes are melt pools generated from directed energy sources like lasers. Melt pools are critical as they function to join powder layers to previous layers during the process. Their criticality extends deeper as most porosity in AM parts stems from melt pool behavior while melt pool solidification dictates the parts’ microstructure. Significant breakthroughs in metal AM are severely hindered by the lack of access to experimental tools to study melt pools and modeling that do not fully capture the complex physics. Thus, melt pool related defects are often difficult to predict in occurrence and location while determining optimal process parameters to eliminate defects is extremely challenging and costly. Furthermore, the many exciting opportunities such as realizing new AM alloys, developing gradient materials/structure, and tailoring microstructure to intended applications are possible only with further understanding of melt pool behavior. With these clear needs, in-process acoustics have been proposed as plausible experimental tools for studying melt pool behavior. This presentation will provide an overview of the current activity in this area in addition to the specific needs the acoustics community can potentially address.

Development and magnetocaloric properties of Ni(Co)-Mn-Sn printing ink

Magnetocaloric (MC) cooling is a vast research field nowadays which needs continuing development of MC materials. Besides, technological approaches of the fabrication and design of MC materials to be applied as the heat exchangers require a reinforcement. Heusler-type metamagnetic shape memory alloys (MetaMSMAs) exhibiting a large MC effect near room temperature, owing to the magnetic field induced first-order transformation, have been shown to be promising candidates for magnetic refrigeration, and the possibility of their fabrication by 3D printing technologies was experimentally demonstrated in the literature. In the present work we have elaborated a route for the room-temperature fabrication of MC ink incorporating the polymer binder and Ni(Co)-Mn-Sn MetaMSMA powder obtained from the preliminary melt-spun ribbon with tuned MC properties. The ink is used to print 2D films which do not require a subsequent heat treatment. The field-induced adiabatic temperature measurements reveal that the screen-printed samples displayed the same inverse MC effect as the ribbon, evidencing that room-temperature ink printing technology of MC intermetallics, elaborated for the first time in the present work, is promising for 2D printing of cooling microdevices for MEMS, flexible electronics etc. • A magnetocaloric powder based on metamagnetic shape memory alloys for additive manufacturing has been successfully obtained. • A magnetocaloric ink was developed using a sustainable approach, avoiding any hazardous product during its preparation. • Magnetocaloric materials printed by screen-printing technique show performance similar to that observed in the bulk ribbon.

Microstructure prediction of eutectic high entropy alloy using physical and computer simulation for additive manufacturing condition

The additive manufacturing (AM) of eutectic high-entropy alloys (EHEAs) with seven components was simulated. The as-cast alloy comprised of primary dendritic phase and eutectic region between the FCC and Laves phase. The additive thermal cycle generated by the analytical model was used for phase-field and physical simulations. A thermomechanical simulator was used to perform the physical simulation. Scanning electron microscopy (SEM) was used to characterize the effect of AM on the thermal cycle of the test samples and the results showed that the sigma phase was formed in the primary dendritic phase. The formation of the sigma phase was correlated with thermodynamic predictions and heat treatment studies. The thermal cycle of the microstructure, which was predicted using the phase-field simulation, was correlated with the experimental results. The integrated approach that was adopted in the current study can be utilized for the accelerated exploration of alloys for additive manufacturing.

Influence of Stress Relief Annealing Parameters on Mechanical Properties and Decomposition of Eutectic Si Network of L-PBF Additive Manufactured Alloy AlSi10Mg

This paper evaluates the effect of stress-relieving heat treatment on the AlSi10Mg alloy prepared by additive manufacturing using the Laser Powder Bed Fusion (L-PBF) with print parameters: 370 W, 1400 m/s, and 50 μm. The as-built state and four different annealing modes (240 °C/2 h, 240 °C/6 h, 300 °C/2 h, and 300 °C/2 h/water-quenched) are investigated. To determine the effect of the annealing mode on the mechanical properties of the L-PBF AlSi10Mg alloy, heat-treated samples were compared with the as-built state and with each other. The mechanical properties of the samples were determined by tensile and hardness tests. The strength in the as-built state is 488 MPa, depending on the method of heat treatment, the strength values range from 296 MPa to 417 MPa, and the HV10 hardness values are in accordance with the measured strength values. Furthermore, the microstructure of the samples was investigated by scanning electron microscopy (SEM) analysis, which was then linked to the measured mechanical properties. The composition of the microstructure of the alloy and its influence on the mechanical properties were determined by energy dispersive spectroscopy (EDS) analysis. Furthermore, the differences between the individual heat treatments in comparison with the as-built state were analyzed and the phenomenon of decomposition of the silicon network after reaching specific temperatures was discussed and confirmed. The paper evaluates the effect of dwelling time on stress relief annealing. It was found that if annealing at intermediate temperatures of 240 and 300 °C is applied, changes in structure and mechanical properties are more temperature- than dwell-time-dependent.

Mechanical spectroscopy study of as-cast and additive manufactured AlSi10Mg

The AlSi10Mg alloy produced by casting (AC) and additive manufacturing (AM) technology of laser powder bed fusion (L-PBF) has been investigated through mechanical spectroscopy (MS). In addition to the grain boundary peak PGB the Q−1 curves of both materials exhibit two other relaxation peaks, P1 (H = 0.8 ± 0.05 eV; τ0 = 10−11±1 s) and P2 (H = 1.0 ± 0.05 eV; τ0 = 10−13±1 s), depending on the interaction of dislocations with solute elements (Si and Mg). Relaxation strengths of P1, P2 and PGB of AM alloy are greater than those of the AC one owing to the finer structure of Al cells and the higher amount of Si and Mg in supersaturated solid solution induced by the rapid solidification typical of the L-PBF process. After successive MS test runs relaxation strengths of P1 and P2 peaks in both the examined materials decrease due to the precipitation of Si atoms and dislocation density recovery. Such decrease is more pronounced in AM alloy where change of cell shape and increase of cell size is observed. Dynamic modulus of AM alloy exhibits an anomalous trend in the first test run that is no more present in successive runs. The irreversible process giving rise to such anomalous behavior is the closure of pores of nanometric size.

Mechanical analysis characteristics of bionic structure based on NiTi alloy additive manufacturing

In recent years, the demand for protective structures in aerospace, transportation and other fields has become increasingly intense. In this paper, multi-rotation structure(MRS) and single rotation structure (SRS) are designed based on the microstructure of grass stem cross-section. Selective laser melting (SLM) is used to fabricate the structural model. The mechanical properties of two structures are investigated by numerical simulations and experiments. Results show that the specific absorption energy (SEA) of MRS is 33% higher than SRS. In addition, MRS is tested with cyclic compression and shape recovery experiments, which show the deformation recovery rate of MRS is 96%. Based on the superiority of MRS in mechanical and recovery performance, this paper also analyzes the influence of cell thickness t and cell angleθ on the performance. It is found that the sample with t = 0.45 mm, θ = 60° has the best comprehensive performance. Compared to SRS and initial design structure of MRS, its SEA is improved by 129% and 72.2%, and mean crushing force (MCF) is increased by 330% and 74%. This provides a theoretical basis for the development of new bionic protective structures.

4D Investigation of new Aluminum Alloy for Additive Manufacturing

4D Investigation of new Aluminum Alloy for Additive Manufacturing