With increasing life expectancy and an aging global population, the demand for orthopedic and dental implants is increasing. Recently developed, citric-acid-based anodization processes facilitate the production of more bioactive oxide layers by incorporating important bone minerals such as Ca, P, and Mg and forming bone-like crystalline compounds such as carbonated apatite on titanium implant materials. The primary goal of the present study was to evaluate the applicability of these anodization processes to solid and 3D-printed titanium alloy substrates. The anodized oxides produced on each solid or 3D-printed lattice substrate revealed multi-scaled surface roughness profiles as evidenced by scanning electron microscopy, optical microscopy, and surface roughness analyses. Additionally, each oxide group was shown to incorporate substantial amounts of Ca, P, and Mg bone-mineral dopants and form AB-type carbonated apatite, as shown using a combination of energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and attenuated total reflectance-Fourier transform infrared spectroscopy analyses. Finally, each oxide group showed sustained Ca, P, and Mg ion release during an inductively coupled plasma spectroscopy dissolution assessment, and demonstrated early apatite-forming ability during simulated body fluid bioactivity testing. The findings of this study show much promise for the applicability of these novel oxide coatings to a wide variety of future titanium implant applications.

This study utilizes linear elastic fracture mechanics to assess the fatigue criticality of volumetric defects in notched specimens with varying geometries. Contrasting to the existing literature, this study assesses the fatigue criticality of defects, prior to fracture, via a non-destructive inspection technique, that is, X-ray computed tomography (XCT). Treating volumetric defects as cracks, based on Murakami's definition, the approach calculates their Mode-I stress intensity factor (SIF) with their local stresses obtained via linear elastic finite element analysis and utilizes the SIF to represent their criticality. For validation, cylindrical and flat specimens with notch root radii of 5 and 50 mm of AlSi10Mg and 17-4 precipitation hardened stainless steel were fabricated, XCT scanned, and tested under fatigue loading. All crack initiating defects, observed from fractography, fell within the 99.3 percentile of the defects with the highest stress intensity factor in the respective specimens.

This study investigated the synergistic effects of volumetric defects and notch geometry on the fatigue behavior of laser powder bed fused AlSi10Mg and 17-4 precipitation hardening (PH) stainless steel (SS) cylindrical notched specimens. Among the considered notch root radii, rho, of 0.1, 5, and 50 mm, 0.1 mm showed the shortest fatigue lives. All fatigue cracks initiated from the notch root for rho 0.1 mm and from volumetric defects or turning grooves for rho 5 mm and 50 mm specimens. The mode-I stress intensity factor, taking into account the synergistic influence of notch geometry, defects' size, and location, was found to correlate well with experimental fatigue lives of AlSi10Mg and 17-4 PH SS notched specimens.

This study investigated the fatigue behavior of additively manufactured flat, edge-notched AlSi10Mg and 17-4 precipitation hardening (PH) stainless steel (SS) specimens. The novelty lies in the identification of notch, defect, and microstructural features influencing the fatigue behavior of edge-notched specimens, and assessments of their fatigue criticality. Specimens with varying notch root radii, ligament widths, and defect contents were subjected to uniaxial cyclic loading. For AlSi10Mg, notch geometry and volumetric defect features such as size and location (within the rectangular cross-section and at different heights relative to the notch root plane) influenced the fatigue behavior. On the other hand, for 17-4 PH SS, there was an additional influence of the microstructural features on the fatigue behavior. In near defect-free 17-4 PH SS specimens, delta ferrite (delta-Fe) phase acted as weak points in the microstructure, promoting crack initiation and short crack growth along delta-Femartensite interfaces to form crystallographic facets, leading to fatigue failures. Larger ligament width resulted in shorter fatigue lives for specimens with notch root radii of 0.1 mm and 5 mm. Compared to the ligament width of 5 mm, 10 mm induced higher plastic damage at the notch root, thus promoting early crack initiation and failures. For notched specimens with negligible plasticity at the notch root, the mode-I stress intensity factor exhibited a correlation with the experimental fatigue lives. On the other hand, for specimens experiencing significant plasticity at the notch root, the equivalent plastic strain showed a correlation with the experimental fatigue lives.

Tantalum (Ta) is a refractory metal with excellent corrosion resistance and biocompatability, high melting temperature and density, and good electrical and thermal conductivity, with applications in capacitors, medical implants and devices, linings in the chemical industry, penetrator projectiles, and nuclear reactors. In this work, we examined the mechanical isotropy and corrosion behavior of tantalum produced through laser beam powder bed fusion (PBF-LB). Electron backscatter diffraction (EBSD), tensile tests, nanoindentation, and environmental and galvanic corrosion tests were utilized to establish structure-property relationships as a function of orientation, temperature, and pH. EBSD showed the horizontal and vertical orientations had different grain size distributions and weak texture. From tensile testing, PBF-LB Ta exhibited comparable strain-at-failure relative to wrought Ta, with significantly higher yield and ultimate strengths relative to ASTM B708. Room-temperature nanoindentation confirmed weak mechanical anisotropy via complementary EBSD images and showed small variations in reduced modulus and hardness after annealing to 800 °C due to oxide formation. The environmental corrosion tests in HCl (acid), NaCl (neutral), and KOH (basic) suggested the corrosion current density for PBF-LB Ta was lower than wrought, signifying slower corrosion for PBF-LB Ta. The passive nature of PBF-LB and wrought Ta was observed during galvanic corrosion; when coupled with titanium, aluminum, or stainless steel, most systems did not show corrosion after 24 hr. In all, the results showed that PBF-LB Ta has comparable or, in some cases, superior mechanical and corrosion properties to wrought Ta.

Ti-5V-5Mo-5Al-3Cr (Ti-5553) is a near-beta titanium alloy commonly used in aerospace applications. It is currently being explored for additive manufacturing (AM), but the fatigue behavior of this AM alloy needs to be well-understood for adoption. This paper explores the tensile and high-cycle fatigue behavior of laser powder bed (LPBF) manufactured Ti-5553 that has been post-print heat treated with a beta anneal and age (BAA), with a focus on the microstructural evolution and effects of surface roughness and print defects. Fatigue lives of as-LPBF and BAA material are nearly identical and both are far below fatigue lives of conventionally manufactured Ti5553. As-built samples contain columnar (3 grains with a [001] texture in the build direction with a negligible fraction of alpha phase confirmed by electron backscatter diffraction (EBSD). The BAA material contains HCP alphaphase precipitates: grain boundary alpha, primary alpha, and secondary Widmanstatten alpha. Fatigue samples were printed in the vertical direction and tested with an as-printed and machined surface. Both the as-LPBF and BAA samples exhibit similar fatigue strengths despite their vastly different microstructures. Machined surfaces led to an increase in tensile strength, ductility, and fatigue strength. This work emphasizes the importance of heat treatment and minimization of flaws inherent to AM processing of near-beta Ti-5553.

Additive manufacturing (AM) maintains a wide process window that enables complex designs otherwise unattainable via conventional production technologies. However, the lack of confidence in qualifying AM parts that leverage AM process–structure–property–performance (PSPP) relationships stymies design optimization and adoption of AM. While continuing efforts to map fundamental PSPP relationships that cover the potential design space, we first need pragmatic and then long-term solutions that overcome challenges associated with qualifying AM-designed parts. Two pragmatic solutions include: (1) AM material specifications to substantiate process reproducibility, and (2) component risk categorization to associate system risk relative to part performance and required part quality. A novel qualification paradigm under development involves efficient prediction of part performance over wide-ranging PSPP relationships through targeted testing and computational simulation. This paper describes projects at Sandia National Laboratories on PSPP relationship discovery, these pragmatic approaches, and the novel qualification approach.

Many industries are embracing additive manufacturing (AM) approaches for development and production of end-use parts. In comparing to traditional manufacturing processes, the surface finishing of AM is increasingly recognized as a critical production concern. Each AM process demands distinct postprocessing operations and can consequently influence the viability of a specific technology for commercial use. This chapter outlines the various motives for postbuild surface treatments, ranging from design specifications and their influence on mechanical and corrosion resistance properties to removing build support structures, enhancing surface characteristics, geometrical accuracy, or aesthetics of AM-built parts. Different postbuild surface finishing is discussed, highlighting the basic attributes, advantages and disadvantages of their processing steps on AM parts. The challenges associated with addressing special requirements presented by complex part geometries and internal surfaces are also discussed. The impact of a component's mechanical and corrosion properties upon surface finishing is addressed. Finally, the influence of these processes on component characteristics, like near-surface defects and microstructure, and possible residual stress are examined.

Density-functional theory (DFT) is used to identify phase-equilibria in multi-principal-element and high-entropy alloys (MPEAs/HEAs), including duplex-phase and eutectic microstructures. A combination of composition-dependent formation energy and electronic-structure-based ordering parameters were used to identify a transition from FCC to BCC favoring mixtures, and these predictions experimentally validated in the Al-Co-Cr-Cu-Fe-Ni system. A sharp crossover in lattice structure and dual-phase stability as a function of composition were predicted via DFT and validated experimentally. The impact of solidification kinetics and thermodynamic stability was explored experimentally using a range of techniques, from slow (castings) to rapid (laser remelting), which showed a decoupling of phase fraction from thermal history, i.e., phase fraction was found to be solidification rate-independent, enabling tuning of a multi-modal cell and grain size ranging from nanoscale through macroscale. Strength and ductility tradeoffs for select processing parameters were investigated via uniaxial tension and small-punch testing on specimens manufactured via powder-based additive manufacturing (directed-energy deposition). This work establishes a pathway for design and optimization of next-generation multiphase superalloys via tailoring of structural and chemical ordering in concentrated solid solutions.

Pulsed laser assisted additive manufacturing has been demonstrated as a promising technology for controlling grain structure in 3D-printing processes. The integration of a nanosecond laser onto a wire arc additive manufacturing tool has enabled the localized printing of Inconel 718 with grain sizes meeting ASTM 9 standards (average measured grain size of 13.7μm) for wrought material within a single bead under solidification conditions that would otherwise produce 340μm columnar grains. The observed grain refinement holds promise, provided scale up is possible, for overcoming the highly anisotropic mechanical properties and microcracking associated with large columnar grains of Inconel 718 that have long stood in the way of leveraging the advantages of direct energy deposition printing techniques of difficult to machine alloys. Experiments on large bead sizes allowed for decoupling surface versus bulk nanosecond laser/liquid metal interaction mechanisms to determine that the source of the observed grain refinement is the collapse of cavitation bubbles originating from acoustic waves generated by momentum transfer into the melt of an ablation plasma. Additionally, experiments that increased the cavitation bubble density within the mushy zone during solidification by tuning the nanosecond laser scan path went beyond the 25 times reduction in grain size to a 70 times factor of refinement with a minimum average grain diameter approaching 4μm.

High entropy alloys are a promising group of materials with seemingly limitless and unexplored composition spaces, capable of producing extraordinary physical/mechanical properties that exceed those of conventional materials. Utilizing an additive manufacturing enabled high throughput materials discovery framework, Ta and Nb graded additions to CoCrFeMnNi are explored. Compact metallurgical Ta,Nbx(CoCrFeMnNi)1-x specimens spanning x = 0 – 100 at.% were fabricated by powder based directed energy deposition. Microstructure evolution as a function of specific Ta,Nbx(CoCrFeMnNi)1-x compositions is investigated through a combination of XRD/XRF and SEM-EDS/EBSD. Microhardness measurements were also performed to rapidly establish baseline structure–property relationships. Results revealed that eutectic microstructures were largely suppressed throughout the explored composition ranges resulting in limited ductility and extraordinary hardness.

Lattice structure metamaterials offer a variety of unique and tailorable properties, yet industrial adoption is slowed by manufacturability and inspection-related difficulties. Despite recent advances in laser powder bed fusion additive manufacturing, the sub-millimeter features of lattices are at the edge of process capabilities and suffer from low geometric quality. To better understand their complex process-structure-property (PSP) relationships, octahedron structures were manufactured across a power spectrum, inspected, and mechanically tested. X-ray computed tomography was used to characterize lattice geometry, and demonstrated that lattice strut geometry measures, increased significantly as a function of laser power. Furthermore, lattices are shown to exhibit a direct correlation between laser power and mechanical performance metrics. Performance variations up to 60% are shown as a function of process parameters despite nominally identical geometry. Significant geometry variations are found to be the cause of performance variation, while material properties as measured by microindentation hardness are constant across the studied parameter range. PSP relationships are modeled, and the limitations of these models are explored. It was found that resulting models can predict mechanical performance based on geometric characteristics with R-2 values of up to 0.86. Finally, mechanistic causes of observed performance changes are discussed.

Additive manufacturing provides new opportunities to manipulate local microstructure to enable strengthening pathways for austenitic stainless steels. Laser beam powder bed fusion techniques, however, are limited by their narrow process window, as compared to other additive manufacturing techniques. In this work, the use of layerwise remelting is explored to expand the available process window in laser powder bed fusion to manipulate the microstructure and increase strength while minimizing porosity. Several single melt process conditions are considered for 316L stainless steel along with additional low energy and high energy remelts to evaluate the effect on grain morphology, texture, porosity, and hardness. Results demonstrate remelting as an effective approach to tune grain size and texture to achieve high hardness while reducing the overall porosity. While the data suggest that the optimal single melt process set results in the lowest porosity, remelting provides a pathway to reduce porosity for non-optimal process parameters, minimize grain growth, and increase strength.

Commercial electrical steels, Fe-Si alloys with < 4 wt.% Si, are inexpensive and efficient materials for electrical power conversion. Further efficiency improvements require increasing the silicon concentration to 6 wt.%, at which point the material becomes brittle and difficult to form by conventional rolling and sheet fabrication methods. Additive manufacturing stands to overcome challenges with commercial manufacturing techniques by leveraging near-net-shape fabrication. The wide array of process conditions provides additive manufacturing with increased flexibility, enabling control over the microstructure and mechanical properties. This work explores the microstructures and magnetic properties of ring-shaped Fe-Si alloys produced using concentric and cross-hatch tool paths on a laser-directed energy deposition additive manufacturing system. Concentric-built samples exhibit elongated grain structures while cross-hatch-built samples comprise lower aspect ratio grain structures. Thermal finite element analysis simulations model the stress conditions produced by the different scan path geometries. Microhardness measurements probe the mechanical properties as a function of anneal temperature, providing a qualitative understanding of the intergranular defect density. Soft magnetic properties measured under quasistatic and AC conditions show frequency- and microstructure-dependent coercivity and permeability. Finally, analysis of the core loss quantifies how the build strategies and thermal treatments influence efficiency in electrical power conversion applications. Understanding the influences of scan path geometry and thermal treatment provides a pathway towards application of additively manufactured soft magnetic materials.

The temperature-dependent hardness of additively-manufactured near-eutectic Ni–Nb was investigated. This alloy was found to have solidified into a two-phase nanoscale microstructure with peak hardness of H ≅ 14–17 GPa at temperatures up to 400 °C, above which irreversible softening was observed despite retention of significant strength compared to traditionally-synthesized Ni-based superalloys. Experiments and molecular-dynamics simulations show that deformation for single-phase nanocrystalline volumes was confined to intragranular slip-band formation in δ -Ni 3 Nb and to intergranular grain-boundary sliding in μ -Ni 6 Nb 7 . However, microscopy in the nanostructured two-phase regions after severe plastic deformation indicated that phase boundaries acted as nucleation sites for dislocations, promoting twinning-induced plasticity (TWIP) in the μ -Ni 6 Nb 7 grains. This work highlights (1) that additive manufacturing techniques enable formation of unique microstructures that exhibit superior mechanical properties, and (2) that multi-phase intermetallic compounds provide a route to mitigate brittle fracture though the promotion of twinning-induced plasticity. High strength and the absence of interface decohesion (cracking) suggests that multi-phase intermetallic systems may be a viable route for design of new printable superalloys. These results suggest that additive manufacturing methods and rapid solidification via non-equilibrium pathways may enable a pathway for achieving high combined strength and ductility.

Laser powder bed fusion (L-PBF), also known as selective laser sintering or direct laser melting, is an additive manufacturing process in which part geometries are formed simultaneously with the underlying material. The microstructure, defect content, and surface quality are all synthesized conjointly with the part shape. While the geometric design freedom allowed by this process enables new complex features and parts with small (similar to 1 mm) features, challenges associated with process qualification can deter wider adoption. Furthermore, a lack of historical performance data for statistical process control of witness coupons, for either bulk material or for small features, makes the barrier to entry more difficult. Here, we demonstrate long-term, property-based process monitoring and variability assessment using both small-featured (1 mm) and larger, bulk-representative material witness coupons. Over a one-year period, more than 550 tensile bars and 80 Charpy impact bars were printed alongside 316 L stainless steel parts built using L-PBF and tested to detect shifts in the process over time. Miniature tensile bars with a 1 mm(2 )gage area were tested using a high throughput mechanical testing system. In parallel, a larger test coupon was used to monitor density, hardness, and Charpy impact toughness. This collection of measurements was used to determine detectable property shifts correlated to L-PBF process changes including powder feedstock, machine hardware, software versioning, and machine parameter settings. The benefits of using small featured, high-throughput samples are discussed based on process sensitivity and the number of repeat tests possible for each build. This study not only reveals the utility of property-based process monitoring but illustrates the sensitivity of these measurements to detect process changes and provides further evidence for property stability in modern L-PBF.