This study aimed to optimize ball milling conditions for preparing recycled zirconia powder (RZP) for esthetic dental restorations. Initial RZP and four ball milling groups, including 3-WM (3 mm beads, wet milling), 3-DM (3 mm beads, dry milling), 5-WM (5 mm beads, wet milling), and 5-DM (5 mm beads, dry milling), were characterized. The sintered samples were compared with commercial zirconia in terms of the microstructure, transmittance, translucency parameter (TP00), color difference (Delta E-00), density, hardness, fracture toughness, and biaxial flexural strength. Smaller beads enabled more effective RZP refinement. Wet milling proved superior to dry milling in achieving finer particles and reducing crystal defects. Recycled zirconia sintered from 3-WM powders, particularly after 3 h of milling, exhibited microstructure, optical, and mechanical properties comparable to commercial zirconia (Delta TP00 and Delta E-00 below perceptibility threshold; strength >800 MPa). Initial RZP and 3-DM samples showed microstructural flaws, leading to poorer mechanical and esthetic outcomes.

Metal material extrusion, which is based on debinding and subsequent sintering of 3D-printed green bodies, is gaining attention as a low-cost additive manufacturing process. In this study, we comprehensively examined the densification behavior, microstructure, and tensile properties of 17-4PH stainless steel prepared using bound metal deposition (BMD). The specimens were fabricated in the standard and dense modes, with the latter programmed to apply a higher extrusion pressure. The dense mode resulted in a relative density of approximately 98%, surpassing the 95% achieved in the standard mode. We investigated the impact of the build angle (0° or 90°) relative to the build direction (BD) and various printing parameters, including the specimen thickness, hatch spacing, print speed, and nozzle temperature, on the relative density and tensile properties. The results highlight the crucial role of the build angle in determining the tensile properties, leading to mechanical anisotropy. X-ray computed tomography captured linear printing defects aligned perpendicular to the BD, which contributed to premature fractures during tensile loading along the BD. The as-sintered microstructures contained α- and δ-ferrite with spherical nanoscale copper precipitates. The solution-treated and subsequently aged H900 specimens exhibited strength levels comparable to or superior to those of their wrought counterparts. These findings provide fundamental insights into the production of industrial parts using BMD.

In this study, through electron-beam powder bed fusion additive manufacturing, we prepared Co–27Cr–6Mo (wt.%) alloys with different C concentrations up to the eutectic composition (~2.5 wt.%). The Rockwell hardness of the as-built alloy specimens increased linearly with an increase in the carbon concentration, reaching approximately 60 HRC at 2.5 wt.% C. The as-built 2.5C alloy contained a fine carbide network consisting of M7C3- and M23C6-type carbide phases. Increasing the carbon concentration not only increased the carbide fraction and changed the carbide phases but also altered the solidification behavior from cellular at low carbon concentrations to dendritic and finally to eutectic. Quantitative X-ray tomography revealed that carbon addition also affected the gas pore behavior in the melt pool, significantly reducing the porosity when a flat solid/liquid front existed upon solidification (i.e., planar and eutectic). The developed high-carbon alloys cannot be obtained through conventional metal processing; hence, this study opens new avenues for industrial applications of additive manufacturing.

Non-equiatomic high-entropy alloys (HEAs) that exhibit transformation-induced plasticity show great potential as a novel class of structural materials. To further strengthen such alloys, this study explores the synergetic effect of nitrogen doping and thermomechanical processing on Co20Cr20Fe34Mn20Ni6 alloy. The recrystallized specimens of original N-free and N-doped (0.3 at %) compositions represent single-phase face-centered cubic (FCC) microstructures. The alloys are processed by hot-caliber rolling at 800 and 1000 degrees C. Adding nitrogen not only enhances solid solution strengthening but also leads to significant strengthening upon hot-caliber rolling. Quantitative analysis of dislocation density via time-of-flight neutron diffraction measurements reveals a monotonic increase in dislocation density with rolling reduction, which governs the alloy strength of the hot-caliber-rolled alloys. Notably, adding trace nitrogen significantly increases the dislocation density to 1.6 x 10(15) m(-2) at 800 degrees C, attributed to interactions between dislocations and interstitial nitrogen atoms. While a higher rolling temperature decreases the dislocation density as slight grain refinement via dynamic recrystallization occurs, additional strengthening due to planar defects is activated. The addition of nitrogen suppressed early yielding, which, in the N-free alloys, occurs at lower stress levels than those predicted based on the measured dislocation density. Consequently, the hot-caliber-rolled N-doped alloys obtained at both rolling temperatures represent an excellent combination of high yield stress (similar to 1 GPa), four times greater than the original alloy, with similar to 40 % elongation-to-failure. This study provides insights into the processing and strengthening of HEAs at intersections, during alloy designs.

Co–Cr–W–Ni–Mn–B alloys, potentially applicable for implant materials, with boron contents of 0, 0.01, and 0.05 wt

In this study, we investigate the influence of dislocation strengthening in the metastable parent phase on the deformation-induced martensitic transformation behavior of a face-centered cubic (fcc) Co20Cr20Fe34Mn20Ni6 high-entropy alloy. Annealed and hot-swaged specimens were prepared. In-situ neutron diffraction experiments captured an accelerated transformation kinetics in the hot-swaged specimen due to accumulated dislocations. The phase-specific macrostress development showed that the hexagonal close-packed epsilon-martensite predominantly accommodated the macroscopic plastic deformation of the annealed counterpart. Conversely, the matrix dislocation strengthening promoted cooperative plasticity of the gamma-matrix and the epsilon-martensitic phase, thus enhancing yield stress while preserving ductility.

Titanium and its alloys are highly desirable materials for biomedical metallic implants due to their superior specific strength, excellent corrosion resistance, and exceptional biocompatibility. Among these alloys, Ti6Al4V is widely used in practical biomedical applications because it offers an excellent combination of strength, fracture toughness, and corrosion resistance. However, recent research has revealed limitations in its biocompatibility attributed to the presence of toxic elements such as Al and V. In addition, it has been reported that Ti6Al4V is costly due to the addition of Vanadium and has the potential for post-implant inflammation. As a result, researchers have been investigating new biomedical beta-Ti alloys using biocompatible, affordable, and easily accessible beta-stabilizers like Mo, Fe, and Cu, to achieve similar performance as Ti6Al4V alloys. The present study aims to develop a novel biomedical alloy through the arc melting method, to obtain an implant material possessing low elastic moduli, biocompatibility, and antibacterial properties to mitigate the risk of post-implant inflammation. Microstructural analysis was conducted using microscopy and x-ray diffraction, while the mechanical properties were evaluated through micro vickers hardness testing machine and elastic moduli measurement utilizing the impulse excitation technique. Cytotoxicity assessment was performed using the (Cell Counting Kit-8) CCK-8 method, followed by an examination of the alloy's antibacterial properties using the point counting method. β-Ti single phase was obtained in this study with the addition of ≥1% Fe and ≥1% Cu. The Ti-8Mo-2Fe-2Cu alloy was found to have the lowest elastic moduli of 95 GPa. Electrochemical measurements show that the Ti-8Mo- xFe- yCu alloys have a lower corrosion current density of around 0.319–2.317 µA/cm2 compared to Ti6Al4V of 16.543 µA/cm2. The Ti-8Mo-1Fe-3Cu, Ti-8Mo-3Fe-1Cu, and Ti-8Mo-3Fe-3Cu alloys have comparable biocompatibility with Ti6Al4V with the viability of mesenchymal stem cells (MSCs) above 75% and have a positive antibacterial response. Ti-8Mo-3Fe-3Cu alloy demonstrates the most favorable blend of microstructure, mechanical attributes, corrosion resistance, cell viability, and antibacterial properties as an alternate biomaterial for implant applications.

Ti–6Al–4V alloys undergo a multiple phase transformation sequence during electron beam powder bed fusion (EB-PBF) additive manufacturing, forming unique dislocation substructures. Thus, determining the dislocation density is crucial for comprehensively understanding the strengthening mechanisms and deformation behavior. This study performed time-of-flight neutron diffraction (TOF-ND) measurements of Ti–6Al–4V alloys prepared via EB-PBF and examined the dislocation density in the as-built and post-processed states using convolutional multiple whole profile (CMWP) fitting. The present TOF-ND/CMWP approach successfully determined the bulk-averaged dislocation density (6.8 × 1013 m−2) in the as-built state for the α-matrix, suggesting a non-negligible contribution of dislocation hardening. The obtained dislocation density values were comparable to those obtained by conventional and synchrotron X-ray diffraction (XRD) measurements, confirming the reliability of the analysis, and indicating that the dislocations in the α-matrix were homogeneously distributed throughout the as-built specimen. However, the negative and positive neutron scattering lengths of Ti and Al, respectively, lowered the diffraction intensity for the Ti–6Al–4V alloys, thereby decreasing the lower limit of the measurable dislocation density and making the analysis difficult.

Metallic phase change materials (MPCMs) are attracting considerable attention for their application in thermal energy storage. Al-Si alloys are considered potential MPCMs; however, to develop storage systems/modules, it is crucial to fabricate corrosion-resistant materials for MPCMs. In this study, the corrosion behavior of Co-28Cr-6Mo-1.5Si (wt%) alloy was examined via immersion tests in commercial Al-Si alloy (ADC12) melt at 700? for 10 h. The results were compared to those obtained for pure Al. Substrate thickness loss measurements revealed that the liquid metal corrosion was more severe in the Al-Si melt than that in pure Al, suggesting an increased reactivity due to Si addition. Interfacial analysis elucidated a direct reaction between the alloy substrate and molten Al in both cases. Furthermore, the formation of oxides such as Al2O3 and SiO2 did not contribute to corrosion resistance.

Hardening of Ni-Cr-Mo corrosion-resistant alloys facilitates the expansion of their industrial applications; however, it remains challenging. Herein, we report significant hardening in a Co-, Cu-modified Ni-Cr-Mo alloy under appropriate cold swaging/aging conditions. Age-hardening occurred over a relatively short period ( '0.5 h) and became clear upon cold-swaging to an area reduction of >60%, exhibiting peak hard-ness at 50 0-60 0 degrees C. Exceptional hardness (HV599), unattainable in conventional Ni-Cr-Mo alloys, was obtained after aging. Scanning transmission electron microscopy revealed that multiple nanoscale segre-gation mechanisms, including Suzuki segregation at stacking faults and Cr-rich nanodomains within the severely cold-swaged face-centered cubic matrix, were responsible for the resultant hardening. Further-more, segregation of Cu, alongside Cr and Mo, along the deformation-induced boundaries induced a fine dispersion of nanoscale Cu precipitates throughout the matrix, imparting further hardening. A superior combination of hardness and corrosion performance was realized through this strategy. (c) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Strengthening of biomedical Co-Cr-Mo alloys has been explored via thermomechanical processing for enhancing the durability of their biomedical applications. However, the effects of cold and hot deformation on the cellular activity continue to be unclear. In this study, we prepared Co-Cr-Mo alloy rods via cold swaging and hot-caliber rolling and studied the relationship between the microstructure and cellular response of pre-osteoblasts. The cold-swaged rod experienced strain-induced martensitic transformation, which increased the volume fraction of the hexagonal close-packed (hcp) epsilon-martensite to similar to 60 vol.% with an increase in area reduction (r) to 30%. The 111 gamma fiber texture of the face-centered cubic (fcc) gamma-matrix followed the Shoji-Nishiyama orientation rela-tionship with epsilon-martensite. Cell culture results revealed beneficial effects of cold swaging on the cell response, in terms of adhesion, proliferation and morphology of cells, although increasing r did not significantly affect cellular metabolism levels. The addition of small content of Zr (0.04 wt.%) led to enhanced focal adhesion of cells, which became more significant at higher r. The microstructural evolution during hot-caliber rolling, namely, grain refinement without any phase transformation and strong texture development, did not appreciably affect the cellular activity. These findings are envisaged to facilitate alloy design and microstructural optimi-zation for favorable tuning the osseointegration of biomedical Co-Cr-Mo alloys.

This study demonstrates transformation-induced plasticity (TRIP) in conjunction with twinning-induced plasticity (TWIP) in alpha + beta titanium alloys by introducing metastable retained beta-phase. By annealing at 850 degrees C followed by water quenching, metastable retained beta-phase (similar to 25%) was obtained in Ti-6Al-4V alloy. Stress-induced phase transformation in the retained beta-phase produced orthorhombic alpha ''-martensite associated with (021)(alpha '') twinning, which significantly increased the work-hardening rate and uniform elongation. The findings reveal that the minor retained beta-phase is responsible for macroscopic deformation behavior and could aid in novel alloy design that can increase work hardenability with fewer alloying elements than currently available metastable beta-titanium alloys. IMPACT STATEMENT The minor metastable retained beta-phase in an alpha + beta titanium alloy with low alloy content enhanced work hardening because of the combined TRIP/TWIP effect.

Ti–6Al–4V alloys prepared via electron beam powder bed fusion (EB-PBF) generally exhibit a hierarchical microstructure consisting of columnar β-grains, an acicular α-matrix, and nanoscale β-precipitates at α-lath interfaces. In this study, we performed time-of-flight neutron diffraction measurements to investigate the texture and volume fraction of EB-PBF Ti–6Al–4V alloys via Rietveld texture analysis (RTA). The high-intensity neutron source enabled the analysis of the nanosized β-phase precipitates at the α-lath interfaces. The results indicate that the α- and β-textures of the as-built specimen can be ascribed to multiple Burgers orientation relationships among the prior β-phase, α-laths, and nanosized β-phase precipitates, which are not clearly understood. The as-built texture was maintained during post-processing, suggesting that texture manipulation in EB-PBF fabrication is important for controlling the crystallographic orientations of the built components, even after post-processing. RTA allowed a precise quantification of the β-phase fraction, which was found to have increased in post-processed specimens. The results would contribute to a comprehensive understanding of the microstructural evolution of such alloys, which is vital for the modeling and optimization of alloy performance.

An increased carbon content strengthens Co-Cr-Mo alloys for use in a broad range of industrial applications. In this study, we investigated the influence of the carbon content (0.04-2.5 mass%) on the porosity and microstructure of Co-27Cr-6Mo (mass%) alloys during atomization and electron-beam powder bed fusion (EB-PBF). Quantitative X-ray computed tomography clarified that the volume fraction of pores in the raw powders monotonically increased with the carbon content, as a potential effect of the significant reduction in the liquidus temperature. In contrast, the porosity evolution in the investigated alloys during EB-PBF under identical building conditions suggested an influence of carbon concentration that was distinct from that in the powder. These alloys exhibited negligible porosity fraction for 0.04 and 0.22 mass% and a maximum volume fraction (similar to 0.3 vol.%) at 2.0 mass%, followed by a remarkable reduction caused by further carbon addition. The porosity of the as-built alloys could be correlated to the solidification behavior varying with carbon concentration. The smoother and more flat solidification front during the cellular (0.04 and 0.22 mass%) and eutectic (2.5 mass%) solidification could effectively eliminate the gas bubbles from the melt pool, whereas the complicated morphology at the solid-liquid interfaces during the dendritic growth (1.5 and 2.0 mass%) hindered the pore elimination in the melt pool. Adding carbon significantly increased the Rockwell hardness of the as-built specimens, reaching a significantly high value of HRC59 at 2.5 mass% of carbon, primarily due to the formation of hard carbide precipitates. The obtained findings could be beneficial to reduce entrapped gas pores thereby contributing to the development of highly durable metal components.

Ti-6Al-4V alloy is widely used in aerospace and biomedical industries, and its preparation using additive manufacturing techniques has recently attracted considerable attention. Herein, the dislocation structures developed during electron beam and laser beam powder-bed fusion (EB-PBF and LB-PBF, respectively) of the Ti-6Al-4V alloy were quantitatively examined via X-ray diffraction (XRD) line profile analysis. The microstructures of both as-built samples were characterized, revealing fine acicular microstructures attributable to a beta -> alpha' martensitic transformation. While a fully alpha'-martensite matrix with a high dislocation density was formed and preserved during the LB-PBF process, the decomposition of the alpha'-martensite toward the thermodynamically stable alpha + beta microstructure occurred during EB-PBF as a result of post-solidification exposure to high temperatures. Accordingly, a higher dislocation density and finer crystallite size were observed at the top cross-section from the XRD line profile analysis, suggesting that the extent of phase decomposition depended on the duration of the exposure to the elevated temperature. Nonetheless, the saturated dislocation density was as high as 10(14) m(-2), where dislocation strengthening affected the overall strength of the EB-PBF specimen. Diffraction peaks of sufficient intensity that enabled the analysis of the dislocation structures in both the alpha (alpha')-matrix and the nanosized beta-phase precipitates at the alpha (alpha')-laths were obtained under high-energy synchrotron radiation; this revealed that the beta-phase had a much higher dislocation density than the surrounding alpha (alpha')-matrix. The enhanced dislocation accumulation in the nanosized beta-phase precipitates probably reflects the elemental partitioning that occurred during post-solidification cooling. The valuable insights provided in this study are expected to promote further development of alloy preparation using additive manufacturing processes.

Cu-doped martensitic steels (Fe–(13, 16)Cr–3W–2Cu–1C) (mass%) with multiple carbide precipitates were prepared at different quenching temperatures, and their corrosion behaviours were examined by measuring the weight loss during immersion in a 0.5 M H 2 SO 4 solution. Lower weight losses and corrosion rates were obtained for the alloy samples prepared at higher quenching temperatures. Surface Cu enrichment was observed for all specimens with a large fraction of dissolved Cr species. Moreover, quenching from higher temperatures not only reduced the amount of M 23 C 6 carbide but also decreased the local electrochemical potential difference between the carbide phase and the martensitic matrix via enhanced surface Cu accumulation, thus increasing corrosion resistance by suppressing microgalvanic corrosion between the constituent phases. The corrosion behaviour of the studied steels was remarkably different from those of the Cu-doped stainless and low-alloy steels with passive oxide surface films, suggesting the strong effect of multiple carbide precipitates on their corrosion behaviour.

High-entropy alloys (HEAs) have emerged as a class of structural alloys with various attractive properties, and their application in additive manufacturing, which enables unprecedented thermal history and geometrical complexity, is promising for realising advanced materials. This study investigates the corrosion behaviour and passive film characteristics of an equimolar AlCoCrFeNi HEA additively manufactured by electron beam melting (EBM). Potentiodynamic polarisation in a 3.5 wt% NaCl solution revealed that the bottom part of the EBM specimen shows better corrosion performance than a conventionally prepared cast specimen in terms of both corrosion and passivation current density, while a continuous increase in the current density without any apparent passivity was observed during the anodic polarisation of the top part. The electrochemical impedance spectroscopic study indicated significant differences in the passive film characteristics between the specimens, and revealed an enhanced charge-transfer resistance and the formation of a more protective passive film of the bottom part. The elemental redistribution, in particular, the enrichment of Cr in the B2 phase during the post-melt high-temperature exposure of the alloy during EBM, was responsible for the improved stability of the passive film, retarding the selective dissolution of the B2 phase in the bottom part. These findings indicate that the microstructural evolution caused by ‘in situ annealing’ during the EBM process significantly influences the corrosion behaviour of the HEA.

Co-Cr-Mo alloys have various remarkable properties and in recent times their use has been extended in biomedical applications in recent times. In this study, small-diameter Co-Cr-Mo alloy rods, which can be used in spinal instrumentation surgery, were prepared using a developed manufacturing system that enables hot-caliber rolling immediately after the induction heating of a rod workpiece. The effects of rolling temperature (850-1150 °C) and the amount of deformation (up to 0.45 in equivalent strain) on the microstructure, mechanical properties, and cytocompatibility of the rods were examined to determine the processing-microstructure-property relationship and to optimize the processing parameters. The microstructural evolution, which was found to be associated with grain refinement due to the simultaneous dynamic recrystallization (DRX) and accumulation of lattice defects during hot-caliber rolling, significantly strengthened the alloy and maintained the ductility. Bi-directional deformation during hot-caliber rolling at higher rolling temperatures enhanced the DRX, thus realizing uniformly distributed fine grains without preferential orientations, which resulted in the homogeneous mechanical properties of the obtained rods. Consequently, an enhanced strength-ductility combination, which was superior to those obtained in the existing literature, was achieved. Moreover, the cytocompatibility experiments using human MG-63 osteoblast-like cells at various intervals (3, 6, and 10 days) revealed a limited detrimental influence on the cell proliferation and cell migration on the sample hot-rolled at 1150 °C. The developed manufacturing system can be employed for the fabrication of high-strength Co-Cr-Mo alloy rods with high durability, and it can be implemented in low-profile systems for spinal instrumentation surgery.

We prepare a high-strength Co-28Cr-6Mo-0.14N-0.04C (mass%) alloy by multipass hot rolling and clarify the influence of the associated microstructural evolution on the corrosion behaviour. Potentiodynamic polarisation, static immersion tests, and electrochemical impedance spectroscopy indicate that the corrosion behaviour and passive film characteristics do not vary significantly between the annealed and hot-rolled samples. However, hot rolling was found to weaken the active-to-passive transition during anodic polarisation. These results suggest that significant grain refinement and accumulation of dislocations, which occurred simultaneously during multipass hot rolling, enhance the passivity.

Cobalt-chromium-molybdenum alloys exhibit good mechanical properties (yield strength: ~530 MPa, ultimate tensile strength: ~1114 MPa, elongation-to-failure: ~47.3%, and modulus: ~227 GPa) and corrosion resistance. In recent years, from the perspective of osseointegration, they are considered to be lower in rank in comparison to the widely used titanium alloys. We elucidate here the significant and favorable modulation of cellular activity of Zr-modified Co-Cr-Mo alloys. The average grain size of Co-Cr-Mo alloy samples with and without Zr was 104 ± 27 and ~53 ± 11 μm, respectively. The determining role of small addition of Zr (0.04 wt. %) to the Co-Cr-Mo alloys in favorable modulation of cellular activity was accomplished by combining cellular biology and materials science and engineering. Experiments on the influence of Zr addition to Co-Cr-Mo alloys clearly demonstrated that the cell adhesion, spread and cell-substrate interactions were enhanced in the presence of Zr. The spread/growth rate of cells was ~120% on the Co-Cr-Mo alloy and 190% per day on the Co-Cr-Mo-Zr alloy. While the % area covered by the cells increased from ~5.1 to ~33.6% on Co-Cr-Mo alloy and ~19.2 to ~47.8% on Co-Cr-Mo-Zr alloy after 2 and 24 hr of incubation. Similarly, the cell density increased from ~1354 to ~3424 cells/cm2 on Co-Cr-Mo alloy and ~3583 to ~7804 cells/cm2 on Co-Cr-Mo-Zr alloy after 2 and 24 hr of incubation. Additionally, stronger vinculin focal adhesion contact and signals associated with actin stress fibers together with extracellular matrix protein, fibronectin, were noted.