Delta Phase Research Articles

Heat treatment effects on Inconel 625 components fabricated by wire + arc additive manufacturing (WAAM)—part 1: microstructural characterization

Wire + arc additive manufacturing (WAAM) is a versatile, low-cost, energy-efficient technology used in metal additive manufacturing. This WAAM process uses arc welding to melt a wire and form a three-dimensional (3D) object using a layer-by-layer stacking mechanism. In the present study, a Ni-based superalloy wire, i.e., Inconel 625, is melted and deposited additively through a cold metal transfer (CMT)-based WAAM process. The deposited specimens were heat-treated at 980 °C (the recommended temperature for stress-relief annealing) for 30, 60, and 120 min and then water quenched to investigate the effect of heat treatment on microstructure and phase transformation and to identify the optimum heat treatment condition. Microstructural results show that the heat treatment, in general, eliminates the brittle Laves phases regardless of the time without changing the grain morphology. However, an increment in the amount of the delta phase is observed with the longer heat treatment periods. Additionally, the size of MC (metal carbide) of Nb is also observed to increase with heat treatment time. This study provides an in-depth understanding of the correlation between heat treatment time and microstructure in additively manufactured Inconel 625, which can facilitate determining the optimum heat treatment condition in a later study.

Rhythmicity facilitates pitch discrimination: Differential roles of low and high frequency neural oscillations

Previous studies indicate that temporal predictability can enhance timing and intensity perception, but it is not known whether it also enhances pitch perception, despite pitch being a fundamental perceptual attribute of sound. Here we investigate this in the context of rhythmic regularity, a form of predictable temporal structure common in sound streams, including music and speech. It is known that neural oscillations in low (delta: 1–3 Hz) and high (beta: 15–25 Hz) frequency bands entrain to rhythms in phase and power, respectively, but it is not clear why both low and high frequency bands entrain to external rhythms, and whether they and their coupling serve different perceptual functions. Participants discriminated near-threshold pitch deviations (targets) embedded in either rhythmic (regular/isochronous) or arrhythmic (irregular/non-isochronous) tone sequences. Psychophysically, we found superior pitch discrimination performance for target tones in rhythmic compared to arrhythmic sequences. Electroencephalography recordings from auditory cortex showed that delta phase, beta power modulation, and delta-beta coupling were all modulated by rhythmic regularity. Importantly, trial-by-trial neural-behavioural correlational analyses showed that, prior to a target, the depth of U-shaped beta power modulation predicted pitch discrimination sensitivity whereas cross-frequency coupling strength predicted reaction time. These novel findings suggest that delta phase might reflect rhythmic temporal expectation, beta power temporal attention, and delta-beta coupling auditory-motor communication. Together, low and high frequency auditory neural oscillations reflect different perceptual functions that work in concert for tracking rhythmic regularity and proactively facilitate pitch perception.

Micro-mechanisms and precipitation kinetics of delta (δ) phase in Inconel 718 superalloy during aging

The formation of δ phase in Inconel 718 superalloy during aging was quantitatively studied based on improved analyzing techniques to unambiguously determine the mechanism of δ phase precipitation and its kinetics. Based on the general transformation rate expressed in terms of the time corresponding to the transformed fraction of 0.5 or 50% and also the modified Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation, the average activation energy for the formation of δ phase was determined as 212.4 kJ/mol and 197.5 kJ/mol, respectively. These values are comparable to the activation energy for diffusion of Nb in Ni (202.59 ± 4.71 kJ/mol). Therefore, the micro-mechanism for the formation of δ phase was characterized as the diffusion of Nb in the matrix. Based on the kinetic studies, the temperature of 1055.7 K (782.7 °C) was found as the lower bound for the formation of δ phase, which was consistent with the precipitation-temperature-time (PTT) plot developed for this material. Finally, a formula was obtained to quantitatively show the effects of aging temperature and cold rolling reduction on the transformation rate for the precipitation of δ phase.

Stability of Cubic FAPbI3 from X-ray Diffraction, Anelastic, and Dielectric Measurements.

Among the hybrid metal-organic perovskites for photovoltaic applications, FAPbI3 (FAPI) has the best performance regarding efficiency and the worst regarding stability, even though the reports on its stability are highly contradictory. In particular, since at room temperature the cubic α phase, black and with high photovoltaic efficiency, is metastable against the yellow hexagonal δ phase, it is believed that α-FAPI spontaneously transforms into δ-FAPI within a relatively short time. We performed X-ray diffraction and thermogravimetric measurements on loose powder of FAPI, and present the first complete dielectric and anelastic spectra of compacted FAPI samples under various conditions. We found that α-FAPI is perfectly stable for at least 100 days, the duration of the experiments, unless extrinsic factors induce its degradation. In our tests, degradation was detected after exposure to humidity, strongly accelerated by grain boundaries and the presence of δ phase, but it was not noticeable on the loose powder kept in air under normal laboratory illumination. These findings have strong implications on the strategies for improving the stability of FAPI without diminishing its photovoltaic efficiency through modifications of its composition.

Green template-free synthesis and characterization of mesoporous alumina as a high value-added product in aluminum black dross recycling strategy

Aluminum black dross (ABD) is a solid waste of aluminum smelting process that causes serious environmental and public health problems. In addition, it imposes significant disposal costs to the aluminum industry. In this study, synthesis and characterization of mesoporous alumina (MA) from the ABD using a novel recycling procedure consisting of leaching at low temperature (85 °C) and atmospheric pressure, co-precipitation, separation through selective dissolution, re-precipitation, aging and finally calcination at 600 °C for 2 h. No hard or soft template was used during the formation of the gel. The as-synthesized MA had a specific surface area, total pore volume and average pore diameter of 123–162 m2/g, 0.37 cm3/g and 10.6 nm, respectively which were obtained by nitrogen sorption analysis. The as-synthesized MA possessed more than 98% purity. Its XRD pattern exhibited the characteristic peaks of gamma, eta, theta, and delta phase alumina. FESEM and TEM analyses revealed nanoscale morphology of the as-synthesized MA; having crystal size of ∼11 nm. The TGA analysis showed that the as-synthesized MA is thermally stable and exhibits only ∼5 wt% mass loss for heating from 30 to 800 °C. The characterization of solid residue at the end of the proposed process proved that it contains mainly silica phase which can alternatively be reused as filling agent or aggregate in concrete materials applications. It is quite clear that the process of production of MA from the ABD is feasible and practical and provides a novel mitigation to the environmental problems of the ABD.

Precipitation behavior and hardness response of Alloy 625 weld overlay under different aging conditions

The hardness response of Alloy 625 weld overlay on low alloy steel was evaluated under a range of aging conditions to determine how the properties of the overlay change during postweld heat treatment (PWHT). It was presumed that the hardening compared to the as-welded condition occurs due to the precipitation of gamma double-prime (γ″). To confirm this assumption, an investigation was conducted on weld overlay samples under different aging conditions, using Vickers hardness testing, SEM microstructure characterization, SEM/EDAX analysis, and nanoindentation. The Alloy 625 weld overlay hardness values initially increased but eventually decreased with increasing aging temperature. γ″ precipitation was found in the interdendritic regions of the weld overlay samples. In the overaged condition, dissolution and coarsening of γ″ precipitates occurred. Delta (δ) phase also formed in the interdendritic regions, generally at higher temperatures than for γ″ precipitation. Nanoindentation revealed that the precipitation of γ″ is responsible for the hardening in the interdendritic regions of Alloy 625 weld overlay. The time-temperature-precipitation curves of interdendritic regions are altered from that of wrought Alloy 625 due to higher Nb, Ti, and Mo contents and lower dislocation density. The peak temperatures achieved in service for heating coke drum may result in interdendritic γ″ precipitation which can cause significant hardening of the overlay and promote cracking.

The Effects of 4%Fe on the Performance of Pure Zinc as Biodegradable Implant Material.

The efforts to develop structural materials for biodegradable metal implants have lately shifted their focus from Magnesium and Iron base alloys towards Zinc. This was mainly due to the accelerated corrosion rate of Mg that is accompanied by hydrogen gas evolution, formation of voluminous iron oxide products with reduced degradation rate in the case of Iron implants and the crucial role of Zn in many physiological processes. However the mechanical properties and degradation capabilities of pure zinc in physiological environment are limited and do not comply with the requirements of biodegradable implants. The present study aims at evaluating the effect of 4%Fe on the in-vitro and in-vivo behavior of pure Zinc. This was carried out in order to address the inherent disadvantages of pure zinc in terms of mechanical properties and biodegradability. The results obtained clearly indicate that the biocompatibility and mechanical properties of the new material system was in accord with the prospective requirements of biodegradable implants. However the corrosion degradation of the new alloy in in-vivo conditions was quite similar to that of pure zinc in spite of the significant micro-galvanic effect created by Delta phase Zn11Fe.

Boosting electron population in δ-Bi2O3 through iron doping for improved photocatalytic activity

We successfully stabilize the delta phase of bismuth oxide (δ-Bi2O3) down to room temperature through a simple hydrothermal method. The prepared δ-Bi2O3, which is composed of ultrathin nanosheets, possesses excellent crystallinity. When δ-Bi2O3 is doped with Fe3+, the photocatalytic activity for the mineralization of a number of refractory organic compounds is improved. The improved photocatalytic activity is caused by an increased electron population upon the Fe3+ doping. Additional thermal treatment through a post-calcination at 500 °C under air atmosphere results in further increases of photocatalytic activity due to the improved crystallinity, extended light absorption, and better incorporation of Fe3+ into the host lattice.

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%.

The influence of B and P in the impregnating solution on the properties of NiMo/γ-δ-Al2O3 catalysts for VGO hydrotreating

The effect of the addition of boric and phosphoric acids to impregnating solutions on the structure and properties of NiMo catalysts for VGO hydrotreating was studied. The catalysts contained a wide-porous support on the basis of a mixture of γ- and δ-Al2O3 phases. The catalysts were studied by XRD, HRTEM, IR CO, ATR-FTIR, XPS. The catalytic activity was evaluated in hydrotreating of heavy VGO. It is established that the NiMo-citrate complex is formed in impregnating solutions. At the same time, the introduction of phosphoric and boric acids into NiMo-citrate complex solution does not lead to a distortion of the complex compound structure. It has been found that calcining of the support at 900 °C makes it possible to obtain a mixture of gamma and delta phases. It was determined that phosphoric and boric acids react with OH groups of the support, but the introduction of phosphoric acid leads to the formation of POH groups on the surface. The presence of P and/or B in a catalyst composition results in an increase in the number of MoS2 layers in a slab. However, with the introduction of B, a small decrease in the amount of Mo on the surface of a catalyst in the form of Mo4+ is observed. The change in textural and acid characteristics allows us to conclude that bulk particles of BO3 are formed. Testing of catalysts in hydrotreating of heavy VGO made it possible to establish that the introduction of B into composition of the impregnating solution significantly reduces the activity of the catalysts in hydrotreating, while the introduction of phosphorus leads to an increase in the activity of a catalyst. The introduction of phosphoric and boric acids into the impregnating solution simultaneously increased the activity of the catalyst as compared to the sample containing boron only.

The High-Temperature Loading Influence on Orthorhombic Ni3Nb DOa δ - Phase Formation and its Effect on Fatigue Lifetime in Alloy 718

The orthorhombic DOa Ni3Nb delta phase is naturally presented in microstructure of cast or wrought Ni - Cr - Fe base alloy 718. It is a reason of chemical composition heterogeneity. For delta phase formation is a minimum Nb content about 8% needed and temperature above 650°C and higher. A typical place, where delta phase is situated are grain boundaries in alloy 718, where its role is discutable. Some references saying about lowering the mechanical properties when delta phase is segregated at grain boundary. To approve or disprove of this fact, the wrought alloy 718 with ASTM 12 grain size was subjected to high-temperature loading at push - pull fatigue at low cycle and low frequency (LCLF) and obtained results were compared to results from very high cycle and frequency (VHCF) push - pull loading datas obtained in previous experiments done at room temperature. To support results about influence of delta phase formation an observation on light microscopy and SEM was made too. To increase and make easier identification of delta phase, the techniques of polarised light (DIC - Differential Interferential Contrast) and dark-field (DF) observation were used too.

The Atlantida 3.1_2014 Program for Earth Tide Prediction: New Version

The main distinctive features of ATLANTIDA3.1._2014, the first domestic program for the prediction of Earth tides, are discussed in comparison to similar programs of international authors, and some examples of the practical application of the program by different researchers are presented. The main functional features of the program are listed. Among them, the features for calculating amplitude delta factors of tidal waves for an oceanless Earth, as well as amplitude delta factors and phase shifts for an Earth with an ocean, tidal time series, and amplitudes and phases of the oceanic gravimetric effect, are especially distinguished. The theoretical developments included in the program are briefly described. The main differences of the latest version of the program are identified. The theoretical values of the amplitude delta factors for an inelastic self-gravitating rotating Earth, calculated with respect to the action of relative and Coriolis accelerations, as well as dissipation, are considered in detail. A total of 12 model variants are considered, which differ from each other by the inclusion or exclusion of separate factors affecting the result. The closeness of the results yielded by the program and the observations using the European superconducting gravimeters of the Global Geodynamic Project (GGP) is evaluated. It is shown that according to this criterion, our program surpasses the world’s most well-known counterparts. Tasks are listed that after their solution will expand the functional features of the program and clarify the results obtained so far.

A Comparative Microstructure Evolution of AISI H21 and Inconel 718 in Cyclic Heating

The AISI H21 steel used for dies in copper hot extrusion softened only after several runs. To improve production parameters a new material was necessary for the die, and, as a first choice, Inconel 718 was preferred. Prior to adopting this material for new extrusion dies an experimental program with temperature exposure cycles was performed so as to study microstructure evolution within AISI H21 and Inconel 718. The samples were studied by optic and scanning electron microscopy (SEM) and were also submitted to X-ray diffraction (XRD) and microhardness tests. The results showed carbide coalescence, which led to softening, followed by a re-precipitation in the steel, while, in Inconel 718, the precipitation (in small amounts) of delta (ä) phase was observed.Using these results and combining them with practical experience with steel, we could predict that the Inconel 718 die performance is such that at least a double quantity of copper could be extruded per die.

Predictive entrainment of natural speech through two fronto-motor top-down channels

ABSTRACT Natural communication between interlocutors is enabled by the ability to predict upcoming speech in a given context. Previously we showed that these predictions rely on a fronto-motor top-down control of low-frequency oscillations in auditory-temporal brain areas that track intelligible speech. However, a comprehensive spatio-temporal characterisation of this effect is still missing. Here, we applied transfer entropy to source-localised MEG data during continuous speech perception. First, at low frequencies (1–4 Hz, brain delta phase to speech delta phase), predictive effects start in left fronto-motor regions and progress to right temporal regions. Second, at higher frequencies (14–18 Hz, brain beta power to speech delta phase), predictive patterns show a transition from left inferior frontal gyrus via left precentral gyrus to left primary auditory areas. Our results suggest a progression of prediction processes from higher-order to early sensory areas in at least two different frequency channels.

Influence of Delta Phase Morphology in Galvannealed Coated Steels on Formability

It is well known that coating microstructure can affect the frictional behavior and the formability of galvannealed steels. Several studies are available in literature describing the influence of different coating phases, such as, gamma, delta and zeta phases, on press formability. In the present study, the authors have investigated the effect of the surface morphology, specifically of the delta phase of galvannealed coating on press formability. Formability tests including conditions of (a) complete metal lockdown and (b) significant metal movement in the dies were conducted. It was found that cubic delta coatings seem to perform better (reduced splitting) in forming operations which are accompanied by significant sliding in the blankholder area than rod delta coatings. This paper presents the results of the formability evaluation for samples with different delta phase morphology and correlation with traditionally used measures for evaluation of surface behavior such as the frictional behavior and surface roughness.

Spin density stabilization of local distortions induced by a monovacancy in δ -Pu

Density functional theory calculations elucidate crystallographic and electronic structural responses of the fcc delta phase of plutonium (\ensuremath{\delta}-Pu) to point defects. Discussed in this paper are responses that vary from a defect exhibiting a local structural instability common in fcc metals to an unusual defect structure that mimics properties similar to the monoclinic \ensuremath{\alpha} phase. In the prior case, the existence of a self-vacancy when ionic relaxation is allowed induces in the fcc lattice a local tetragonal instability in nearest-neighbor atoms, slight electronic charge increase, and a spin-density decrease. However, in the latter case, after ionic relaxation, the defect is not recognizable as the structure of a vacant site common to many simple fcc metals, but is a complex extended defect involving neighboring atoms to collectively exhibit loss of lattice symmetry through formation of short Pu-Pu bonds and associated narrow bands at the Fermi energy. Partial density of states (PDOS) indicates that these narrow bands form as spectral weighting from the less energetic $6d$ electronic states is shifted to the $5f$ electronic states by means of the spin density, which occupies states at the Fermi energy. The PDOS of a $5f$ system exhibiting narrow bands at the Fermi energy is associated with the formation of an unusual defect structure in the lattice.

Effect of solution treatment on the formability and part performance of IN718 sheet material

ABSTRACTIN718 sheets were separately solution treated to two different temperatures i.e. 970°C (HT970) and 1070°C (HT1070). Due to higher solution treatment temperature (1070°C), the microstructure altered considerably i.e. grain size increased, volume fraction of both strengthening phases () obliterated from the matrix (), and delta phase () dissolved. Further, both the heat-treated samples were deformed using limiting dome height (LDH) setup along different strain paths ranging from tension-compression to tension-tension deformation modes. It was observed that all the samples failed catastrophically without any significant hint of necking, and hence, fracture forming limit diagrams (FFLD) were estimated. It was found that the FFLD of HT1070 was marginally higher in comparison to that of HT970 material. The formability in terms of LDH, crack location and strain evolution for biaxially deformed cup was predicted successfully by finite element model incorporating Hills-48 plasticity theory. The results showed higher LDH with well-developed strain distribution in case of HT1070 material in comparison to that of HT970 material. However, the surface topography of biaxially stretched cup showed 116% increase in roughness for HT1070 material. The higher intensity of Brass and lower intensity of Cube components were responsible for higher surface roughness in case of HT1070 material.

Neural tracking of auditory motion is reflected by delta phase and alpha power of EEG

It is of increasing practical interest to be able to decode the spatial characteristics of an auditory scene from electrophysiological signals. However, the cortical representation of auditory space is not well characterized, and it is unclear how cortical activity reflects the time-varying location of a moving sound. Recently, we demonstrated that cortical response measures to discrete noise bursts can be decoded to determine their origin in space. Here we build on these findings to investigate the cortical representation of a continuously moving auditory stimulus using scalp recorded electroencephalography (EEG).In a first experiment, subjects listened to pink noise over headphones which was spectro-temporally modified to be perceived as randomly moving on a semi-circular trajectory in the horizontal plane. While subjects listened to the stimuli, we recorded their EEG using a 128-channel acquisition system. The data were analysed by 1) building a linear regression model (decoder) mapping the relationship between the stimulus location and a training set of EEG data, and 2) using the decoder to reconstruct an estimate of the time-varying sound source azimuth from the EEG data. The results showed that we can decode sound trajectory with a reconstruction accuracy significantly above chance level. Specifically, we found that the phase of delta (<2 Hz) and power of alpha (8–12 Hz) EEG track the dynamics of a moving auditory object.In a follow-up experiment, we replaced the noise with pulse train stimuli containing only interaural level and time differences (ILDs and ITDs respectively). This allowed us to investigate whether our trajectory decoding is sensitive to both acoustic cues. We found that the sound trajectory can be decoded for both ILD and ITD stimuli. Moreover, their neural signatures were similar and even allowed successful cross-cue classification. This supports the notion of integrated processing of ILD and ITD at the cortical level. These results are particularly relevant for application in devices such as cognitively controlled hearing aids and for the evaluation of virtual acoustic environments.

Research on Nitrogen Solubility of Fe–Cr–Mn–V–N System Alloys in Liquid and Solid Phases

In this paper, the thermodynamic model of nitrogen solubility in vanadium nitrogen microalloyed high strength weathering steels of Fe–Cr–Mn–V–N system, according to Hillert’s model for Gibbs energy of its various phases, was established and validated. In the model, the effect of the nitrogen partial pressure on the activity coefficient and the lattice structure characteristics of the vanadium nitrogen precipitated phase were considered. It would be of guiding significance for the design and smelting of Fe–Cr–Mn–V–N system alloys. Based on the established model, the nitrogen contents in $$\delta$$ , $$\gamma$$ , $$\alpha$$ phase and liquid were calculated as a function of the temperature for Fe–Cr–Mn–V–N system alloys. The results show that: first, the maximum solubility of nitrogen in the solidification process is obviously affected by the phase transition when there is a sudden change in the solubility of nitrogen at the phase transition point. The maximum nitrogen solubility of the molten steel in the delta phase region determines whether nitrogen bubbles are formed during the solidification process. The nitrogen solubility is lowest in the solid–liquid region (about 1673 K). Secondly, the increase of Cr and Mn content is beneficial to improve nitrogen solubility in liquid and solid phases. However, the increase of V content mainly affects the nitrogen solubility in the solid phase because the nitrogen in this temperature range is precipitated in the form of vanadium nitride, as the second phase plays a role in strengthening. In addition, the alloying element Mn has a significant effect on nitrogen solubility since the Mn element is the promoting element of austenitic formation. During the solidification process, the delta ferrite region gradually reduces and may disappear with increasing Mn content. Therefore, increasing the Mn content of the alloy system in the design of alloy composition, can reduce the precipitation trend of the nitrogen during the solidification process, which can effectively avoid bubble formation in high nitrogen weathering steels. Lastly, with the increase in the nitrogen partial pressure, the solubility of nitrogen increases during the liquid and solid phases.

Delta activity encodes taste information in the human brain

The categorization of food via sensing nutrients or toxins is crucial to the survival of any organism. On ingestion, rapid responses within the gustatory system are required to identify the oral stimulus to guide immediate behavior (swallowing or expulsion). The way in which the human brain accomplishes this task has so far remained unclear. Using multivariate analysis of 64-channel scalp EEG recordings obtained from 16 volunteers during tasting salty, sweet, sour, or bitter solutions, we found that activity in the delta-frequency range (1–4 Hz; delta power and phase) has information about taste identity in the human brain, with discriminable response patterns at the single-trial level within 130 ms of tasting. Importantly, the latencies of these response patterns predicted the point in time at which participants indicated detection of a taste by pressing a button. Furthermore, taste pattern discrimination was independent of motor-related activation and encoded taste identity rather than other taste features such as intensity and valence. On comparison with our previous findings from a delayed taste-discrimination task (Crouzet et al., 2015), taste-specific neural representations emerged earlier during this speeded taste-detection task, suggesting a goal-dependent flexibility in gustatory response coding. Together, these findings provide the first evidence of a role of delta activity in taste-information coding in humans. Crucially, these neuronal response patterns can be linked to the speed of simple gustatory perceptual decisions – a vital performance index of nutrient sensing.