Preferential Precipitation Research Articles

Microstructure and corrosion properties of sensitized laser powder bed fusion printed Inconel 718 to dissolve support structures in a self-terminating manner

This manuscript expands the existing framework for single-material laser powder bed fusion printed dissolvable supports to Inconel 718 (IN718). Prior work with stainless steel leveraged a sensitization heat treatment using sodium hexacyanoferrate to precipitate chromium carbides over the top 100 μm to 200 μm of material, decreasing the corrosion resistance within this top layer relative to the bulk material. The component is then etched at an anodic potential with a high selectivity toward the “sensitized” surface over the base component material. This creates an etching process that self-terminates once the sensitized layer is removed. Since supports are typically less than 200 μm thick, they are completely sensitized and dissolved. Additionally, the surface roughness of the component is often improved once the sensitized region is removed. In this work, two different sensitization heat schedules were investigated: 750 °C for 24 h to understand the impact of preferential chromium carbide precipitation and 1050 °C for 8 h to understand the impact of primary carbide precipitations. At 1050 °C, the formation of a protective oxide scale inhibits material removal in an electrolyte of 0.48 M HNO3. At 750 °C, 70 μm of material is removed after quenching to avoid the precipitation of corrosion resistant oxides. This manuscript investigates the effect of targeting different carbide precipitation regimes and oxides to produce an ideal microstructure for dissolvable supports post-sensitization. To demonstrate the utility of the process, the supports from a mock IN718 turbine blade were removed using this process.

Nucleation of Y-X-O (X=Al, Ti, or Zr) NCs in nano-structured ferritic alloys: A first principles comparative study

Nucleation of Y-Al-O, Y-Ti-O, and Y-Zr-O enriched nano-clusters (NCs) in nano-structured ferric alloys were comparatively investigated using first-principles calculations. Formation of various possible cluster configurations was energetically evaluated with respect to individually dissolved solute atoms, to explore the preferential precipitation and growth sequence of the NCs. Key results include the following observations. During the earliest nucleation stages, Y-Zr-O NCs are always the most energy favored to form in the supersaturated bcc-Fe based matrix, followed by Y-Ti-O and Y-Al-O NCs. All the three type NCs follow the same nucleation path that begins from the O-O pairs. Y has the strongest thermodynamic driving force to precipitate with the O-O pairs. The most stable six-atomic cluster configuration is predicted as –[2Y-3O-X]–. The (O-Y)-cores may constitute the stable nuclei of larger NCs which grow consistently by attracting extra solutes available nearby.

Preferential Precipitation and Selective Separation of Rh(III) from Pd(II) and Pt(IV) Using 4-Alkylanilines as Precipitants.

Rhodium (Rh) is the most expensive platinum group metal (PGM) and is of great industrial importance. Although the recycling of PGMs from secondary sources is in high demand, the preferential and selective separation of Rh from PGM mixtures remains a great challenge. Here, a selective Rh separation method involving the precipitation of Rh from an HCl solution containing palladium (Pd), platinum (Pt), and Rh is reported. 4-Butylaniline and 4-hexylaniline were used as precipitants for Rh, and selective Rh precipitation was achieved at high HCl concentrations. We revealed that Rh in HCl selectively forms a unique and highly stable ion-pair complex comprising [RhCl6]3–/anilinium/chloride ions in a 1:6:3 ratio. The formation and high stability of the Rh complex were found to play important roles in the selective recovery of Rh from PGM mixtures.

Influence of delta phase precipitation on static recrystallization of cold-rolled Inconel 718 alloy in solid solution treatment

Due to the improvement in fatigue strength of cold-rolled blades, the static recrystallization behavior of cold-rolled Inconel 718 alloy in the solid solution treatment was investigated with the methods of optical microscopy and electron backscattered diffraction. The effect of δ phase precipitation on the static recrystallization process was also analyzed. The results show that δ phase preferentially precipitates comparing to static recrystallization. Affecting by the δ phase preferential precipitation process, sub-grain migration is the main nucleation mechanism in the static recrystallization of cold-rolled Inconel 718 alloy at 980 °C. Meanwhile, strain-induced boundary migration also exists as an aided nucleation mechanism when the rolling reduction is less than 30%.

Effect of post processing on the creep performance of laser powder bed fused Inconel 718

In this study, the creep performance of laser powder bed fusion manufactured Inconel 718 specimens is studied in detail and compared with conventional hot-rolled specimens alongside as-built then heat-treated and as-built then hot-isostatic pressed specimens. Hot-rolled specimens showed the best creep resistance, while the hot-isostatic pressed specimens yielded the worst performance, inferior to the as-built condition. Creep testing of all samples showed increased secondary creep rate was consistently correlated with a reduced life. Fractography revealed intergranular fracture was the primary failure mode for all as-built samples. Preferential intergranular precipitation in the case of the hot-isostatic pressed specimens during hot-isostatic pressing extensive intergranular cracking as the primary failure mechanism. Heat-treated specimens possessed only sparse intergranular precipitates, thereby explaining an improved creep lifetime. The hot-rolled specimens, having smallest grain size, showed the least extensive cracking, particularly in locations of finest grains, explaining avoidance of intergranular fracture as a key creep mechanism, thereby explaining the ductile creep fracture surfaces in the case of the hot-rolled samples.

Bio‐Inspired Hydro‐Pressure Consolidation of Silica

AbstractRoom‐temperature hydro‐pressure‐driven densification of amorphous silica (nanoparticles and microbeads) is developed. This technique is inspired by biological silicification with reference to dissolution, precipitation, and hardening mechanisms. Cold sintering based on uniaxial pressure is taken as a benchmark. Starting from a green‐body relative density of 70%, densification exceeding 99% is achieved by adding distilled water or caustic solution to an amorphous powder under a hydrostatic pressure of 450–600 MPa for 5–30 min. Translucent samples are obtained. Silica microbeads are employed as a model system to define the effect of the sintering parameters: pressure, pH, and soaking time. Densification is attained through a preferential precipitation of a second phase from silica dissolution under hydro‐pressure. Precipitation is governed by minimization of the surface energy (Ostwald ripening). Transmission electron microscopy, NMR, thermal gravimetric analysis/differential scanning calorimetry, and Fourier transform infrared spectroscopy reveal the mechanisms of the process and the analogies with biosilicification.

Surface composite microstructure and improved mechanical property of YG10X cemented carbide induced by high current pulsed electron beam irradiation

The surface microstructure evolution and its effect on mechanical property was systematically investigated for YG10X cemented carbide irradiated by high current pulsed electron beam (HCPEB) with a steady energy density of 6 J/cm2 and different pulse numbers. The surface morphology was characterized by optical microscopy (OM), three-dimensional laser scanning microscopy (LSM) and scanning electron microscopy (SEM); and energy dispersive spectrometry (EDS) and X-ray diffractometry (XRD) was carried out to reveal the elemental profile and phase transformation under HCPEB irradiation. During the HCPEB-induced rapid re-melting and re-solidification process, the redistribution of chemical elements, grain refinement and phase transformation WC(hex) → graphite + β-WC1-x(fcc) occurred. Moreover, the preferential precipitation of nano-grained graphite in the Co-rich region of melt pool was discovered. The drastic structural change led to a maximum ~34% increment of the initial state in microhardness and about a two third reduction in friction coefficient.

Encapsulation of anthocyanin-rich extract from blackberry residues by spray-drying, freeze-drying and supercritical antisolvent

The extract obtained from blackberry (Rubus fruticosus) residues was encapsulated in polyvinylpyrrolidone (PVP) by three methods: the conventional spray-drying (SD) and freeze-drying (FD) techniques, and the new method of supercritical antisolvent (SAS), using CO2 as antisolvent and ethanol as solvent of the organic solution (extract + PVP). The methods and their produced particles were evaluated in terms of precipitation yield, residual ethanol and moisture contents, anthocyanin concentration, antioxidant capacity, morphology, crystallinity and thermal stability. SD,FD and SAS achieved particles with good anthocyanin yields (above 76%), high antioxidant capacity (above 100 μmol TE/g particle) and were effective to concentrate anthocyanins in PVP without great degradation. Using SAS, particles with 1.42 mg ECy3Gl/g were achieved. Nevertheless, SAS particles presented high residual ethanol (8.17% w/w) and moisture (11.30% w/w), whereas in SD and FD particles these contents remained below 2 and 5%, respectively. Scanning electron microscopy revealed a spherical shape in the particles obtained by SD, while those produced by SAS and FD presented irregular agglomerates. The encapsulation processes were equivalent in terms of thermal protection of the extracts and they did not modify the crystallinity and thermal behavior of PVP. The SAS process achieved preferential precipitation of anthocyanins when compared to SD and FD, since supercritical CO2 does not have any affinity to such compounds.

Variant selection in metastable β Ti-V-Fe-Al alloy during triaxial and uniaxial compression

In the present study, metastable β-Ti alloy Ti-10V-3Fe-2Al (wt%) alloy was subjected to either triaxial or uniaxial compression followed by aging of both as-deformed as well as solution-treated samples. Microstructural characterization and measurement of crystallographic texture were performed to elucidate the underlying mechanism affecting the measured hardness of these differently processed samples. The microstructure of the as-deformed material was highly inhomogeneous consisting of β grains fragmented by microbands. Aging of the solution-treated as well as deformed samples resulted in the formation of a two-phase α + β microstructure. The texture of the β phase in the triaxial compressed alloy was dominated by cube component, while in uniaxial compression it exhibited strong fiber texture. The differences in texture in the parent β matrix influenced the transformation texture of the α phase formed during aging. A strong variant selection of the α precipitates was observed in both triaxially and uniaxially deformed samples. A mechanism of variant selection is proposed wherein, the inhomogeneous deformation leads to preferential precipitation of α phase along the crystallographic microbands resulting in a variant selection. The variation in texture resulting from the difference in strain path affected the mechanical property and its anisotropy. Hardness after uniaxial compression, was anisotropic because of the texture evolved during the process, whereas, triaxially compressed material was found to have isotropic hardness properties. Aging led to a reduction in anisotropy as the effect of precipitation dominated over the orientation effect on overall strengthening. Thus, coupling strain path with aging treatment can be used to tailor the mechanical properties in a Ti-V-Fe-Al alloy.

Characterization and mechanical properties of cladded stainless steel 316L with nuclear applications fabricated using electron beam melting

The ability to fabricate or join components of 316 L austenitic stainless steel using additive manufacturing (AM) processes such as laser and electron beam melting (EBM®) offers several advantages including enhanced part complexity, narrow or absent heat affected zones, increased part precision, avoidance of filler materials (such as traditional welds), and the ability to create metallurgically sound bonds. These attributes can contribute to improved mechanical properties of the fabricated components and component repair in nuclear, aerospace, and chemical industries. In the present work, we report that austenitic 316 L stainless steel additively manufactured by EBM exhibits a 76% increase in the yield strength and a corresponding increase of 29% in the ultimate tensile strength in contrast to the wrought substrate and commercial forged 316 L stainless steel. The EBM clad 316 L stainless steel elongation was 36%. The wrought substrate equiaxed grain size was ∼30 μm in contrast to elongated, columnar grains ∼0.1 mm wide and >1 mm in length for the EBM cladding. Transmission Electron Microscopy (TEM) analysis revealed that these columnar grains, which exhibited very straight, and presumably special grain boundaries having a very high (100) texture, contained a variety of sub-grain microstructures consisting of low-angle sub-grain boundaries containing dislocation tangles and stacking-fault arrays, and homogeneously distributed Cr23C6 carbide precipitates, with no preferential carbide precipitation on either the straight, special columnar grain boundaries, or the very low-angle sub-grain boundaries. This observation and the formation of hierarchical microstructures which produce high strength and possibly corrosion resistance as a consequence of the absence of grain boundary carbide precipitation, illustrate the prospects for AM as a novel concept for achieving grain boundary engineering to promote high-strength and corrosion resistant alloys for high-temperature, corrosive environments, including elevated temperature nuclear reactor applications.

In silico, in vitro and antifungal activity of the surface layers formed on zinc during this biomaterial degradation

Zinc (Zn) has been proposed as an alternative metallic biodegradable material to support transient wound-healing processes. Once a Zn piece is implanted inside the organism the degradation will depend upon the physiological surrounding environment. This, by modulating the composition of the surface layers formed on Zn devices, will govern the subsequent interactions with the surrounding living cells (e.g. biocompatibility and/or antifungal behaviour). In silico simulation of an implanted Zn piece at bone-muscle interface or inside the bone yielded the preferential precipitation of simonkolleite or zincite, respectively. To study the impact of these surface layers in the in vitro behaviour of Zn biomaterials, simonkolleite and zincite where synthesised. The successful production of simonkolleite or zincite was confirmed by an extensive physicochemical characterization. An in vitro layer formed on the top of these surface layers revealed that simonkolleite was rather inert, while zincite yielded a complex matrix containing hydroxyapatite, an important bone analogue. When analysing the “anti-biofilm” activity simonkolleite stood out for its activity against an important pathogenic fungi involved in implant-device infections, Candida albicans. The possible physiological implications of these findings are discussed.

Jagged cracking in the heat-affected zone of weld overlay on coke drum cladding

Abstract Jagged cracks were observed in SA240 Type 405 stainless steel cladding of Inconel 625 overlay repaired coke drums. It is found that intergranular cracking is the dominant fracture mode in the fine-grained heat-affected zone (FGHAZ) of the boat specimens. The sensitization effect from the operation and welding thermal cycles leads to the depletion of Cr with the preferential precipitation of Cr-rich M23C6 carbides along the grain boundaries. The cladding FGHAZ has the largest frequency of grain boundaries with higher local strain levels and the highest fraction of grain boundary Cr-rich M23C6 carbides. Thermal stress distributions predicted by finite element analysis clearly show the maximum shear stress to exhibit the typical “jagged” pattern near the cracked regions. Thermal expansion coefficient and strength mismatch among the shell base metal, cladding, and overlay is believed to have caused the unique jagged maximum shear stress distribution in the cladding HAZ of Inconel 625 overlay. The magnitude of this thermal stress can reach the yield strength of the cladding at 900 °F (482 °C) service temperature, therefore, provides the driving force for the jagged cracking formation in the sensitized HAZ.

Influence of grain boundaries on the distribution of components in binary alloys

Based on the free-energy density functional method (the Cahn–Hilliard equation), a phenomenological model that describes the influence of grain boundaries on the distribution of components in binary alloys has been developed. The model is built on the assumption of the difference between the interaction parameters of solid solution components in the bulk and at the grain boundary. The difference scheme based on the spectral method is proposed to solve the Cahn-Hilliard equation with interaction parameters depending on coordinates. Depending on the ratio between the interaction parameters in the bulk and at the grain boundary, temperature, and alloy composition, the model can give rise to different types of distribution of a dissolved component, namely, either depletion or enrichment of the grain-boundary area, preferential grainboundary precipitation, competitive precipitation in the bulk and at the grain boundary, etc.

Crystal Structure of DMF-Intermediate Phases Uncovers the Link Between CH3NH3PbI3 Morphology and Precursor Stoichiometry

We found for the first time a new origin of selection of perovskite crystallization pathways from DMF solutions containing MAI and PbI2 to present here a comprehensive study of a full set of essential intermediate phases determining the perovskite’s morphology. For all three discovered structurally different intermediate phases forming at a given precursor ratio, we refined their crystal structures by synchrotron X-ray radiation and investigated dynamics and phase assemblage in the course of decomposition. As a result, we revealed a clear correlation between the composition of the intermediate phases, peculiarities of their crystal structure, and the morphology of the final perovskite films. Using the DFT method we calculated formation enthalpies of these intermediate phases and explained the preferential precipitation of DMSO-adduct rather than DMF-adduct in an antisolvent approach. This finding opens up a possibility of design-on-demand of perovskite materials using simple soft chemistry approaches.

The First Asymmetric Pilot-Scale Synthesis of TV-45070

TV-45070 is a small-molecule lactam containing a chiral spiro-ether that has been reported as a potential topical therapy for pain associated with the Nav1.7 sodium ion channel encoded by the gene SCN9A. A pilot-scale synthesis is presented that is highlighted by an asymmetric aldol coupling at ambient temperature, used to create a quaternary chiral center. Although only a moderate ee is obtained, the removal of the undesired isomer is achieved through preferential precipitation of a near racemic mixture from the reaction, leaving the enantiopure isomer in solution. Cyclization to form the final API uses an uncommon diphenylphosphine-based leaving group which proved successful on the neopentyl system when other traditional leaving groups failed.

Oligotrophic and eutrophic MICP treatment for silica and carbonate sands

The terms ‘oligotrophic treatment’ and ‘eutrophic treatment’ have been introduced to differentiate between whether fixation liquid or nutrients have been administered during the on-site process for microbially induced precipitation of calcite. Results from scanning electron microscopy images for small-scale soil column tests have shown the different treatments to have markedly different precipitation patterns, crystal morphology and bond formation and eventual bond failure in silica sand. In the case of oligotrophic treatment, the fixation phase led to a more widespread pattern of precipitation in silica sand particles, which resulted in large single rhombohedral crystals being formed on the surface of particles or at particle contact points when nutrients were withheld on site. In contrast, eutrophic treatment involving the on-site delivery of nutrients promoted preferential precipitation at particle contact points in the form of micritic dome-like structures of vaterite that acquired a new layer of crystal with each delivery of nutrients. The different crystal morphologies were found to influence particle-bond failure mechanism in the form of either a particle-bond interface mode of failure or an internal failure of the carbonate crystal along a suture.

Relation between precipitation location and antecedent/subsequent soil moisture spatial patterns

AbstractRecent evidence has shown that relations between soil moisture and precipitation at spatial and temporal aspect are contrary to each other: afternoon precipitation tends to occur at times in which conditions are overall wet and heterogeneous in the morning, but preferentially over those patches that are relatively drier than the surroundings. This study expands the notion of soil moisture‐precipitation spatial coupling by analyzing the preferred precipitation location over a range of different soil moisture patterns. Using global observations of precipitation and observationally constrained evaporative stress estimates, we confirm that relatively drier patches have more chances of receiving rain, but the preference is weakened under wetter soil conditions. During extremely wet times, wet patches have more chances of receiving rain. Moreover, the preference of precipitation to occur on drier soils is stronger when soil moisture conditions are heterogeneous. Such results indicate that the positive feedback mechanism becomes more positive as soil wetness increases and the negative feedback mechanism becomes more negative as soils become drier and more heterogeneous. The strength of these two feedback mechanisms jointly affects preferential precipitation location. Counterintuitively, analysis from 1 day after‐event soil moisture pattern shows that negative soil moisture‐precipitation coupling may in turn further heterogenize soil moisture patterns, because dry patch gets extremely wet with no or less rain in surrounding. Although results here do not necessarily imply a causal relationship, this work contributes to enhancing our understanding of soil moisture‐precipitation spatial coupling and exposes the complex nuances of these land‐atmosphere interactions.

Preferential adsorption and surface precipitation of lead(II) ions onto anatase in artificially contaminated Dixie clay

During TEM-EDS (transmission electron microscopy coupled with an X-ray energy dispersive spectrometer) analysis of Dixie clay artificially contaminated with Pb(II), we observed that Pb(II) was preferentially adsorbed and precipitated on the surface of TiO2. To deepen the understanding of the mechanism and importance of this phenomenon, batch sorption experiments, XANES (X-ray absorption near edge spectroscopy) analysis, and sequential extraction analysis were performed. The TiO2 in Dixie clay was found to be anatase, and anatase showed a higher Pb(II) sorption propensity than rutile, α-FeOOH, and one of two MnO2 investigated in this study. Our experimental results indicated that the Pb precipitates preferentially formed on the surface of anatase was Pb(II) hydroxide or Pb(II) oxide. Additionally, sequential extraction analysis showed that at least 32% and 42% of Pb(II) was sorbed onto anatase in the Dixie clay contaminated with a Pb content of 736mg Pb/kg and 1,958mg Pb/kg, respectively. These results demonstrated that in addition to Fe and Mn oxides that are well-known metal oxides that serve as sinks for Pb(II) in the soil environment, TiO2 is also a metal oxide that controls the behavior and fate of Pb(II) in soils.

Formation of Fluorohydroxyapatite with Silver Diamine Fluoride

Silver diamine fluoride (SDF) is found to promote remineralization and harden the carious lesion. Hydroxyapatite crystallization is a crucial process in remineralization; however, the role of SDF in crystal formation is unknown. We designed an in vitro experiment with calcium phosphate with different SDF concentrations (0.38, 1.52, 2.66, 3.80 mg/mL) to investigate the effect of this additive on the nucleation and growth of apatite crystals. Two control groups were also prepared—calcium phosphate (CaCl2·2H2O + K2HPO4 in buffer solution) and SDF (Ag[NH3]2F in buffer solution). After incubation at 37 oC for 24 h, the shape and organization of the crystals were examined by bright-field transmission electron microscopy and electron diffraction. Unit cell parameters of the obtained crystals were determined with powder X-ray diffraction. The vibrational and rotational modes of phosphate groups were analyzed with Raman microscopy. The transmission electron microscopy and selected-area electron diffraction confirmed that all solids precipitated within the SDF groups were crystalline and that there was a positive correlation between the increased percentage of crystal size and the concentration of SDF. The powder X-ray diffraction patterns indicated that fluorohydroxyapatite and silver chloride were formed in all the SDF groups. Compared with calcium phosphate control, a contraction of the unit cell in the a-direction but not the c-direction in SDF groups was revealed, which suggested that small localized fluoride anions substituted the hydroxyl anions in hydroxyapatite crystals. This was further evidenced by the Raman spectra, which displayed up-field shift of the phosphate band in all the SDF groups and confirmed that the chemical environment of the phosphate functionalities indeed changed. The results suggested that SDF reacted with calcium and phosphate ions and produced fluorohydroxyapatite. This preferential precipitation of fluorohydroxyapatite with reduced solubility could be one of the main factors for arrest of caries lesions treated with SDF.

Microstructure and mechanical properties of Fe-Al-Nb-B alloys

ABSTRACTDoping of Fe–Al–Nb alloys with boron results in precipitation of stable C14 Laves phase Nb(Fe,Al)2 instead of metastable Heusler phase Fe2AlNb as in case of the ternary system. The boron stimulated precipitation of the Laves phase leads to preferential precipitation of the Laves phase along grain boundaries and – with higher supersaturation of Nb in the Fe-Al matrix – to an even distribution of additional precipitates within the grains. Though these microstructures seem to be more favourable than in the boron-free alloys, which show an uneven distribution of rather large Laves phase precipitates, no marked strengthening effect by the Laves phase in the Fe–Al–Nb–B alloys is observed.