Annealing Stage Research Articles

Solid‐state NMR investigation of fast sodium ion‐conducting glass–ceramics: The system Na3+3x−yRE1−xPySi3−yO9 (RE = Sc, Y)

AbstractGlasses and glass–ceramics of composition Na3+3x−yRE1−xPySi3−yO9 were synthesized using RE = Sc and Y, x = 0.4, and y = 0.0 and 0.3 to obtain multiple‐phase glass–ceramics containing the highly conducting Na5RESi4O12 (N5) phase. In addition, the two model compounds Na5ScSi4O12 and Na5InSi4O12 were synthesized. Samples were characterized at two distinct annealing stages using X‐ray powder diffraction, electrical conductivity measurements, and multinuclear solid‐state magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The N5 phase is dominantly formed for Sc‐containing glass–ceramics (both with y = 0.0 and 0.3) at crystallization temperatures above 900°C. For the other glass–ceramics, the crystallized phases were dominantly Na3RESi2O7 (N3), RE = Sc and Y, and Na9YSi6O18 (N9) phases. 29Si MAS‐NMR peak assignments were done with the aid of 29Si{45Sc} rotational echo adiabatic passage double resonance (REAPDOR) experiments. 29Si and 23Na MAS‐NMR spectra reveal complex phase compositions and local environment distributions, which could be largely assigned based on known semiempirical chemical shift correlations with average Si–O and Na–O bond distances. 31P MAS and 31P{45Sc} REAPDOR NMR results suggest the presence of orthophosphate groups, arguing against the literature model of isostructural substitution of silicon by phosphorus in the N5 phase.

Effect of High Magnetic Field in Combination with High-Temperature Tempering on Microstructures and Mechanical Properties of GCr15 Bearing Steel

The microstructures and mechanical properties of GCr15 bearing steel after high-temperature tempering with and without a 5 T high magnetic field (HMF) were investigated. It was found that the application of the HMF at the stage of high-temperature tempering slowed down the growth of the tempered sorbite (TS) structures, increased the density of the carbides, and reduced the carbide size and the volume fraction. XRD diffraction patterns showed that the HMF resulted in a higher dislocation density. Hardness testing indicated that the HMF led to an increase in the Vickers hardness in the tempered sample. It is inferred that the change in carbide size stems from the reduction in nucleation barrier in the HMF and the increase in dislocation density originates from the interaction between dislocations and carbides. Additionally, the decrease in diffusivity in the HMF also contributes to the reduction in the size of TS structures and the refinement of carbides. This work demonstrates that high-temperature tempering with an HMF can slow down the growth of TS microstructures in GCr15 bearing steel, control the carbide size, and improve Vickers hardness, which provides a new heat treatment method to regulate the microstructure and properties of GCr15 bearing steel.

Influences of pre-aging precipitates on static recrystallization behavior of Mg–6Al–1Zn alloy

Due to the dynamic evolution of precipitates during thermomechanical processing, the intricate effects of second-phase particles on recrystallization behavior are still far from being clear. In this work, the relevance between static recrystallization and pre-aging precipitates in AZ61 (Mg–6Al–1Zn) alloy was systematically investigated. Our results reveal that the presence of pre-aging precipitates increases stored deformation energy by facilitating the generation of dislocations, thus accelerating the recrystallization rate during the initial recrystallization stage. Besides, these uniform distributed dislocations could act as heterogeneous nucleation sites and promote precipitation of fine dispersoids during the subsequent annealing stage. These dispersoids hinder the movement of dislocations and grain boundaries, leading to the increase of Zener pinning pressure. Therefore, the effect of pre-aging particles on recrystallization kinetics gradually transforms from acceleration to retardation as the annealing time prolongs. This work demonstrates that manipulating the features of precipitates through pre-aging treatment is an applicable strategy to control the static recrystallization behavior of Mg alloys.

Study and Comparison of Different Routes to Synthesize Reduced Graphene Oxide

The feasibility of graphene oxide (GO) obtained by both Hummers and Tour method to prepare reduced graphene oxide (rGO) as well as chemically reduction under different experimental conditions were evaluated with the objective of establishing the key items that should be considered when performing the synthesis of GO and rGO. This key items can be supportive to select the most feasible methodology to synthesize GO and rGO depending on the future application. Reduced graphene oxide was prepared by combining chemical and solvothermal as well as combined reduction adding a final thermal annealing step. Obtained GO and rGO were characterized by XRD, Raman spectroscopy, XPS and BET analysis. A higher oxidation degree was achieved for samples from Tour method than those oxidized by Hummers method. On the contrary, lower oxidation degree from Hummers graphene oxide (GO-H) facilitates the subsequent reduction process, leading to a higher reduced rGO. Hence, rGO samples obtained from the Hummers method in the different reduction treatments presented higher C/O atomic ratios than the corresponding Tour method. In addition, the combination of a solvothermal treatment and chemical reduction, including a final annealing stage, increases significantly the value of the C/O ratio as well as it contributes to decrease the defect density and the restoration of π-conjugated structure. Besides, rGO samples obtained from Tour method presented higher SSA and pore volume than those samples obtained from Hummers method. Results from this study suggest the suitability of Tour graphene oxide (GO-T) for chemical functionalization which is very useful for several applications. In addition, GO and rGO coming from Tour method are more appropriate to applications in which high surface area is required. Taking into account the vast possible applications for chemically-exfoliated graphene the findings of this study could help to select the best method for oxidising graphite depending on the intended application.

Multiscale Exploration of Texture and Microstructure Development in Recrystallization Annealing of Heavily Deformed Ferritic Alloys

We present a multi-scale study of recrystallization annealing of an 85% cold rolled Fe-3%Si-0.1%Sn alloy using a combination of dark field X-ray microscopy (DFXM), synchrotron X-ray diffraction (SXRD), and electron backscatter diffraction (EBSD). Grains of interest from high stored energy (HSE) regions in a 200μm-thick sample are studied using DFXM during isothermal annealing. The intra-granular structure of the as deformed grain reveals deformation bands separated by ≈ 3–5° misorientation. Geometrically Necessary Dislocation evolution during recrystallization and growth is investigated. These findings are supported by a quantitative non-destructive texture analysis using SXRD in terms of pole figures and orientation distribution functions. Although no significant macroscopic texture change is observed up to 50% recrystallization, the calculated texture index indicates different nucleation and growth processes at various stages of annealing. Our results show that zones of local misorientation in the HSE regions are decisive for the formation and growth of recrystallized grains.

Ultrahard BCC-AlCoCrFeNi bulk nanocrystalline high-entropy alloy formed by nanoscale diffusion-induced phase transition

In the current work, the BCC-AlCoCrFeNi bulk nanocrystalline high-entropy alloy (nc-HEA) with ultra-high hardness was formed by nanoscale diffusion-induced phase transition in a nanocomposite. First, a dual-phase Al/CoCrFeNi nanocrystalline high-entropy alloy composite (nc-HEAC) was prepared by a laser source inert gas condensation equipment (laser-IGC). The as-prepared nc-HEAC is composed of well-mixed FCC-Al and FCC-CoCrFeNi nanocrystals. Then, the heat treatment was used to trigger the interdiffusion between Al and CoCrFeNi nanocrystals and form an FCC-AlCoCrFeNi phase. With the increase of the annealing temperature, element diffusion intensifies, and the AlCoCrFeNi phase undergoes a phase transition from FCC to BCC structure. Finally, the BCC-AlCoCrFeNi bulk nc-HEA with high Al content (up to 50 at.%) was obtained for the first time. Excitingly, the nc-HEAC (Al-40%) sample exhibits an unprecedented ultra-high hardness of 1124 HV after annealing at 500 °C for 1 h. We present a systematic investigation of the relationship between the microstructure evolution and mechanical properties during annealing, and the corresponding micro-mechanisms in different annealing stages are revealed. The enhanced nanoscale thermal diffusion-induced phase transition process dominates the mechanical performance evolution of the nc-HEACs, which opens a new pathway for the design of high-performance nanocrystalline alloy materials.

In-situ electrostatic field regulating the recrystallization behavior of P(VDF-TrFE) films with high β-phase content and enhanced piezoelectric properties towards flexible wireless biosensing device applications

Fabrication of flexible piezoelectric polymers is essential for the development of wearable biosensors. Nevertheless, the piezoelectric coefficient of polymers is usually an order of magnitude lower than the inorganic piezoelectric materials, which limits the miniature of the devices. Herein, a simple and cost-effective technique is proposed by applying an electrostatic field to in-situ regulate the recrystallization behavior of the poly(vinylidene fluoride-trifluorethylene) (P(VDF-TrFE)) film during the thermal annealing and recrystallization stage. Significantly enhanced properties are obtained, including a large piezoelectric coefficient (d33~30.7 pC/N) and a high voltage sensitivity of 167.12 mV/kPa. The outstanding performance is mainly attributed to the applied electrostatic field maintained during the film growth stage, which promotes the generation of nucleation sites for the polar β lamellae crystals. A wireless sensor system is further established with the obtained P(VDF-TrFE) film, demonstrating great potential applications in movement monitoring. The proposed facile approach could potentially be applied to the large-scale production of polymer films with excellent piezoelectric properties for flexible wireless biosensing device applications.

Free‐Volume Extended Defects in Structurally Modified Ge–Ga–S/Se Glasses

Herein, transformation of free‐volume extended defects in selected chalcogenide glasses caused by thermal annealing for 10, 25, and 50 h is studied. For 80GeSe2–20Ga2Se3 as well as for GeS2–Ga2S3 glasses with different GeS2 and Ga2S3 contents (80GeS2–20Ga2S3, 82GeS2–18Ga2S3, 84GeS2–16Ga2S3), positron annihilation lifetime spectroscopy and Doppler broadening of annihilation radiation methods are applied. By analyzing the positron annihilation lifetime spectra decomposed into two components, it is shown that the observed changes in the second defect‐related component for the 80GeSe2–20Ga2Se3 glasses confirm the agglomeration of free volumes in the initial stage of annealing (10 h) with further fragmentation (25 h) and shrinkage (50 h). Increased content of Ge‐related subsystem in the GeS2–Ga2S3‐based glasses results in the agglomeration of free‐volume defects in the 82GeS2–18Ga2S3 glasses with their further expansion in the 84GeS2–16Ga2S3 matrix.

On the Measurability and Predictability of HAZ Softening in GMAW of Automotive DP980 Steel

Dual Phase (DP) steel, composed of a ferrite matrix with dispersed islands of martensite, has become popular in auto-body car construction due to its outstanding mechanical properties (i.e., high strength and good ductility). DP steel softens at the sub-critical heat-affected zone (SC-HAZ) when subjected to welding thermal cycles, owing to the tempering of the martensite phase. In this work, DP980 steel was subjected to varied thermal cycles: (a) furnace-tempering treatment, (b) gas metal arc welding (GMAW), and (c) resistance spot welding (RSW), in order to characterize the tempering of martensite below the Ac1 critical temperature and at the sub-critical heat-affected zone (SC-HAZ) in the case of the welded specimens. The coarsening stage of cementite phase was characterized through microstructure observations and hardness measurements. As expected, the comparative results indicated an advanced stage of the martensite tempering in the furnace heat-treated specimens, followed by the GMAW and the RSW specimens. Further, developed softening kinetic models have been suitably employed and adjusted in order to predict the extent of softening along the SC-HAZ of the GMAW specimen. Finally, as the advanced stage of cementite coarsening is due to the influence of the arc welded thermal cycle, a reasonable estimation of the hardness profile was obtained, particularly for tempering temperatures above 400 °C.

Improving photocatalytic hydrogen production via ultrafine-grained precipitates formed nearby surface defects of NiFe-LDH nanosheets

New types of photocatalytic systems formed by coupling annealed large-sized NiFe-LDH nanosheets with small-sized TiO2 nanosheets were used to facilitate the rapid separation of photo-generated electrons and holes. The photocatalytic hydrogen production for optimized photocatalytic systems can reach 209 mmol/g, which is 8 times of that for TiO2. To understand the photocatalytic mechanism, in-situ annealing transmission electron microscopy (TEM) investigation of the microstructural evolution of large-sized NiFe-LDH nanosheets identified typical microstructures at different annealing stages. The microstructure of the optimized system contains plentiful ultrafine grains distributed along surface delaminated defects, which can provide abundant active sites for photocatalytic hydrogen evolution. Electrochemical and spectroscopic techniques were further used to determine the Z-scheme mechanism, guiding photo-generated electrons to fast transfer onto large-sized NiFe-LDH nanosheets to achieve high efficient carrier separation.

In situ tempering of martensite during laser powder bed fusion of Fe-0.45C steel

During laser powder bed fusion (L-PBF), materials experience cyclic re-heating as new layers are deposited, inducing an in situ tempering effect. In this study, the effect of this phenomenon on the tempering of martensite during L-PBF was examined for Fe-0.45C steel. Detailed scanning electron microscopy, transmission electron microscopy, atom probe tomography, and hardness measurements indicated that martensite was initially in a quenched-like state after layer solidification, with carbon atoms segregating to dislocations and to martensite lath boundaries. Subsequent tempering of this quenched-like martensite was the result of two in situ phenomena: (i) micro-tempering within the heat affected zone and (ii) macro-tempering due to heat conduction and subsequent heat accumulation. Hardness measurements showed that although both influenced martensite tempering, micro-tempering had the most significant effect, as it reduced martensite hardness by up to ∼380 HV. This reduction was due to the precipitation of nano-sized Fe3C carbides at the previously carbon-enriched boundaries. Lastly, the magnitude of in situ tempering was found to be related to the energy input, where increasing the volumetric energy density from 60 to 190 J/mm3 reduced martensite hardness by ∼100 HV. These findings outline the stages of martensite tempering during L-PBF and indicate that the level of tempering can be adjusted by tailoring the processing parameters.

Effect of Prior Cold Reduction of C–Si–Mn Hot-Rolled Sheet on Microstructures and Mechanical Properties after Quenching and Partitioning Treatment

This paper studies the microstructures and mechanical properties of quenching and partitioning (Q&P) samples prepared with 35% and 75% cold reduction sheets at an annealing temperature of 810 °C (intercritical temperature). The results indicate that prior cold reduction could significantly influence the ferrite recovery and recrystallization during intercritical annealing, which changes the size and distribution of the ferrite and retained austenite in the Q&P samples. Compared with the 75%—Q&P sample, the 35%—Q&P sample had smaller recrystallized ferrite and retained austenite grains, a higher volume fraction of retained austenite, and a more uneven size distribution of retained austenite. The 35%—Q&P sample presented better total elongation and a higher product of strength and elongation (PSE) than the 75%—Q&P sample. The higher total elongation was related to the higher content and uneven size distribution of retained austenite for they strengthened the TRIP effect and improved the uniform elongation of the sample. The results proved that Q&P steel prepared with a cold-rolled sheet with lower reduction exhibits a better combination of strength and plasticity due to the fact that lower reduction can delay the growth rate of austenite and recrystallized ferrite grains during the intercritical annealing stage.

Microstructure, Thermal and Mechanical Properties of Refractory Linings Modified with Polymer Fibers

The reduction in the inherent brittleness of coatings applied on parts of ceramic shielding used for continuous steel casting (CSC) processes is highly desired, since it can significantly diminish losses occurring during post-application handling and mounting. One of such coatings, prepared mostly from fused silica, ludox, tabular alumina, chamotte, cenospheres, dextrine and aluminum powder, is known commercially as Thermacoat™. The present experiment is focused on the effect of the modification of its composition by rising the content of the cenospheres (max. 2.5 wt.%) or by introducing up to 1.5 wt.% of polymer Belmix™ fibers (~34 μm diameter/12 mm length) on the microstructure and mechanical properties. The maximum amount of introduced additions was limited by the accompanying loss of mass viscosity, which must allow for deposition through immersion. Next, the differential scanning calorimetry and differential thermogravimetric analysis techniques were employed to evaluate the extent of the weight change and heat response of the mass during the drying and annealing stages. The dried materials’ microstructure was investigated with light and scanning electron microscopy, while the chemical composition was studied by energy dispersive spectroscopy. Finally, a three-point flexural bending method was used to determine changes in the material mechanical properties. The performed experiments proved that the small addition (~1 wt.%) of polymer fibers is sufficient for the significant improvement of the Thermacoat™ green mechanical strength at ambient temperature, presenting a reproducible ultimate flexural strength of ~0.2 MPa.

4D microstructural evolution in a heavily deformed ferritic alloy: A new perspective in recrystallisation studies

We present a multiscale study on the recovery and recrystallisation of a heavily deformed (85% reduction in size) Fe–Si–Sn alloy using a combination of dark field X-ray microscopy (DFXM), synchrotron X-ray diffraction (SXRD) and electron backscatter diffraction (EBSD). By utilizing DFXM, we focus on a grain within the high stored energy (HSE) regions, and track it through consecutive isothermal annealing steps. The intra-granular structure of the as-deformed grain reveals deformation bands separated by ≈3–5∘ misorientation. During the early stages of annealing, cells with 2–5∘ misorientation form while new nuclei appear. The recrystallized grains nucleate near prior grain boundaries, having a typical internal angular spread of <0.05∘. The SXRD results suggest no significant macroscopic texture change after annealing for 1400s at 610∘C in the HSE regions. All results indicate that higher misorientation zones such as grain boundaries or junction points of deformation bands are preferential nucleation regions.

Annealing-temperature-dependent evolution of hydrogen-related donor and its strong correlation with X-photoluminescence center in proton-irradiated silicon

We have investigated the formation and decay of hydrogen-related donors (HDs) and irradiation-induced intrinsic defects. N-type m:Cz and FZ silicon wafers, which were irradiated with 2 MeV protons and subsequently annealed at 100–600 °C, were analyzed using spreading resistance profiling and photoluminescence (PL). HDs formed at 260 °C and then disappeared in two stages at 400–440 and 500–540 °C. This decay behavior indicates the existence of two types of HDs with different thermal stabilities. PL measurements showed interstitial silicon clusters (W and X center), a carbon–oxygen complex (C center), and exciton lines bound to unknown shallow centers. The origin of the HDs was investigated based on the correlation of the formation and decay temperatures between HDs and irradiation-induced defects. The predominant defects at the early stage of annealing, such as the C and W centers, are ruled out as candidates for the core defects of HDs because annealing above 260 °C is indispensable for the HD formation. In contrast, the X center was found to be thermally generated above 200 °C and disappeared at 580 °C. The similarity of the formation and decay temperatures between the X and HD centers suggests that HDs are associated with the formation of the interstitial silicon-related defects attached to hydrogen. Our results suggest that controlling the formation of interstitial silicon-related defects is important for realizing desirable doping profiles with high accuracy and reproducibility for power devices. Annealing above 400 °C exclusively provides thermally more stable HDs, leading to the realization of more rugged power devices.

Microevolution of grain boundary character distribution in Hastelloy C-276 during the annealing process

Grain boundary character distribution and disconnectivity of random boundaries were observed “in-situ” in the Hastelloy C-276 alloy sample through thermomechanical processing. The role of Σ3 boundaries in microstructural evolution of grain boundary character distribution was analyzed by electron back-scattered diffraction (EBSD) and the mechanisms of grain boundary engineering (GBE) during annealing were elucidated. The results showed that the fraction of Σ3n boundaries (including Σ3 boundaries) consistently increased in number with annealing time; however, the Σ3 boundaries had different effects on the disconnectivity of random boundaries because of their variants, i.e., coherent and incoherent Σ3 boundaries. At the initial annealing stage, new incoherent Σ3 boundaries were generated, according to the “Σ3 regeneration mechanism” model; Σ9 and Σ27 boundaries appeared and increased in number with increasing Σ3 boundary interactions. These incoherent Σ3 boundaries could disrupt the connectivity of the random grain boundaries and form large clusters. However, at the annealing stage, some incoherent Σ3 boundaries were annihilated, and new coherent ones emerged. As a result, the random grain boundary network evolved by obtaining significant connectivity with larger clusters, attributed to the reduction of the incoherent Σ3 boundaries. This implies that the incoherent Σ3 boundaries play an important role in the optimization of grain boundary engineering.

Domain size control in all-polymer solar cells

SummaryIn all polymer solar cells (all-PSCs), the domain size is critical for device performance. In highly crystalline polymer blends, however, precisely adjusting the domain size remains a significant challenge because of the simultaneous crystallization of both components. Herein, a strategy that promotes acceptor and donor to crystallize separately was proposed. Take PBDB-T/N2200 blends for instance; the solution state and confined crystallization were combined, which induced the crystallization of N2200, and PBDB-T occurred during the film-forming process and at thermal annealing stage. This separated crystallization process lowers the driving force of phase separation without affecting the degree of crystallinity of the blends. Thus, an interpenetrating network with high crystallinity and proper domain size was obtained, which boosted the power conversion efficiency to 7.59%. Importantly, the relation between pre-aggregation and domain size was established, which may be a guide to precisely adjust the active layer’s domain size in all-PSCs.

High-precision molding simulation prediction of glass lens profile for a new lanthanide optical glass

Precision glass lens molding (PGLM) is a recently developed method for fabricating glass optical components with high precision in large volumes. Lanthanum optical glasses are extensively used as optical materials owing to their superior optical properties, such as high refractive index, low dispersion, and high transparency. However, the transformation temperature of currently available high refractive index glass is generally above 650 °C and poses a challenge in manufacturing ultra-hard molds, durable coatings, and high-temperature molding equipment using PGLM. In this study, a preparation method for obtaining high refractive index, low -melting -point lanthanide optical glass (B-ZLaT198) used in PGLM was developed to reduce the transformation temperature. The developed method also characterizes the glass refractive indices and thermal-mechanical properties. To achieve the high-precision prediction of a molding shape in a simulation, a viscoelastic constitutive model of glass was established based on a micro-deformation uniaxial compression creep test. Moreover, by solving the Tool-Narayanasway-Moynihan model parameters based on the specific heat capacity fitting of optical glass at different heating and cooling rates, the input parameters of the structural relaxation model (SRM) for simulation prediction of aspheric glass lens profile deviation in the annealing stage were obtained. Finally, the profile deviation of the aspheric lens was predicted using a finite element model simulation. The results showed that the simulation’s predicted profile of an aspheric lens using the SRM model was in good agreement with that of experimental molding profile. In addition, using the SRM provided a higher prediction accuracy than that of the thermal expansion model in the annealing stage. Adopting the SRM was necessary for the annealing simulations of molding pressing and also verified the accuracy of the proposed viscoelastic characterization method for calculating the thermomechanical parameters of optical glasses.

Development of cube recrystallization textures in high-purity Al

Abstract High-purity (99.99 wt.%) Al containing 50 wt. ppm Cu was cold rolled to 98% reduction in thickness and annealed by varying the heating rate of annealing and annealing cycles. Textures developed at various stages of annealing were investigated with the orientation distribution function analysis. The observed results were compared with those obtained on standard high purity (99.99 wt.%) Al without Cu addition. In slow heating rate annealing, it was found that in high purity Al the addition of 50 wt.ppm Cu significantly enhanced the development of {100}&lt;001&gt; recrystallization textures. Intensities of {100}&lt;001&gt; developed in high purity Al with 50 wt. ppm Cu were about twice as high as those observed in high purity Al without Cu addition. {123}&lt;634&gt; R orientations were completely eliminated by the addition of 50 wt. ppm Cu. In rapid heating annealing, on the other hand, annealing at temperatures above 325 °C resulted in the formation of very coarse recrystallized grains with weak {100}&lt;001&gt; recrystallization textures irrespective of Cu content. Such grain coarsening could be suppressed by pre-annealing at temperatures between 225 and 300 °C. In the specimens subjected to this pre-annealing, strong {100}&lt;001&gt; recrystallization textures could be obtained, even if they were annealed with a rapid heating rate in final annealing.

Predicting the moisture content of organic wheat in the first stage of tempering

The tempering process is a key process in wheat flour milling that requires proper adjustments to achieve a desired level of flour quality and yield. The present study aims to develop a tool to predict the moisture content of organic wheat at the end of the first stage of tempering. A study case was conducted at a mill located in the Quebec region to build and compare flour models: ordinary least squares (OLS), LASSO, RIDGE and ElasticNet. The models are based on wheat properties (initial wheat moisture content, wheat protein content and wheat temperature), process parameters (targeted wheat moisture content, wheat flow rate, water flow rate, wheat quantity and resting time) and tempering conditions (water quantity and day weather). The increase of wheat moisture achieved during the first tempering stage varies between 0% and 5%. The results indicated that ElasticNet model outperformed others in determining the final increase of wheat moisture with an average prediction errors of 0.21%.